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sandy daugherty
02-11-2010, 09:11 PM
Forgive my ignorance; I'm a sailor looking for powerboat to snowbird the US Eastern Seaboard. Is there a design that will carry the accomodations of a 16' travel trailer at 12 knots in coastal waters at 12 nmpg? Since gasoline is currently cheaper than diesel, does that affect the traditional power choices?
Could this be done in a barely trailerable outboard driven vessel? I'm looking for a warm enclosed helm, 15' bridge clearance and very easy access to bow and stern for single-handed docking in moderately adverse winds and currents. I've made a half-hearted attempt to search this site and would be glad to be directed to a previous thread.

The accomodations I would like to find are a double berth, standup head and shower, galley and dinette for 4, stove and oven, H&C pressure water, AC and Heat, 3' max draft, refrigeration, and a comfortable place to read.

Boston
02-11-2010, 09:23 PM
Diesel is going to be your fuel of choice for the time being. Gas would break the bank in about a split second.

barely trailer-able is a mater of extremes
your in the US so 8 is easy 10 is legal in most states with a wide load sign and a light, 12 is doable but you start getting into hassles

in the end trailer-able is a relative term

you could drag a 60' x14' hull down the road but would you want to is the bigger question

define your idea of trailer-able and maybe we can get some of the designers to chime in and begin to pin things down
cheers
B

marshmat
02-11-2010, 10:20 PM
I wouldn't be so quick to dismiss gasoline there, B.... not for a relatively small boat in coastal waters. Yes, the range will be better with diesel, but the capital cost difference must be considered- and the difference between a $6000 gas engine of 40-50 hp or so and its $12000 diesel counterpart buys an awful lot of fuel.

Dave Gerr's 5200 lb "Offshore Skiff" ( http://www.gerrmarine.com/power_30.html ) or his substantially larger, 7-ton "DR Northwest Cruiser" ( http://www.gerrmarine.com/power_50.html ) might be interesting starting points- both are trailerable without special permits (the latter just barely so).

12 knots at 12 nmpg is a pretty tall order. To meet that will require a very long, slender hull optimized more for efficiency than for accommodation. (Even getting 6 nmpg at 10 knots is pretty tricky if you want enough room for a couple of people to sleep aboard.)

Boston
02-11-2010, 10:45 PM
there are some screaming deals to be had on used diesels these days
seems like something could be found to fit the bill and at substantially less than new prices

that and a diesel will loaf along and get way better millage

my two cents

if Sandy is looking to transfer the space available in a 16 x 7 foot box he is going to be looking at a boat in the 25' range with a raised deck. I know some old school designs that are within that range assuming you ignored his speed requirement but I'm sure some of you folks can come up with something more economical and modern.

Rick is working on something like this but its all still in the theoretical stage and his is ultralight and electric
that and so far it looks kinda like a death trap

cheers
B

TollyWally
02-12-2010, 02:40 AM
The short answer is probably not.

sandy daugherty
02-12-2010, 09:24 AM
Great responses, excellant points. Lets limit beam to 8.5 ft, and displacement to 8,000 pounds, to keep the towing issue practical. I'm completely open to the fuel question. Outboards appeal to me because of their weight advantages, and because I could get the running gear out of the water much of the time.

If it were easy,Tolly, I might have figured it out by myself. But I would like to point out that the Nimble 32 has the accomodations, and comes close to the economy while hauling around a ballasted shoal keel. Thirty two feet LOA doesn't bother me, I've hauled a fifty foot sailplane trailer through the Rockies.

And thanks for the lead to Dave Gerr. I had not seen this site before, and at a glance it looks like the rest of the day is going to be spent there!

rasorinc
02-12-2010, 09:35 AM
Here is just one Glen-L design that fits your design parameters. They have others.
http://glen-l.com/designs/hankinson/coastalcruiser.html

marshmat
02-12-2010, 12:36 PM
The Glen-L there would fit the design parameters except for the fuel consumption- you won't get 12 nmpg in that thing, not at 12 knots.

Coming anywhere close to this kind of efficiency at 12 knots in a vessel with the described accommodations is going to mean going long, light and slippery- think of a Nigel Irens power tri, for example. A slender monohull of 40-50 feet or so, displacing maybe two tonnes max, might come close.

Tad
02-12-2010, 02:56 PM
A simple parametric study can pin the magnitude of the problem fairly quickly.

We are offered two fixed numbers, 8000 pounds displacement and 12 knots speed. So run some resistance numbers around length which gives you S/L (speed length ratio). Below are bare hull resistance numbers for an 8000 pound hull of various lengths, all running at 12 knots. These are representative, not exact.

At 25' s/l = 2.4, required HP is 94 and gph (diesel) is 4.5.
At 35' s/l = 2.02, required HP is 53 and gph (diesel) is 2.54
At 45' s/l = 1.82, required HP is 38 and gph (diesel) is 1.82
At 55' s/l = 1.61, required HP is 28 and gph (diesel) is 1.34
At 65' s/l = 1.48, required HP is 21 and gph (diesel) is 1.01
At 75' s/l = 1.38, required HP is 17 and gph (diesel) is .82
At 85' s/l = 1.30, required HP is 14.5 and gph (diesel) is .69

The specific power output of gas is less than diesel, so more gas (gph) will be used to produce the same HP. For the 85' requiring 14.5HP, you're already using more than 1 gph of gas. So that's not going to happen as building an 85' boat at 8000 pounds will require it be rather tiny in cross section.

sandy daugherty
02-12-2010, 04:42 PM
Those are some lovely vessels, Tad. What would you consider a more reasonable set of parameters? This level of accomodation is available in a 6 nmpg spec, at something like 6 knots. Can we split the difference? Eight at eight? I think it would be prudent to have a higher top speed available that disregards fuel consumption, such as fighting adverse wind to get across a rough section of water. So a pure displacement hull fine tuned to a fixed speed might not be optimal.

TollyWally
02-12-2010, 07:40 PM
Sandy,
Not trying to be dismissive. I don't have the answer and haven't really seen one despite being attracted to similar but more modest goals myself. Someone like Tad can explain the minutia far better than me, but it is sort of like trying to get 30 mpg out of an RV.

I will be following your thread and paying attention to see if anything new turns up. You are on the right track asking Tad for reasonable parameters. There is a book that always keeps getting mentioned. The Nature of Boats by Dave Gerr. It will get you up to speed on some basics without having to pester people for the elementary stuff. It's sort of like Naval Architecture for Dummies. Once you've grasped some of this book you will be able to ask better more tightly focused questions and will learn more much faster. Best of luck!

sandy daugherty
02-12-2010, 08:17 PM
Thanks Tolly. Amazon says it will be here Wednesday! I'm fairly knowlegeable about outboards, thanks in part to Gerr's prop book so I was thinking about Honda's venerable B50 propped for 12 knots. I got a gallon per hour out of one at low rpm (for 7 knots) on a previous catamaran. I'm not adverse to running small outboards at full throttle; we get 1500+ hours out of Yamaha high thrust 9.9s doing that (with good care) but they are noisy.

I'm looking forward to hearing from Tad: he has some pretty sweet looking designs on his site. I like the lean and narrow look, as purposeful as a WW II Destroyer.

Tad
02-12-2010, 09:32 PM
Sandy,

Thank you for your kind words concerning my work.

If we work backwards a bit....this is very (rough) ballpark.....;)

One (1) gph is our goal. One US gallon of diesel is 7.485 lbs of fuel, .36 pounds of diesel produces approximately 1 horsepower/hour. So 7.485/.36 = 20.8 HP.

A 30' waterline at a speed/length of 1.45 is running at 8 knots. A properly shaped hull running at S/L 1.45 might require approximately one HP per 375 lbs of displacement. 20.8 * 375 = 7800 pounds, close to your 8000.

An 8000 pound 30' boat is quite achievable, but it will be smallish, beam of about 8'-8'6".

Willallison
02-12-2010, 09:39 PM
Sandy,
In essence, you have laid down your most basic design parameters - which is good. The trick now is to find an appropriate design to meet those goals, or to commision a designer to come up with one. That may seem like stateing the bleeding obvious, but as often as not, it's done the other way around...." I like this boat that does 40 knots and gets 0.5 mpg... can you make it 10 feet shorter, I only want to do 20... oh, and I'd like it to do 10mpg..."

We have:
Tailerable coastal cruiser
Max 8000 lb
Max cruising speed approx 12 knots (negotiable by the sound of it...)
"double berth, standup head and shower, galley and dinette for 4, stove and oven, H&C pressure water, AC and Heat, 3' max draft, refrigeration, and a comfortable place to read."
.... and economical.

I've attached the fuel flow data of a recent design of mine, Graphite, which is a planing cruiser with a top speed of 32 knots, so is not appropriate for your application, but otherwise meets most of your goals. You can see that at a speed of around 7 knots she can manage 6.5 nmpg, and that's from a hull that's intended to travel at between 10 and 25 knots and is powered by a 260hp diesel. The point being that your goal should be achievable without too much trouble... though 12 mpg might be pushing things a bit, at least with anything resembling a 'normal' boat.
In order to manage it, however, you will need to achieve a relatively low D/L (light weight relative to its length), so complications like air con may make things a bit tricky. Removing weight is going to be the surest way of reducing fuel consumption

Boston
02-13-2010, 11:41 AM
I been loving this question and these answers
always an interesting read guys
B

oh
and I also like the idea of an outboard
back in the day it was the cheapest thing for a kid to get ahold of
and I could always make the bastad run

even an old beat up one can generally be brought back to life somehow
that and changing out an outboard is no big deal
so you could get one that works and stick it on there
while you find the one you want and work on it till it runs like a top

my two cents
B

erik818
02-13-2010, 01:13 PM
Sandy,
If you're satisfied with a top speed less than 20 knots I think that you have the best chance to approach your requirements if you go for long and narrow displacement hulls. "Hull speed" is no absolute limit for a displacement hull if it is long and narrow. In the range of 10 - 15 knots it's more efficient to use a long and narrow hull and force it past "hull speed" than to go for a planing hull. A long and narrow displacement hull will be very efficient at lower speeds, like 8 knots, which a planing hull will not.

Regardless of hull type, I think you should consider to reduce your accomodation requirements so it fits within a boat displacement of 2 - 3 (metric) tons. The alternative is to go for a conventional full displacement hull restricted to "hull speed", which for a trailable length boat would mean 7 - 9 knots. Assuming of course that fuel economy is high on the priority list.

A power catamaran would use two long and very narrow hulls, and would reach your target spec of 12 knots and 1 gallon/hour for a displacement that might be close to your needs for accomodation. A cat would need two outboards (or inboards) and I believe the beam restriction to 8.5 ft would make stability problematic. A scheme to reduce the beam for trailering would in that case be needed.

Another possible route would be to use a stabilised monohull, essentially a trimaran hull, where the central hull is maybe 10 m long and 1 m wide at the waterline. Above the waterline the beam can wider, and stability is provided by two small, long and narrow hulls. There are several threads on this type of hull, mainly for smaller and lighter application like pedal powered boats and electric boats. Look at the threads "Pedal Powered Boats" and "Coastal Cruiser" in this forum, both started by Rick Willougby. Rick has named the hull type "faux tri".

There is however a succesfull scale (up) model of a "faux tri" with a length to displacement ratio that would scale close to your needs. The US Navy has ordered trimaran combat ships that are very interesting. Look at the thread "Ultimate Multihull - a Trimaran" in the Multihulls forum. The trimaran in question is 127m long and displaces 2784 tons. This is more or less a 10:1 scale modell of the boat you need. It would be interesting to get data on power vs speed for that one and see how it scales to a 12m boat.

The problem with the "faux tri" (trimaran type stabilised monohull) is that as far as I know there are no ready plans to be bought. The suspicious mind asks why, but maybe the simple answer is that the market hasn't asked for it yet. There might be plans for power cats with reducible beam to allow trailering, I don't know.

Erik

sandy daugherty
02-13-2010, 01:17 PM
This IS getting pretty exciting, Boston!

So now we have a @ 30' boat, longer if possible, less than 7800# and 8.5' or narrower beam, that will cruise 8 knots on a 20 to 35 hp diesel. Or (since there just aren't any very efficient FWC gas inboards in that range,*) an outboard or two. Something closer to 34' would have a better ride in the chop found on coastal bays.

I think the head and shower are the only things that need to be enclosed, so they might be positioned forward. The pilot house likely needs to be over the engine and mechanical spaces which hopefully won't be wrapped too tightly, for very accessible maintenance (in addition to being old, I'm wide and don't bend voluntarily.)

* Or are there? And we are definitely not talking Atomic Four here.
If diesel, I would like to stick to Yanmar.

Thanks Erik; thats rich food for thought. Another thought is a folding tri, ala' Farrier or Gemini, for added deck space afloat as well as stability. Maybe a "condo-ized" Corsair 30?

Willallison
02-13-2010, 05:51 PM
Sandy
Can I suggest that you wait until the results of the latest Proffessional Boatbuilder Magazine are released ( www.proboat.com ). The design brief for that comp will almost certainly fit your needs.

One of the biggest problems, as I see it with a stabilised monohull / trimaran, is that they can be a real pain to berth. This has to be considered right from the outset. the one that Marshmatt is developing is likely to be better than most in this regard ( see http://www.boatdesign.net/forums/projects-proposals/trailer-cruiser-revisited-trimaran-27032.html ). My most recent experience of this was on board the Ady Gill (formerly Earthrace, and now lying on the bottom...) where it took a team of 4 of us almost an hour to trun the boat around 90 degrees in the berth it was in!!

Willallison
02-13-2010, 06:26 PM
I would also question eriks assertion that a displacement hull that is 'pushed' beyond its theoretical hull speed - and that is designed to do so - is a better proposition than a planing hull that is designed to operate at the lower end of the speed spectrum. Depending on circumstance, one may well be favoured over another, but it's certainly not a hard and fast rule.
Clearly, at true displacement speeds the displacement hull is likely to be better, but beyond this, an argument can be made for either solution IMHO

Eric DEBORDE
02-13-2010, 07:14 PM
A pic to illustrate "faux tri"
http://4.bp.blogspot.com/_fv_Crzh0h54/S3cxHKtODsI/AAAAAAAAAMI/oQ_vNTh0CwM/s400/big+sam.bmp
500 to 600 kg for the hull / 12m long / 30 hp for 15 knots.

TollyWally
02-13-2010, 07:22 PM
Will,
What is it that makes such a vessel so inherently hard to manuever?

sandy daugherty
02-13-2010, 07:47 PM
Uulp! I just started reading the Faux Tri string. I wish I had studied it before I jumped in here. Many answers are now questioned!

Willallison
02-13-2010, 09:11 PM
Will,
What is it that makes such a vessel so inherently hard to manuever?

Well, to be fair, it depends a great deal on the vessel itself. Mostly it stems from an inability to get near the bow. Obviously, the longer the ama's are, the less of an issue this is. And Earthrace was about as bad an example as I've seen - movement aboard was about as difficult as it could get!

TollyWally
02-13-2010, 11:41 PM
Wow,
If I'm understanding you (IF) it's because the crew can't physically get to where it would be convenient to do their jobs?.

Willallison
02-14-2010, 12:42 AM
Yep... that's much of the problem. But then you have to remeber that this particular boat was made to circumnavigate the worlds flatter oceans to publicise the use of biofuels... not to be managebale at the jetty.

TollyWally
02-14-2010, 02:03 AM
LOL,
I realize the boat's purpose was to cirumnavigate the world without using any demon oil. But me, after a long voyage around the globe, I'll be a little tired and cranky and don't want a bunch of hassles tieing up at the dock keeping me from getting off that boat! :)

Boston
02-14-2010, 02:41 AM
funny thing is the whale wars folks converted it to that demon oil if I remember it correctly

which I may not

FAST FRED
02-14-2010, 09:20 AM
Just a note , wide beam , over 8ft 6 inches can mostly be overcome with a permit.

TOO LONG , usually over 65 ft from front of vehicle to end can not be permitted in most states.

Yes there are some states that will allow longer , but keeping the tow vehicle and trailer down under 65 is required.

Towing with a motor home would make loads of sense 30 -35ft being the most common with an engine that can drag a 10,000 load at highway speeds.

Using this concept might shrink the boats LOA a bit .

FF

sandy daugherty
02-14-2010, 04:20 PM
Does anyone know of a production boat that approaches this goal? I mentioned the Nimbles, and have discovered the Rosborough 246, which are very close, but I have to ask myself whether a small, narrow displacement diesel coastal cruiser is all that practical or desireable, if none have been built?

Yes, I err to ask here about conventional market approval....

rasorinc
02-14-2010, 04:31 PM
How much money do you have to build and outfit this boat you want to build?
Once that is known then you can weigh the plus and minus and know what you have to settle for. Were all kinda stabbing in the dark right now.

Boston
02-14-2010, 04:55 PM
Hey Sandy
if you really want to get around the tow restrictions get Farm Plates for your vehicle and you can tow anything
no permits
no restrictions
all you need is a light and your good to drag anything
at least thats how it works here

come to think of it you dont even need the light

best of luck
B

Willallison
02-15-2010, 01:42 AM
Take a look at Tom Lathrops BJ series www.bluejacketboats.com

graftonian
02-16-2010, 01:16 PM
Sandy,
I echo the recommendation to check out Tom Lathrops Bluejacket boats website. He seems to to have the answer, at least for me. We have trailered 22 and 25 foot C-Dorys around the US and Canada. Also spent 3 months aboard on a trip up the Illinois to the Great Lakes. Tom has come up with a lighter, longer, more efficient hull without the $100K price tag.
Regards,
Duane

FAST FRED
02-17-2010, 08:02 AM
The Bluejacket 28 seems to solve all the problems. Trailerable , light , a yet with scantlings to go fast as you can stand in rough water.

AIREX , (for the insulation and low noise with light weight ) would be my construction choice , but under $100K might be hard with core material as expensive as Airex.

FF

marshmat
02-17-2010, 09:49 AM
The Bluejacket is about as efficient as you will get in a planing hull. If your mission is mainly lakes and fair-weather coastal cruising at higher speeds than you'd get from a sailboat, with a decent sprint speed to get out of the way of bad weather, the Bluejacket is hard to beat at any price- and they appear very economical to build.

If heavy weather is in the cards on a regular basis, or you plan to carry large quantities of cargo, the Bluejacket may be too light for you. It gets its remarkable performance in large part by being extremely lightweight relative to its planing surface. Tom may be able to confirm this, but I doubt it's capable of 12 nmpg at cruising speeds- almost nothing this size is. Even my nearly flat bottom runabout, with only 30 hp and weighing about a quarter tonne empty, can't reach this level of economy.

sandy daugherty
02-18-2010, 10:37 PM
Dave Gerr's book arrived this morning, and I'm enthralled. My criteria WILL change after I've read it cover to cover. In the mean time I have some questions:

Are there any 40 to 75 hp diesel engines with N2K data output?

What would the issues be with loading a boat in a shipping container on its beam? The doors to a container are something like 7'8" wide and something like 9' tall. It would require a cradle that could be broken down and shipped via motorfreight to the destination port. The cradle might be designed to help roll the boat on it's side. The boat would need a collapsing cabin top. I'm sure it would neccessitate draining all fluids.

I'm leaning towards a displacement design for the economy, and hope to see a very traditional look, like a 20's commuter. Gerr's 34' DR Northwest Cruiser really rings my bell!

FAST FRED
02-19-2010, 08:24 AM
"What would the issues be with loading a boat in a shipping container on its beam?"

I have been contemplating a cruising boat that could ship by container for a couple of years.

My conclusion so far is upright , on simple wooden rollers would be superior to a special cradle , nothing to ship , store , chase down later etc.

Additionally narrow beam is usually a big help in terms of speed and fuel consumption.

The ATKIN "box keel with reverse deadrise" seems to be my answer , but I am willing to cruise at just below plaining speeds SL 2.8 or so.

On a 39 ft boat 18K as fast cruise , with about 12-14 as LRC would work fine as a good boat for touring.

If you need heavy cargo ability , it might be OK as the original Box Keel boats were both beachable and an 18 ft boat could take a ton of load easily.

There have been a number of "Pocket Cruiser" discussions and others on the Atkin efficiency claims on this board in the archives..

If you come across the insert for Herrishoffs "STROLLER" 1929 commuter , its my idea of what a skiney boat should look like.

FF

sandy daugherty
02-19-2010, 01:26 PM
Dave Gerr's DR Northwest Cruiser is a boxed keel round-bilged boat, a "Jersey Sea Bright Skiff". Powered by a small diesel it seems to fit my original ideas. But all those compound curves must make it a bit expensive to build.

TollyWally
02-19-2010, 08:17 PM
Sandy,
Glad you like the book. Strangely enough, I too am drawn towards the box keel boats for my mind's eye dream boat.

Study the parts about speed, hull shape, engines, horsepower and torque, gears and props. These are the parameters that need to be tweaked and tuned to deliver whatever the desired optimization you demand.

Everything costs money. At this point I wouldn't worry too much about the cost of curvaceous vs. simpler hulls. Get the engineering parameters figured out roughly, then you can concentrate on simplifing hull lines for cost effective construction if all else is still a go.

tom28571
02-19-2010, 10:35 PM
Hello guys, I see that my Bluejacket has drawn some discussion here on a thread that I missed. I am just coming off serious heart surgery last week and it will be several weeks before I'm up to speed.

Speaking of speed, I need to answer the following:
"I would also question eriks assertion that a displacement hull that is 'pushed' beyond its theoretical hull speed - and that is designed to do so - is a better proposition than a planing hull that is designed to operate at the lower end of the speed spectrum. Depending on circumstance, one may well be favoured over another, but it's certainly not a hard and fast rule.
Clearly, at true displacement speeds the displacement hull is likely to be better, but beyond this, an argument can be made for either solution IMHO"

In my design brief to myself for the Bluejacket, this was precisely my objective. That is, to see whether a good cruising boat could be designed to run at very low planing speed rather than drive the semi-displacement hull beyond its natural top speed. You may take a look at my website at: www.bluejacketboats.com That particular goal is covered in the "Designing Liz" page. You should use Internet Explorer which is kinder to my site than Mozilla.

I can report that, to my complete satisfaction, a very normal cruising boat can be built that does this. Some are built at 24', 27' and 28' and the prototype has been running for 10 years. I am currently planing to run fuel use details this spring but I do have some averages. While I doubt that these boats can meet the 12kts and 12nm/hr goal, I don't think any one else can either with similar cruising boats. Fuel use has always been less than 2 gal/hr on all cruises and speeds run from 6 to 23 mph. The boat can be run at any speed desired from zero to 23mph with no apparent planing hump. We often cruise at 12mph to 17mph unless in restricted water where the speed is controlled at lower rate.

I direct attention to the series of photos for the BJ24 on the "Galleries page".
This series show that there is no stern squat from zero to top speed. There is undoubtedly a planing hump, but it is not detectable from the helm.

I have discussed a cruising hull with Will and a couple others here that may have the best chance of meeting that 12/12 goal. I call my version the BJ Glider which has a slim and high L/B canoe central body and a normally appearing topsides. I do know that the Gerr skiff cannot meet the goal and is well short of the Bluejacket in performance other than offshore capability. No free lunch yet.

I'm not completely free from operation nausea yet so will sign off for now.

sandy daugherty
02-20-2010, 02:23 PM
Congratulations on your surgery, Mr. Lathrop! The results are very uncomfortable, but the alternatives are completely unacceptable!

I am impressed with your designs, and most interested in your customer's experiences with the 28, which very nearly meets my (ever-changing) needs.

What is the smallest engine in use on the 28, and what are its fuel consumption figures? It would help to know what the boat displaced at those numbers, too.

I liked my old BF-50, and am watching the newest engines in the 60 to 90 hp range with interest, but these numbers (and the resultant tank sizes for 200 to 400 miles between fuel stops) are wildly variable.

I would also like to know if these engines can be raised completely out of the water, and if you have ideas for heating the cabin.

FAST FRED
02-22-2010, 08:16 AM
" But all those compound curves must make it a bit expensive to build"

With foam core a cheap plug (of house grade wood) is required , so the cost of building and scraping it adds to the overall building costs .

BUT compound or really difficult curves (in wood or aluminum) are a snap!

"No free lunch yet." TL

Probably never will be , but GET BETTER!!

The world needs guys that will push the envelope a bit!!

Hope to see the BJ Glider sometime soon.

FF

tom28571
02-22-2010, 10:18 AM
Sandy,

The first BJ28 is due to launch this Spring. The owner, who is dong the interior finish work, is a fine woodworker and can't be pushed too fast. Of course he is trying to work in NW PA, which this Winter, is not fun.

This BJ 28 will be powered by an Etec 90. The engine on all Bluejackets lift completely free of the water. Unfortunately, that does not include the mount and tilt mechanism but nothing is perfect. I expect speed performance to be greater than the smaller boats with less power but fuel use will undoubtedly be somewhat higher at higher speed.

Below is the first model of a BJ Glider. I had a hard time visualizing just how the bow shape could be fitted in and this is the result. A main reason for doing such a boat is an attempt to provide a spacious cruiser that can have all the amenities for long cruises without fuel penalties. The initial design LOA is about 30' and the beam would be over normal highway limits but acceptable with permits. The initial snap at displacement is about 6000# with about 75% of that in the canoe body. The L/B ratio of the canoe body is ~ 16 and the aft bottom has zero deadrise. The idea is that the canoe body speed will run in the teens with very low drag and wave making while the upper body will plane at the same speed because of its very low bottom loading. All my boats must be trailerable so that is a limiting factor, which I am pushin in this case.

It is only an interesting project for me since I have neither the money nor available effort to complete such a big job. I do expect to get into a towing program with a 4' model.

Ideally, I see a small Beta diesel with horizontal shaft and all other heavy stores to be in the canoe body. Some thought is to create a bit of a tunnel behind the canoe body to allow a larger diameter prop for greater efficiency. I see fuel efficiency to be similar to a small displacement cat of similar LOA.

With outboards, I see a pair of small 4 strokes very close to each other and on or just inside the transom so that cruise could be on one or both depending on which offers the best performance for the need. The aft length of the canoe body would depend on which power is used and where it is placed.

Pierre R
02-22-2010, 11:58 AM
I always jump into these discussions looking over my shoulder a bit. Let's look at your original post. You state you would like the boat for snow birding the Eastern Seaboard. If that is your goal then let's look at the real situation for dollars and cents practicallity.

When you consider an RV, the miles you can travel in a year can easily exceed 15,000 miles. The miles you can reasonably do on a boat doing the snowbird route is at best 4,000 miles. It does not take much thought here to see that the boat can get substantially less mileage than the RV yet not exceed the RV in yearly fuel cost even though the RV gets far better mileage.

Now the length of time that you will be in the boat to do the 4000 miles will be more time than you will have in the RV. The RV does not rock in waves. Weight must be removed from boats to get better mileage. Removing weight removes comfort items and a comfortable ride in waves. Is that a good tradeoff in your case? That is the question you must answer. Study chapter 14 in The Nature of Boats.

For 4,000 miles, (not NM), a boat that gets 5 mpg at 9 mph will burn a total of 800 gallons. Now the current price is $3.00 per gallon. That is a total of $2,400 per year or $200 a month. Your current utitlity bill is probably higher. Is cutting your fule bill to say, $1,400 a year worth giving up subtantial comfort in a seaway. Only you can answer that.

The miles per gallon a boat gets does not tell the whole story.

tom28571
02-22-2010, 03:54 PM
Some good thoughts Pierre. Just as MPG does not cover the real expense of cruising, these numbers don't either. First, you have to look at the demographic being served by the proposed economical cruiser. So far, the people here seem to be more middle class in economics than are able to buy any boat they want, have it delivered anywhere they want it and have all the attendant systems cost whatever falls out.

We seem to lean in the direction of trailerable boats that we can haul to our desired cruising grounds to cruise for the period of time in our vacations from the work required to pay for it. After our cruise, we haul the boat back to dry storage and go back to work. For many of us, this is the only way, other than chartering, that distant cruising grounds become practical. Its desirable that no special vehicle be required for the towing also. Many of us, me included, consider this the most enjoyable way to cruise distant or inland locations rather than trapped by the demands of a larger boat.

I agree with you that fuel costs are not the bugaboo of annual costs of larger boats, considering the amount of time spent on them. For the family saving for the kids college fund, it may be critical to the amount of time a boat is used. Also, some just want to make a smaller footprint, GW or not. One end of the Option One thread is my 24 footer and the other end at present is Will Allison's Graphite,which is larger, faster and a bit more lavish in appointments.

For me, I can go out to my inexpensive selfbuilt boathouse, hook up the boat, launch it free and take off. The ONLY immediate cost is fuel. Our RV compares in about the same way to the bigger ones you mention. 15mpg, parks just about anywhere in a legal space, gets underway in a flash and has probably been more places that most. There is no best solution, just one that is best for the individual looking at it.

Pierre R
02-22-2010, 05:34 PM
Tom I certainly was not trying to slight your BJ series of boats. They look pretty nice to me for what they were designed for. I can see trailering one to take a vacation on the Erie Canal, the Tennessee river system or the ICW south of your present position. Maybe even live on the St. Johns river in the winter. I would expect that I could build the BJ 28 for in the neighborhood of $20k with outboard. Something like Gerr's DR 28 would be more in the neighborhood of $90k.

That said there is a world of difference between the BJ 28 and the DR 28. Those contemplating building either should be aware of the differences.

I will keep you web site saved. I run into a lot of folk for whom the BJ series would work well.

sandy daugherty
02-22-2010, 05:58 PM
Since I like to see all the sights from the water, my choice of RVs would be severely limited (or very expensive) To tell the truth, I intend to continue sailing my PDQ 36, and was inspired to start this thread with the thought that it would be nice to go to the Miami Boat Show via the IC, but it would be better to do it at more than 6 knots and without a full set of foulies. So I started looking at small trawlers on the internet. Plastic rocket ships are out because I'm green and cheap.

I have to thank all of you for intruducing me to a world of new concepts and practices. I've been bit and I'm going to put at least one foot on the dark side. I gotten to "quarter-beam buttock lines" in Dave Gerr's book, and I am hanging on, if reading slower. So Tom Lathrop's BJ Glider is "veeerrryy intelesting" to say the least. Where can I read more?

tom28571
02-22-2010, 07:04 PM
Tom I certainly was not trying to slight your BJ series of boats. They look pretty nice to me for what they were designed for. I can see trailering one to take a vacation on the Erie Canal, the Tennessee river system or the ICW south of your present position. Maybe even live on the St. Johns river in the winter. I would expect that I could build the BJ 28 for in the neighborhood of $20k with outboard. Something like Gerr's DR 28 would be more in the neighborhood of $90k.

That said there is a world of difference between the BJ 28 and the DR 28. Those contemplating building either should be aware of the differences.

I will keep you web site saved. I run into a lot of folk for whom the BJ series would work well.

Pierre, No slight detected or taken. It is only because of lengthy recuperation from heart surgery that I am hammering away at the computer so much and perhaps dominating this thread way too much.

You are certainly correct that the BJ28 and the Offshore 28 are very different in just about every way. Either is better in its own element than the other. I do have one quibble. I doubt that the materials building cost of either is much different. What difference either might be built for is more closely related to the level of finish desired and interior elements included than the basic materials. In any case it would be more than the lower figure for the BJ28 and far less than $90K for the DR28. I don't know where that much money could be used. Cheers!

Pierre R
02-22-2010, 07:49 PM
Ah Tom, I misstyped. I was thinking the DR 34 Northwest not the DR 28 at a cost of $90k.

What do you estimate is the cost of materials for the BJ 28 and what kind of time to you estimate for construction to a medium commercial finish?

graftonian
02-25-2010, 05:36 PM
Tom,
Good to see you up and about. Wishing You a speedy recovery.
Duane

u4ea32
02-26-2010, 01:00 AM
OK, maybe I'm missing something. I see the 8K lbs displacement as a maximum, not a minimum nor a target.

If we do the same as Tad, and parametrically explore the possibilities, it sure looks simple to me.

Let's say it does need to be 8.5 feet wide, and light. That suggests a hard chine shape, which suggests a planing hull. So let's use the old and very well proven Crouch method.

http://www.go-fast.com/boat_speed_predictions.htm

Gasoline: 10hp/gal/hr, Diesel 20hp/gal/hr.

So for gasoline power, we need 12 HP. For diesel, we can use 24.

Let's assume a well designed, stepped bottom, so the Crouch number is about 250.

That allows a weight of 5208 lbs uses 12 HP to go 12 mph.

Now, to be fully planing, as one must be for the Crouch equation to work, you've got to have very light bottom loading.

What is the bottom loading required to plan at, say, 9 knots? It must be computable, and its certainly possible as there are plenty sailing dinghy classes that plan at less than 9 knots.

Building a 40 foot 15 degree V bottom that weighs 5000 lbs is trivial: epoxy glass and nomex yields a 0.5 lb per square foot finished boat that is mighty tough (again, plenty of racing dinghys are this weight, but so are STP 65 racing yachts -- but they are carbon not glass, but have ENORMOUS loads). The entire hull and deck and interior structure for the STP 65 Rosebud, built by Westerly Marine in 2007 of carbon, epoxy, and nomex, weighed 2200 lbs!

Let's make the planing requirement simpler: If the engine is diesel, we can go 17 knots with the same 1 gallon per hour, same displacement of 5208 lbs. A shorter hull with more conventional loading will plane flat at 17 knots.

In other words, reduce the displacement, make it plane with an efficient (stepped) bottom, and the 12 mpg target is not tough to hit. You can't hit it if you try and go 30 knots, but if you get fully planing at low speed, you can.

Willallison
02-26-2010, 01:26 AM
Wow - that's an interesting conclusion...
A 40 x 8.5ft, 2,300kg boat that will plane at 9 knots, using 12hp to do 12....
Good luck with that.....

Willallison
02-26-2010, 01:26 AM
Apology for the sarcasm....

TollyWally
02-26-2010, 02:45 AM
Might I be so bold as to suggest that one problem with a 40 foot hull with low enough bottom loading to plane at 9 knots with 17 hp no matter how exotic the hull materialis is keeping that 40' hull free from all the accumulated gear that a cruiser naturally collects.

FAST FRED
02-26-2010, 08:28 AM
40 foot hull with low enough bottom loading to plane at 9 knots with 17 hp

Would be interesting to be able to compute weather taking 75% of the hull weight in the box keel canoe body would lower the plaining bottom loading enough to get even greater efficiency.

Either a higher cruise or smaller fuel burn? But I sure cant do the math!

FF

Pierre R
02-26-2010, 09:52 AM
I can understand wanting to be super green but so often lately this seems to be trumping practicallity in these discussions.

Generally speaking, a boat getting 4 mpg will not be able to burn enough fuel annually while traveling north and south along the US Eastern Seaboard to offset what even modest living on land will produce in terms of energy use. By moving aboard you are almost always greener than if you live on land.

A nice boat that will not trash you when it hits a boat wake, not be uncomfortable and unsellable can be made to do what you want for around 4 mpg. Even at 2-3mpg you are still plenty green enough.

I know that we are a bunch of thinkers and dreamers but when the money hits the table most of us don't approach the impractical things discussed here.

I know that I play these stupid numbers games with my own boat. If I slow down my own boat one knot off hull speed I can increase my mileage by a whopping 30%. Think of all the money I can save in a day. In a 10 hour day I will burn three gallons less but also travel 10 miles less. Now over the same distance that translates to about 2.1 gallons less. Wow, I am saving $6.00 at todays prices. That is 60 cents and hour. Now on a 4000 mile annual basis I could save and additional $489 and only pay a 133 hour penalty.

So after all these calculations, what do I say to myself and do? Oh piss on it. run the damned engine at 65% power and pay the additional 60 cents an hour penalty you frikin greeny cheapskate . I am flying at 6 knots and poking at 5 knots. I'm not on land so my energy usage is still less even at the whopping 30% increase in dinosaur juice. My fuel bill is around 7% of the budget even at the higher fuel burn. I can burn $489 in the car in less than a couple of months. Such is the silly games I often play with myself.

sandy daugherty
02-26-2010, 09:55 AM
Much of the Waterway is speed posted, as low as 6 knots. Long stretches cross some moderately snotty conditions of steep chop in shallow water, such as Pamlico sound, or pounding down the Delaware Bay. Is a stepped hull such a good idea there, with dishes in the sink?

Oh, Pierre, thy lash doth sting. Your point is taken, with a heavy seasoning of grumbling. So I have to quit pretending to be all that virtuously green. If that were really my goal I should ride a bicycle to the train, and sleep under the stars. Or just stick to sails and live on raw fish and bilge-grown bean sprouts.

Not.

I'm too old, I creak, and I worked 45 years to afford a little ease in my dotage. So its back to the wishlist to decide how much a sufficient level of comfort weighs. There should be spreadsheet where you simply check off what you know you need to be comfortable, that would calculate the weight, then the size and shape of right boat.

Do you designers have to go through this with every customer that comes along?

TollyWally
02-26-2010, 10:58 AM
"So its back to the wishlist to decide how much a sufficient level of comfort weighs. There should be spreadsheet where you simply check off what you know you need to be comfortable"

Those are both damn good ideas.

Pierre R
02-26-2010, 11:12 AM
"So its back to the wishlist to decide how much a sufficient level of comfort weighs. There should be spreadsheet where you simply check off what you know you need to be comfortable"

Those are both damn good ideas.I attempted a solution on another forum here:
http://www.livingaboard.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=3;t=000848#000002

u4ea32
02-26-2010, 11:14 AM
Will, your Graphite design looks close to what's asked for. The 4nmpg at cruise: what speeds?

u4ea32
02-26-2010, 11:16 AM
I agree with the risks of gear accumulation. One must be extremely diligent

marshmat
02-26-2010, 12:44 PM
Let's say it does need to be 8.5 feet wide, and light. That suggests a hard chine shape, which suggests a planing hull. So let's use the old and very well proven Crouch method.

http://www.go-fast.com/boat_speed_predictions.htm

Gasoline: 10hp/gal/hr, Diesel 20hp/gal/hr.

So for gasoline power, we need 12 HP. For diesel, we can use 24.

Let's assume a well designed, stepped bottom, so the Crouch number is about 250.

That allows a weight of 5208 lbs uses 12 HP to go 12 mph.

Now, to be fully planing, as one must be for the Crouch equation to work, you've got to have very light bottom loading.

What is the bottom loading required to plan at, say, 9 knots? It must be computable, and its certainly possible as there are plenty sailing dinghy classes that plan at less than 9 knots.

Building a 40 foot 15 degree V bottom that weighs 5000 lbs is trivial: epoxy glass and nomex yields a 0.5 lb per square foot finished boat that is mighty tough (again, plenty of racing dinghys are this weight, but so are STP 65 racing yachts -- but they are carbon not glass, but have ENORMOUS loads). The entire hull and deck and interior structure for the STP 65 Rosebud, built by Westerly Marine in 2007 of carbon, epoxy, and nomex, weighed 2200 lbs!

Let's make the planing requirement simpler: If the engine is diesel, we can go 17 knots with the same 1 gallon per hour, same displacement of 5208 lbs. A shorter hull with more conventional loading will plane flat at 17 knots.

In other words, reduce the displacement, make it plane with an efficient (stepped) bottom, and the 12 mpg target is not tough to hit. You can't hit it if you try and go 30 knots, but if you get fully planing at low speed, you can.

An interesting approach, but I have my doubts about the numbers and the validity of the Crouch method in this case.

A Crouch number of 250 is what one might apply to a 3-point racing hydro; using a more realistic 200 and the figures above, we get 23 hp to do 12 mph. Still an underestimate, if you ask me, because we haven't considered wind, waves, or the planing hump yet.

As a rough empirical estimate, the bottom loading to skip the "hump" altogether and be on plane at 12 mph would be on the order of about 100-150 kg per square metre or about 20-30 psf- so 16 to 23 square metres of planing surface. This suggests a very long, wide boat for the weight- almost like the proverbial kitchen-table-with-an-outboard.

I don't think Crouch's method is very accurate at these speeds- it's an empirical formula for boats well above the planing hump. And at 12 mph / 23 hp, headwinds and waves are going to sap proportionally more power than they do for a 400 hp boat at 40 mph.

Can we build a 40-footer that weighs less than 2.3 tonnes with full tanks, all gear, engine, and a full crew on board?

To get 12 mpg at 12 mph, I think, would- in a planing hull- call for a boat about half this weight.

***

The points made earlier about the risk of gear accumulation, and the minimum standard of luxury desired, are critical.

The point made earlier that the actual cost savings from such stinginess might be pretty small is also worth considering. In the smaller, relatively powerful boats I use, trips to the gas pump are one of the big expenses- as you get to cruiser size, though, this becomes secondary to insurance, maintenance and mooring. The balance seems to stay that way- fuel cost being a relatively small fraction of TCO- until you get up to commercial craft such as light freighters and fishboats.

u4ea32
02-28-2010, 01:20 PM
An interesting approach, but I have my doubts about the numbers and the validity of the Crouch method in this case.

A Crouch number of 250 is what one might apply to a 3-point racing hydro; using a more realistic 200 and the figures above, we get 23 hp to do 12 mph. Still an underestimate, if you ask me, because we haven't considered wind, waves, or the planing hump yet.

As a rough empirical estimate, the bottom loading to skip the "hump" altogether and be on plane at 12 mph would be on the order of about 100-150 kg per square metre or about 20-30 psf- so 16 to 23 square metres of planing surface. This suggests a very long, wide boat for the weight- almost like the proverbial kitchen-table-with-an-outboard.

I don't think Crouch's method is very accurate at these speeds- it's an empirical formula for boats well above the planing hump. And at 12 mph / 23 hp, headwinds and waves are going to sap proportionally more power than they do for a 400 hp boat at 40 mph.

Can we build a 40-footer that weighs less than 2.3 tonnes with full tanks, all gear, engine, and a full crew on board?

To get 12 mpg at 12 mph, I think, would- in a planing hull- call for a boat about half this weight.

***

The points made earlier about the risk of gear accumulation, and the minimum standard of luxury desired, are critical.

The point made earlier that the actual cost savings from such stinginess might be pretty small is also worth considering. In the smaller, relatively powerful boats I use, trips to the gas pump are one of the big expenses- as you get to cruiser size, though, this becomes secondary to insurance, maintenance and mooring. The balance seems to stay that way- fuel cost being a relatively small fraction of TCO- until you get up to commercial craft such as light freighters and fishboats.

Yes, I totally agree with all your statements, except the 250 number: modern long narrow deep V stepped bottom designs by Fountain, Donzi, etc are 250 to 265.

The point I was making was that one could explore a planing hull rather than restricting the design to only a displacement hull.

Certainly, the Crouch method works well for craft that are fully planing, and 12 knots or so is only a planing speed for very light bottom loads.

And I also agree that one would probably need to go to about half the design weight -- 2500 lbs instead of 5000 lbs -- to get there. And at that weight, carrying much of anything gets tough.

However, just because the problem is tough, does not mean its impossible. By focusing on such numbers, perhaps a design is there. Perhaps we will see such a design in the current Wooden Boats magazine contest. I'm looking forward to those submittals!

Oh: And there are existence proofs of such boats, but you won't find them in a showroom.

sandy daugherty
02-28-2010, 02:32 PM
This discussion is nudging me dangerously close to buying an old Marinette.

Entirely too much common sense and practicality; we're talking BOATS, remember?

Willallison
02-28-2010, 05:53 PM
Will, your Graphite design looks close to what's asked for. The 4nmpg at cruise: what speeds?

Graphite will burn a little over 1 litre per nautical mile at anything from 10 to about 25 knots, depending on how much is on board. Like all boats, she is a compromise - a middle ground between amenities and the ultimate persuit of light weight. Without too much difficulty, I could shave quite a bit off the overal total.

Pierre - I have to say, you are the 1st person I've actually heard suggest that owning a boat could be considered to be being green! Bravo!:p
Not that I agree with you mind you;)

Easy Rider
03-01-2010, 12:38 PM
Sandy,
Reread your original post and the best boat to fit that bill that I know of is an Albin 25 8.5 x 25 x 2.30'. 1/2 gph at 6 knots .. 1 gph at 9 knots. I know where there is a trailer for sale and several boats for less than 30K. The best value is in the higher priced boats.

Easy Rider

u4ea32
03-01-2010, 07:13 PM
OK, here's some more data. Graphite, designed by our friend Will Allison, gets about 4 nmpg at any speed from 9.5 to 23 knots. So its fully planing at 9.5 knots: planing boats exhibit this flat "nmpg" performance when fully planing. Probably about 7000 lbs as tested (two people, 40% fuel, 70% water, some gear).

Since planing boat performance is pretty much linear with weight, all you've gotta do is go to a third the weight to get three times the mileage.

An example of this is:

http://www.biekerboats.com/Bieker_Boats/25_Footer.html

which, using an outboard and so about half the fuel efficiency of a diesel (about 10 hp/gal/hr for the outboard .vs. about 20 hp/gal/hr for the diesel), gets about 6 nmpg. About a third the weight, about three times the energy efficiency.

By the way, both Graphite and the Bieker Shearwater have warped bottoms, which are supposed to have Crouch numbers of 125 to 150. Plug those numbers into here, and you'll see the proper results. Therefore, the Crouch numbers do in fact still work at low planing speeds, IF the boat has light enough bottom loading to fully plane at those speeds. (try this again: http://www.go-fast.com/boat_speed_predictions.htm)

So, the key to achieving the high target efficiency numbers are light weight (like 2500 lbs all up), diesel, and a planing bottom.

Unlike a displacement boat, the length is pretty much irrelevant for a planing boat efficiency. However, the longer it is, the slower the motion, the smoother the ride. Since 40 feet on a trailer is generally no problem whatsoever, might as well shoot for that length target. Especially as weight of a box 8.5 feet wide and high enough for comfort is simply linear with respect to length.

The Bieker boat is 2250 lbs including power, yet is built of wood. So a glass/nomex/epoxy boat would weigh about a third as much -- about 650 lbs. So double that for a 40 foot, and the boat is still lighter than Bieker's Shearwater.

Hence, I think its not tough to reach these targets, but you've got to go LIGHT.

Fortunately, that way one also ends up with a boat on trailer of about 3500 lbs, and you can tow that with almost any small SUV, like a RAV-4. So you might see high teen's for MPG on the road too. That's sweet!

Willallison
03-01-2010, 07:40 PM
David,
Some of your logic is a little way off reality there, but the main problem is that it's not always feasible to simply build lighter. For Graphite, for instance, the hull is a strip-plank composite structure - ie a timber core, in this case kirri (or paulownia). I investigated using foam-cored construction techniques for the hull (as are used in the bulk of the remaining structure) but in order to achieve the necessary puncture resistance, the skins would have to have been substantially thicker. So any weight savings in the core were offset by the skins. In fact the hull itself would have weighed almost the same with either method. The cost of both materials and labour thus 'weighed' heavily in the favour of the strip-plank.
Sure, I could have engineered it to be somewhat lighter, but almost certainly at a cost in terms of durability and definitely at a cost in terms of $.

Likewise, I could have shaved a considerable amount off the total by reducing the amenities on board. But the the boat I would have ended up with would have been a far more spartan affair and not in line with the design goals that were set for it.

u4ea32
03-01-2010, 08:07 PM
Well, I'll respond the same way, Will. Your logic is a little way off reality.

There do exist much, much larger yachts with substantially lighter displacements than can be obtained via a strip plank hull. For example, as I mentioned earlier, the STP 65 Rosebud, a 65 foot racing yacht with a 20,000 lbs lead bulb on the end of a 14 foot carbon fin. That keel juncture absorbs astronomical loads, far higher than the boat we are proposing here. To say nothing of the tens of tons of rigging loads. And the broad flat bottom needed to be designed to absorb tremendous pounding loads at sea, far more vertical accelerations than anyone would chose to experience while cruising. Yet that 65 foot by 18 foot yacht, with 6 foot of headroom throughout below, weighed 2200 lbs: that's hull, deck, and all internal structure and floors.

Now that's an expensive carbon/nomex/epoxy structure, carefully constructed. But its MUCH more area, and many times as strong, as required in this case.

That's reality, Will. Your chosen construction method aint close to optimal for weight. Its a nice cheap way to build perhaps, but its very heavy compared to the state of the art. Light compared to some other methods, true. But there is no reason to lock into outdated heavy technology.

Its all part of the engineering trade space.

You traded, and High Modulus traded, and two different solutions were found. Sorry, Will, but in engineering, that isn't unrealistic logic, its just different weightings for value functions.

TollyWally
03-01-2010, 10:01 PM
The state of the art is not always the correct answer for a given engineering exercise. Perhaps the term unrealistic logic is the wrong one here. Different weightings for value functions doesn't neccessarily imply one set of weightings is logical and another is not.

Expensive bleeding edge technology is often cost prohibitive and unavailable as a viable solution for a specific engineering exercise. I think that may be the case for a carbon/nomex/epoxy structure as an engineering solution when Economical coastal cruiser is the defining mission statement. Graphite, while not the lightest conceivable structure available, seems an elegant, relatively cost effective solution .

Willallison
03-01-2010, 10:53 PM
Wow David... glad to see you edited out the last line of your post.... there was nothing personal intended about my comments.
As I said, I could have engineered Graphite's structure to be lighter, I have no argument with you there. And yes, in the recreational field, any designer that doesn't consider cost as a part of the design spiral is not doing his/her job properly. She is light by production standards, but is conservatively specced - intentionally. The BJ24 is evidence that you don't need to go high-tech in order to save weight.
I never suggested that you couldn't build lighter than using strip plank, and the larger you go the easier it is to achieve substantial weight reduction using composites, but to suggest that it's nothing more than outdated technology is missing the point.
We are not talking about a 65 ft racing yacht that will likely be outdated, valueless and probably scrapped in a few of years. It will almost certainly undergoe repairs during that time. We are looking at a recreational coastal cruiser that will get smacked into jetties, driven onto its trailer and the like every weekend. Owners of racing yachts are prepared to shave safety factors in order to improve performance. Not many weekend boaties would do the same.

As an example of where your comments are a little off target, Graphite's bottom shape is not warped, it is a monohedron for about the aft 40%.

By way of another example, let's look at the MJM series of boats. The 29Z is probably the closest in size compared to Graphite. She incorporates some fairly high-tech construction and the designer has gone at least some way towards keeping things simple ( at least to the extent that their market segment will permit)"
29z is the only 29 footer in the
world specifically designed to maximize fuel efficiency with a high-tech epoxy wet
pre-preg Kevlar/E-glass/Corecell composite laminate, vacuum-bagged and oven-postcured.
This is a building method perfected over 25 years by Boston BoatWorks in
building custom racing yachts, including America’s Cup contenders. 29z is stronger and
lighter than conventional fiberglass or SCRIMP construction.

The result of all that effort? A dry weight of 7600lbs & a bit over 3 nmpg at cruise speeds.
So whilst you may poo-poo strip-plank epoxy composite construction as being out-dated technology, I'll await for you to provide a comparable example that weighs significantly less.

marshmat
03-01-2010, 10:56 PM
TollyWally - bang on.

I've designed and built ultra-light carbon/nomex composite structures (solar cars, in my case); I can say with confidence that while these are amazing materials, they will not work miracles.

Will is quite correct that when you have to consider such loads as running aground, or ramming a dock at four knots in a nasty crosswind, many of the "advanced composite" weight advantages are nullified. A racing boat built to overall safety factors of 1.2 or so is a very different animal than a cruising boat built to safety factors of between 3 and 10.

Multiaxial S-glass over strip plank wood is, indeed, one of the most structurally efficient construction materials available for situations where both large global loads and large, random point loads must be considered (ie, boat hulls). Holger Danske, arguably the lightest (for her length- D/L of 40, of which 43% is the keel) bluewater racing monohull around, was built in this method.

Outside of NASA and the big racing syndicates, cost usually gets a pretty big weighting. This alone rules out most "advanced" materials for the vast majority of projects.

TollyWally
03-01-2010, 11:46 PM
An old hot rod maxim comes to mind;

Speed costs money, how fast do you wanna go? :)

erik818
03-02-2010, 06:14 PM
I still don't see why a long narrow displacement hull wouldn't fit the bill, a faux tri, stabilised displacement hull or whatever they may be called. I also count "displacement gliders" like the BJ Glider Tom is working on as basically a stabilised narrow monohull.

OK, there are yet no ready plans to buy and I know of no suitable production boats, so a comparision with existing reasonably efficient boats is unfair. Sandy asked us to not be so down to earh practical so why not explore possibilities? If he isn't going to buy or start building a boat this spring there's no reason to go for existing conventional boats yet.

My understanding is that a 12m long narrow (1m) displacement monohull will meet the requirement on fuel consumption at 12 knots for 3 - 4 tons displacement if using a diesel inboard. There's a challenge to make a hull like that into a practical boat, and not looking like something from Star Trek. I'm not convinced that it cannot be done though.

Erik

u4ea32
03-02-2010, 07:34 PM
A comparable example that weighs substantially less than Graphite.

Well, the Bieker boat is only 2 feet shorter and weighs a third as much, using a very similar construction approach. So one does not even have to leave wood core to get a much lighter vessel.

But for these comparisons, I assume Graphite without engine is about 4500 lbs (about 1200 lbs for the engine, outdrive, essential bits (pumps, batteries, engine mounts, fluids, ...).

How about an Olson 30, without a keel. Same length and beam, less freeboard, but 1600 lbs without a keel instead of 4500 lbs without an engine. Olson 30 is just glass, polyester, and balsa core.

Or a 1D35: longer, about same headroom, more beam. 4000 lbs without keel but with engine, mast, rod rigging, ... and the additional strength and structure for the keel and rigging. Glass, foam core, epoxy.

Or a Farr 40: a substantially larger boat, a bit less that 5000 lbs again with all the structure for a sailboat, with mast, engine, ... Again, just glass, foam, and epoxy.

Or even a crazier example: a 30 square meter, 40 feet long, 6500 lbs including 3500 lbs of lead. Built of wood planking 70 years ago.

So lighter structures are pervasive, even when they need to be designed to MUCH higher loads than a cruising powerboat, and even when built using cheap materials (plain glass, cheap cores).

So again, my point is that to achieve dramatically different performance, some things must be dramatically different. In the specific case we are discussing, the desired performance is high fuel efficiency at moderate speed, and trailerability. Both are clearly greatly advantages primarily by weight. Weight matters more than any other aspect of the design.

Low weight is the essential enabler to achieve the 10 to 12 nmpg of the original query. Without light weight, the goal can't be achieved. Only with very light weight (like 2000 to 2500 lbs) can the goal be achieved, and then it can fairly easily, regardless of hull design: planing or displacement.

Obvious, correct?

Willallison
03-02-2010, 07:35 PM
What's wrong with Star Trek?

sandy daugherty
03-02-2010, 07:35 PM
A 12m cat would not be an outrageous or even distasteful consideration. Does anyone believe one can be built for less than the price of two boats?

Willallison
03-02-2010, 08:02 PM
Quite how you can say that any of those are comparable in anything but size is beyond me...
Graphite has 4 permanent berths, 2 showers, a microwave, a galley and saloon / cockpit with space to rival most 40 footers. It can comfortably accomodate its crew for extended cruises, offers a range of well over 400nm and carries 400l of water. There are separate batteries for starting and house loads (2 x 120AH). Whilst it wasn't a major design objective, it has a top speed of 32 knots, so the far greater slamming loads must be accounted for when considering the stucture.
I don't have a problem with justifying the construction choices for Graphite. Suffice to say that I examined all the available options and the strip-plank hull came out trumps. I don't have the figures in front of me, but from memory, the hull shell (topsides and bottom) totals just 350 kg of the total weight, so even if you can manage to make a considerable % saving, the effect on the total will be minimal. The bulk of the rest of the boat is made from foam or balsa cored composite panels, so major weight reduction there would be difficult.
Now - yet again - let me say, Graphite is intentionally conservatively specced in terms of scantlings & I am not suggesting you can't build a similar boat that weighs less. But the only way you will do so in any meaningful way will be to have 'less' boat.

Willallison
03-02-2010, 08:03 PM
A 12m cat would not be an outrageous or even distasteful consideration. Does anyone believe one can be built for less than the price of two boats?

No :(

u4ea32
03-02-2010, 08:22 PM
Now - yet again - let me say, I am not suggesting you can't build a similar boat that weighs less. But the only way you will do so in any meaningful way will be to have 'less' boat.

I agree. A boat weighing only 2000 to 2500 lbs will be a lot less boat, not simply different scantlings.

u4ea32
03-05-2010, 05:29 PM
OK, now that Will and I seem to agree again, as we usually do, and I'm not taking things personally (sorry, that was inappropriate, and my only lame excuse is that I had the flu for a MONTH).

Sandy, I think you hit the nail on the head with the suggestion that a spreadsheet is needed to first figure out how much all the stuff you want to take along actually weighs.

One fellow told me that you should not start really designing until you've identified the absolute minimum you want in the boat. Its all the extras that drive the cost and weight, and not simply the hull and deck.

And yes, I think this is in fact something every boat design needs from the beginning, and it gets maintained throughout the design and build process.

Anyone care to start?

sandy daugherty
03-06-2010, 06:36 PM
I'm piddling around with the idea, but I'm not very adept with spreadsheets. I think the idea can be expanded a bit to a list of options and costs in dollars, weight, man hours, added structure and systems. I'm thinking of a question and answer concept that starts with the buyer/builder's broad goals and limits, such as finances, time, trailered or kept in water at a dock or mooring, cruising area, realist berthing, and so on. Part of the table would include parameters that can be set for the cost of resin, the price of an engine, and the size of fuel and water tanks, etc.

It's beginning to sound like a book, too. I think that arriving at a total weight of accumulated crap/bare necessities, and some idea of the type of vessel envisioned, we could calculate the approximate size and complexity.

Gazing deeper into my fishbowl/crystal ball, I could see this quiz working for a boat shopper too. Fred the fish just looks back at me like I'm off my meds. He thinks my time could serve a higher purpose by dropping a few food flakes
in a convenient location....

Pretty wild, huh?

FAST FRED
03-07-2010, 11:14 AM
There's a challenge to make a hull like that into a practical boat, and not looking like something from Star Trek. I'm not convinced that it cannot be done though.


Stability under way could be done with out the drag of a set of Amas.

Think of a simple Maurice Griffiths style center board case made 3x wider than usual.

A well shaped board could have a simple ram to give it a slight angle of attack , voilla roll stability, with out huge hydraulic fins sticking out the side.

Go fast , need less drag,pull 3/4 of the board up.

Run aground? no problem with $10K fins holing the hull , the board simply does what it does on sailboats for 500 years.

There would be no outside unusual shapes required .

FF

sandy daugherty
03-07-2010, 12:59 PM
Do you mean dynamic roll stability control? On my budget?

erik818
03-07-2010, 04:57 PM
FF,
I've searched the net best as I can to understand what a Maurice Griffits style center board is, without success. How is it different from a normal center board?

Erik

sandy daugherty
03-07-2010, 06:10 PM
Gee. Erik, it should be obvious! A normal centerboard is easier to find on the net.

u4ea32
03-08-2010, 06:23 PM
Dynamic roll control does not need to be astronomically expensive. The least expensive Naiad system is less than $15000 USD. A roll-your-own could be substantially cheaper:

Imagine using moth foils. These generate 200+ lbs of lifting force. Thye are mechanically controlled by a wand that kisses the surface of the water: when the foil is deep, the wand causes the foil trailing edge tab to be pushed downward, increasing lift. For a fully mechanical system, a couple of moth T foils mounted perhaps at the transom outboard corners so they would kick up on impact. The cost of a moth T foil is about $2500 USD. Buy two, that's $5K. The mechanical control won't lead to zero roll, but could lead to greatly reduced roll, and its easy to tweak and play with.

Or, one could use the computer you'll probably have onboard anyway, add a USB IMU (inertial measurement unit) for less than $1000, write a little control system, add some motor controllers and motors, and then actively control those foils.

If you've never been on a boat with active roll control, you will be amazed. A typical installation results in ZERO roll up until the seas get amazingly wild, at which time you might see a few (like 3) degrees of roll in, say, 10 foot beam seas. It really seems like magic!

I think its highly likely that a NAIAD system is cheaper than amas, and for certain stabilizers result in MUCH less roll motion than amas.

When you are anchored, use flopper stoppers to get just a few degrees of low rate roll.

Or, use a planing V bottom for dynamic roll control. The dihedral stability at even low planing speeds is very noticeable. Try sailing a planing dingy like a Laser, 505, Windsurfer: at about 6 knots, as the boat is starting to plane, it gets MUCH more stable.

I've gone around and around on this, within the constraints of 8.5 foot beam for trailering. Cat, Tri (really, augmented thin monohull), displacement, planing, ...

I think that the simplest, cheapest to build and to own over long term, is a VERY light planing V bottom monohull. If its very light, then planing can occur at essentially displacement speeds, so you always get that dynamic roll stability. At anchor, use the flopper stopper. Its the simplest structure: most internal volume per unit surface area. Its therefore the lightest, all things being equal (surface area equals weight and cost, so minimize!).

How light? Use that spreadsheet, try to always choose the simplest: e.g., the minimum number of engines is one, so choose one. Minimum number of heads is one, so choose one. And so on. Then figure on 0.5 to 0.7 lbs per square foot for the hull and deck and bulkheads and stringers and floors (you can achieve 0.5 lbs pretty easily). Then just design to fit that weight.

I find that the design needs to be a stepped bottom with a pad, just to get the displacement down to the design displacement.

sandy daugherty
03-08-2010, 07:07 PM
Eric: its Maurice Griffiths, who passed away in 1997. He wrote a book that inspired many British readers to build their own boat: sort of like Phil Bolger did for the Hippy Boomer generation.

U4ea32: I thought I was the starry-eyed far-sighted dreamer here! But that is what Forums are for. You suggestions are interesting, but a little bit of a stretch for someone who admires Dave Gerr's 1920's-looking DR Northwest Cruiser. Getting a bedroom, 3/4 bath and kitchen up on foils would be challenging to say the least!

TollyWally
03-08-2010, 07:13 PM
Sandy,
I may be mistaken but I don't think he is referring to foils. Think of the Lulworth mentioned in Gerr's book with a flat spot aft to ride on.

u4ea32
03-08-2010, 08:40 PM
Oh, I was not suggesting being up on foils, just using the foils for roll control.

u4ea32
03-08-2010, 08:57 PM
To review these 6 pages of posts: there are five specific existing boats mentioned in this and previous posts that at least approximate the design target:

Blue Jacket 24 or 28 (bluejacketboats.com, by Tom Lathrop). Tom sees 6.5 to 8.5 nmpg using an outboard.

Shearwater by Bieker. They see 6+nmpg over a 690 mile trip, using an outboard.
http://www.biekerboats.com/Bieker_Boats/25_Footer.html

WHIO by Peter Sewell (http://www.woodenboat-digital.com/woodenboat/20060506/) that gets 10 nmpg at 10 knot cruise.

Graphite by Will Allison that sees 4+nmpg using a diesel.
http://www.imaginocean.net/index1.html

MJM 29 that sees 3nmpg using a diesel.


Each of the above vessels meet performance predictions of the Crouch method
http://www.go-fast.com/boat_speed_predictions.htm
using "Constant" values about 150.

The diesel boats get about twice the HP per gallon of fuel as the outboards.

The Graphite boat is lighter than the MJM, and that difference in displacement matches the higher efficiency of Graphite over MJM.

Similarly, the Blue Jacket and Bieker's Shearwater are smaller and about a third the displacement, but use half as efficient engines, so get 1.5 times the mileage of the smaller boats over the larger ones.

So I still think that a planing boat weighing about 2500 lbs lightship, 3500 lbs cruising, powered by diesel instead of outboard, should get about 12 nmpg at 12 knots using about 24 HP. Or about 6 nmpg using 24 HP of an outboard.

Of course, one would want some power in reserve, so 50 HP should probably be the actual engine, just like with Shearwater and Liz (the BJ24).

Still, I think that longer is better, and no harder to tow, and so I'd try and design it to be 40 feet long or so, but still carrying the same interior as, say, the BJ28.

In other words, pretty much what that Wooden Boats design contest is all about!

http://www.woodenboat.com/wbmag/designchallenge2.php

FAST FRED
03-09-2010, 08:19 AM
The diesel boats get about twice the HP per gallon of fuel as the outboards.


The gaggle of car builders with tiny diesels is expanding.

Soon enough we may get efficient diesel outboards , that don't need a derrick to mount.

Will solve the problem of fuel poisoned with PC alcohol that wont even store for a month.

FF

u4ea32
03-09-2010, 02:34 PM
I am planning on outboards, personally. That way, as new technology comes along, its just a few bolts to swap the obsolete for the new. The savings on an outboard over an inboard pays for that fuel cost difference.

6 nmpg would make a $300 weekend only $50. That's pretty dramatic! Getting the fuel cost down to only $25 by going diesel... not so compelling. A really good thing!! But just not so compelling.

That $25 per weekend savings would need to repay the costs of the diesel installation, the costs of the elaborate fuel polishing and filtration system, the sound deadening technologies (soft engine mounts, soft shaft coupling, super high precision shaft installation, sound insulation materials, air pathways with sound suppression, ...), the pain of broken running gear when an outboard would just kick up, ...

So while I'd like that ultimate fuel efficiency, I'd be willing to wait a few years for it to be provided in a well engineered package by, say, a Mercury Marine outboard.

sandy daugherty
03-10-2010, 11:23 AM
This thread has turned into a perpetual Christmas Morning, full of wonderful presents. Thanks for the link to WHIO, U4ea32, it's helping me shed some weight from 'dreamboat'. I've never heard of ANYBODY building their own propeller!

I'm going to explore car engines a little more thoroughly now, but I was disappointed to see that Volkswagen's smallest marine engine weights 500 pounds!

Tom Lathrop tells me that someone building his 28' is using an ETEC 90. Interesting.

u4ea32
03-10-2010, 07:52 PM
Sandy, I really think your desires are possible (12 nmpg at 12 knots), but as with Whio, the resultant boat will be quite far from ordinary. I think this can be a very good thing, but clearly, the mass market disagrees. That's OK with me.

Rick is very clear on the concept that custom designed props can make a large difference in efficiency, and are probably essential to achieve your goals. They are not all that difficult to create or to source. Many boats use conventional looking props that were in fact specifically made for that boat. I did so on my last boat. Cost was hardly more than stock off-the-shelf props.

The fuel efficiency of gas outboards is pretty darn good. Besides ETEC, the orbital combustion Mercury Optimax, and the Mercury Verado (when at cruise settings) are very fuel efficient at all speeds and loadings, unlike diesels that really have to be at special RPMs and loads to achieve their potential.

Willallison
03-10-2010, 08:13 PM
Like all things in yacht design, props are a compromise. With an outboard, they are more so, because the diameter is strictly limited. For the same reason, you may find it difficult (or at least not worth the effort) to try to custom build a more efficient one. Though, of course, few off-the-shelf ob props are designed for travel at such low speeds

Guest625101138
03-10-2010, 10:05 PM
Like all things in yacht design, props are a compromise. ...s

Wrong attitude but not uncommon. Designs should aim to optimise not compromise. Consider all the important factors and arrive at an optimal solution. Not just keep compromising on the requirements.

Compromise is a sloppy approach to design. I detest the concept.

The requirements for boats are changing and the the designs need to be redirected. Twenty years ago very few people got too concerned about fuel economy. Now it is a more significant requirement for a raft of good reasons. Would seem a shame to reduce the weight of a boat by 30% by using expensive materials to improve fuel economy then use a prop with 60% efficiency when it could be replaced with one 85% efficient. Surely the optimum result for money would be to save on the materials, build the boat a bit heavier and then spend money on a custom prop.

Unless more people are uncompromising and push the design envelope, as is the case with WHIO, the recreational boat world will be left in the current state where compromise is the accepted wisdom. Just the lazy way out.

Rick W

Willallison
03-10-2010, 10:25 PM
I shall follow the lead of your tone and follow in kind.

Wrong attitude but not uncommon. Designs should aim to optimise not compromise. Consider all the important factors and arrive at an optimal solution. Not just keep compromising on the requirements.

Compromise is a sloppy approach to design. I detest the concept.

The requirements for boats are changing and the the designs need to be redirected. Twenty years ago very few people got too concerned about fuel economy. Now it is a more significant requirement for a raft of good reasons. Would seem a shame to reduce the weight of a boat by 30% by using expensive materials to improve fuel economy then use a prop with 60% efficiency when it could be replaced with one 85% efficient. Surely the optimum result for money would be to save on the materials, build the boat a bit heavier and then spend money on a custom prop.

Unless more people are uncompromising and push the design envelope, as is the case with WHIO, the recreational boat world will be left in the current state where compromise is the accepted wisdom. Just the lazy way out.

Rick W


Spoken like a true 'expert' with absolutely no yacht design qualification whatsoever. I've tried to be respectful Rick, but the absurdity of those comments ought to give anyone with even the slightest hint of boating experience, some inkling of how seriously they should take your remarks. I suggest to re-read your post and than go away and have a little think about what you've written.

Guest625101138
03-10-2010, 11:04 PM
I shall follow the lead of your tone and follow in kind.




Spoken like a true 'expert' with absolutely no yacht design qualification whatsoever. I've tried to be respectful Rick, but the absurdity of those comments ought to give anyone with even the slightest hint of boating experience, some inkling of how seriously they should take your remarks. I suggest to re-read your post and than go away and have a little think about what you've written.

You are right about my yacht design "qualification:. I have not been trained in the same school as you where compromise seems pervasive. Although I certainly know at least one NA who is not apt to compromise. I dare say those designing AC yachts are not quick to compromise either.

My education and engineering expertise has been aimed at maximising value through a no-compromise approach to finding optimum solutions. In project engineering that means best return on investment. So decisions are reduced to the determination of life costs against return over lifetime. I can give you many examples how optimum solutions are determined.

Some things that were designed for boats 20 years ago are no longer applicable to the world today. Even large bulk carriers are finding that there is more value in going a bit slower.

Generally the people involved in this thread are contemplating going a little slower than in the past but saving a large amount of fuel. It may not even be an overall economic decision - it could be more conscience. Irrespective of the reasons they should put as much effort into the prop design they choose as anything else and not accept the common wisdom of compromise. The props designed for planing a boat when fuel was plentiful is no longer the optimum choice for the boat contemplated on this thread.

You are suggesting that they accept your compromise of 6.5nmpg at 7kts. They have asked for 12nmpg at 12kts. If they accept your compromise they are going to be a long way off their objective. The WHIO gets 10nmpg at 10kts. Still a compromise on the important requirement but much better than you are offering.

I have no doubt I could engineer a boat that would exceed their requirements for speed, economy and accommodation but it would involve some clever thinking and considering many aspects. One key aspect is the prop design and manufacture.

Rick W

Willallison
03-10-2010, 11:39 PM
You are suggesting that they accept your compromise of 6.5nmpg at 7kts. They have asked for 12nmpg at 12kts. If they accept your compromise they are going to be a long way off their objective

No - I'm not... Right from the outset I stated that Graphite was not the best solution for this application:

I've attached the fuel flow data of a recent design of mine, Graphite, which is a planing cruiser with a top speed of 32 knots, so is not appropriate for your application

This is a typical example of the way that you only absorb the information that fits your own (very) biased view on the world and on boats and the people who use and design them in particular. It's true that you and I differ in our opinions on a number of fronts, but if you had taken the time to actually consider what I wrote regarding the compromise of props, you would see that I was responding to the remarks about outboards and custom made props. I was simply pointing out that by their very nature, outboards dictate a compromise in prop design because one of the main design considerations - diameter - is severely restricted.

Regarding your other comments:
1. I don't believe you when you say you know an NA who doesn't accept compromise. If that's what he say.. then I don't believe him either.

2. I would guarantee that every AC boat designed &/or built involved a multitude of compromises.

3. I never suggested that optimum solutions shouldn't be sought. Indeed that's the very reason I pointed out the diameter compromise in regards to ob's. I'm simply stating that along the way, compromises will have to be made.

Reason has failed in the past to convince you, so let me give you a little example. Attached is a pic of a boat that I'm sure you will recognise. Now, we know that the best solution for a slippery little boat like this is for it to be long and skinny. Problem is, if you just built it long and skinny, it'd 'fall over'. So... what did you do Rick.... you compromised and put outriggers on it. Probably would have been less drag without the hard chine construction too... and maybe a little more length would have been advantageous too
Detestable....

Like I said before... have a think about what you are saying.....

Ad Hoc
03-10-2010, 11:56 PM
Compromise is a sloppy approach to design. I detest the concept.

Rick W

Will

This is the problem with those that are not naval architects nor trained yacht designers. They know of nothing other than their own little world. They have no concept of what design is, so rather than take my word for it, attached are just 2, yes just 2, (I could use hundreds of quotes, but restricted to just 2 for simplicity). See attached two most often quotes comments about compromise.

It seem the ex chief designer of the UK’s MoD Navy is sloppy…..but hey Rick knows better, why:



You are right about my yacht design "qualification:. I have not been trained...

Rick W

I supposed being completely untrained and having never designed a real boat for a client for a fee in the real world before, just gives one a feeling of superiority.

Just like all those armchair amateurs who watch sport and shout at the TV, “I can do better than that…”…yeah must be so easy sat from the comfort of ones own little myopic world. Self-delusion is a wonderful thing.




In project engineering that means best return on investment. So decisions are reduced to the determination of life costs against return over lifetime.

Rick W

So, when one cannot demonstrate any form of track record, let alone formal qualifications, one resorts to changing tack in the hope one does not recognise the incredibly weak position one is debating from.

So, lets ignore the difficulties and compromises made all the name of design…lets now call it project engineering, because you don’t want to highlight your own inadequacies. Since to call a design “project engineering” means what…..well you choose, since there is no formal guidance from the armchair amateur, again, from the mouth of a self-deluded person who thinks any form of compromise in design is sloppy.




I have no doubt I could engineer a boat that would exceed their requirements for speed, economy and accommodation but it would involve some clever thinking and considering many aspects.

Rick W

So ”… but it would involve some clever thinking…" hahahaha:D :D

See, only an untrained and severely lacking in any form of technical naval architecture/engineering/yacht design would say such nonsense.


It doesn’t require some clever thinking…I just requires sound logic based upon the known laws of engineering and science along with an enquiring mind. But one who is not educated in such ways would say as such… Just like asking my surgeon how is he going to repair my ACL…ooohh..some clever thinking….!!! Just because I can’t repair it doesn’t mean someone else can’t.

The only thing sloppy here the nonsense that is posted by Rick. People like Rick give boating, especially small boating a very bad reputation with their unprofessional attitude and extreme lack of knowledge. Anyone who read the post above and agrees with Rick is clearly not a professional in the marine/design field in any shape or form and is unwilling to admit as such for fear of ridicule.

tom28571
03-11-2010, 12:26 AM
Wow,

I took a short recess and things got blown up a bit. I'm sure Rick has lots of value to say about a lot of things as I've followed some of his posts with interest if not always with agreement.

However, to say that Whio or any other boat was built without compromise shows a lack of understanding of the boat design process. All boats, without a single exception are products of compromise of one kind or another. The compromise could be speed, comfort, accommodation, seakeeping, safety, economy, beauty, money or a number of other factors that may be important, or not, to the client or designer. In Whio, the compromises are accommodations which are spartan to say the least, a pretty technical build that is out of the expertise of many backyard builders and more expensive than most of its competition. The designer met his goals very well, but not without compromise.

Raceboats compromise safety for speed.
Other boats compromise rough water capability, accomodation, amenities, first cost or operating cost to gain economy.

You want to go 12kts at 12nmpg, no problem. Why not 20kts at the same fuel burn, no problem. Oh, you want to carry along your lunch and another passenger or two and a top to keep the rain off and take a few big waves and you want to store it in your apartment, well, that might be a problem.

Name any boat you like and there those who can show that there are compromises in its design. Compromise is not a dirty word but just dealing with limitations of physics or other real world and human factors.

Guest625101138
03-11-2010, 01:00 AM
...
Reason has failed in the past to convince you, so let me give you a little example. Attached is a pic of a boat that I'm sure you will recognise. Now, we know that the best solution for a slippery little boat like this is for it to be long and skinny. Problem is, if you just built it long and skinny, it'd 'fall over'. So... what did you do Rick.... you compromised and put outriggers on it. Probably would have been less drag without the hard chine construction too... and maybe a little more length would have been advantageous too
Detestable....

Like I said before... have a think about what you are saying.....

You are INCORRECT here. I considered and tested a whole range of options. The main hull might be unstable but that is not the boat. I have managed to achieve a very stable platform with no compromise in performance for the conditions it is designed to operate in. The twin stabilisers offer little to no hydrodynamic drag, add a little extra weight and a little extra windage. They are the optimum solution. You may view them as training wheels or add-ons but they are a key component of the boat.

The things I evaluated and tested were:
Catamaran - wetted surface up by 26% power up by 40%
Single outrigger - added drag about 10% over the optimum
Inherently stable single hull - added drag about 7% over optimum and very twitchy - almost impossible to board
Deep ballasted keel on slender hull - added drag about 10%
Many combinations of form stability and ballast with keel ranging in depth
Submerged buoyancy with stabilisers - much higher drag - too much to bother with data
Foils on small outboard pods - weed collectors
Wing with flaps
Dynamic stability with relatively large control surfaces - drag of control surfaces always present

The actual V14 boat you have pictured included additional key requirements for weight, length constraint and ease of build as well, over the previous V11 design. I expected this would reduce overall efficiency but was pleasantly surprised. You may yet see flat bottomed olympic rowing shells. More common wisdom about round bottoms down the gurgler.

This video shows hows it gets up goes when pushed:
http://www.boatdesign.net/gallery/data/500/V14_Rick_16kph.wmv
The V11 hull squated but had no noticeable lift.

The previous V11 design was nominally a no-compromise shape constrained only by power level and displacement. It too used the twin stabiliers - the optimum solution on the long slender hull. The version that was built from carbon fbire holds the current world record under human power over a 24 hour period. The V14 boat you have pictured would do even better:
http://www.adventuresofgreg.com/HPB/2008_09_15_archive.html

You do not look at a racing trimaran these days and consider the outriggers a compromise. They become the key hull at speed. When tris first arrived in the modern world the amas were viewed as training wheels. Many people are fashion conscious, which impairs their ability to weigh the merits of various features without preconception.

There is no reason why outboards could not be designed to take much larger diameter props to get them in the 80+% efficiency range for moderate speeds proposed on this thread. The bottom end would be somewhat different to what you see now - bigger gearbox, bigger ratios, more thrust capability, no anti-ventilation plate, power head relatively smaller to the leg, etc They would have the bollard pull to get out of trouble in very heavy conditions with relatively small power.

So while not given all the preconceptions and compromise seeking that seem to come with training as a naval architect, I do have an enquiring mind, am able to work from first principles, am able to test and evaluate data and I have a no-compromise approach to engineering solutions. The V14 boat is the current no-comprise solution for the design objectives. Principally it can be carried in one hand; can be easily car-topped; averages 6kts with my modest 0.13kW output; can be operated in shallow, log and weed infested water with little loss of speed; is very stable and comfortable; is relaxing peaceful exercise I look forward to using each week. It has taken me 8 years to get to its current state and V15 is on the board but that is the nature of learning and seeking the optimum solution - that solution is always constrained by the available knowledge.

Point is if you take current outboard prop as the best there is on offer for the proposed application of this thread then you are indeed compromising.

Rick W

Willallison
03-11-2010, 01:23 AM
AARRGHH !!!!! :confused: :confused: :confused:
Were it not for the fact that I've been up for 36hrs, so feeling a little testy, I'd probably throw my arms in the air and give up....

The twin stabilisers offer little to no hydrodynamic drag, add a little extra weight and a little extra windage

So, by your own words, the stabilisers are a COMPROMISE. The vessel has insufficient inherent stability in its optimum form, so you were forced to compromise a little in terms of drag, weight and windage.
It may (or may not) be the optimum solution to a set of problems, but to suggest that there are no compromises involved when you've listed at least 3 yourself is a demonstration of the complete absence of logic in what you are saying.

And that your display of arrogance in the matter has coerced Ad Hoc out of 'retirement' ought to make you reconsider my suggestion once again. Go away and have a think about what you've said....

Willallison
03-11-2010, 01:26 AM
Still not enough?

My V14 hull started out as a shape compromise with flat panel for ease of construction

Now... who do you think said that...?

Guest625101138
03-11-2010, 01:34 AM
Attached gives an introduction to some of the optimisation techniques that engineers are trained in. If you want to read more then there is part of a book here:
http://books.google.com.au/books?id=nuoryE4IwMoC&printsec=frontcover&dq=engineering+optimization&source=bl&ots=PgdbqO0qK3&sig=z9KsUyYqmW51o1aLCqrajh76RAM&hl=en&ei=YX6YS86xK4f0sgOIi_g_&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBQQ6AEwAw#v=onepage&q=&f=false


Rick W

Willallison
03-11-2010, 01:42 AM
Yes... and your point is...?

Guest625101138
03-11-2010, 01:58 AM
I added a new variable, being the method of construction, so the shape had to be consistent with the new method of build, to arrive at the overall optimum that included flat panel construction. Within these new constraints I sought the best overall performance. I did not just accept that it was "not worth the effort" to do a complete redesign of the hull to optimise with the new constraints. I put in the effort to arrive a completely different shape based on the additional constraint.

This is very different to saying that it is not worth the effort to consider an alternative propeller to the current crop of outboard props. What basis do you have for this wisdom?

Rick W

Guest625101138
03-11-2010, 02:01 AM
Yes... and your point is...?

Engineering optimisation is a concept understood by most engineers. I get the impression it is not part of the training that naval architects receive.

Rick W

Guest625101138
03-11-2010, 02:22 AM
What does the attached mean.

Attached suggests an exacting outlook. It does not mean the mathematical optimum that I am seeking but it does set expectations about the boats.

It is clear that some here are happy with "she'l be right mate - no need to look into that - it is not worth the effort - just compromise." That is not the way to get the best outcome. You have to ask what is the difference? Is there a benefit? How good could it be?

Rick W

Guest625101138
03-11-2010, 03:40 AM
Seems some of the designers of the America's Cup yachts understand design optimisation:
http://www.esteco.com/case_studies/marine2.jsp

Anyone putting a lot of effort into the design of an efficient coastal cruiser who simply accepted the current available outboard propellers as an acceptable compromise without question is likely missing the most easily won gains.

Rick W

Willallison
03-11-2010, 05:12 AM
No - the attached is a discussion about optimisation. Which has no direct relationship to the discussion about compromise. I've always regarded you as a fairly intelligent, if somewhat fanatical, sort of bloke Rick - but I gotta say, your testing my faith here!
Just a few posts back, you effectively stated yourself that you compromised the pursuit of efficiency for the sake of construction simplicity. And in the quote that I posted, you said exactly that. I fail to see how you can't comprehend that you are deriding the very same process that you have used yourself....
And once again, you are misinterpereting my posts..... I didn't say 'she'll be right mate...no need to look into that... it's not worth the effort". What I said is that the diameter of an outboards prop is severely restricted, and so is compromised from the start. And that any gains you may achieve by custom building an outboard prop might not be worth the effort. I never said you shouldn't look into it.
You go right ahead and design these guys a custom made outboard that can swing its custom made prop for the custom made boat that it's going to push. I'm pretty sure that when they get the bill, they'll pretty quickly teach you a thing or two about compromise.
It's now been 38 hours since I slept. To put it bluntly, your stupidity astounds me... I'm going to bed.

Guest625101138
03-11-2010, 06:12 AM
Like all things in yacht design, props are a compromise. ...

Just a reminder of what I responded to initially.

Why do props have to be a compromise? Do you know what the most efficient prop would look like? What is being thrown away by accepting what an outboard has? The props on these have changed very little in the last 40 years. The title of this thread is indicative of the changing requirements. Are props suited to planing boats 40 years ago still suited to the current requirements?

What would an uncompromised prop look like - that is one where there was complete design freedom without any constraints other than the thrust required at a certain speed?

How will the optimum prop change as the design space is constrained by material limitations, space limitations, draft limitations and so forth?

I disagree that all things in design are a compromise. (Maybe in your own little world of yacht design but not in the engineering field in general). A design should aim to optimise within the design space. A good designer will test the constraints and have a very good undertstanding of the trade-offs between the various constraints. The constraints should be tested as well to see how strict they are. It is not unusual during a design spiral certain constraints become obsolete because of new understanding.

Compromise is a sloppy approach without clear understanding of the constraints and how they impact on design objectives. It is not good enough to offer "may' and "might' as wisdom.

Rick W

Pierre R
03-11-2010, 08:50 AM
I like to think of optimization as being associated with the word "Open Checkbook" and compromize being associated with the word "Budget"

The minute you hesitate on cost you have just compromised, not optimized.

TollyWally
03-11-2010, 08:55 AM
What Pierre said.

fcfc
03-11-2010, 09:38 AM
...
A design should aim to optimise within the design space.
...
Rick W

Yes, but the design space does include the following:

1) Make a living for the draftman/designer if professsional.
2) Time and resources allowed for the design unless the design is to be never finished.
3) Buildable within planned resources and price unless the design is never built.
4) Final paying customer expectations unless you do not want to sell it.

u4ea32
03-11-2010, 04:17 PM
I totally agree with FCFC.

A spacecraft is certainly highly optimized. The engineering challenges across the vehicle are very, very tough. Yet one can never just say "Let's do subsystem X using technology Y." One must do trade studies that examine values across the entire mission. Cost is usually tightly constrained. Schedule is usually absolute (launch windows refer to proper alignment of planets -- not easy to push planets around to accept a month schedule slip!). Mass is extremely fixed. Power. Volume. Center of gravity. And on and on.

So the problem is optimizing across a very large number of dimensions, not just one. So an "optimum propellor" may well be optimized to achieve some combination of qualities, the combination being optimized. That might mean, say, top speed is below the absolute that may be obtained.

In this discussion, I think the function we are trying to optimize includes the following factors, in no particular order or significance:

1) Cost
2) Ease of supply (off the shelf being best, hand built by the Dwaves of Narnia being perhaps not so good)
3) Propulsion efficiency
4) Diameter
5) Pitch (limited reduction in outboard gearboxes)
6) Some specific speed range, not maximum speed
7) Sufficient thrust, not maximum thrust

Guest625101138
03-11-2010, 04:21 PM
I like to think of optimization as being associated with the word "Open Checkbook" and compromize being associated with the word "Budget"

The minute you hesitate on cost you have just compromised, not optimized.

As noted earlier on the design space I most often work with is return on investment. That means bang for buck. The way to achieve this is through optimisation of the design.

Rick

Guest625101138
03-11-2010, 04:31 PM
I totally agree with FCFC.

A spacecraft is certainly highly optimized. The engineering challenges across the vehicle are very, very tough. Yet one can never just say "Let's do subsystem X using technology Y." One must do trade studies that examine values across the entire mission. Cost is usually tightly constrained. Schedule is usually absolute (launch windows refer to proper alignment of planets -- not easy to push planets around to accept a month schedule slip!). Mass is extremely fixed. Power. Volume. Center of gravity. And on and on.

So the problem is optimizing across a very large number of dimensions, not just one. So an "optimum propellor" may well be optimized to achieve some combination of qualities, the combination being optimized. That might mean, say, top speed is below the absolute that may be obtained.

In this discussion, I think the function we are trying to optimize includes the following factors, in no particular order or significance:

1) Cost
2) Ease of supply (off the shelf being best, hand built by the Dwaves of Narnia being perhaps not so good)
3) Propulsion efficiency
4) Diameter
5) Pitch (limited reduction in outboard gearboxes)
6) Some specific speed range, not maximum speed
7) Sufficient thrust, not maximum thrust

This is exactly what needs to be done. The designer needs to know the trade-offs between objectives. Not simply dismiss the possibilities of something because it "may" or "might" not be worth the effort.

I can guarantee that the design of an economical cruiser to do 12kts would benefit from a thorough understanding of the cost, in terms of performance, certain prop constraints impose. Very sloppy design to dismiss it without this effort. Test the constraints and establish the design space to optimise within. Not make the bland compromise that it is not worth the effort.

Rick W

Willallison
03-11-2010, 05:06 PM
Rick, would you be so kind as to explain what you mean by this statement
The designer needs to know the trade-offs between objectives
Trade-offs...? No...surely you don't mean COMPROMISE....

And, whilst you're at it, could you please explain where exactly I said that one should simply "dismiss the possibilities of something because it "may" or "might" not be worth the effort"? As usual you are intentionally misinterpreting my statements. I simply said that building a custom prop to fit an outboard, which by its very nature imposes significant constraints may or may not be worth the effort.... not that the idea shouldn't be explored.

Lastly - as this all started based around prop design - you quoted me as saying that "like all things in yacht design, props are a compromise". I stand by the statement. For example, let me quote from one of the well known prop texts
"In other words, at low to moderate speeds, for a given horsepower, the slower the shaft RPM and the larger the diameter, the more efficient the propellor will be".
With this in mind, could you please explain how one might go about designing and building a prop that imposes no compromise? And how is it that you came to decide upon the diameter for the prop on your pedal boat?

Guest625101138
03-11-2010, 05:30 PM
....
With this in mind, could you please explain how one might go about designing and building a prop that imposes no compromise? And how is it that you came to decide upon the diameter for the prop on your pedal boat?

First step is to define the design objectives in which to optimise.

Rick W

Willallison
03-11-2010, 05:56 PM
There were 4 questions there Rick.
You've answered none of them

Pierre R
03-11-2010, 06:37 PM
First step is to define the design objectives in which to optimise.

Rick WOkay, I want to know how you optimize a design when the customer is never quite sure what they really want? In my opinion customers do not understand how comfort relates to what is possible on paper. The customer has an inate sense of the comfort level that they want but cannot put it into a quantitative value from which an optimum design can be drawn. In the absence of perfect data the NA must err on the conservative side lest he find himself in a lawsuit.

Most customers come with a dream boat in mind. The very idea of the word "dream" indicates a disconnect between reality and optimum design no?

With you little pedal design you are the customer and comfort is clearly not on your high priority list.

Guest625101138
03-11-2010, 06:50 PM
To establish the design space I have found it instructive to start with looking at what the conditions are for the completely unconstrained case.

This helps in understanding what each constraint is going to cost.

In this case we do not know a lot about what the optimum solution is going to look like so I have set a relatively wide space for speed and displacement. The end result may be outside the range provided. It could be extended but most of what has been discussed so far is close to this. So displacement ranges from 0.5t to 2t and speed from 3m/s to 6m/s.

The attached shows the power level required to drive the respective displacements at the various speeds.

The design optimistation needs to start somewhere and establishing objectives for speed and target weight are good starting points.

If someone cares to nominate values, the optimisation process can continue.

I have found hull length to be the most demanding constraint so I can look at how that impacts on power next.

Rick W

Guest625101138
03-11-2010, 07:29 PM
Okay, I want to know how you optimize a design when the customer is never quite sure what they really want? In my opinion customers do not understand how comfort relates to what is possible on paper. The customer has an inate sense of the comfort level that they want but cannot put it into a quantitative value from which an optimum design can be drawn. In the absence of perfect data the NA must err on the conservative side lest he find himself in a lawsuit.

Most customers come with a dream boat in mind. The very idea of the word "dream" indicates a disconnect between reality and optimum design no?

With you little pedal design you are the customer and comfort is clearly not on your high priority list.

Pierre
Clearly the "customer" who started this thread and a few others who have asked questions on it are reasonably well informed.

My aim is to improve their understanding of how certain constraints or objectives impact on others not just offer accepted wisdom that others are apt to do. This is the process of optimisation - understanding the interplay of variables. This is the uncompromising approach to arrive at the best solution for the customer.

I am very comfortable on my little pedal boat. There are not many other ways to get fit while laying on your back completely destressed.

Rick W

Pierre R
03-11-2010, 07:34 PM
I have found hull length to be the most demanding constraint so I can look at how that impacts on power next.

Rick WYou might find length and I love longer boats but I have found comfort to be the most demanding constraint in the real world of boats built and not on paper. I can easily design a boat to meet the 12/12 requirement and the size of 28' to 34'. I very much doubt that the original poster would be satisfied with the comfort level while taking the boat south along the ICW, north in the summer and south in the winter. To much time spent on the boat to have comfort as secondary. I think in sight of the port of departure that the original poster would be displaying the middle index finger at every go fast boat that passed him either direction. I also think the original poster would be disatisifed with the level of convienences and interior provided.

My guess is that if the boat where built, the orginal poster would be more than willing to give up some mileage for some creature comforts. Not to mention the difference in resale values. That would be little consolation once he spent dearly on a boat that could not be resold easily. It's fun to sit here and waste bandwidth on your dream charades but the original poster, I think ,was actually serious.

Myself I don't mind spartan accomodations and lack of real goodies but I don't want my drink to depart the table every time a boat passes me in the ICW. In my own designs, comfort and expectation trumps high tech and ultra green PC crapola nonsense and I sensed the same in the original poster.

Pierre R
03-11-2010, 07:39 PM
Pierre
Clearly the "customer" who started this thread and a few others who have asked questions on it are reasonably well informed. I am not as sure of that as you seem to be.

I am very comfortable on my little pedal boat. There are not many other ways to get fit while laying on your back completely destressed.

Rick WOh really, where is the beer cooler? Where is the food? Where is the shade? Done don't seem to comfortable to me!

Guest625101138
03-11-2010, 07:48 PM
Y...
My guess is that if the boat where built, the orginal poster would be more than willing to give up some mileage for some creature comforts. Not to mention the difference in resale values. That would be little consolation once he spent dearly on a boat that could not be resold easily. It's fun to sit here and waste bandwidth on your dream charades but the original poster, I think ,was actually serious.

Myself I don't mind spartan accomodations and lack of real goodies but I don't want my drink to depart the table every time a boat passes me in the ICW. In my own designs, comfort and expectation trumps high tech and ultra green PC crapola nonsense and I sensed the same in the original poster.

You are guessing about the customers requirements. That is gambling not designing. You need to ask the customer and then give engineering definition to those requirements. You may find the customer is more aligned with your personal requirements or preferences.

Rick W

Guest625101138
03-11-2010, 07:58 PM
I am not as sure of that as you seem to be.

Oh really, where is the beer cooler? Where is the food? Where is the shade? Done don't seem to comfortable to me!

Esky under the seat. Bottle holders in front of the seat. Hat and tights provide shade as well as evaporative cooling once wet. All ready for 8 hours of fun and healthy exercise on the water. More fun and satisfaction than most will ever have the opportunity to experience.

Rick

Pierre R
03-11-2010, 08:20 PM
You are guessing about the customers requirements. That is gambling not designing. You need to ask the customer and then give engineering definition to those requirements. You may find the customer is more aligned with your personal requirements or preferences.

Rick WNo I am not guessing. Read the entire thread from beginning to end and you will see what the original poster has indicated. The original poster has indicated that the comfort level he has in mind is above what he is likely to get with the 12/12 requirement and if necessary he is willing to give a bit on those numbers to achieve the comfort level he has in mind.

Brian@BNE
03-11-2010, 08:21 PM
Ah yes! In Pierre's world where comfort is everything you end up with a few thousand lbs down below .... and optimise wake production.

but in the process make comfort sub-optimal due to noise, vibration and angry co-users of the ICW.

Pierre, just add a couple of out-riggers. You can optimize stability! That'll keep your beer and apple pie from sliding off the table - don't accept compromise, you dont have to hold onto everything!

Guys, I'm glad no-one has blown a cerebral fuse yet - seemed close at one point. Could we leave the semantics now? Yes, I'll try and leave my sins off the keyboard too.

Pierre R
03-11-2010, 08:24 PM
As noted earlier on the design space I most often work with is return on investment. That means bang for buck. The way to achieve this is through optimisation of the design.

RickDuh! that is not what come out of your wordprocessor to the rest of us.

Pierre R
03-11-2010, 08:28 PM
Boy Brian do you read me wrong.

Willallison
03-11-2010, 08:32 PM
Post #124
The end result may be outside the range provided

How is it that when I use the word 'may' it's because I'm espousing laziness, yet when you do, you are promoting thorough design?

And I see you've still not chosen to answer any of my last 4 questions. The only conclusion one could draw from that is that either you don't know the answer or realise that it will obviate the absurdity of your position.

Even this statement "I have found hull length to be the most demanding constraint so I can look at how that impacts on power next", confirms that you must often compromise the ideal length in order to fulfill other conflicting requirements.

I've never chosen to belittle the value of your opinion on the basis of your lack of appropriate qualification. But what I do take exception to is the notion that you know better than every single professional designer who accepts that compromise is an inescapable component of naval architecture (with the rather notable exception of your one anonymous NA, for whom compromise is unneccesary).
That you are unable to distinguish between the terms opimisation and compromise suggests that your grasp of the variables at play is not just tenuous... it's completely non-existent.

Willallison
03-11-2010, 08:39 PM
Brian,
I think you are missing the point of Pierre's posts. It would be a rare vessel indeed where there were not a set of design objectives, of which at least two were not in conflict with each other. The competent designer is one can find the best solution to satisfy the conflicting requirements. Invariably, that involves compromise.
Comfort is a fine example - and I can assure you that the motion provided by many a multihull would score pretty poorly on that front.

Brian@BNE
03-11-2010, 08:52 PM
Will, i understood Pierre's posts. I used his name and took a few cheap shots (several sins there) in an attempt to inject levity as the thread seemed to be forming ever-diminishing concentric circles and heading for the plug-hole fast.

I generally enjoy both Rick and your posts and don't want either you to end up so teed off that you leave the forum. I think this 'debate' has got down to splitting hairs and a bit off thread. I want to acquire an economical coastal cruiser soon, and comfort will be a consideration. I'd like to see the thread advance.

Guest625101138
03-11-2010, 09:37 PM
... I'd like to see the thread advance.

As the next step how about nominating the displacement and speed you would like to do the first iteration with.

Rick W

Willallison
03-11-2010, 09:44 PM
Brian - I take your point... I've typed a suggestion that we move back on track a number of times, but I've deleted it each time because I'm so deeply concerned that there will be people reading this who will believe the nonsense that Rick is putting forth.
Just consider the mythical vessel that is put forward every now and again... the one where the customer comes along and says something along the lines of, "I'd like a boat that I can tow behind my small family sedan, that is capable of crossing oceans, with its crew of 6 (in 3 cabins), gets the same mileage as my car, has a jacuzzi on the aft deck, does 35 knots and only costs 25K, etc"
It's often put forward as a fairly extreme tongue-in-cheek example of the kind of conflicting requirements that designers are expected to solve. In Rick's utopian fantasy world, he can deliver it. And all without compromise.
It's such a fundamental and inescapable aspect of design - often a very frustrating one - that I feel an obligation to point out the absurdity of Rick's position to any and all who accept his words as anything resembling the truth.

Guest625101138
03-11-2010, 09:49 PM
Brian,
I think you are missing the point of Pierre's posts. It would be a rare vessel indeed where there were not a set of design objectives, of which at least two were not in conflict with each other. The competent designer is one can find the best solution to satisfy the conflicting requirements. Invariably, that involves compromise.
Comfort is a fine example - and I can assure you that the motion provided by many a multihull would score pretty poorly on that front.

The "best" is the best. It is an uncompromised outcome. It is finding the optimum solution within the design space.

You are beginning to understand the difference between compromise, where you have no idea of the interaction, and the optimum or "best" of all possible solutions. This requires knowing and defining to some precision not wishy-washy words like "might" and "may".


Rick W

Willallison
03-11-2010, 10:09 PM
The "best" is the best. It is an uncompromised outcome. It is finding the optimum solution within the design space.

You are beginning to understand the difference between compromise, where you have no idea of the interaction, and the optimum or "best" of all possible solutions. This requires knowing and defining to some precision not wishy-washy words like "might" and "may".


Rick W

:?:
That's it.... I give up... your inability to grasp any sort of reality seems to know no bounds. I've been trying to explain to you - in the MOST BASIC TERMS - the difference between optimisation and compromise and you come back with a ridiculous statement like that.
You choose not to answer any of the questions that I, or others have put forth. You are hypocritical in your condemnation of the use of words like "may". That you cannot - and will not attempt to - see that compromise is necessarily evident in every design - including your own - defies belief. You are the worst kind of forum contributor - so single-minded in self-belief that you are prepared to mislead others. You are a FOOL:mad:

Willallison
03-11-2010, 10:10 PM
Did I make myself clear?

Brian@BNE
03-11-2010, 10:16 PM
Before joining the forum i trawled over a lot of it, picking up tid-bits along the way. I joined because I figured there was a lot of pragmatic knowledge on tap and that if I wanted help later I should try and participate sooner rather than later. I can mostly tolerate grumpy old men with short fuses – I am one.

I’ll share an overview of the thought-journey, as this thread I think at its heart is going in a similar direction.

Budget is finite, so low running costs are important. Obviously sail… but

one day I might want to leave Australia’s coast for another coast. Need a bit of size. Probably want closer to 50 ft than 40 ft. That’ll help for av. speed also– I’ll come back to that later.

Ouch, large sail rigs are expensive! Not so obvious ‘sail’ then..

Displacement cruisers. Slow old tubs with deep draft. Lots of thinking about motor sailers. I’ve been in love with the Nauticat 44 etc for a long while but that deep fin keel is not going to cut the mustard in the tropics.

Ok, a cat then. Many points about motion on multihulls including Will’s reminder above. Not to be overlooked!

OK, Dashew has the answer, perhaps, but even the FPB 64 is well beyond my budget. But Dashew might be onto something - a power boat that isn’t power hungry, has shallow enough draft for the tropics.

Can it be done around 40-45 ft so I just might be able to afford it?

Back to the speed. Initially I’ll hop along the cost from port-to-port. Might have to be single-handed some of the time. But I’m not going to go and sleep and have a large working-boat run over me so I need enough speed to get from port to port in one long sleepless stint. I’ve yet to do the calcs. on distances and fine tune required speed, but 12 k might just do it.

My ‘mini-Dashew’ would have a single diesel. I like the straight 6 out of the BMW X5 as its often acclaimed as the best of breed. Yanmar use it in one of their models, so I don’t have to ‘marinise’ it.

I’d like to swing a 4 ft (well, abnoramlly large at least) prop with the diesel sitting at relatively low revs – I guess its 1800-2000 rpm when the X5 is in its economical highway cruise mode – for max. efficiency. My big prop would be for blue-water operation, and lift up when I need shallow draft. Perhaps power could be switched over to a small prop or jet (no drag when not in use) for shallow water travel. But I’m sure that having a big prop that can be lowered ‘on demand’ and take the full 5000 rpm of power if required is going to have a few structural engineering issues to manage.

Now, are there any existing sailboats that could be converted to a 'mini-Dashew' or will it be better to start with a blank canvass and take a long time to even get a hull that I can fit-out?

Pierre R
03-11-2010, 10:39 PM
Let's see, if I am taking Rick's approach and optimizing then I certainly would not start with boat design parameters like length, weight or mileage. I would start with what you want in it, the level of comfort you expect from the boat in ride and creature comforts and the real intended use for the boat.

I think these things start to optimize a boat much more so than picking the boat design parameters and then trying to fit what you want into those numbers. I think the later approach is a recipe for playing in fantasy land, not optimizing design.

Its easy to pick number out of thin air and make a boat around them but the end results are ususally not satisfactory to a customer. The reason being is that the customer almost never realizes what is truely practical and that is why they went to an NA in the first place. A good NA needs to educate the customer throughout the process. Having the basics of purpose and expectation of comfort nailed down can help the customer wade through the many decisions they must make.

To me its easy to throw out speeds, displacements, mileage, beam, cubes and a whole host of other numbers but its far more difficult to quantify something like comfort. How do you put a number on it so you can add it to the numbers being pulled out of nowhere?

Guest625101138
03-11-2010, 10:56 PM
...
one day I might want to leave Australia’s coast for another coast. Need a bit of size. Probably want closer to 50 ft than 40 ft. That’ll help for av. speed also– I’ll come back to that later.

Ouch, large sail rigs are expensive! Not so obvious ‘sail’ then..

Displacement cruisers. Slow old tubs with deep draft. Lots of thinking about motor sailers. I’ve been in love with the Nauticat 44 etc for a long while but that deep fin keel is not going to cut the mustard in the tropics.

...
Can it be done around 40-45 ft so I just might be able to afford it?

Back to the speed. Initially I’ll hop along the cost from port-to-port. Might have to be single-handed some of the time. But I’m not going to go and sleep and have a large working-boat run over me so I need enough speed to get from port to port in one long sleepless stint. I’ve yet to do the calcs. on distances and fine tune required speed, but 12 k might just do it.

My ‘mini-Dashew’ would have a single diesel. I like the straight 6 out of the BMW X5 as its often acclaimed as the best of breed. Yanmar use it in one of their models, so I don’t have to ‘marinise’ it.

....?

Sounds like you are at the top end of the weight and want 12kts. I have attached the curve showing the lowest drag hull for the indicated length. This shows the cost in terms of power for restricting the length.

If you choose the length you would like to go forward with we can start to talk about stability requirements.

You may want to revisit the length depending on the stability requirements. The doors are far from closed on length yet.

Rick W

Willallison
03-11-2010, 10:57 PM
Brian, one solution to the two different props for different tasks, is to use a controllable pitch prop.
On the engine front, the Yanmar 6BY, which is the one that you refer to is the unit that I have fitted to Graphite. It is a lightweight high-speed diesel and is not really likely to be the best solution for a large, heavy displacement boat. John-deere', Luggers etc are more likely to be suitable.
I also agree with Pierre - you are looking at the solutions before you've considered the problems- or at least you appear to be. Size (in this instance) ought to be the result of considering what needs to be contained

Brian@BNE
03-11-2010, 11:15 PM
Pierre, i think comfort is a bit elastic. As an analogy you might like the comfort of an S-class but when you realsie the capital and operating cost be quite happy with less comfort.

I'd like 2 cabins that can give enough privacy if someone needs to 'chill' for a bit. Personal space is what some people don't realise is often an important missing element of a boat. Extra people? Convert the dining table for occasional use, its comfortable enough for casual visitors. The other crucial 'boat comfort' elements of enough shade and weather protection won't necessarily drive 'speed, displacement etc' numbers being tossed about. Condominium comfort I think is going to be at odds with 'economical coastal cruiser' and be in the marina most of the time, and on a different thread.

Skinny and >40 ft will give 'reasonable' speed. But no, I don't want to have to hold onto my drinks all the time so I'll take a bit of extra beam. And probably some displacement/draft hits as well. And i don't think i need an NA to educate me and tell me what i need. If I'm paying the bills, I'll find someone who can listen and think. Tell me I'm dreamin'. OK, but isn't a design forum where we can test what might be possible?

Pierre R
03-11-2010, 11:18 PM
Now, are there any existing sailboats that could be converted to a 'mini-Dashew' or will it be better to start with a blank canvass and take a long time to even get a hull that I can fit-out?Now you have the discussion back on track. In a short answer, there might be a sailboat hull out there that might do the trick but I have come to the conclusion that you might just be better off building from scratch. Scary but true.

I have been toying around with long slender monohulls and kind of speced one out around 52' LOA with a 49' LWL, a 10' beam, 4' draft, 11' air draft with a D/L of 135. The boat would be comfortable for a couple but rather simple in systems. With a single John Deere 135hp 4 cylinder engine the boat will top out just under 12 knots and cruise around 10 knots. At 10 knots the fuel burn would be about 4 gph with a range of 2200 NM.

The design I had in mind was optimized to take full advantage of canals, rivers, coastal, island hopping in the tropics and shallow crusing areas throughout the world while still retaining the ability to make an ocean crossing. The boat is also ideal for deck shippment on a RO-RO boat if ocean crossing is not in the game plan.

I think something like this could be built in a few years time using all new materials for just over $300k Aussie dollars if my converter is correct.

The Dashew FPB 64 is not a cheap boat to build at all. When you want that kind of fuel and systems aboard the building time and precision is a real headache.

Brian@BNE
03-11-2010, 11:23 PM
Posts too fast for me!

Rick, no attachment?

Will - i dont want displacement to be any larger/heavier than necessary hence the lightweight diesel. I like the concept of CPP, and have wondered if it can be mated to a continuously variable gearbox. Recently on my brothers' farm he demonstrated his John Deere at constant speed (final drive rpm for CPP in my case) with onboard computer increasing rpm and changing gearing to suit higher loads (cultivator going deeper). So the same system could be adpated to a CPP?

I haven't meant to put solutions first, and nothng is fixed yet! I just wanted to provide some bounds - I don't want a 20 ft dayboat or a 100 ft expedition yacht (well, just can't afford to buy or run the latter)

Brian@BNE
03-11-2010, 11:32 PM
"I have been toying around with long slender monohulls and kind of speced one out around 52' LOA with a 49' LWL, a 10' beam, 4' draft, 11' air draft with a D/L of 135. The boat would be comfortable for a couple but rather simple in systems. With a single John Deere 135hp 4 cylinder engine the boat will top out just under 12 knots and cruise around 10 knots. At 10 knots the fuel burn would be about 4 gph with a range of 2200 NM."

Pierre those a very impressive specs. I'm not quite ready to move yet, but I'd love someone to run with what you've described so it can get to the next stage. I don't think there is anything quite like it floating around anywhere, is there?

Guest625101138
03-11-2010, 11:43 PM
Posts too fast for me!

Rick, no attachment?

...)

It is there. It has already been opened by someone.

This gives the basis for testing what it will cost, in terms of performance, to apply a length constraint.

I expect that your upper limit of 45ft (say 14m) will be close to the optimum for moving along if you agree with that. This is a judgement call at this stage and needs to be narrowed down once there is more design detail on the boat structure.

Is 14m within your acceptable range to consider the stability aspect?

Rick

Brian@BNE
03-12-2010, 12:02 AM
got it thanks Rick.

i'll end up like most people - buy/build the longest boat i can afford! BUT Not park it in a marina, use it and have it on a swing mooring in the river for 'dirt under the feet periods'.

My budget is going to be largely governed by what i clear from a house in Melbourne that is 'surplus to current requirements' but tenanted until later in the year.

Guys i appreciate your constructive suggestions and willingness to help. But as i'm a few months off key decision criteria (budget being one) i don't want to trouble any of you further just now with details that take time to put forward but wont be acted on immediately.

fcfc
03-12-2010, 04:06 AM
What is the price tag of the intended boat ?

It will be the first question any salesman will ask you if you are on the buying market.

I have not found it in the 12 pages of this thread. It has to be answered to check if it is a real request, not like I want an cheap luxury item.

erik818
03-12-2010, 05:13 AM
Rick,
I think 2 tons could be too light, at least for what I guess is the weight penalty of my own comfort requirements (or wish-list). It would be interesting to see the power vs. length graphs for 3 tons and 4 tons as well. Actually I think 3 tons is the limit to what I could handle on my own, when aproaching a jetty in waves and wind.

Reagarding size, the central hull also needs to be wide enough for an engine installation, and wide enough to stand in when standing height is needed in the forward cabin. In my opinion this means that the width should be more than 0.8m.

Active roll stabilisation with servo-controlled foils as suggested earlier in the thread shouldn't be ruled out, although for me it's an undesired complication. Everything considered it might turn out to be the best solution after all.

Erik

Guest625101138
03-12-2010, 05:42 AM
Rick,
I think 2 tons could be too light, at least for what I guess is the weight penalty of my own comfort requirements (or wish-list). It would be interesting to see the power vs. length graphs for 3 tons and 4 tons as well. Actually I think 3 tons is the limit to what I could handle on my own, when aproaching a jetty in waves and wind.

.....
Erik

I have attached for 3t.

You can see the trade-off. Unless there is some other major objective like Marina costs somewhere around 16m will be getting close to the optimum for this displacement.

If you are happy with this we can move on to stability constraint.

Rick W

erik818
03-12-2010, 05:39 PM
Thank you Rick,
My conclusion is that 3 ton displacement still should meet the 12/12 requirement if the length isn't too severely constrained.

I've checked some issues that have bearing on boat length in Sweden. They may not apply to other countries.

1) License. With the present laws, no licenses or permits are required as long as the boat isn't longer than 12m and wider than 4m. For once, formal logic applies to laws. "And" really means "and", so length doesn't matter as long the width is less than 4m. Speed doesn't matter either. Unfortunately the law is expected to change soon, so a license will be needed if the boat is longer than 10m or faster than 15kn. Larger than 12m*4m will require a tougher license, as will speeds faster than 30kn.
Most owners of the type of coastal cruiser discussed in this thread can be expected to go for a license anyway, in order to be able to drive boats faster than 15kn. Restraining the length to be <10m will therefore not be important. I don't expect such a license to be a big deal, but I'd rather minimize my dealings with authorities.
Width should be kept <4m to allow the length to go beyond 12m without the need for a tougher license.

2) Harbour fees. At several popular guest harbours there is a fixed standard fee, in my opinion quite low, for any boat shorter than 12m. Longer boats get charged more.

3) Marina fees. The tradition in Sweden is to lay the boats with the stem towards the jetty. Width is cost driving, not length. Where I have my boat we're charged per meter jetty we need.

4) Trailer requirements. The total length for towing car plus trailer must not exceed 18m. I used to be 24m, but harmonization within EU has forced us to put the limit at 18m to not distort competition within EU. The 18m requirement leaves something like 12m for the boat.
The width restrictions for a trailer are similar to most other nations, and probably identical within EU. Of course it's no major problem to get an exception for any width that is physically possible to tow the desired route, but the practical arrangements are awkward. In reality <2.5m is preferred but up to 3m is OK.

To summarize it: Length should be <12m and width <3m (or rather <2.5m) to keep cost down.

Erik

Brian@BNE
03-13-2010, 12:15 AM
Eric
interesting to read the issues you noted. Licencing in Australia isn't that problematic yet, but i've no doubt we'll end up heading that way and so i take your comments as forewarning!

trailers are pretty similar, but vary in detail from one State to the next at present which can be frustrating. Typical and likely to be uniform soon is width 2.5m max, height max 4.3m and trailer length max 12.5m. Likewise, exceptions are possible (but very different from State to State) and up to 3m not too onerous although 'daylight hours only' typically applies.

although i'm aiming for a 'mini-Dashew' in the medium term, i've had a reality check and will go with Sandy's original concept 'barely trailerable' for a 'test' period. I've been almost exclusively been 'day-boat' in the past with things such as a 28 ft cat with 2 x 200HP outboards. I no longer need to do 40k to rush home for work or kids school, and am no longer inclined to 'feed' that many horses which inevitably get used if they are there. My 'test' is to confirm happy for days on end on the water, which would be weeks and maybe months at a time if in due course i go with something like Pierre briefly spec'd a few posts ago.

I agree with your summary of dimensions and as someone posted, the competition that is soon closing

http://www.woodenboat.com/wbmag/designchallenge2.php

should deliver some possibilities. A pity that they specified just 1555kg (assume dry boat, with allowance for trailer, fuel/water and essential junk as extra). Another 1000kg in the boat would still be trailerable. Our weight rules have a number of categories, but large cars/SUV can tow a suitable trailer with all up weight of 3500kg. Some SUV can go to 4500kg, with higher spec coupling etc. Of course for any distances a pickup truck or motorhome as tow vehicle will be give a better comfort/safety margin. If i get serious about visiting lots of distant places then an 'old' trayback 4WD with Fifth Wheel coupling will likely be the answer. I'll be nervous about leaving an expensive SUV in a public parking area for too many nights!

i'm hoping one of 'our' professional forum designers tweak their ideas to fit the challenge criteria, but then as a 'possible option' provides a heavier solution also as i fear the weight limit is going to mean much less than 12m length. The $1000 prize is minimal but the kudos are priceless aren't they?:D

Guest625101138
03-13-2010, 02:51 AM
Thank you Rick,
My conclusion is that 3 ton displacement still should meet the 12/12 requirement if the length isn't too severely constrained.

....

To summarize it: Length should be <12m and width <3m (or rather <2.5m) to keep cost down.

Erik

ERik
We can move foreward with this as a first pass. 3t, 12m, 12kts, 2,5m. The length and beam seem to be hard constraints important to you oblective. It is unlikely the optimum solution will be less than 12m. There is still some possibility of coming in under 3t.

The next most significant factor from a powering point of view is stability. I have analysed quite a few options and can offer the following comments.

1. Satbility is a function of the second moment of area of the waterplane.

2. The best initial stability will be achieved with a catamaran form with slender hulls set to the maximum width. The cat will have high power requirement than a mono if the length is not heavily constrained. Anything that is limited to 2.5m wide could probably be made self-righting.

3. You can achieve reasonable initial stability with a monohull. It should not be difficult to achieve self-righting.

4. There can be combinations of form stability and ballast that give a superior overall result. I have previously determined for a lower speed case that placing the smallest ballast weight as deep as possible is the most efficient from a powering perspective. Obviously it creates issues for draft and trailering.

5. A stabilised slender monohull is the most power efficient method. The boat does not snap roll as much as a cat and there is no extra power needed for calm water operation over the lowest drag length constrained hull.

I expect the optimum method of achieving the required stability will be either based on 4 or 5. For operation in the southern ocean I would likely favour 4. That said the Ady Gil (Earthrace) operated successfully in the southern ocean. Note though that its beam was considerably greater than 2.5m and it is unlikely to be self-righting.

The attached shows the power and beam for the lowest drag hulls having the respective stability constraint. A beam limit of 2.5m beam will give a KMT of 2.8m, which I expect will be more than adequate as the detail unfolds. At this beam the power required is 12.4kW.

The stabilised monohull requires 8.3kW and can achieve the same initial stability with tolerably large stabilisers.

It is clear that the stabilised monohull has a distinct advantage here. Unless you have particular reservations about the concept I believe it will result in the optimum vessel. The concept is now finding growing use. Here is a good example:
http://www.marinelog.com/DOCS/NEWSMMIX/2009jul00291.html

I have tested this concept extensively at my pedal boat scale and find it to be the best of all ideas so far. I can understand why it is growing in popularity.

Rick W

Pierre R
03-13-2010, 07:51 AM
Rick I notice there is never any mention or asking what a person might want inside one of your hulls. How do you do an optimum design without knowing what a person wants? Are you just assuming that you will put the stuff where ever you can and what weight to much just leave out? Is a constraint the same as a compromize or is it a optimization word?

Milan
03-13-2010, 09:21 AM
… aiming for a 'mini-Dashew' … a reality check …

How about building something similar to these, in steel, aluminium or wood \ plywood epoxy?

http://www.georgebuehler.com/Wunderberg.html
http://www.georgebuehler.com/ellemaid.html

Tad
03-13-2010, 02:56 PM
There's lot's going on in this thread...appears to be several different boats are being discussed now.....:confused:

One set of specs was mentioned for a mini Windhorse or a "low-cash" FPB64. The sketch below is my take, a scaled TimberCoast 22 hull. Full displacement, vee-bottom, plywood, foam/glass, or aluminum sheet material construction. Essentially a direct descendant of LFH's Marco Polo.

I don't really think a 55' boat makes much sense as a coastal cruiser, something about 38' would be a lot handier if one is in and out of harbours, not to mention moorage fees.

41436

erik818
03-13-2010, 06:43 PM
Rick,
I really appreciate the effort you are putting into this, and have absolutely no reservations about the stabilized monohull. To the contrary, I’m interested to see how far this concept will carry, hopefully all the way.
An iterative design process has to start somewhere, and an assumption on size and type of hull is in my opinion not a wrong start. We’ll find out what kind of boat we can make out of it. I’m reasonably positive a weight budget summing up to 3 tons will allow the comfort I need for cruising the Baltic in summertime, but there is no way to know that until we have an idea of what the weight of the basic empty boat will be. I’m also a little concerned that the physical shape makes the available volumes in the boat difficult to use. I guess we'll get an answer to that later on.
Erik

Guest625101138
03-13-2010, 06:51 PM
Rick I notice there is never any mention or asking what a person might want inside one of your hulls. How do you do an optimum design without knowing what a person wants? Are you just assuming that you will put the stuff where ever you can and what weight to much just leave out? Is a constraint the same as a compromize or is it a optimization word?

You are impatient.

We are close to establishing the footprint to work within. I am certain the client has some reasonably firm requirements for his layout within that footprint. The designer's objective is to take those requirements and optimise the use of the available space to match the requirements.

It is cart before the horse to present a layout that may not fit within the footprint or make assumptions about what the requirements might be rather than what they actually are.

Rick W

Pierre R
03-13-2010, 07:18 PM
Rick if your client will give on 12 knots and 12 nmph to get more stuff then you have not established anything. You have wasted your time and must start over to find the optimum hull for the stuff you customer wants.

Talk about impatient, you wanted to move to stability before you knew whether you client wanted air conditioning underway , a shower or even a queen size bed! You want to optimise a hull and then force the customer to fit inside, no?

Guest625101138
03-13-2010, 07:52 PM
Rick,
I really appreciate the effort you are putting into this, and have absolutely no reservations about the stabilized monohull. To the contrary, I’m interested to see how far this concept will carry, hopefully all the way.
An iterative design process has to start somewhere, and an assumption on size and type of hull is in my opinion not a wrong start. We’ll find out what kind of boat we can make out of it. I’m reasonably positive a weight budget summing up to 3 tons will allow the comfort I need for cruising the Baltic in summertime, but there is no way to know that until we have an idea of what the weight of the basic empty boat will be. I’m also a little concerned that the physical shape makes the available volumes in the boat difficult to use. I guess we'll get an answer to that later on.
Erik

Erik
There will be interplay between the available volume, stability, motions and ultimate safety. But for now we will go with the stabilised monohull and see where it leads.

In the first iteration I would like to get as quickly as I can to the power requirement as I entered this thread on the basis that it "may" not be worth the effort to consider an alternative to a standard outboard prop. I believe prop selection is an important element in economic cruising and should be optimised.

With a relatively easily driven hull windage becomes a big factor in determining power - with the stabilised monohull it could be considerably more than wave drag. Even in relatively protected water the wind is still present.

For the first pass we have a firm constraint on beam of 2.5m. So the height is yet to be fixed. I suggest 3m above water level for this first pass. So total frontal area will be 7.5sq.m.

You know your waterways better than I do so you need to advise the operating conditions that you would like to maintain design speed in. The attached chart shows what additional power will be required to push the 7.5sq.m superstructure through the water at 12kts into the nominated headwind.

The chart is based on a Cd of 0.3 on frontal area. It may be possible to get better than this and it should not be impossible to achieve 0.3. Point is the windage is a significant constraint and is going to be a consideration for the optimum solution.

For the waters I am familiar with I would work on 20kts in the first pass - means 5.2kW extra required to drive the boat. If you are in a windy location with short fetches then you may want to select higher than 20kts.

Are you happy with 20kts. Do you want higher? Are you prepared to accept reduced speed at 20kts and select something lower?

Rick W

Brian@BNE
03-13-2010, 09:49 PM
There's lot's going on in this thread...appears to be several different boats are being discussed now.....:confused:

One set of specs was mentioned for a mini Windhorse or a "low-cash" FPB64. The sketch below is my take, a scaled TimberCoast 22 hull. Full displacement, vee-bottom, plywood, foam/glass, or aluminum sheet material construction. Essentially a direct descendant of LFH's Marco Polo.

I don't really think a 55' boat makes much sense as a coastal cruiser, something about 38' would be a lot handier if one is in and out of harbours, not to mention moorage fees.

41436

Getting off topic at least partly my fault ....apologies to all. But a short word if I may:

Milan, Tad: Thanks for comments and suggestions. Tad i think you're right on 38'

But over to Erik and Rick, who are on topic.

On that one, could some of the height be achieved with a 'pop-top' like some caravans? No windage saving on the water but towing would be a lot better and as the W x L dimensions are close to fitting inside a shipping container, could the 'top-down' height be also trimmed likewise? Er, maybe that is another thread or merging with another thread also. Even if containerised shipping is not required, reduced height offers more undercover storage options.

Pierre, i'd agree with your approach if it was a non-trailerable design. And i'll be honest and concede that i will place 'comfort' into the mix early, like you advocate. But for a trailerable, i think getting the max. volume possible with sufficient stability is the best approach. The interior is somewhat compromised at the outset, and a minimalist approach to that might be best. For a couple of weeks on the water at a time, some of the interior of the pop-top caravan could work well (suggest omit the aircon :p ). Before someone tells me to just put pontoons under said caravan when at the launching ramp, i'll remember that we are talking 'coastal' and not 'smooth water'.

The pop-top could be for the salon/fwd section only, and have zip open clears etc for ventilation or weather protection. It would be raised at anchor and lowered & fastened when underway.

Willallison
03-14-2010, 04:05 AM
I'm sorry, but this is all rather absurd - how one can begin to develop even the basics of hullform when there is not even the most basic list of design objectives - an SOR as it is often called - I find quite extraordinary. It is THE most important document in the whole design spiral process. Without a well written SOR, the project is doomed to failure.
I tend to agree also that there is probably enough boats in this discussion to be worthy of at least 3 separate threads... it all becomes way too confusing otherwise.

Pierre R
03-14-2010, 07:43 AM
I'm sorry, but this is all rather absurd - how one can begin to develop even the basics of hullform when there is not even the most basic list of design objectives - an SOR as it is often called - I find quite extraordinary. It's really quite easy. All one needs is a computer program to generate hull forms and presto, you can scrap one hull after another as "constraints" become known. I believe it is called optimisation.

fcfc
03-14-2010, 11:39 AM
I am repeating myself.

What is the price tage and allowed yearly cost of the intended boat ?

Because I think it is a primary issue.

We are speaking here at design stage, so NEW boats.

And when I see people advocating trailer boats 40 ft long, IMHO at least 150 000€ built as new , on a 10 000€ trailer, towed by a 60 000€ SUV (either dedicated to trailering the boat only, or daily used for commuting). I forecast heavy problems. The guy who can afford to spend a 150 000 + 10 000 + 60 000 = 220 000€ for purely leisure or pleasure, and at least 15 000€ for yearly maintenance of the boat, trailer and SUV, will never drive himself the thing. Waiting for the crane to finish the previous operation before loading/unloading his boats, making half a turn on a crowded parking with his 40 ft trailer is not for him. He is largely wealth enough to subcontract this to a professional trucking company, or conveyors, or even renting a boat where he wants to sail. And trucking or conveyors have a completely different limitations in beam and weight than that guy driving his SUV/light truck.

So I think a Statement of Requirements is needed, and even more, a coherent one, one that makes a balance between the money needed to buy and maintain the boat, and the boating expectations of people who can spend this amount of cash strictly for leisure purpose.

erik818
03-14-2010, 01:21 PM
I don’t agree that we’re working without a statement of requirements. The topic of the thread is also the draft statement of the requirements: “Economical coastal cruiser”. More explicit requirements can be found in Sandy’s first post.
…”12 knots in coastal waters at 12 nmpg”
…”the accommodations of a 16' travel trailer”
...”a warm enclosed helm, 15' bridge clearance and very easy access to bow and stern for single-handed docking in moderately adverse winds and currents.”
Some posts later Sandy amended the requirements:
…”Lets limit beam to 8.5 ft, and displacement to 8,000 pounds, to keep the towing issue practical.”

I have currently stolen the role of the client, but tried to stay true to the original requirements. They are very close to my own anyway, so that didn’t involve any trade.
Acting as the client I have chosen to prioritize economy and put a restriction on the length as well. The max 12m requirement is motivated because increased length would drive cost. I also believe that the requirement on single-handed docking puts a constraint on length, but exactly what limit is debatable.
Right now we have made a design assumption on a 3 ton stabilised monohull and will see where this leads.
Accommodation is left as the variable; the success of the concept will be judged by the amount of accommodation we can achieve while meeting all other requirements, of which some will be decided along the road.
There’s nothing wrong with making another design assumption and see where that leads, but why not pursue this one first?

Regarding wind, 20 knots headwind (plus own speed) is a good value for maintained 12 knot cruising speed where I live. It should be possible to make progress into a headwind of 30 knots. At higher wind speeds we will have to let the course depend on the wind. I have so far avoided being caught out in my boat in winds above 30 knots so my hands-on experience is limited. I don’t have a boat suitable for coastal cruising yet so I’ve never been far away from a suitable port.
I’ve read up on transport container size. Door width is 2.34m and door height 2.28m. I fear that would be too restricting for the concept and suggest that we don’t include container size as a requirement. Limiting to container size is otherwise a realistic way to get ocean-crossing capability. Personally I’m satisfied to explore this side of the ocean with this boat.
Regarding trailer width and length, in my opinion it’s a usable feature. I would like to have the option to trailer the boat every year to winter storage. I can rent a boat trailer for that, and can borrow or rent the car to pull it. I don’t have the proper driving license for such a heavy load so I would ask a friend to drive for me. I don’t see the need to invest in trailer and car for this.

I’ve been working with product development for many years. A key to success is to prioritize the requirements. In the best of worlds we should put weight factors on every requirement, and thus have the input for an optimization. I understand that some prefer to call this compromising, but English isn’t my native language so I’ll keep out of that debate. I know that we have problems with the word “compromise” when we translate to and from Swedish. The flavour of the word is different in Swedish and (British) English.
I’ve been involved in competitions where the customer has put weights to the requirements, sometimes with absurd consequences. Once we had a situation where we concluded that we would get the highest score if we made the land vehicle in question immovable. We would lose all the points on mobility, but gain much more in other areas. Somehow we figured we wouldn’t get the contract with such a product, even if we got the highest score.

What we’re doing now on this thread is what I would call a concept study. We do them quite often where I work, financed from the marketing budget, R&D budget or by a customer. A detailed SoR isn’t needed for such a study; the SoR can be the outcome of the study.
For a concept study, I think we’re attacking the problem in the right way by making a design assumption and then investigate the consequences.

Erik

Tad
03-14-2010, 02:48 PM
Everyone has his own approach to design....all are valid....this is the cool thing about boat design. Give a concept to 6 folks and everyone comes back with unique questions.....

1) Eric has a list of requirements
2) Will wants a list of requirements
3) Pierre wants to know what it will look like
4) Fc wants a budget
5) Rick wants to explore the hull form and power reqirements
6) I want to make quick pencil sketches

Every designer has his own method of designing a boat...this is the part you can't teach, it is arrived at via experience.

tom28571
03-14-2010, 05:19 PM
Regarding trailer width and length, in my opinion it’s a usable feature. I would like to have the option to trailer the boat every year to winter storage. I can rent a boat trailer for that, and can borrow or rent the car to pull it. I don’t have the proper driving license for such a heavy load so I would ask a friend to drive for me. I don’t see the need to invest in trailer and car for this.
Erik

This deviates from the basic utility of a trailerable coastal cruiser. The inability to trailer the boat to far destinations with a personal vehicle severely limits what can be done in the way of cruising these distant locations. The presumed comfort of the large and heavy boat begins to fade when it must be either motored on its own bottom to all locations and returned, or a commercial carrier hired to do the job at great expense. These are very real concerns and make the smaller boat much more attractive to many who have actually done much of this kind of cruising. Certainly those who need to operate within a limited budget or a limited time schedule need to think about the ease and costs of trailering and storing their boat.

The above reasoning is based, not on work at the design table, but from years of actually using both sizes of these boats.

fcfc
03-14-2010, 05:47 PM
I can rent a boat trailer for that, and can borrow or rent the car to pull it. I don’t have the proper driving license for such a heavy load so I would ask a friend to drive for me. I don’t see the need to
invest in trailer and car for this.
...
Erik

No. You have not investigated the problem.

At least in france, but I fear in Europe it is the same :
It is very unfrequent to find for hire a boat trailer above 25 ft (7m50).
It is next to impossible to rent a car or SUV with towing ability. As a trailer is dependant of the towing vehicule insurance, most if not all rental companies prohibit towing. You need to hire professionnal equipement (trucks) at professionnal prices under a professionnal contract to have legal trailering capabilities.

Willallison
03-14-2010, 06:07 PM
It's really quite easy. All one needs is a computer program to generate hull forms and presto, you can scrap one hull after another as "constraints" become known. I believe it is called optimisation.

Ahhh... so that's how it's done...;)

Tad - I agree that everyone has there own way of going about things, but surely you would agree that everything else must stem from a well thought out design brief....? I too like to start scribbling very early on in the process... it is the most fun bit afterall:p

It is true that Sandy listed some of the basics of his SOR, but also agree with fcfc - the cost is one of the most important elements of that list.
Erik, to suggest that you can 'act as client' for someone you've never met is almost as absurd as Rick designing a hull for which the constraints are yet to be determined. There will be a myriad of decisions that need to be made - decisions that only the real client can make. I agree that there are a number of people who are on the face of it after a similar thing, but already everyone's comments would suggest that there are at least 3 quite different boats on the go here.

The other point to consider - one which Tom has quite rightly alluded to, is that there is a big difference between a trailer boat, a trailerable boat, and a transportable boat. Each has its advantages and disadvantages. Each 'client' must think carefully about exactly how he/she is really likely to use their boat and make a decision about which camp to pitch his tent in. And, yes - that will involve a number of compromises in itself...

fcfc
03-14-2010, 06:11 PM
Again for france, legal towing limitations with car license are 12m 3500 kg. But the practical towing limit is around 7m50 (25 ft) 2000kg (4500lbs) trailer included. This can be done with the smallest SUV. Beyond that, the price of the car + trailer + boat and all the hassles involved in trailering make people prefer a trucking company.

Just look at big boating companies at what size they stop advertising trailerable boats.

Guest625101138
03-14-2010, 08:35 PM
.......

Regarding wind, 20 knots headwind (plus own speed) is a good value for maintained 12 knot cruising speed where I live. It should be possible to make progress into a headwind of 30 knots. At higher wind speeds we will have to let the course depend on the wind. I have so far avoided being caught out in my boat in winds above 30 knots so my hands-on experience is limited. I don’t have a boat suitable for coastal cruising yet so I’ve never been far away from a suitable port.
....
Erik

Erik
My objective was to get as quickly as I could, with some specific and maybe realistic requirements, to a first pass of the required thrust to get an idea of the optimum prop.

We are really close enough for that now.

We have a total power to drive the 3t boat into a 20kt wind at 12kts of 13.5kW. Unless you are in sheltered water there will be waves. Power loss to waves peaks at about 30% for waves of the worst length relative to hull and a reasonable average allowance is 20% - so 13.5 gets to 16.3kW with wave allowance. Determining added wind wave resistance is complex and requires the shape above the waterline as well as under.

With a small allowance for rudder drag we arrive at 2700N (16.7kW) as the design thrust for the propeller.

I have attached the power absorbed by nearly optimised props for the nominated diameter ranging from 0.9m to 0.3m. The hull draft I have in this iteration is 550mm. So up to 900mm 2-bladed prop can be fitted without reducing static draft and trailering. Of course it will need at least 1m to operate in. Below 400mm the blade number can go up without impinging on static draft. The curve shown makes this allowance.

It is clear to me that it would be remiss of a designer looking at the most economic cruiser not to consider the prop and simply accept what is available on an outboard.

The optimum diameter needs to take into account such things as hard draft constraints; method of prop protection; the required range; available engine selection.

In terms of arriving at the engine power you need to make allowance for house loads under way, transmission losses and engine parasitic loads to arrive at the engine power. Then you get into fuel BSFC maps of the engine range to see what size is going to be near the optimum. I expect something around 30kW for the 0.9m prop and 45kW for the 0.3m prop.

Of course the bollard pull from 0.9m prop will be more than the 0.3m prop even with the higher installed power on the smaller prop.

Prop losses have a huge bearing on the engine power required. The 0.3m prop will burn up 12.64kW to produce a useful output of 16.32kW - almost as much lost as it delivers. The 0.9m prop burns up 3.52kW to get 16.32kW of useful output.

With the 0.3m prop the motor has to be almost 50% bigger; the fuel consumption almost 50% more and these factors are going to increase the displacement. So going forward with a small diameter prop we enter the slippery slope where everything has to get heavier, hull drag goes up and prop losses get even worse.

Hopefully this gives you and others an idea of why the prop should come into calculation. It is an essential consideration for the optimum "efficient coastal cruiser".

I will do a rough boat shape of where we are so you can get a better idea of the envelope you have to play with based on the requirements and constraints you have established so far. I will explain a couple of the design optimisations that are still required for that envelope. You may be able to encourage someone who likes to make quick pencil sketches to get you something that looks good within that envelope and also satisfies your accommodation requirements.

My expectation is that as you iterate around the design loop the large diameter prop will result in weight savings and you will easily get under 3t - right now the proposed boat will get about 9nmpg at 12kts into a 20kt wind with associated wind waves. Reducing weight and windage are needed to get to 12nmpg. An interesting outcome of reducing weight will be that prop losses go down as well and something less than 0.9m may prove to be the best.

My boat shape will give you the plate area for the main bits. You can get engine weights from motor specs. You can now determine fuel load to suit the desired range from published engine data. You should then narrow down on the weight by listing all the things you want in it.

Rick W

Brian@BNE
03-14-2010, 08:52 PM
Barely trailerable was i think noted by Sandy somewhere early in the thread and is the 1 of the 3 boats on the thread that i think is of most interest.

Erik - you may well be right that containerable is too restricting. Such a boat had a thread here http://www.boatdesign.net/forums/motorsailers/containerable-motorsailers-11797-10.html
but was more on sail than power and thread seems to have died, but still worth a read.

I hear fcfc on budget and hassles, but think that firstly trailer boats to 7.5m (2nd type of boat on this thread) are already on the market in large numbers. But few if any would meet the 'coastal cruiser' spec of Sandy or Erik and i doubt that such a limited LOA will enable it. The hassles part can be overcome, read on....

So i'd still kinda like the containerable aspect - ideally take road wheels off boat trailer, slide trailer and boat into container on some HDPE rollers and truck to/from house to destination. Trucking a standard 40' container is going to be much easier and cheaper than craning a slightly wider boat on and off transport. Drive SUV there by itself. At destination slide boat out and refit road wheels and use SUV to launch at various localities. At 'home' store boat in container, perhaps even at commercial facility. This way, a small SUV can handle the 'freight yard to waterfront' part - a large expensive tow vehicle is not required.

Boat might need to have a partly demountable coach house to fit in container. If so, it shouldn't be a huge task to refit - folding, just a few elements or perhaps pop-up.

Tad - i thought you already had something like this (from your posts of a few years ago) but couldn't find it on your website.

Will - can graphite go on a diet? Thin down a bit to slide into a container? It should be easy - graphite is a good lubicant:p) What we are talking here needn't go as fast as Graphite either, so Yanmar 4BY2, and not the 6? I think Graphite is barely trailerable in the sense that you go from home to your local boat ramp OK. But its getting towards the 3rd type on this thread - transportable - if any significant travel around our long Australian coast in planned, so i reckon that 1st type is best. Barely trailerable but just containerable gives maximum flexibility.

Willallison
03-14-2010, 09:16 PM
I'm not going to re-enter the to-and-fro foolishness of a few days ago - I still have a headache from bashing my head against that (very thick) brick wall... but on the prop front, I have just two questions... how does a 900mm prop not impinge on a 550mm draft? Or is the operator required to keep the prop blades horizontal?
The 2nd, is that since "it would be remiss of a designer looking at the most economic cruiser not to consider the prop and simply accept what is available on an outboard", how would you propose that one fits this 900mm prop onto said outboard?

Brian - simple answer, Yes - you could put Graphite on a bit of a diet. But one has to ask, at what cost in terms of facilities and durability. The more sensible approach would, IMHO, be to start from scratch if you want to fit into a shipping container.
I disagree, however, that Graphite is firmly in the transportable category. Clearly with a 2.8m beam and an on-trailer weight of 3500kg, she's would be regarded as somewhat of a heavyweight in the trailerboat segment too. But, from the outset, the boat was designed (from a well considered SOR, I might add too;) ) to be trailerable. In Oz, the restrictions for going to the overwidth beam are not onerous, and the gains in interior volume were considered to be of sufficient value to make the compromise (uh-oh...) worthwhile. There are an increasing number of large trailerboats getting around these days - particularly in the recreational fishing boat sector. Personally, I would regard her as lying at the top end of the trailerboat segment... but then I've had quite a lot of experience in towing quite big boats up and down the East coast of Oz, so don't consider the propect to be at all daunting. To someone who's never trailed a boat before it would be nothing short of terrifying. Again - an example of how the boat needs to be tailored to a specific individuals need... and of why the SOR is so important.

Brian@BNE
03-14-2010, 09:42 PM
Will

I trailed a 28' Shark Cat a bit some years back. Triaxle trailer probably on the limits - thankfully never got weighed by the authorities (fuel was cheaper at roadside servos than at marina, and 2 x 200HP meant large tanks...). I agree it can be done. But isn't fun, and so the boat was mostly left in the water. I'd like easier options to get beyond home port. And for periods of non-use (altogether too long and too frequent!) hardstand somewhere s preferable for both cost and maintenance.

I'm sure you are right re: starting from scratch. Container doors (plus room for lubricant) means a beam of 2.3 max, a long, long way down from 2.8. But even on a trailer, inside a container with enough clearance for towbar, LOA can be close to 11m, I think. The idea is to trade a chunk of beam for a lot more LOA to get even greater interior volume, albeit not as easily utilised.

Couldn't a 900mm prop be raised, eg into a box near the stern (perhaps under a seat) for slow rpm shallow water operation? Just leave 400mm actually in the water for that? Good for on the trailer too.

Willallison
03-14-2010, 09:57 PM
All sorts od things are possible, of course. But with every added complication you tend to add cost. So, let's say it costs you an extra 5 - 10K to engineer a solution that would allow for a very large diameter prop. A guess, of course, but probably not an unreasonable one. For arguments sake, we'll use Ricks numbers - 40hp for the big prop, 60hp for the smaller one. How long will it take you to recouperate the difference in operating expense between the two? And does the complexity of the arrangement force compromise in other areas.... It's all a balance... a compromise as one wise chap pointed out....

Oyster
03-14-2010, 10:05 PM
Forgive my ignorance; I'm a sailor looking for powerboat to snowbird the US Eastern Seaboard. Is there a design that will carry the accomodations of a 16' travel trailer at 12 knots in coastal waters at 12 nmpg? Since gasoline is currently cheaper than diesel, does that affect the traditional power choices?
Could this be done in a barely trailerable outboard driven vessel? I'm looking for a warm enclosed helm, 15' bridge clearance and very easy access to bow and stern for single-handed docking in moderately adverse winds and currents. I've made a half-hearted attempt to search this site and would be glad to be directed to a previous thread.

The accomodations I would like to find are a double berth, standup head and shower, galley and dinette for 4, stove and oven, H&C pressure water, AC and Heat, 3' max draft, refrigeration, and a comfortable place to read.

Reading through this thread I also went back to the original posting to reply with some common sense. Towing on a trailer along the eastern seaboard restricts the beam for sure. But you also do not need an 8000 lb boat to do what you are requesting to do at all. There are numerous trailable outboard motor boats fully cabined which are shallow draft and powered by an outboard that allows you to poke in some really neat coves with the advantage of the trim feature in lieu of an inboard engine setup. I have just finished construction on a 24 footer that weighs approx dry at under 2,000, power included.

The cabin roof for is 90" from keel to the standup cabin interior, and drafts 8 inches with the motor trimmed up. There is another fellow posting here that has a proven runabout simular to these numbers with speeds in the neighborhood of 15 cruise with full accomadations. A three foot draft does nothing for you but truely restrict your access along the ICW since you also do not need that much and only requires more hp and fuel to push it. I have a 90p E-Tec outboard engine on another boat 22 in length that also burns at cruising speeds 2 gph.

Brian@BNE
03-14-2010, 10:37 PM
Will - points taken, but of course its capital cost and weight/size penalty as well as operating cost.

Oyster - quite right in that outboards are likely to offer the best solution. But i'd really like to get away from petol. And i think we're heading for almost double LOA, which will inevitably fill up with stuff. So lightish boat, no 8" draft but i'd think much less than 3' also. What is your beam? Any photos or specs?

Guest625101138
03-14-2010, 10:43 PM
I'm not going to re-enter the to-and-fro foolishness of a few days ago - I still have a headache from bashing my head against that (very thick) brick wall... but on the prop front, I have just two questions... how does a 900mm prop not impinge on a 550mm draft? Or is the operator required to keep the prop blades horizontal?
....

Anyone familiar with high performance trailerable yachts readily accept the idea of lifting a keel that weighs maybe half the boat displacement so the boat can be beached or trailered. I don't think it is overly demanding to expect to place a 2-bladed prop horizontal for the same purpose. No doubt there are other options worth working through if it is indeed an issue for the final solution.

We are at a point where the weight and or windage has to be reduced to achieve one of the prime objectives. I don't think reducing weight below 3t will be challenging.

To achieve the 12kts/12nmpg (for US gallons) limits input power to about 16kW. So the optimised prop to achieve this will likely come in smaller diameter than 0.9m.

Rick W

Oyster
03-14-2010, 11:00 PM
Will - points taken, but of course its capital cost and weight/size penalty as well as operating cost.

Oyster - quite right in that outboards are likely to offer the best solution. But i'd really like to get away from petol. And i think we're heading for almost double LOA, which will inevitably fill up with stuff. So lightish boat, no 8" draft but i'd think much less than 3' also. What is your beam? Any photos or specs?
Well to enjoy the eastern seaboard and do it in a trailable boat, there are severe restrictions without petrol. There has been several discussed here by some highly qualified professionals in this thread. My response was targetted. So I will not attempt to reinvent the wheel. I know every single inche of the waters from the gulf coast to New York, and have lost nothing outside of the sea buoys any more. So this was the reason I stuck to a really shalllow but managable and marginable draft in a wharped bottom design for decent handling while transitting the semi open waters and ease of loading and launching too.

Willallison
03-15-2010, 12:43 AM
Anyone familiar with high performance trailerable yachts readily accept the idea of lifting a keel that weighs maybe half the boat displacement so the boat can be beached or trailered. I don't think it is overly demanding to expect to place a 2-bladed prop horizontal for the same purpose. No doubt there are other options worth working through if it is indeed an issue for the final solution.

We are at a point where the weight and or windage has to be reduced to achieve one of the prime objectives. I don't think reducing weight below 3t will be challenging.

To achieve the 12kts/12nmpg (for US gallons) limits input power to about 16kW. So the optimised prop to achieve this will likely come in smaller diameter than 0.9m.

Rick W

Fair point - though of course in this case you suddenly won't have an engine....

Given that we don't have a list of the stuff to go onboard - except in the broadest sense, how are we to determine the displacement? As I keep saying, without the SOR, all of this is meaningless. Sandy has already said he wants aircon. That means a genset. There will probable need to be at least 200-300AH of batteries. The head / shower will in many places require the inclusion of black & greay water tanks. So the list goes. But until it has been compiled, hullforms and powering requirements are of no value beyond entertainment

Brian@BNE
03-15-2010, 12:43 AM
Oyster - ok, and i'm assuming i'm not the target as i've felt no pain yet.:p but your beam is? construction materials? Photos to share?

And a chance for me to clarify - not double your 24', but to an LOA up to 11m or 36'.

Rick - prop horizontal for transport is fine with me anyway, i've scraped outboard skegs on kerbs in the past. Obviously it has to drop down for running? With the greater prop efficiency comes smaller motor, so is the guess of $5-10k for the drop-dpwn solution more than will be needed?

Will your stabilisers take beam off the main hull (to stay trailerable etc) or are they demountable, perhaps carried adjacent the bow while on the trailer?

Guest625101138
03-15-2010, 01:08 AM
Fair point - though of course in this case you suddenly won't have an engine....

Given that we don't have a list of the stuff to go onboard - except in the broadest sense, how are we to determine the displacement? As I keep saying, without the SOR, all of this is meaningless. Sandy has already said he wants aircon. That means a genset. There will probable need to be at least 200-300AH of batteries. The head / shower will in many places require the inclusion of black & greay water tanks. So the list goes. But until it has been compiled, hullforms and powering requirements are of no value beyond entertainment

Outboard manufacturers would make a bundle of money if outboard engines were destroyed every time a prop hit the bottom or a log. The optimum design would surely take this as a standard requirement and do it quite a bit more elegantly than what is done in a typical outboard.

We were given a displacement of 3t to work with in the first iteration. It is more than I would want but the customer is always right. He now has a bit more information to refine his requirements. Having got to where we are I can say with some confidence that a diesel powered 3t boat of 12m length is very unlikely to achieve 12nmpg in 20kts of wind and associated see conditions if the superstructure is 3m high and beam is 2.5m.

So the design space needs to be changed. My first place would be to revisit the weight estimate. We already have some reasonable data for the hull and powering to base that on now.

I can also see possibilities for reducing the height of the superstructure.

I am happy to entertain those that want to know more about the design space. No doubt there are some who know all this and have already built an efficient coastal cruiser capable of 12kts at 12nm/USG for their own use but others need to start somewhere. It only takes a few minutes of my time and is a diversion from other more boring things that people pay me lots of money to do.

Rick W

Guest625101138
03-15-2010, 01:46 AM
.....

What we’re doing now on this thread is what I would call a concept study. We do them quite often where I work, financed from the marketing budget, R&D budget or by a customer. A detailed SoR isn’t needed for such a study; the SoR can be the outcome of the study.
For a concept study, I think we’re attacking the problem in the right way by making a design assumption and then investigate the consequences.

Erik

In my working world we call it a feasibility study. And this study is unfinanced - just a diversion.

In a post or two back I have stated that a diesel driven 3t/12kts/12nmpg/12mlong/3mhigh/2.5mwide/20ktswind-waves is not feasible unless you approach a divine order who can change the laws of physics.

We are not far from it being feasible. I assumed USG rather than Imperial as well and nm rather than statute. With Imperial we are close but there are things you may not like in the current configuration.

Rick W

Willallison
03-15-2010, 02:02 AM
Ask most designers and I'm pretty sure they'd tell you that the customer is usually wrong - just that it's not always prudent to tell them so:D

I'm intrigued about the prospect of a setup the provides protection to a prop that could be as much as 1.7m below the surface (550mm draft, 20% tip clearance, 900mm diameter). Any idea's on how you would actually do this?

Brian@BNE
03-15-2010, 02:03 AM
Rick -in this part of the world, above 8m and used inshore, we will need grey/black water management of some kind and even if not mandatory elsewhere it is the responsible thing to do. So more weight and some internal volume gobbled up.

I agree with weight of boat <3t, and aim is as light as practical. But the 'ton of gear' as well as supplies & people will be pretty real and not all metaphorical. Personally i'd have height closer to 2m than 3, and beam no more than 2.2 but realise, perhaps i'm still dreamin' about what can be achieved. I've had a lot more than 2 cents worth today so will now (try!) to wait and see where Erik and fcfc want to steer discussion from what has been put forward today. I'm very interested but not yet committed and i think they are likely to start a build before me. I also want to see what comes out of the 'Competition II' thing sometime after mid-April before setting anything is stone (or expoxy).

As to SOR, I'll have everything that will fit in the external dimensions that now seem fairly well constrained, please. A marginal improvement of telling the designer i want a full condo at the outset. I'll leave the aircon for the next stage (bigger boat) and am slowly 'being educated' by the designers about what will add too much weight or height and has to be ditched for economy on motor size and fuel consumption. But i'll likely trade-off fuel economy eventually (but not the 12k speed!) after considering what perhaps surprisingly small proportion of the Total Cost of Ownership per annum is taken by fuel. Some of this gets away from Sandy's original post, but it seems he is not following the thread now? Perhaps he is building the solution as we chatter? I don't think he indicated crew - i'm think of two adults and up to 2 kids for cruising, with capacity to take an additonal 4 adults on day trips only. The latter is intermittent but shouldn't cripple performance.

And i'm sure i'm not the only one to appreciate the input of all experienced builders and designers contributing here in particular, and glad to hear that it isn't too much of a hassle or too time consuming for you guys.

Willallison
03-15-2010, 02:21 AM
Brian - and when this 'concept' comes back and says to you - oh sorry, you can't take most of that 1 ton of gear with you, can't have a shower on board, can't go to 1/2 the places you want to because the draft is almost 6 feet:!: ... what will you do....?
Why not approach this in the way a professional would... compile a detailed list of all the things you want on board, where you want to go, how far and fast, what you want it to look like, what you don't want it to look like, etc, etc.
Then - and only then - does it make any sense to go down the path of custom building a boat. Otherwise you might as well go buy yourself a Whittley or Bayliner. It will DEFINITELY be cheaper, you will probably get better resale value, and you could be on the water tomorrow....

Brian@BNE
03-15-2010, 02:59 AM
will - Shower can be a pump and a self draining cockpit floor if too cold for a swim (or too scared of bull sharks in that location). Sure, no soap for those showers, so back to shore now and then and if not feasible then 'bird bath' with a bucket and down the sink is fine. But enclosed head might be ok for shower too, even though after a short time 'on our next boat ....better shower' will reverberate around the cabin.

My mission is to have something barely trailerable and just containerable to decide whether I want to do extended cruising bordering on liveaboard. Something like your K5 is certainly a consideration for that - not readily transportable. Yes i could buy a cheap one that size to try out for a while, but it would likely need some repairs, perhaps repowering and new electronics and other gear. Would the post-purchase repairs be greater than the trailerable boat? Could be quite easily. If in due course the decision is, no the extended cruise is not for me, then there is a lot more capital tied up in something that could be hard to unload without taking a big hit. And testing my enthusiasm for lots of time on the water with a heavily compromised largeish old boat could well predjudice the answer.

But you have got my attention. 2.2m beam, 11m LOA - that should carry a lot of weight and surely you are joking about the 6' number.

The trouble with approaching it 'as a professional' is that you end up with something that is quite likely already available on the market, which doesn't suit. I'll ignore the mention of Bayliner, some bait just isn't attractive enough to take a bite. Different outcomes can arise many ways but different approach and thinking aloud here looks to be working.

Brian@BNE
03-15-2010, 03:01 AM
Ask most designers and I'm pretty sure they'd tell you that the customer is usually wrong - just that it's not always prudent to tell them so

I'm intrigued about the prospect of a setup the provides protection to a prop that could be as much as 1.7m below the surface (550mm draft, 20% tip clearance, 900mm diameter). Any idea's on how you would actually do this?
__________________
.

will - even if there 500mm draft at the finish of this, back where the prop is the hull should/could be higher surely?

ok, i can't stay away - this place is addictive!

Brian Eiland shows a belt drive concept for a yacht, which is similar power http://www.runningtideyachts.com/power/

It might only be concept rather than reality somewhere. In one place he shows uni-joint shaft connected to a fixed engine, but i think somewhere else he may have shown the whole motor/drive lifting up. Perhaps that is not too good for stability though unless we do end up with a big battery bank! I suppose small pod drives, if raisable, would also work. The motor might not have to be lifted more than say 450mm (shallow water & slow speed travel on water, could be higher for on the trailer) and if located in the cockpit area then temporarily putting up with it would be OK. For those folk in the ICW who apparently have to (or want to) deal with long distances of quite shallow water, then a smaller prop, larger motor (or even the trim/tilt outboard) might be better, i accept.

Guest625101138
03-15-2010, 03:08 AM
Ask most designers and I'm pretty sure they'd tell you that the customer is usually wrong - just that it's not always prudent to tell them so:D

I expect that the designers with this view not inundated with design briefs.



I'm intrigued about the prospect of a setup the provides protection to a prop that could be as much as 1.7m below the surface (550mm draft, 20% tip clearance, 900mm diameter). Any idea's on how you would actually do this?

I am intrigued why you think the prop needs to be under the deepest part of the hull?

Another little gem of common wisdom that needs to be dispelled is the idea of a 20% of diameter clearance. A large diameter prop with high blade aspect achieves high efficiency because there is low velocity ratio and low induced drag. The extra 10kW that is wasted in the 0.3m prop is creating a huge amount of unwanted turbulence that will impact on anything near it. It needs at least 20% of diameter clearance. A large diameter efficient prop can have less tip clearance for the same impact on the hull.

The draft to swing a 900mm prop is about 1m. It could be reduced by going to a tunnel. The static draft without doing anything fancy like folding or elevating is the draft of the hull. That is why I limited consideration to 900mm. Anything deeper will impose extra drag to support it that is going to offset the small gains in efficiency above this diameter.

In any event these questions do not need to be resolved yet because we know there is no solution possible within the current design space.

Rick W

Willallison
03-15-2010, 03:54 AM
I expect that the designers with this view not inundated with design briefs.

Rick W

How about I start a thread and we'll ask shall we...?

http://www.boatdesign.net/forums/boat-design/client-always-right-31899.html

Can you point me towards the research that suggests that a large, slow-turning prop needs less than 'normal' tip clearance?
And how would you propose to deal with the rythmic vibration often caused by insufficent tip clearance - and which is worsened by having a two-bladed design?
As to the draft, you will note that I said as much as 1.7m But even allowing for placing it under possibly shallower aft sections it is still likely to be approaching 1.3m.
I guess you could put it in a tunnell, the top of which is marginally above the waterline - as was done succesfully by Aitkin with his skiff - but imagine the size of the tunnell to allow for such a big prop...! Sorry Brian... there goes your cockpit!

And now, I really hate to bring this up, BUT....
The draft to swing a 900mm prop is about 1m. It could be reduced by going to a tunnel. The static draft without doing anything fancy like folding or elevating is the draft of the hull. That is why I limited consideration to 900mm. Anything deeper will impose extra drag to support it that is going to offset the small gains in efficiency above this diameter

Wouldn't this suggest that you compromised on the most efficient diameter for the prop for the sake of lower draft...????

Guest625101138
03-15-2010, 04:57 AM
..Can you point me towards the research that suggests that a large, slow-turning prop needs less than 'normal' tip clearance?


I doubt that you will find this written up because there are no marine props designed for such low blade loading. However if you sit down and do your own analysis of the blade loading you can approximate the local tip pressure and you will see why you do not need a large tip clearance.


And how would you propose to deal with the rythmic vibration often caused by insufficent tip clearance - and which is worsened by having a two-bladed design?

If the pressure disturbance is small the force exhibited on hull panels is small. It is also lower frequency so not as hard to stiffen the panel beyond harmonic range.

As to the draft, you will note that I said as much as 1.7m But even allowing for placing it under possibly shallower aft sections it is still likely to be approaching 1.3m.
I guess you could put it in a tunnell, the top of which is marginally above the waterline - as was done succesfully by Aitkin with his skiff - but imagine the size of the tunnell to allow for such a big prop...! Sorry Brian... there goes your cockpit!

And now, I really hate to bring this up, BUT....


Wouldn't this suggest that you compromised on the most efficient diameter for the prop for the sake of lower draft...????

Not at all. Prop efficiency is only one factor in the overall design space that we have to optimise within.

After almost a week now you still do not understand the difference between compromise and optimisation. The distinction is something all designers should have an acute appreciation of. I have attached some definitions for your education.

One involves giving-in or giving ground while the other is a search for the win-win outcome that goes to the best solution - of course for a complex design it is only the best solution in that time frame because there will always be unknowns and better ways in the future. This is the basis of continuous improvement. But then if you already know everything then the journey has ended.

I can see compromise pervades your thinking. You have already placed the customer in the "dumb git" bin who you are going to spend a lot of time bringing around to your way of thinking because you are always right and he is always wrong.

I my world the designer enters a partnership with the customer to go on the journey together, learning from each other to find the most satisfying solution - the optimum.

In past lives, for my paid work, I have been the client representative and I have invariably found the engineers and senior personnel in the design team have great respect for the knowledge of the customer. They spend a lot of time seeking out why there are certain preferences and objectives and explaining how these impact on the result. They provide the basic input for making value based decisions. They get to know the economic drivers of the customer's business reasonably well.

Rick W

Willallison
03-15-2010, 06:03 AM
My mission is to have something barely trailerable and just containerable to decide whether I want to do extended cruising bordering on liveaboard. Something like your K5 is certainly a consideration for that - not readily transportable. Yes i could buy a cheap one that size to try out for a while, but it would likely need some repairs, perhaps repowering and new electronics and other gear. Would the post-purchase repairs be greater than the trailerable boat? Could be quite easily. If in due course the decision is, no the extended cruise is not for me, then there is a lot more capital tied up in something that could be hard to unload without taking a big hit. And testing my enthusiasm for lots of time on the water with a heavily compromised largeish old boat could well predjudice the answer.

But you have got my attention. 2.2m beam, 11m LOA - that should carry a lot of weight and surely you are joking about the 6' number.

The trouble with approaching it 'as a professional' is that you end up with something that is quite likely already available on the market, which doesn't suit. I'll ignore the mention of Bayliner, some bait just isn't attractive enough to take a bite. Different outcomes can arise many ways but different approach and thinking aloud here looks to be working.

Sorry - bypassed this earlier...
Let's start at the end 1st. I couldn't disagree with you more - the very reason that you engage a professional and go through the proven process is so that you can ensure the you DON'T get the what's already out there in the marketplace (assuming that's not what suits, of course). As far as Bayliner's go, I wasn't tossing out a baited hook... they don't fit with everyone's needs, but they fill their market niche - which is a pretty broad one - very well.

No - I wasn't joking about the 6 foot draft... based on the quoted draft of 550mm (which I agree could be somewhat less towards the transom - though often isn't in slender hullforms) the 900mm prop and the 20% tip clearance (which I'll await for Rick to show any published data to suggest is too much) The draft would indeed be close to 6 feet.

As to the cost of ownership, I have absolutely no doubt that buying a near new - or even new - production boat, like those I mentioned, would be FAR less expensive than having one professionally built to the same standard. Fortunately for the design community, there are enough people out there who are prepared to pay extra to get exactly what they want.
Which sort of brings us full circle..... why go through all the effort to custom build if you aren't going to get what you want? Preparing a detailed SOR won't cost you anything but a bit of time.....

Willallison
03-15-2010, 06:13 AM
I doubt that you will find this written up because there are no marine props designed for such low blade loading. However if you sit down and do your own analysis of the blade loading you can approximate the local tip pressure and you will see why you do not need a large tip clearance.


If the pressure disturbance is small the force exhibited on hull panels is small. It is also lower frequency so not as hard to stiffen the panel beyond harmonic range.


Not at all. Prop efficiency is only one factor in the overall design space that we have to optimise within.

After almost a week now you still do not understand the difference between compromise and optimisation. The distinction is something all designers should have an acute appreciation of. I have attached some definitions for your education.

One involves giving-in or giving ground while the other is a search for the win-win outcome that goes to the best solution - of course for a complex design it is only the best solution in that time frame because there will always be unknowns and better ways in the future. This is the basis of continuous improvement. But then if you already know everything then the journey has ended.

I can see compromise pervades your thinking. You have already placed the customer in the "dumb git" bin who you are going to spend a lot of time bringing around to your way of thinking because you are always right and he is always wrong.

I my world the designer enters a partnership with the customer to go on the journey together, learning from each other to find the most satisfying solution - the optimum.

In past lives, for my paid work, I have been the client representative and I have invariably found the engineers and senior personnel in the design team have great respect for the knowledge of the customer. They spend a lot of time seeking out why there are certain preferences and objectives and explaining how these impact on the result. They provide the basic input for making value based decisions. They get to know the economic drivers of the customer's business reasonably well.

Rick W

Ohhh... we're not back there again are we...? I'm not even going to bother to respond anymore Rick... you simply don't get it....

In an effort to keep this remotely on track, how about we start a thread on that one too...

http://www.boatdesign.net/forums/boat-design/compromise-31901.html

fcfc
03-15-2010, 06:39 AM
The trouble with approaching it 'as a professional' is that you end up with something that is quite likely already available on the market, which doesn't suit. I'll ignore the mention of Bayliner, some bait just isn't attractive enough to take a bite. Different outcomes can arise many ways but different approach and thinking aloud here looks to be working.

Big names in boating (thoses who sell boats in the thousands) have very good marketing dept, very good design offices, and very good production lines. Otherwise they wont stay big names for long and would go bankrupcy rather soon.

Differents approach might be working, but when I see 900 mm prop, I see very high bucks custom made gearbox, or a subscription for frequent use of rescue services. :P

Oyster
03-15-2010, 08:29 AM
Oyster - ok, and i'm assuming i'm not the target as i've felt no pain yet. but your beam is? construction materials? Photos to share?

And a chance for me to clarify - not double your 24', but to an LOA up to 11m or 36'.
Target? I dealt in facts for the sake of this discussion. A towable and launchable boat at standard boat ramps along the eastern seaboard requires in almost all cases no more than an 8'6" beam with 9'6" and a few inches fudge inches for daylight only towing without escorts and big banners. If you add that to the fact that touring couples need to be able to do this without owning a tractor used for heavy hauling too, the boat has its restrictive perimeters. A 36' power boat using the guildlines for the beam is not avaliable unless you build a "Bolger' type boat. People in the production of power boats do not build boats using these perimeters here in the states.

This also restricts where you take a boat like that in the water also because of its bottom design centered around shallow draft and beam which makes the boat uncomfortable too. If you add this to the requirement and desire to have minimal fuel burn, you need to consider building your own boat because of the costs and materials not normally used in boat unless they are high dollar hulls using high tech materials and construction methods.. All boats are a compromise.
I went with glued lapstrake plywood which is pound for pound the strongest and lightest per square inch with a composite cabin, top, and sandwich bottom of glue and plywood.

FAST FRED
03-15-2010, 08:30 AM
"I see very high bucks custom made gearbox."

Most V belts are fine when loaded to 10 hp. 4 belts with matching reduction pulleys is hardly that costly.

The flat or Glimmer belts will pass even more HP , but their pulleys are even more expensive.

The question of compromise is best answered with a prioritized list.

Is 12k at 12mpg on top or the hot tub?

To me legally no hassle trailerable would be #1

Efficient (if its worth the extra construction cost of really light).

Common build/ez repair , no Unobtanium engine or other parts.

And the really hard part for this design BEACHABLE .

This common list always seems to lead me back to the Atkin , box keel + reverse deadrise.

FF

Willallison
03-15-2010, 08:36 AM
Oyster... shame on you... compromise...?
And you too FF.... you guys are in real danger of bringing a dose of reality to this scene!
It's important here not to get confused between projects. Sandy (who seems to have vanished...?) is in the US, Brian is looking for something possibly similar for the E. Coast of Oz, where trailering restrictions may be different. For minimum hassle though, I agree a max 2.5m beam (again, for Brian in Oz) is probably a good starting point for one of the items on that list I keep harping on about...

Oyster
03-15-2010, 08:58 AM
Oyster... shame on you... compromise...?
And you too FF.... you guys are in real danger of bringing a dose of reality to this scene!
It's important here not to get confused between projects. Sandy (who seems to have vanished...?) is in the US, Brian is looking for something possibly similar for the E. Coast of Oz, where trailering restrictions may be different. For minimum hassle though, I agree a max 2.5m beam (again, for Brian in Oz) is probably a good starting point for one of the items on that list I keep harping on about...

Well I have been accused of being a bit "slow". No problem, towing for an inidividual no matter what the beam is, is restricted by the towing vehicle and the prior experiences in doing so unless you do not care about your investment either. 11' beam dictates a special use vehicle and an operator that meets a certain criteria over and above your weekend warrior in almost all cases. Add that to the ramps which is also another fact finding mission before you take the leap, you are surely restricted by no fault of your own.
Oh compromises? Even cruise ships have them too.

Brian@BNE
03-15-2010, 11:55 AM
FF - agree on belts and different size pulleys for required gearing. I'd hope the big prop can be a CPP. Can't see any need for a gearbox at all, but still plan on some kind of clutch!

If the prop is more sensibly a 'standard' size than the as yet nominal 900mm being used as a strating point, or outboard power asserts itself as an obvious choice i don't really mind. I'm just aiming for max efficiency at the start of the optimisation process. If i get to client status i will compromise any any decision i'm involved with (automatically then the optimum - client is always right, refer above:D) and be pissed about any compromises where i'm bypassed. (sub-optimal situation, unless of course the designer/engineer prefers to retire and not have any clients, when of course its optimal). Oh hell, i'm not getting sucked into this as well am I?:P

My desire for containerable is so that the SUV/trailer combo only ever does the short hops. Long transits in the container. Thus minimize owner's time with the long trailer on the highways even though it would be legal all hours without flashing lights, escorts etc. Such things as boat overhang behind trailer wheels might make some ramp locations challenging.

Draft of 'my' 2.2m beam is looming as an issue. Obviously the whole shebang will have to be light as possible, but avoid expensive exotic materials.

I'll have to be careful now or i might end up spelling out an SOR, but bear with me a bit. I don't envisage much internal fitout to be frank. From bow - almost certainly v-berth, enclosed head then a largish convertible dinette (total is overnight for 4), and minimalist galley - and thats the saloon, apart from some storage. Galley within the saloon might just be a sink and really usefull amount of bench space. I have a bunch of camping stuff - cooking and 12/240 fridge freezer, plus assorted associated items. When i've previously said i want the lot i was bieng a bit facetious, but with the range of camping gear I've got i'll be pretty comfortable. Its not as light as specialist hiking stuff, but weight/volume considerations are just as relevant for camping trips as they will be for this boat so i think it should be fit for purpose. I'd load just what was needed for the trip each time, not leave it in the boat. This would be as much for durability of non-marinized items as for some weight discipline.

Cooking might get changed from a camping 2 burner LPG unit to a small LPG BBQ unit. Either would preferably stay in the cockpit/helm area except when secure lockup required. I dont want LPG or other highly flamable/explosive stuff inside the saloon, or to bother with plumbing it into place. Needless weight/time/effort. Cockpit to be quite generous in size. Helm area a bit smaller and able to have sufficient weather protection for destination as noted above. Battery bank - yes, will have laptop and some other carry on/carry off electronic items. A little portable genny to top up batteries if required can live in a 'box cum seat' in the cockpit. Probably not even take the genny on short trips.

I don't envisage aircon, but in deference to Sandy's original post, an aftermarket car/truck unit, belt driven compressor on the diesel, might be ok. Tricks here would be to ensure good insulation as part of construction and have a 'proper' door between helm area and saloon. Probably not 'watertight bulkhead' door, but heading that way. Then just cool saloon/v-berth down while motoring. Some required ventilation means things will warm up during night but hopefully nighttime is cooling down anyway and will compensate enough. If anchored and its that damn hot and uncomfortable maybe go home, or have shore power and the capacity to drive compressor electrically as well?

Helm area to have 'runabout style' windscreen with triangular sides, fold flat somehow. A bit trickey with curves but there'll be a solution. GRP hardtop with long posts at rear, short ones to edge of windscreen but leave about 6" gap between top of 'screen and hardtop. The ventilation with that set-up is magic in warm weather. Readily detachable -30 minutes? For poor weather roll down 'clears' from hardtop and zip closed, ditto along the sides.

Now folks from cold weather climates might want a more completely enclosed helm area. It shouldn't be too difficult to design a demountable setup that can be assembled at the ramp, even if time required might then be a couple of hours. For local tralering trips it would be left in place. For longer towing or containerisation, it would come off.

I'd look hard at a pop-up roof over the saloon, a la the caravans of same style. This would give more headroom at anchor. It would block the view out of the windscreen and have to be lowered for transit periods. It would wind up but have gas strut assistance. A good rubber seal on the perimeter, and external catches for secure water tightness when motoring. When the pop-up is lowered, 'headroom' in the saloon would be limited to sitting height only. This configuration helps keep overall CoG as low as possilbe for stability, and and you will realise windage of this boat (assuming you can follow my description) will be pretty low also.

Erik - if there is something you'd want to do different, put it into the mix. We're both thinking broadly the same way i believe? And both thinking of a longer boat then fcfc unless he wants to buy into the containerisation idea. With a few 'semi-clients' input we might be able to get enough of a consensus and clarity of 'brief' that Rick, Will and others can audit for sanity and do-ability.

Brian

fcfc
03-15-2010, 12:26 PM
Again and again and again, no tag price !!!!


For the belt reduction, how do you clutch and go reverse ?

And are you sure the efficiency, price and reliability of a 4 V belt drive (+ clutching system and reversing system) and a big prop will be better than a stock 1:3 proven and available marine transmission with standart shafting and prop ?

If you want to go direct drive where will you find a low power engine revving slow enough to drive directly a prop ?


How do you put a convertible dinnette (for 4) convertible as a double bunk in a boat 2,2m beam (7ft4in)

BTW, where is the engine in your layout ?

Do you expect to have headroom in the head ?

Oyster
03-15-2010, 12:28 PM
My desire for containerable is so that the SUV/trailer combo only ever does the short hops. Long transits in the container.

Then you are required by the laws of the lowest common denominator which allows for trailering and launching in the particular region of your intended uses. Yes, this also will be compromise from the top end requirements, beam, width, and weight for a 36' long x 11' in beam boat and the required scantlings for the shell and structual intergrity for the boat unless you truely go the highend materials route and the requirements in the form of controlled manufacturing.

Oyster
03-15-2010, 03:39 PM
Photos to share?
Here you go Brian. The boat is in the final stage of paint work but has the rigging all roughed in. I am into efficency and with some usefull and previous experiences I have built this one after selling my sharpie=skipjack gaff rigged sailing vessel.

The boat's cabin is sandwich divinicell skinned with white cedar emulating T&G and on the outside its also skinned 1/4" plywood and then glued lap white cedar 1/4" for stability and the wooden planked look and grain texture.

I also rigged a double helm unit for several reasons as we fish and also boat in four seasons climates. I rigged the inside with a RV type galley arrangement for my grandson to sleep which also doubles as a love seat arrangment too for two people to sit inside. The dinnette seating is more than adaquate for another passenger to ride and read with the aft facing seating flipping over to convert to a passenger helm seat arrangement which automatically raises to a nice height for veiwing out the window.

I also built a collapsible bunk that rests on a lip across the dinette arrangment for an additional adult bunk which adds another sleeping quarters along with the double sleeping arrangement foward with no head knocker roof top.

The aft seating also is very comfortable facing foward with tackle center and double sink arrangement on top. So you see I do not need a long and massive cruiser for my intended use along the coastal waters on the east coast and the gulf region. Towing is not an issue and bridges non existant. I have a complete walk around to foward with bulwalks and the trunk also doubles as seating foward with ample leg room to the decking. Wooden teak trim compliments the painted hull. This boat will get a 60 hp if someone wants to purchase the boat but will get a 40 hp. four stroke and 12 gallon tank which gives me more than enough for my intended day trips.
I also incorporated a full size head in the step foward of the dinette which gives you some privacy and storage along the exterior too under the decking with lockers foward also in front of the foward most bulkheads. All of the dinette parts also are convertible so that they can fold up or down which makes easy access to the lockers. If you look closely, the dinette is raised so that passengers can see out of the side windows with the step up deck allowing for double drawers for more storage. This boat for two people has enough room for two weeks of stable goods with perishables in a built in ice box and room for an extreme cooler under the port cockpit seat.

If you also notice, I have built in "ac" in the storage boxes foward of he cabin so that I get air inside in inclement weather when underway. The pipe makes a creative stopwater loop for any spray that may be taken over the bow with caps and flappers inside to close it up.

http://img.photobucket.com/albums/v356/Bateau1/DSC07674.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC07677.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC07689.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC07670.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC07578.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC07669.jpg

http://img.photobucket.com/albums/v356/Bateau1/DSC07676.jpg

TollyWally
03-15-2010, 03:43 PM
I'm modestly skeptical about the long term sealability of a pop up type structure over the salon. It's hard enough to get hatches and skylights to work in the real world. I'm on the west coast and to me coastal cruising means a bit of green water. Just saying.

Oyster
03-15-2010, 03:55 PM
I'm modestly skeptical about the long term sealability of a pop up type structure over the salon. It's hard enough to get hatches and skylights to work in the real world. I'm on the west coast and to me coastal cruising means a bit of green water. Just saying.
If you are speaking about the hatch even while replying to Brian's comments, , the intergral workings is not shown in the creative lip which dogs down and seals the lid. I actually used the feature on a working cabin for my sailboat and it never leaked a drop with zero gasketing. I could take the water hose and hit it and I never got a drop inside from around the rim of the curved rooftop.

TollyWally
03-15-2010, 04:13 PM
That's cool. I'd love to see some close up pics of a real world installation. I'm not trying to be negative, I just hate leaks.

Oyster
03-15-2010, 04:29 PM
You taper the inside lip and use duct tape along the joint and fill with thickened epoxy. Let dry and then remove and cover with an additional strip of any size which in the case of the hatch I used 5/8". Pick your poison.
I then faced the lip of the roof top and it worked fine. I have this stored on the computer of the roof top but don't have the shots of the steps for the hatch since photobucket updated early this year while I upgraded my computer and mail service and have not been able to refresh my albums. No matter what your shape, you can use this feature and a dog down and its pretty tough to get water to work its magic in spray over the top. Direct spray especially over the top for a simple coastal cruiser? odds are pretty good that this will work. Gaskets age and I have yet been able to depend on them over the long haul. The natural seal when pulled down after creating the custom seal with the uncured glue and then let glue fits everytime seems to work for me. The duct tape allows for spacing for finish paint or gelcoat depending on the choice of topcoat.

http://img.photobucket.com/albums/v356/Bateau1/resizedgluejoint.jpg

erik818
03-15-2010, 04:48 PM
A week of travelling has started again, so I've not had time to read all new posts thoroughly. I'lö do that.

I'm not trying to represent an unknown client. I'm inserting my very own requirements and the needs I have. I don't expect they will be the same as for the average client, but at least they are applicable for one person. I took the chance to push a very interesting thread in the direction that was of most interest to me.

In my opinion the requirement on fuel efficiency doesn't have to be met with 20 knots headwind. The average wind in Sweden is 6 knots, and the direction relative to the boat could be anything. I suggest the 12/12 requirement should be met without headwind and at a relatively calm sea state.

I note that different people have different needs to trailer the boat. For me personnally it's not very important, and I'm fairly sure I can borrow the equipment for the short hauls I would need. "Barelly trailerable" best discribes my need.

Erik

TollyWally
03-15-2010, 04:53 PM
Interesting, I'll have to study this a bit. I'm still unclear as to just exactly how to do that little trick. Looks like I may learn something valuable today. :)
If you ever get your pics back I'd love a look at them.

Oyster
03-15-2010, 05:12 PM
Interesting, I'll have to study this a bit. I'm still unclear as to just exactly how to do that little trick. Looks like I may learn something valuable today. :)
If you ever get your pics back I'd love a look at them.


See if you can figure it out from these two shots that I have also for the existing hatch. I create the raised trim and angle the edge down. I then fit the initial outside moulding or frame and glue up. I then tape all the parts and sit back in place and mix glue up and fill the void. If you look closely you can see the cured glue before you install the top in the case of a hatch. If you also look at the way I deal with the crown, I also tape the bottom of the frame and the outside of the frame and tape off
the decking and place glue between the hatch frame and decking and let cure. This also makes a flat seal and deals with the crowned decks around the raised trim. I do not have to custom fit the frame either. You can go as high as you wish. Then you just paint everything out.
http://img.photobucket.com/albums/v356/Bateau1/DSC07745.jpg


http://img.photobucket.com/albums/v356/Bateau1/hatchroughin.jpg

u4ea32
03-15-2010, 05:53 PM
Oyster, that is a very nice looking boat to to my eye!

TollyWally
03-15-2010, 05:56 PM
Thanks Oyster,
I'll be studying these. David's right about your boat.

u4ea32
03-15-2010, 06:26 PM
Getting back to the "feasibility study." And I think that's the right term for this effort.

Studies so far (most of the useful data from Rick), and the results:

1) 12/12 is possible, but only with "very light" displacement. It looks like 3t is too heavy to be possible. 2t looks more likely. 1t is demonstrably possible with actual boats (that are "too short").

2) Length looks to be 12m or 40 feet. Although the investigation actually suggests 14m or 46 feet is a more appropriate size for efficiency, other concerns (trailering, moorage, handing, maybe even cost) suggests trying a shorter length over a longer one. And there is that woodenboats competition... ;-)

3) Easily trailerable, meaning approx maximum limits of 2.5 m (8.5 feet) wide and 12m (40 ft) long. Lighter is better for sure. Smaller in all dimensions makes trailering easier.

4) Air resistance study indicates that at this speed and power to meet 12/12 its pretty much got to be a conventional monohull, not stabilized monohull. This wasn't so clear, so let me clarify: At some point we need to put stuff inside, so volume will matter. A stabilized monohull has far more windage for the same volume. Since wind drag is as important as water drag, better to reduce wind drag for a small increase in water drag.

5) Initial stability and water drag power study indicates 2.5m beam is adequate for stability, again supporting the conventional monohull selection.

6) Assume "large" diameter prop is OK, because it might be attached to an outboard, or might be oriented horizontally when on the trailer. Still, "coastal cruising" infers a draft restriction, but not such a firm number as the beam and length due to trailering. Nevertheless, the much larger than "normal" prop shows dramatic efficiency contribution at this very low power 12/12 regime.

Sound correct?

Rick, what's next in your design spiral? I think its nailing the drive train. To get 12/12, that's two different solutions, one for outboard, and one for diesel. At least we've narrowed the power requirement. For outboards, probably need to use one of the "bigfoot" engines to get a tiny bit more reduction. Still not much, and still the 10hp/gallon/hour issue.

Is it possible to reach 12/12 with a bigfoot outboard? How light would we have to go?

u4ea32
03-15-2010, 06:30 PM
Oh, one more thing. Tad, I think your sketches are beautiful, but I agree with your earlier statement that even 4t won't get the efficiency target, and 18t is way too much. For this feasibility study.

Pierre R
03-15-2010, 06:47 PM
I think this has turned into an exercise in dreaming instead of really doing something. If not then I would suggest that those dreamers get together and make the boat. I would suggest in Oz to do it in plywood/epoxy/basaltic fiber for cost and weight.

The prop, who knows how you would make a 2 blade prop three feet in diameter that would be able to be turned by a low hp engine and have the pitch to be able to move the boat forwards at 12 knots.

In the end you will probably save $10 in fuel on a weekend jaunt.

Guest625101138
03-15-2010, 07:22 PM
A week of travelling has started again, so I've not had time to read all new posts thoroughly. I'lö do that.

I'm not trying to represent an unknown client. I'm inserting my very own requirements and the needs I have. I don't expect they will be the same as for the average client, but at least they are applicable for one person. I took the chance to push a very interesting thread in the direction that was of most interest to me.

In my opinion the requirement on fuel efficiency doesn't have to be met with 20 knots headwind. The average wind in Sweden is 6 knots, and the direction relative to the boat could be anything. I suggest the 12/12 requirement should be met without headwind and at a relatively calm sea state.

I note that different people have different needs to trailer the boat. For me personnally it's not very important, and I'm fairly sure I can borrow the equipment for the short hauls I would need. "Barelly trailerable" best discribes my need.

Erik

Erik
To take the first iteration to something that you might use to go forward -

Reducing the windage and wave requirements make the key objectives feasible.

Attached shows one quick option of what it could look like. There are still many aspects to work through of course.

The frontal area of this is about 6.5sq.m and the Cd will be better than 0.3. With no ambient wind the windage underway drops to 180W. So the power drops to 8.5kW. This translates to 1370N thrust.

A 500mm 4-bladed prop will require 10.8kW to produce this thrust. There will be transmission losses and house loads to cater for as well while underway. If you look at engine fuel maps I believe you will find a little diesel that will produce this power with less than 1USg/hr.

So it is feasible within the current weight constraint. There is 44sq.m in the hull and wing plates. The stabilisers, sides, deck and cabin have 72sq.m. You would need to allow for bulkheads as well.

One potential issue with this concept is the width of the hull. It tapers from 700mm wide down to 600mm wide. I expect it can be widened without increasing power demand but this requires another iteration. There are many other aspects that need to be set out before moving on.

Rick W

Guest625101138
03-15-2010, 08:24 PM
I should add that the estimate I made for added power due to waves was somewhat pessimistic. I applied it to to the combined calm water drag and windage at 20kts. The 20% allowance should only apply to the hull drag not the wind drag as well.

So both windage and wave drag allowance, quite a few posts back, were pessimistic. With the reduced area, slicker shape and correct wave allowance it would now be close to meeting the original requirements. The prop diameter would be more like 600mm than 500mm though to avoid throwing too much power into turbulence if the wind/wave requirement was included.

Rick W

Willallison
03-15-2010, 09:15 PM
It's a little unclear as some of your model's appear to be in conflict with one another, but I assume that the main hull is somewhat shorter than the main 'body' of the hull.
I expect you are planning on locating the prop (which I see you have 'optimised' down to a less than optimum diameter of 500-600mm) aft of the central hull in order to keep draft to a more acceptable level? In which case, have you considered the problem of locating the prop so close to the surface without the addition of any kind of (drag-inducing) anti-ventilation plate? The closer a prop is to the surface, the more prone it is...

Also, on a simple, practical note, you show a bridge-deck clearance in the order of 150mm. From personal experience, I can attest to just how unpleasant it is to spend time aboard a boat with such a setup. Every passing wave causes the boat to shudder - both underway and at rest. I think you need to seriously rethink that bit.

u4ea32
03-15-2010, 09:28 PM
Rick, I seem to remember a video of a human powered boat that used a surfacing propeller. How did that work? Is there a reason a boat in this speed regime could not use a surfacing propellor?

Seems like an easy way to get a much larger prop without also taking the hit for shaft and strut drag, or non-horizontal thrust.

Guest625101138
03-15-2010, 09:46 PM
Rick, I seem to remember a video of a human powered boat that used a surfacing propeller. How did that work? Is there a reason a boat in this speed regime could not use a surfacing propellor?

Seems like an easy way to get a much larger prop without also taking the hit for shaft and strut drag, or non-horizontal thrust.

David
A surface prop is limited to about 70% efficiency. There have been none used with great success on HPBs as far as I know. I used one but never video it. It was close to hopeless but the design was not very good either.

Removing the wind/wave requirement gets down to a prop of 500mm before losses are significant compared with going any bigger. I don't think this size present any major issues for mounting and operating.

Rick W

Guest625101138
03-15-2010, 10:20 PM
It's a little unclear as some of your model's appear to be in conflict with one another, but I assume that the main hull is somewhat shorter than the main 'body' of the hull.
I expect you are planning on locating the prop (which I see you have 'optimised' down to a less than optimum diameter of 500-600mm) aft of the central hull in order to keep draft to a more acceptable level? In which case, have you considered the problem of locating the prop so close to the surface without the addition of any kind of (drag-inducing) anti-ventilation plate? The closer a prop is to the surface, the more prone it is...

Also, on a simple, practical note, you show a bridge-deck clearance in the order of 150mm. From personal experience, I can attest to just how unpleasant it is to spend time aboard a boat with such a setup. Every passing wave causes the boat to shudder - both underway and at rest. I think you need to seriously rethink that bit.

Will
You have to draw the distinction between efficiency and optimum. The diameter of the most efficient prop is usually achieved when the diameter reaches the point where the appendages required to carry it create more drag and resulting power loss than the efficiency gain by increasing the diameter will achieve. I have attached the definition of efficiency as applied to physics.

There are many other elements in the design space when considering the optimum. My original aim of entering the discussion was to point out that the prop selection should be the result of optimisation rather than a simple compromise based on limited information.

As to the wave slapping I would need to know what hulls you have experience with to see if it is relevant here.

The wing or bridge clearance is 200mm. The width of the bridge is 400mm. Under way the hull will create a trough under the bridge. The stabilisers will ride on the crest of the wave. It would take a fair amount of study to determine what conditions will result in wave slap. Irrespective the bridge is a very narrow and stiff area compared with what the typical sailing cat has.

At anchor I expect anything bigger than about 500mm waves will cause slap. If you are tired enough you will sleep; some will find it soothing. Others will take time to get used to it or find another anchorage. I have slept in much worse conditions. My annoyance was the halyards slapping inside and outsidse of an aluminium mast.

In any case the sketch is a single solution as the result of a feasibility study. Anyone familiar with design knows that this is about 1 to 2% of the design process. I believe I have demonstrated it is feasible. We do not have anywhere near enough information to know if it will resemble the best solution. From what I can see everyone has their own view on what constraints should be applied and this is reasonable as the optimum will change depending on use. At least now there is some basic relationships between parameters like length, speed, stability, configurations, windage, waves, propeller diameter and power that will have similar relationships for other options that might be considered. I did not set out to design a boat. My object was to make a point about how prop selection is important to the solution.

Rick W

Brian@BNE
03-15-2010, 11:30 PM
Oyster - its looking very nice, and seems to be a lot of boat for 8" draft. Thanks for some good ideas, sharing, and inspiration to build a dream.

I've got to do some work for a few days but will keep on eye on the thread and look forward to Erik and Ricks next stages. This feasibility study is broadly going where i want to be, but obviously still has a while to go before the epoxy gets mixed anywhere. I'll be a sponge for a while, soak up the good ideas and in due course come back. Some compromise of my 'boundary' specs in earlier posts aren't a show-stopper, and interesting potential solutions are coming up anyway.

Pierre R
03-15-2010, 11:35 PM
Rick that boat might be okay in the canals but it would knock the livin snot out of you in Lake Erie, The Chesepeake Bay or the Albermarle Sound on a typical afternoon.

marshmat
03-16-2010, 12:44 AM
Rick that boat might be okay in the canals but it would knock the livin snot out of you in Lake Erie, The Chesepeake Bay or the Albermarle Sound on a typical afternoon.

A valid point, and it could be applied to any boat intended for relatively calm conditions.

I've been working on something ( http://www.boatdesign.net/forums/projects-proposals/trailer-cruiser-revisited-trimaran-27032-12.html ) that's perhaps not quite as fuel efficient as some of the boats mentioned here, but that should be capable of handling awkward/heavy loads as well as taking on relatively rough conditions.

At 2.5 tonnes displacement, it shows 10.9 kW indicated for 12 knots (once propeller efficiency, etc. are considered, figure about 24 hp at 12 knots). With a gas outboard, that's about 6-7 nautical miles per gallon. But she's shaped to max out at 20 knots, and has unusually large outriggers to suit certain service requirements we have. With a bit of massaging, slightly lighter construction, and an inboard diesel with a big, low-speed prop, such a boat could probably get close to 10-12 miles/gallon.

Just a thought....

Guest625101138
03-16-2010, 12:51 AM
I expect it may be useful to give an example of what a large diameter high aspect prop looks like. I happen to have one laying about so I photographed it - refer attached.

This prop is 800X400 and is made of nylon. It is good for a maximum thrust around 500N. It flexes beyond that load. It would need to be quite a lot stronger to take the 3kN bollard pull capable with such a prop connected to a 20kW diesel. That can be achieved by making the blade chord larger and/or using higher strength materials.

The speed being considered on this thread is a region where cavitation can be avoided even when using quite high lift, thick blades. Standard marine props are designed for higher speed and considerably higher disc loading pressure - therefore lower efficiency.

One of the problems with the current state of marine propulsion is that all the moneyed effort is focused on the high speed end. You will not find anyone making props to a design that works efficiently in the application being considered here. The simple 12kt/12nmpg equation means the prop needs to handle 16kW at 6.2m/s. There is a JavaProp screen image attached that shows the efficiency of a 600mm prop under these conditions. JavaProp is a reasonably simple tool for analysing propellers where cavitation does not occur:
http://www.mh-aerotools.de/airfoils/javaprop.htm

I worked this out about 5 years ago and have been making my own props since. About 4 years ago I was pointed to JavaProp as it was doing much the same as the model I had developed from first principles. Where I can, I use off-the-shelf props but they are usually from model airplanes like the one pictured.

The main reason for the image is to show I am not considering the use of a tonne or so of bronze. It could be a low BAR sail-drive prop proves to be a good choice. That is the nearest you will find in the marine industry I expect.

Rick W

Willallison
03-16-2010, 01:20 AM
Rick that boat might be okay in the canals but it would knock the livin snot out of you in Lake Erie, The Chesepeake Bay or the Albermarle Sound on a typical afternoon.

A valid point, and it could be applied to any boat intended for relatively calm conditions

That's the whole point Matt... this is a boat intended for coastal cruising... not the local dam...

There's a whole bunch of stuff here that deserves comment. Sadly I don't have the time just at the moment. But I will offer just one thought...

As to the wave slapping I would need to know what hulls you have experience with to see if it is relevant here.

The wing or bridge clearance is 200mm. The width of the bridge is 400mm. Under way the hull will create a trough under the bridge. The stabilisers will ride on the crest of the wave. It would take a fair amount of study to determine what conditions will result in wave slap. Irrespective the bridge is a very narrow and stiff area compared with what the typical sailing cat has.


Just how much study does it involve to see that a wave with an amplitude of 400mm (trough to crest) will strike that big flat plate?

It matters little what sort of multihull I'm talking about. The simple fact is that with insufficient bridge-deck clearance, waves will cause an intolerable motion and racket. 200mm is IMHO insufficient. I would consider 600mm to be an absolute minimum and as much as 900mm to be desirable

Guest625101138
03-16-2010, 02:08 AM
...

...


Just how much study does it involve to see that a wave with an amplitude of 400mm (trough to crest) will strike that big flat plate?

...

This is too simplistic. A boat when in motion creates divergent waves that produce a trough along the side of the hull that influences the height of the wind waves in proximity to the hull. The bridge is sitting above the trough. It is not like a catamaran where the hulls are usually separated by much more than 400mm. The rule of thumb there is a clearance angle of 45 degrees to the bridge deck. That is what the shape I presented above achieves.

I know from my own experience with a 100mm high clearance that I can operate in waves over 300mm before I start clipping them. And this is with a tiny hull that has miniscule waves - an order of magnitude smaller than what a 12m boat at 12kts with a 500mm deep entry will produce.

The attached shows the divergent wave from a slender hull with high T/B ratio - similar to the 12m shape presented. Displacement is a miserly 100kg though. You can get an idea of the divergent wave pattern at different speeds. The height is also apparent at the slower speeds. 10kph on this 3.6m hull will be roughly equivalent to 12kts for a 12m hull. The angle will be the same but the depth proportionally larger.

I would like some suitable means of analysing the situation short of building a hull as it is certainly and area that needs attention to determine one of the competing constraints for the bridge height. However the method of analysis needs to be considerably more scientific than the simplistic approach you are offering.

Rick W

fcfc
03-16-2010, 08:23 AM
:( :?: :( :?: :( :?:

I am getting used to have no price tag. Generally, buying people do not expect the same from a 20 000$ and a 100 000$ boat. But I may be wrong.

What rules to comply with ? I do not know any professionnal NA what would dare to sign and publish (even for free) a plan non compliant with his country rules (ISO or ABS/ABYC/USCG or ..) even for homebuilders that have not to show formal compliance. Liabilities are way too big.

Payload, sea state (or ISO design category) ? I have noticed in this thread a plan with limited side hull draft and bridgedeck clearance. Is this for loading as minimal operating conditions, or fully loaded ?

Overloading (which leisure boat will never be in this case :P ) tolerance, overpowering tolerance, life expectancy ?? i.e. design safety margins.

Oyster
03-16-2010, 09:11 AM
A valid point, and it could be applied to any boat intended for relatively calm conditions.

I've been working on something ( http://www.boatdesign.net/forums/projects-proposals/trailer-cruiser-revisited-trimaran-27032-12.html ) that's perhaps not quite as fuel efficient as some of the boats mentioned here, but that should be capable of handling awkward/heavy loads as well as taking on relatively rough conditions.

At 2.5 tonnes displacement, it shows 10.9 kW indicated for 12 knots (once propeller efficiency, etc. are considered, figure about 24 hp at 12 knots). With a gas outboard, that's about 6-7 nautical miles per gallon. But she's shaped to max out at 20 knots, and has unusually large outriggers to suit certain service requirements we have. With a bit of massaging, slightly lighter construction, and an inboard diesel with a big, low-speed prop, such a boat could probably get close to 10-12 miles/gallon.

Just a thought....

You are looking at a single number and not a combination of numerous factors. Since you are discussing outboards, I can do this and have done pretty close to your numbers with an outboard in complete comfort without being squeezed into a shoe box. The important number is what want to do in the course of a day, cover ground or spend your time sitting at a helm. How you value your time and your sole intent when boating sometimes places a fuel consumption number at the bottom of the lists in priorities.

The draft is truely the most important thing when considering a power plant for some people, me included and weighs in the decision making process.

There is another little discussed number and thats slippage at dedicated speeds with fuel burns in power boats which can be both looked at in power boat, trawler and motor sailor hull designs.

marshmat
03-16-2010, 09:50 AM
You are looking at a single number and not a combination of numerous factors.
For the purposes of this thread, I brought up that example only to suggest a possible way to approach the OP's desire for 12 nmpg @ 12 kt in something that can handle significant sea states and still carry some accommodations. There are plenty more design parameters that can and should be discussed. I don't design based around a single number and I don't know any successful designers who do.
Since you are discussing outboards, I can do this and have done pretty close to your numbers with an outboard in complete comfort without being squeezed into a shoe box. The important number is what want to do in the course of a day, cover ground or spend your time sitting at a helm. How you value your time and your sole intent when boating sometimes places a fuel consumption number at the bottom of the lists in priorities.
Agreed. This won't be the case for everybody, of course- we each have different priorities, and for many boats the cost of fuel is not a huge factor. For others, it is a major expense (fuel is the single biggest component of my current boat's budget).

The draft is truely the most important thing when considering a power plant for some people, me included and weighs in the decision making process. A valid point, and one that our OP will have to consider, since the low-rpm, large-diameter props that tend to improve the efficiency of the drivetrain tend to be in conflict with a desire for shallow draught.

There is another little discussed number and thats slippage at dedicated speeds with fuel burns in power boats which can be both looked at in power boat, trawler and motor sailor hull designs. As in, propeller slip? That's a parameter used in some prop sizing calculations, but I'm not sure what use it is on its own....

Oyster
03-16-2010, 10:22 AM
With a bit of massaging, slightly lighter construction, and an inboard diesel with a big, low-speed prop, such a boat could probably get close to 10-12 miles/gallon.


Well if you are using a planing hull versus a displacement hull and use an inboard engine versus an outboard engine, you restrict one component in the uses and desire for a coastal cruiser, a very important component in choosing a particular design. As far as fuel costs and burn, if you are burning 2 gallons an hour at 20 mph, versus 1 gallon an hour at ten knots, this becomes apparent that you truely have not saved any money as the big criteria that you state. You also cannot under any circumstances push some of the hull designs with even the modest increased speeds without wasting fuel for an additional one to two mph in speed.

If you are intent on the highend thrust at low speeds and look at the single number as in the fuel burn, then you also loose the advantage of the top end speeds oe even mid range depending on the planing angles of your boat when needed or want it and the shallow draft advantage too if you go inboard. Sure in the days gone by, inboards were more dependable.

But you also loose interior space inside and may create some launching issues too, not withstanding loading and unloading at boat ramps. Under most situations inboards for what you think you may gain looses in so many other areas if you are directing your search to trailable boats and designs. The trailable aspect is the key component and must be the very first criteria in the creation of a new boat build.

As a side note, and for idle time reading, I am not sure if anyone here is familiar with a Glen L Cabin Skiff that was stretched and has about 27,000 nautical miles under his bottom. He decided to change out his outboard even though his reliable mechanic told him that it was not needed. Enjoy..

http://egyptian.net/~raymacke/

marshmat
03-16-2010, 10:33 AM
This prop is 800X400 and is made of nylon. It is good for a maximum thrust around 500N. It flexes beyond that load. It would need to be quite a lot stronger to take the 3kN bollard pull capable with such a prop connected to a 20kW diesel. That can be achieved by making the blade chord larger and/or using higher strength materials.
A prop of that style, perhaps forged from bronze or stainless steel, could be a good choice for a very high efficiency displacement hull. My only concerns would be the availability of suitably steep reduction gearboxes, and the draught issue (may or may not be a concern for our OP).

The speed being considered on this thread is a region where cavitation can be avoided even when using quite high lift, thick blades. Standard marine props are designed for higher speed and considerably higher disc loading pressure - therefore lower efficiency.

One of the problems with the current state of marine propulsion is that all the moneyed effort is focused on the high speed end. You will not find anyone making props to a design that works efficiently in the application being considered here. The simple 12kt/12nmpg equation means the prop needs to handle 16kW at 6.2m/s.
A valid point; however, we should probably take note of why "standard" props are designed with higher blade loading, higher DAR and tend to have lower efficiency. A large diameter, slim bladed prop rapidly becomes far too large in diameter (both for draught and for the structural stiffness of the blades) as we start looking at tens or hundreds of horsepower. "Standard" props do tend to be pretty well optimized for the constraints they face; they just aren't well suited to the rare situation where you have low power and no draught restriction.

Well if you are using a planing hull versus a displacement hull and use an inboard engine versus an outboard engine, you restrict one component in the uses and desire for a coastal cruiser, a very important component in choosing a particular design. As far as fuel costs and burn, if you are burning 2 gallons an hour at 20 mph, versus 1 gallon an hour at ten knots, this becomes apparent that you truely have not saved any money as the big criteria that you state. You also cannot under any circumstances push some of the hull designs with even the modest increased speeds without wasting fuel for an additional one to two mph in speed.

2 gph at 20 knots is clearly the same fuel per distance as 1 gph at 10 knots, yes. Could you clarify how this fact relates to our (admittedly arbitrary) cruise target of 1 gph at 12 knots?

Below about 100 hp (and closer to 150 hp for lighter, planing hulls) I tend to prefer outboards, as do many folks (but not everyone). You'd have to use the boat a LOT for the fuel savings from an inboard diesel to outweigh the cost advantages, easy installation and beachability of a small to midsize outboard.

tom28571
03-16-2010, 12:24 PM
With apologies to Rick, I know that the large diameter props he is discussing have no application that I can think of for a practical trailerable coastal cruiser. All the issues that have already been mentioned will rule it out of any of the coastal cruisers that I am interested in. On the max draft that I would consider for this use with an inboard, I've been able to fit in only a 20" diameter prop without going to a tunnel. Even this boat is much more restricted in launching and beaching than the outboard powered ones. Even poor launch ramps can be hard to find in many places and good ramps are even more scarce. Secure parking for the tow vehicle and trailer can also be difficult to find. Nevertheless, the ability to tow your boat to distant cruising grounds far outweighs these problems.

I wonder how many who post here have actual experience with these issues?

I would be interested if some of that energy was spent in designing an "optimized" propeller for existing outboards. I have a Yamaha T50 that accepts a max diameter of 14". This engine does sport a relatively high gear ratio and is aimed at the lower speed, high thrust market. Is it ideal for the speed range from 10 to 20kts? I don't know and Yamaha will not furnish any details.

I am a bit familiar with the effects of low bridge decks on Cats and can say that high is better. Driving or riding on a cat with a low bridgedeck in any significant chop is one of the most uncomfortable situations situations and an example of poor design. One 44' under construction locally has a clearance of 2' 9" and is projected to be capable of Atlantic crossing.

rasorinc
03-16-2010, 12:33 PM
Tom, just a suggestion about leaving you trailer and truck in the parking lot for a couple of days. Locking hub nuts and wheel locks will slow down thieves but the best I've seen on stealing a truck is find the fuel line and where it turns upward either inside the dash or in the engine bay, cut it in half and put on a manual shut off valve(like the one going to your refrigerator ice maker).
They will only get 100 yards or so and will abandon the theft.

Oyster
03-16-2010, 12:44 PM
2 gph at 20 knots is clearly the same fuel per distance as 1 gph at 10 knots, yes. Could you clarify how this fact relates to our (admittedly arbitrary) cruise target of 1 gph at 12 knots?

Below about 100 hp (and closer to 150 hp for lighter, planing hulls) I tend to prefer outboards, as do many folks (but not everyone). You'd have to use the boat a LOT for the fuel savings from an inboard diesel to outweigh the cost advantages, easy installation and beachability of a small to midsize outboard.

Well its important if you are attempting to design any cruiser to maximize its uses , trailering is at the top of the lists in this discussion when it comes to even the bottom shape. But as a rule an inboard almost always weighs more than an outboard and drafts more and even costs more even if you boat bottom is a shallow draft planing hull. You can purchase a lot of fuel for five grand by comparison to an average inboard setup versus an outboard hull.

When you go to a displacement or semi displacement bottom, you complicate your launching, trailering and restricts for sure the cruising areas of all coastal regions in 2/3rds of the east coast and in the gulf coast region. You have defeated the intended purpose if your intention is fuel efficency if you attempt to use an offshore design or semi displacement primarily inshore. Even with a planing hull and inboard, the draft is just too prohibitive to do much unless you are a marina queen.

So I go back to the idea and notion that pound for pound, dollar for dollar, the outboard on a planing hull with some interior comfort for all weather use is the only way to go especially if you are looking at fuel burns and liteweight builds which assists you in towable hulls. When you do this, you have the advantage for low fuel use and the potential speed when needed which is not much past the intended stated burn.

tom28571
03-16-2010, 02:09 PM
So I go back to the idea and notion that pound for pound, dollar for dollar, the outboard on a planing hull with some interior comfort for all weather use is the only way to go especially if you are looking at fuel burns and liteweight builds which assists you in towable hulls. When you do this, you have the advantage for low fuel use and the potential speed when needed which is not much past the intended stated burn.

Mike, You and I have been all through this kind of decision tree and through experience have arrived at the same conclusion. I hope you will be able to weather the current crisis and that, at the end of it, the boat is still yours and Linda's for your cruises as you intended.

Tad
03-16-2010, 03:11 PM
Here is Phil Bolger and Susanne Altenburger's take on all this. Wading through Susanne's verbose prose is not for the faint of heart, but there is a great deal of information there.....I wish Phil was still around to edit.

41487 41488 41489 41490 41491

Guest625101138
03-16-2010, 05:14 PM
....
I would be interested if some of that energy was spent in designing an "optimized" propeller for existing outboards. I have a Yamaha T50 that accepts a max diameter of 14". This engine does sport a relatively high gear ratio and is aimed at the lower speed, high thrust market. Is it ideal for the speed range from 10 to 20kts? I don't know and Yamaha will not furnish any details.

....

You will find outboard propellers are close to optimised for their size and intended use. You cannot beat the laws of physics. The limited diameter is a constraint on the efficiency possible at lower speeds. If draft is an overriding factor then you can add more outboards and reduce the thrust required from each. The load is spread over a greater area.

For lower speed application there may be benefit in increasing the number of blades up to 6 but strength limitations then become the constraint.

Rick W

Guest625101138
03-16-2010, 05:51 PM
The feasibility study I did earlier has given me some insight into the original objective of 12kts at 12nm/USG.

There is a decision tree that can be explored to set the design space based on this single requirement:

1. The basic requirement means we are considering a powered vessel using liquid fuels. It is not going to be sail or solar powered.

2. It will be powered by a diesel or petrol ICE - we will dismiss other options such as fuel cells and steam plants.

3. A diesel can produce 16kW and the petrol 12kW. (If someone has good specific fuel consumption for particular engines it would be good to have more accurate figures than my estimates)

4. There will be house loads to consider. Things like fridge, nav lights. instruments. These could range. Probably from negligible to maybe 2kW. Lets take midway of 1kW.

5. With the diesel we now have 15kW available and the petrol 11kW available.

6. We then have to transmit the power to a shaft. A good transmission will lose no more than 5%. So the diesel will have 14.25kW on the prop. The petrol 10.4kW.

7. The diesel swinging a 600mm prop can provide a thrust of 1800N. The petrol swinging a 300mm prop can produce 1150N.

8. The power limit means the boat is not going to be planing or even semi-planing so we can dismiss those hull forms. This means it will be a displacement hull.

9. A displacement hull to get to 12kts, able to carry the engine and fuel, plus a few people and be structurally sound while achieving 12kts with the modest thrust will need to be long and slender. If it is diesel powered with a 600mm prop it can have a drag of 1800N. If it is petrol powered with a 300mm prop it can have a drag of 1150N.

So that sets the design space based solely on physics and a single requirement of 12/12. It shows what a choice of diesel or petrol will allow in the final outcome. Either is feasible but the petrol driven one with the small prop will need to be about half the weight.

Rick W

Willallison
03-16-2010, 06:38 PM
4. There will be house loads to consider. Things like fridge, nav lights. instruments. These could range. Probably from negligible to maybe 2kW. Lets take midway of 1kW.


Or... instead of taking a guess... we could actually consider making a list of the things that are required by the client and get an accurate measure of the house loads....
Hey! I've got a great idea..... why not write a design brief... and SOR....:eek:

For those who are interested, here's a link to an article writen by Steven Hollister about the design process. It is just one man's version and everyone has their own take on the process, but it clearly sets out the basic steps that most professional and competent amateur designers would follow to ensure that the optimum design solution is reached:
http://www.westlawn.edu/student_center/lecture1.asp

Oyster
03-16-2010, 06:48 PM
Or... instead of taking a guess... we could actually consider making a list of the things that are required by the client and get an accurate measure of the house loads....
Hey! I've got a great idea..... why not write a design brief... and SOR....:eek:

For those who are interested, here's a link to an article writen by Steven Hollister about the design process. It is just one man's version and everyone has their own take on the process, but it clearly sets out the basic steps that most professional and competent amateur designers would follow to ensure that the optimum design solution is reached:
http://www.westlawn.edu/student_center/lecture1.asp

Oh you just don't understand.;) The proper technical wording is....
Optimisation
Meaning taken from the Oyster Rules of order.
the fine art of coming together to create the perfect union.:D :D

Guest625101138
03-16-2010, 06:55 PM
Or... instead of taking a guess... we could actually consider making a list of the things that are required by the client and get an accurate measure of the house loads....
Hey! I've got a great idea..... why not write a design brief... and SOR....:eek:

For those who are interested, here's a link to an article writen by Steven Hollister about the design process. It is just one man's version and everyone has their own take on the process, but it clearly sets out the basic steps that most professional and competent amateur designers would follow to ensure that the optimum design solution is reached:
http://www.westlawn.edu/student_center/lecture1.asp

A well considerd approach no doubt.

On ballance optimise has it.

Optimise is used 39 times. Compromise is used 4. I note now that you have taking to using the term as well. At least I have contributed that much to your education.

Rick W

Willallison
03-16-2010, 07:11 PM
Rick... you have contributed a great deal to my education... in generaly I read everythig that you write and know the opposite is likely to be true.

We should all be open to continued learning. Tel me... what did you learn from this...?
http://www.boatdesign.net/forums/boat-design/compromise-31901.html

Willallison
03-16-2010, 07:11 PM
Or this

http://www.boatdesign.net/forums/boat-design/client-always-right-31899.html

marshmat
03-16-2010, 07:17 PM
Cut the arguing already, boys. All of you are better than that, I know you are.


Looking at Rick's numbers from post #242 above, the goal of 12 nmpg at 12 knots in something big enough to live on for short periods does appear feasible, if we can keep the weight down. Of course, as Will points out, we have to define our standard of living aboard. So, from post #1:
Forgive my ignorance; I'm a sailor looking for powerboat to snowbird the US Eastern Seaboard. Is there a design that will carry the accomodations of a 16' travel trailer at 12 knots in coastal waters at 12 nmpg? Since gasoline is currently cheaper than diesel, does that affect the traditional power choices?
Could this be done in a barely trailerable outboard driven vessel? I'm looking for a warm enclosed helm, 15' bridge clearance and very easy access to bow and stern for single-handed docking in moderately adverse winds and currents. I've made a half-hearted attempt to search this site and would be glad to be directed to a previous thread.

The accomodations I would like to find are a double berth, standup head and shower, galley and dinette for 4, stove and oven, H&C pressure water, AC and Heat, 3' max draft, refrigeration, and a comfortable place to read.

AC and H&C pressure water, plus a fridge? I suppose we're not talking a kilowatt of house loads, but rather several kilowatts of house loads, probably around 5-8 kW with the AC and fridge cranking away in the Florida sun. And a lot of time spent either on shorepower or with an idling engine. But the rest- double berth (is it OK for this to be a folding dinette?), standup head, galley, a layout conducive to single-handing and with a warm place to drive, no more than 3' draught- all of this appears to be feasible within the given limits.

As an example: My partially-designed 2.5 tonne (loaded) trimaran meets Rick's cap of 1800 N thrust at 12 knots, and has sufficient space for the desired amenities. But since it's designed for an outboard, a 60 cm prop on a diesel is not possible. Furthermore, no outboard I'm aware of can handle the kind of house load being talked about in post #1.

So I think we're looking at a long, slender displacement hull, about two tonnes loaded, quite possibly with stabilizing amas, and, if the client will allow it, an inboard engine (if only for the generating capacity and ability to swing a big prop).... and treating house loads separately from propulsion loads when considering miles-per-gallon. Sound about right to you guys?

fcfc
03-16-2010, 07:22 PM
I fear of the very common error of newbee project planner.

Forgotting ALL the implicit statements the customer did not even think he had explicitely to request, because they were so evident for him that it could not be otherwise.

1) The solution should be within customer budget.
2) The solution should have enough comfort and amenities for the reminder of the family accept to climb aboard.
3) The customer and his family should enjoy the ride.

This was not stated, but implicit for the customer. and ANY solution that does not match the 3 clauses above will be rejected.

u4ea32
03-16-2010, 07:46 PM
fcfc, you are correct.

I think that in this feasibility study, cost isn't specified, but its easy to find examples of very light boats built by skilled home builders for $10K USD. If anyone is thinking very low prices, they will be thinking home built too. There is nothing so far identified that requires highly expensive construction. On the contrary, it appears that even plywood could be used, which means any fiberglass/core will work too. So I think that the cost can be specified, the more $$ the nicer quality.

I think the feasibility studies don't overly restrict volume -- just weight. So meeting 2 should be easy.

Item 3 (enjoy the ride) also does not seem to be restricted.

In other words, there is plenty of room for a designer to meet those requirements, regardless of what they are, as long as the weight stays on target. To meet the 12/12 requirement, the customer will simply have to live within those weight limits.

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