Long - Skinny Power Boats

[SAQuestor]

Folks,

Reading the various design books that I have I've always been puzzled by why displacement hulled power boats aren't longer and skinnier?

I know the standard answers - moorage costs and interior "apartment" space. Both reasons are plus factors for short and fat boats. These are the sorts that stay (mostly) in a marina and are doo-dads to show off to friends/clients/bosses/underlings etc.

So ignoring the costs of moorage and loss of apartment space and speaking only on a theoretical basis…

From my reading it seems that a longer hull would equal a greater speed ... waterline length = V/L ratio = faster.

Skinny boats would seem to be inherently more efficient that shorter beaminer hull shapes, i.e. the same speed for less fuel or greater speed for the same fuel used when compared to 'conventional' hulls.

IIRC the Prismatic Coefficient for displacement hulls is somewhere around .56-.58. Regardless of my memory, does this 'rule' apply to hulls with a L/B ratio above 5:1? If it does apply, how would one achieve that Cp with L/B's above 5?

Though long skinny hulls don't have to be light, it seems that they would inherently have less displacement and therefore be less expensive to build, based on cost per pound being equal for any given length. True? Or is there some other factor besides total displacement that has a greater effect on build cost?

A few of drawbacks that I can think of – can anyone point out others?

The hull might be difficult to control in larger waves – the bow might bury in the wave trough while the stern is high on the last wave crest, thus being more susceptable to a breech or other nasties.

Spanning two wave crests – the bow and stern are `inside' two succeeding crests while the midships area is relatively unsupported in the trough, potentially causing the hull to buckle.

Quartering seas – whether from ahead or astern - might cause quite a bit of hull twist and make the boat perform some sort of a weird dance. This might result in control issues and/or hull failure from excessive twisting.

Beam seas – depending on the underwater hull shape – rounded bilges, multi or single chines or a V bottom or a flat bottom – each will react to beam seas a bit differently, but regardless of hull shape will have a pronounced roll – with the variable being the roll period – i.e., the snappiness of the motion.

How far off are these 4 points? Valid or not? Are these (and other) factors glaring enough faults (if they truly are) to preclude one from designing and building a long & skinny, highly efficient displacement power boat?

BTW, I'm trying to understand this for 'personal' sized boats - 35'-50', not naval destroyers or the like.

I don't have the answers; I'm just trying to learn. Discussion would be appreciated.

Best,

Leo

[Nomad]

Size, room, and stability are some big reasons. Every boat has it's general design that is best suited for it's intended use, although there are exceptions.

[propnut]

Lots of long skinny displacement boats were built for a long time in years past. The drawbacks you mention were probably factors in the reasons that design trends have evolved in modern times. If you want to go faster or have better seakeeping capabilities there are now plenty of options to add horsepower or choose from a variety of hull designs. If you want to be more "fuel efficient" there are options for that too. There are compromises to all designs and the popularity of each is market driven. Long skinny displacement boats still have a place in the market but it is a very small niche.

[PAR]

Quite simply, additional longitudinal volume isn't as usable as extra beam space is. True, a long skinny hull is easier to propel, but the boat has to be sold to folks wanting elbow room so this compromise has worked into the mix.

Production manufacture's are mostly doing this, custom work usually takes a more owner friendly avenue. By this I mean custom designs tend to be less of an attempt to please everyone (fat) and more an effort to please the client's requirements, which generally produces more efficient shapes (skinnyer)

The call for efficient shapes in power craft isn't as necessary as it once was. Power plants have become much more efficient and effective at getting a craft to speed. With this, designs have beam and weight hung on them, knowing the power train can easily propel the craft to the target speed range. Years past, these more effective shapes had to be used, because the power plants available needed all the help they could get. These older engine designs were heavy, much less fuel efficient and produced much less power per pound then engines currently in use.

With modern propulsion units, hull forms can be wider without as big a penalty needing paying in performance and you get the more easily used elbow room.

[Ilan Voyager]

As my pseudo shows, I'm very fond of slim hulls.
Let's talk only on a theoretical basis about slim boats (let's forget room etc) and will stay in small boats.

Like always there are advantages and drawbacks:

Advantages:
- high prismatic coefficients are obtained very easily. The curves are soft, with fine water entries and smooth water exits. The system of waves created by a slim hull is small, so less energy is lost to make waves.
- Under hull speed limit -the true one which is calculated on the basis of displacement (Gerr's formula which has a good precision ) and of coefficient forms of the hull (ratio length/width, prismatic coefficient, concave or convexe bow etc) as the formulae used for warships- slim hulls are very efficient: rowing shells, kayaks, multihulls etc are every day applications.
- Almost no hump in the drag curve before starting planning. A lot of heavy planing hulls need actually more power to start planing than for cruising. It's the famous "get through the hole" where a lot of overweight planing hulls stay stucked.
- As consequence these hulls need less power to get the intented speed in low Froude's numbers.
- Slim hulls have very good average speeds. Top speed is interesting, but good average speed is more interesting as you can maintain the speed whatever the sea condition. A well designed slim hull is seaworthy in bad sea, and where a wide planing hull will be miserable, slamming so badly on the waves thus forced to reduce its speed to ridiculous levels, the slim hull will be able to maintain a good speed.

For further reading on theory;
http://www.greenval.com/jwinters.html
http://www.cyberiad.net/hydro.htm of Mr L. Lazauskas, who is member of this forum, will give you a very deep explanation about slim hulls.

Drawbacks:
- slim hull means little righting moment ie transversal stability. This problem may be solved by different means.
- small mechanical inertia. Slim hulls need very good building; it's not a true problem.
- Disadvantage of the easily driven hull, slim hulls have tendency to cut the waves and to be "wet". Higher forward freeboard is needed. If the bow is too full you'll have strong vertical accelerations.
- While starting to plane the stern has a tendency to bury in the sea.
- Efficient planing need a wide waterplane shape; the shape of a slim hull is not efficient for planing, but very good compromises can be found.

Slim hulls were common at the beginning of the 20th century. The engines had very limited power and it was the way to get the max speed. A 1905 boat 12.2m long, 1.22m wide at the waterline, weighting less than 2 metric tons was able to get 16 knots with 16.5HP (a torquey engine 16.5HP @ only 650 RPM...But it was very wet, and turns had to be taken with precaution.

Solutions of the drawbacks:

Monohulls; one good solution is to have a slim underwater shape getting wider over the water by a pair of strakes. Paragon applies this solution on the VSV PATROL boats
( http://www.vsvboats.com/ ) The strakes give buoyancy and dynamic lift while the boat starts planing, a better planing surface (like a pair of skis), and insures safe turns.

Multihulls:

Powercats are well known, the australian use them extensively: it's the simpler answer to the problem of lateral stability, and room.

It's not a small boat but I cant resist to give the link: the world's fastest car ferry, "Luciano Federico L" competes with the airlines on the 110 nautical mile Buenos Aires to Montevideo route, at the cruise speed of 57 Knots full loaded.
http://www.amd.com.au/vessels/amd1130.php.

Power trimarans are the concept in vogue in warships and cargos/ferries. These tris are more monohulls assisted by outriggers than true multihulls. Nigel Irens ( http://www.nigelirens.demon.co.uk/index2.htm )initiated the trend with Ilan Voyager (21.3m long, wood and glass): 28 knots with a single engine of 180 kW (about 250 HP). this tri made a record-breaking un-refuelled voyage around Britain (1568 nautical miles trip in 72 hours 21.5 knots average with 2000 litres (530 gallons) of fuel (2.97 nm/gallon, the best ratio speed/consumption).

The 40 ft trimaran "YANMAR ENDEAVOUR" goes at 12 knots with 54 HP, has made the record of travelling 4443 nm crossing the Pacific with an average speed of 8.93 knots (4.8 nn/gallon). http://www.morrellimelvin.com/page73.html

The tris are very efficient; a small day tri would not present special difficulties of conception. We are far of a 30 ft 100% fatty "planing" boat with 2 engines of 250 HP sucking 24 gallons/hour (1 nm/gallon !) for a low 27 knots when it can plane...I won't name the builder.

Answering to your specific concerns:

Boats cost mainly per pound. Very true with a light small slim hull as the engine is the major expense on a such boat.

Larger waves; true and false. Depends more on the equilibrium of volumes between the bow and the stern and the undershape. It's not an issue.

Spanning two wave crests, Quartering seas; False. On a small boat is not a concern, we have now the engineering and materials. Hulls are not more made with nailed pine planks.

Beam seas; True and false. More than the rolling rate (the hull is slim so it will react less than a wide beam), THE TRUE ISSUE IS LATERAL STABILITY. On a slim monohull the righting moment is small if it has not features like strakes (sponsons) above the water. The better stability without compromising the speed is obtained with the multihulls, that explains their rapid growth in the market.

I hope I gave a beginning of answer.
Best.

[FAST FRED]

MY DREAM SHIP !!

The bigest problem I envision is the inability to afford dock space, as its charged by the foot.
Some East coast places charge $3.00 per ft per night!!!

For a true cruising boat this would not be a problem as all systems etc would be stand alone , either underway or moored , with no Shore power required.
Just fuel & water service at times.

Plaining is EZ on a box boat (with mucho power), and dock space cheaper , so thats why we see so many boats "almost" as wide as they are long , and 3 or 4 stories high ,with "oxygen tent"-(fly bridge) stuck on top . Cheaper to dock an apartment house , and more room to cottage.

The thin cruiser should be able to carry much higher speeds with less fuel use than the box boats , making voyaging more affordable .

Always easier to get a few crew for a 2 week juant than a months , and weather windows are more accurate the shorter the forecast.
Less time, less fuel, less stores are all apealing to me.

To do it "Right" plate cooling (no keel cooler drag) , and good stability underway with out either stabilizers , or flopper stoppers would be helpfull.

Mitsubishi is releasing a gyro stabilizer unit in Oct , but I am not sure it would be right sized for a very slim boat.


Building costs and time (for me ) would require the compromise of building in sheet material.

Either aluminum , or GRP pre covered foam core where the sheets are stretched over the bulkheads and GRP is simply taped over the seams.

The trimiran shape would make loads of sense only if the amas could fold (Matamona style big complex $$$) or were carried so far aft a std travel lift (16-18ftwidth )could haul the vessel.
Tris do great at anchor in rolly harbors , so might be worth the extra expense & hassle for cruising.

Anyone sugest a hull that can be made developed ?

With our desires only 2 crew for costal and 4 for ocean work would be desired , so a loa of about 65 with 8ft Bwl would hold all the volume we need.

Width on deck should be -12ft Best or 14MAX , so the boat could be easily (cheaply) moved on land.

All help appreciated,


FAST FRED

[Ilan Voyager]

A gyro is useless unless you have computers and a dynamic stabilizing device. With the price of a such device you have the fuel for the next 15 years. There are simpler and more reliable solutions for stabilizing a small boat.

A very slim monohull is more difficult to design than a cat or tri which are naturally stable. The study of the placement of the strakes, the calculation of the dinamic lifts, roll frequency and so are a good piece of work. The problem is that the US Navy or the DERA are not paying the bills and mistakes...

Folding amas on a medium sized tri is not a technological challenge. On sail boats the outriggers have a lot of stresses, but on a power tri these stresses are small. Several simple solutions are possible; sliding tubes, hinges, and others, but the solution designed by Farrier is the best, and I believe that the patents have expired...

The best (and simpler) architectural way for room is to consider a platform over the main hull, so you have not to make (bad) compromises with the hull shape which is the key of a successfull tri. Elliptical sections as those drawn by Nigel Irens (who worked a lot on the problem, and he is a master in multihulls design) are the best.

Compounded plywood or cylinder mold would be the simplest ( do not means the easier...) method but may be tricky: it is eyeball building. An hybrid method with bottom in strip plank (with a bit of kevlar for impact resistance) or simply monolithic FRP (too heavy, rigidity issue if kept light) with topsides in compounded sandwich, honeycomb or simply plywood would be simple AND easy.

Nidacore is perfect for floors, roofs, walls etc... it's price is more than competitive compared to foams and it's very easy to use because of the polyester fiber screening. Phenolic impregnated paper honeycomb Tricell is another alternative.

On a 35 foot I would stick to marine plywood/epoxy/glass with maybe a botton in strip plank; the ratio price/weight/strength/easiness is hard to beat. Aluminium is too heavy and complicated until 70-80 feet, but a Strongall (thick plates) structure is worth to be studied even on a 50 feet. http://www.reducostall.com/HTML/pagetwo.htm


Ilan Voyager is "cheaply" built in strip plank/glass and, after years of hard work in the rough seas of Cabo Verde (like a permanent tropical storm in Florida: 30 knots trade winds, 10 to 12 feet waves...) the boat is perfectly sound.

Thanks to Yipster for pointing out the "writing lacks". It's corrected now.

[yipster]

Compounded plywood or cylinder mold would be the simplest method but may be tricky: it is eyeball building. An hybrid method with bottom in strip plank (with a bit of kevlar for impact resistance) or simply monolithic FRP (too heavy, rigidity issue if kept light) with topsides in compounded sandwich, honeycomb or simply plywood.
Ilan Voyager was "cheaply" built in strip plank/glass and after a lot of hard work in rough seas (Cabo Verde sea is like a permanent tropical storm in Florida) the boat is perfectly sound.
witch one or what is a "a Strongall structure"?
as said, tri's are not the easyest design and whats the price pic?
can i start saving leaving the boat in its slip?
no, seriously: tis is good stuff !

witch one or what is a "a Strongall structure"? ok found the link above :o now...

[FAST FRED]

The Strongall sysem looks promising but the site doesnt give lots of info.

Is it similar to cold moulding , except in one layer and welded?

Had my first tri Headly Nichol Voyager 45 ft built in Belize British Honduras back in the 60's.

A great deal as 6000 man hours only cost $4,800.US

I have worked with Airex for a number of hulls , but the price is so insane (about $18 a sq ft in 3/4) it must be rulled out , however fine the hulls come out.

In playing on the computer the power requirements dont seem to grow out of range with simpler construction.
Aluminum or cored GRP is still first choice for resale, as in the US burried wood , or glass covered ply has virtually no resale value , no matter how finely done.

Anywhere in the world the world the Strongall system is used with low labor prices.

I looked into Poland for the std style built aluminum hull , but the legal system is not up to standards to not get shafted.

Sugestions anyone?

FAST FRED

[Portager]

I suggest that you look at the thread on the Ironheart design by David Gerr http://www.boatdesign.net/forums/showthread.php?t=1976&highlight=ironheart

At 66 feet long and 11 foot beam, it has a L/B of 6.6, cruises at 10 to 12 knots on 180 HP and has a 5,000 NMi range.

If you’re serious about making it transportable, then height will be a bigger limitation than beam. You can get an over height permit and go up to about 16' height, but then you need to carefully plan your route and your liable if you hit any bridges. I prefer to keep to the legal height of 13' 6". Actually about half the states have a 13'6" legal height and the rest have 14' (actually one state allows 14'6") but I digress.

Regards
Mike Schooley

[SAQuestor]

Wow – Go sailing for the weekend and look what appears – lots of excellent posts! Thanks to everyone. Some comments from the various posts.

Propnut wrote: “there are now plenty of options to add horsepower” and “"fuel efficient" there are options for that too”.

Let’s try to define ‘efficient’ in this context. First, this definition is not about maximum accommodation volume, so we don’t design wide or tall – those options are out of bounds. Efficient here is the highest average cruising speed using the least amount of fuel. In my mind higher horsepower to go faster is not the way to achieve this goal. A long slippery hull that needs the minimum amount of horsepower to propel is at a V/L ~1.1-1.15 probably will give the highest average speed at the lowest fuel burn. Anyone disagree?

Par wrote: “True, a long skinny hull is easier to propel, but the boat has to be sold to folks wanting elbow room so this compromise has worked into the mix.”

Very true if it is a commercial product. This concept isn’t for sitting in a marina. This would be a one-off boat that harkens back to Beebe’s original Passagemaker concept. This concept is for folks that want to go places under power in a (relatively) quick and comfortable manner while maintaining a high average speed with low fuel burn. Beebe’s concept is ~50 years old and what advances have been made that will enable us to improve on Capt. Beebe’s ideas – if we are able to?

Ilan Voyager makes several excellent points and provides links to much information that is way beyond my feeble brain capacity to understand the mathematics of.

But I can’t help but wonder if the same principals that are being applied to canoes are also applicable for boats in the 10-15m range? As general theories I’d take a SWAG and say yes, but the caveat is that we’re talking about human power intermittently applied in the fractional horsepower range versus mechanical horsepower continuously applied in the 20-50 horsepower range. Are the apples still apples or have they transmogrified into some weird sort of orange?

Fast Fred wrote: “all systems etc would be stand alone , either underway or moored, with no Shore power required. Just fuel & water service at times.” And [snipped] “making voyaging more affordable.”

Per-zactly FF!

But then FF goes on: “"Right" plate cooling (no keel cooler drag)”

Why a liquid cooled engine at all? If we still want diesel for all its virtues, why not a Duetz Air/Oil cooled industrial engine? See http://deutzusa.com/Products/2011.html I’ll leave it to everyone to make up their mind if this ubiquitous industrial engine with its long service intervals and life makes sense for your particular concept.

If your ‘dream boat’ isn’t to be used for ocean crossings, (or even if it is) then why not consider a suitable 4 stroke outboard engine? Although somewhat new on the scene, they seem to be proving themselves (mostly) reliable.

Either alternative would obviate through hulls and their potential for flooding the boat.

Finally, Portager wrote about Dave Gerr’s Ironheart. I’d seen that design some time ago and even exchanged communication with Mr. Gerr (I heard a rumor that he died recently?) about the design. As of 2002 no one had yet built Ironheart.

Ironheart is a great example of the concept, but for me Ironheart is 6-9m too long and 10-12 tonnes too heavy. But the concept is excellent.

Finally, to echo FF, and dovetail in with the Portager concept, albeit with about 800-900mm less beam, what details would one design into the concept to make it suitable for:

The Inside Passage from Puget Sound to Skagway and back?
Trucking to New England for a summer’s cruise to Newfoundland and back?
Crossing the Gulf Stream to spend winter in the Bahamas?

Fast Fred mentioned sheet goods – and Ilan Voyager mentioned ply/epoxy. So instead of going with Ironheart in steel or aluminum – way too expensive – let’s see what can be suggested when we stick to simple hull forms and ply/epoxy materials so that we can home-build this creation. Maybe something like this from Reuel Parker, http://www.parker-marine.com/50dorypage.htm only 3m shorter and 1m less beam.

Again,

Thanks to everyone for responding to this thread.

Best,

Leo

[CDBarry]

You should probably take a look at the NPL series of hulls.

[SAQuestor]

You should probably take a look at the NPL series of hulls.

I searched RINA's archives and publications and came up with a fat zero.

Can you provide a link or some other information that will lead to the discovery of where one can obtain this information?

Thanks

[Portager]

Why a liquid cooled engine at all?

Three reasons; reliability, fuel efficiency and hot water. Industrial engines may be reliable in industrial conditions, but they have proven to be less reliability in marine conditions where they are constantly sucking salt laden air through their insides. To accommodate wide temperature extremes with a less efficient cooling mechanism, air cooled engines need to make certain compromises, such as lower compression ratios to prevent premature combustion due to hot spots. These compromises equate to lower efficiency which is the bane of long range power boats. Finally liquid cooled engines provide a free source of hot water so you can take a warm shower once in awhile.

Plate cooling means the waste heat is conducted through the hull plate and no through hulls are required for cooling. Plate cooling works best on thermally conductive metal boats. Keel coolers are usually used on less thermally conductive boats such as fiberglass and wood/epoxy. With a keel cooler the coolant is passed through the hull to a heat exchanger on the outside of the hull and then back inside. It does require a through hull but the coolant loop is isolated from the sea water, so it would require two simultaneous leaks allow sea water in.

If your ‘dream boat’ isn’t to be used for ocean crossings, (or even if it is) then why not consider a suitable 4 stroke outboard engine?

First diesel is intrinsically safer than gasoline. Diesel has a higher vapor pressure so it will not evaporate and create combustible fumes like gasoline will.

Second, the difference between a high reliability gasoline engine and a high reliability diesel engine mean time between failures is a factor of 5 or more (and the jury is still out on four stroke outboards). If you look at boats designed for offshore operation you will see that most gasoline engine boats have two engines and most diesel boats have a single engine or a main plus an auxiliary. This is because diesel boats only need one engine to make reliable passages and a single engine boat is more efficient than a twin. If your not sold on the single engine approach then consider a get home sail, or a wing engine/generator with a self feathering prop, or …

Third, outboards do not have the ability to heat water, so I repeat my previous statement about warm showers.

Finally, to echo FF, and dovetail in with the Portager concept, albeit with about 800-900mm less beam, what details would one design into the concept to make it suitable for:

The Inside Passage from Puget Sound to Skagway and back?
Trucking to New England for a summer’s cruise to Newfoundland and back?
Crossing the Gulf Stream to spend winter in the Bahamas?

That depends on you and your significant other if applicable. Everyone has their standard of adequate comfort. In my case I’d definitely require a warm shower (there I go again), a real pilothouse, standing headroom throughout, an aft owners stateroom and air conditioning for those warm Bahamas nights. For a more detailed list feel free to look at Portager’s requirements http://www.portager.info/Portager_reqmts.htm and start crossing out things you don’t need.

let’s see what can be suggested when we stick to simple hull forms and ply/epoxy materials so that we can home-build this creation

I wouldn’t be too quick to jump to the conclusion that ply/epoxy is the best or cheapest option for home building. In the size range that you are talking about, aluminum would also be a good candidate (steel would be too heavy). Aluminum is higher cost per pound than ply/epoxy but since it has a higher strength to weight ratio it is not higher cost per boat and it will yield a lighter weight hull. Aluminum is harder to weld than steel, but it is as easy to work as ply wood and can be shaped with wood working tools. It also does not require any toxic chemicals or produce noxious fumes. Aluminum will also be easier to maintain and will retain a higher resale value than wood/epoxy. Finally metal boats are intrinsically safer in a lightning storm.

I would shy away from the 50’ Dory. Flat bottom boats tend to pound in rough seas. If your really interested in ply/epoxy construction then maybe you should look at Devlin Boats http://www.devlinboat.com/dcfp.htm . You should also consider the excellent designs of Tad Roberts http://www.tadroberts.ca/ .

Regards;
Mike Schooley

[Ilan Voyager]

I'm truly very happy that this thread is becoming a true exchange of opinions.
I'll try to give mines in some order;

Hydro:

- Hydrodynamics laws applies on all body going on the surface or inside the water like gravity law applies on any object. Corrections are made for scale of size and/or speed. An example illustrating the "universality" of hydro laws: the excellent Michlet software applies as well on canoes as destroyers or submarines.

The hydro links were given in purpose to show the first principles, and unhappily for the most of us, poor mortals, good design needs maths.

- NPL series from CD Barry; very good idea. If I remember well the NPL forms can be gotten roughly from sheet (metal or ply) and work very well in semi displacement. I'll check it and I'll try to find a link with pics. Let me the time to make a search on internet.

Another classic possibility is round bottom with chine (and maybe a small strake)

- sharpie forms (flat bottoms). I became allergic to flat bottoms while spending 6 months as lieutenant on an old mine sweeper. Flat bottoms make your life miserable when the seawater surface takes another shape than flat as a mirror. To have the pounding of planing boat without the speed is a fustrating feeling. The roll may be hard and "dry", but something will be always wet: the inside bottom. With only one bucket of water you have water everywhere inside...
This shape is not efficient for a semi displacement boat.

- Last in hydro but not the least: the ratio width/length. To exploit fully the advantages of the slim hulls you have to go to a ratio superior to 6. It's very hard to find the optimum ratio, which depends of these too numerous factors that make boat design a kind of art and not a tidy mathematical process.
But generally it lies somewhere between 8 and 10.

That explains why I prefer a multihull configuration with a preference for trimaran (one engine only) for a slim boat. A small monohull with a ratio of 8/1 would be dangerous.

Boat design has progressed a lot since Cpt. Beebe times (that does not retire any merit to the genius of Beebe). Simply look a the 2.97 nm/gallon at 21.5 knots and the 28 knots top speed with 250 HP of Ilan Voyager or the 4.8 nm/gallon at 8.93 knots and the top speed of 12 knots with 54 HP of Yanmar Endeavour... Nowadays a passagemaker is not boxing in the same category.

The following link

http://www.users.globalnet.co.uk/~fsinc/yachts/spreads/fred.htm

gives a hull resistance calculator (written in java) whose results are to be taken with great caution as these resistances are calculated for a very peculiar hull shape. For engineering I would use another soft, and I do so ... That does not retire any merit to this java soft, which is a nice piece of programming.

This calculator has a great educational advantage; for the same hull mathematical shape, you can play with the variables, and see the obtained resistances and the shape of the curves.

So keeping the same lenght, displacement, and prismatic coefficients, you'll see the influence of the width on the total resistance and the famous hump of hull speed limit. Very instructive... After you can play with the other variables.

Construction:

- Beyond engineering considerations, personal tastes and affinity guide in part the choice of the material. Personally I do love work with wood, plywood and epoxy as I begin as aprentice in a shipyard working these materials.
I do hate the smell of polyester so I'll never use it. I do like aluminium but I think that all the work and cost of the insulation annihilates any advantage in small boats; a metal hull without a thick insulation under the tropics, no thanks.

Maintenance on composite wooden boats is not an issue if you use enough epox and fibers. The boats built in strip plank and plywood with biaxial and UD age very well.

Lightning is not a concern if you take the precautions needed whatever the hull material.

- Personal tastes guide the choice of accommodations and amenities. I'm rather on the spartan side, and I have tendency to see things like air conditionning as potential nuisances. As I'm definitely against cold and wind after a few years spent on warships in North Atlantic I prefer a tent and hamacs over the deck while at mooring close to coco trees. Personal taste again.

- Size: by experience, and from the experiences of many others I think that around the 40-50 feet is the max size you man manage with a good probability of success for a homebuilt boat. However my thought is not written in stone by God's finger.
After the project becomes very big. Or the size of your wallet permits other building options.

Engine:

- 4 Stroke outboard is a good option in recreationnal use near the coast.

- Industrial air cooled engines may be used as it's done on small fishing boats
but the first drawback I see is noise. Air cooled engines (oil cooled is a variant) need big blowers, big openings and big exits for the big air flux...it's very difficult to get a whispering engine when it's air cooled. Sound dampening becomes almost impossible.

The dry escape may be a security issue in a tight engine compartment. Salt coming with the cooling air will cause corrosion. So a fresh water cooled engine is preferable with the simpler cooling system: heat exchanger.

Against common belief, surface propellers may be a good option for a semi displacement boat. Efficiency, simplicity, little draught, "clean" bottom, easiness of maintenance of bearings and rudder are some of the advantages of a simple fixed surface propeller in the kind of the Levi drive.

[CDBarry]

D. Bailey, "The NPL ... " Maritime Technology Monograph No. 4, The Royal Institution of Naval Architects, 1976.

[SAQuestor]

D. Bailey, "The NPL ... " Maritime Technology Monograph No. 4, The Royal Institution of Naval Architects, 1976.

As I said before, "I searched RINA's archives and publications and came up with a fat zero."

Perhaps I did not know how to use their search engine properly, but nothing I saw on the RINA site lead me to believe that the cited monograph is available.

Again I ask, "Can you provide a link or some other information that will lead to the discovery of where one can obtain this information?"

I'm afraid that just citing the The Royal Institution of Naval Architects isn't much help. If you can, please provide a link or other source for this document. Otherwise it seems pointless to mention this monograph if it isn't available for purchase or viewing.

Thanks.

[FAST FRED]

My lust for a "needle boat" is mostly driven by cruising costs , primarily fuel.

The referenced 4.8nm/gal is really impressive.

Is the long skinney boat the ONLY way to get good performance , range and sea keeping?

I think so , but perhaps others could sugest a way to better 5n/mpg in a usefull offshore cruising boat.
12K cruise or better ,
No cargo , besides normal interior,ground tackel and usual cruising stores.

Thanks,

FAST FRED

[SAQuestor]

I agree with Ilan Voyager, this is becoming a very interesting thread. Thanks again to all that are participating.

Again, taking from separate posts and commenting.

Portager wrote: “Three reasons; reliability, fuel efficiency and hot water.” And further, “where they are constantly sucking salt laden air through their insides.”

What’s the difference between a marine-ised diesel and an industrial diesel in this regard? Does the marine-ised diesel have some special air filter that precludes it from “sucking salt laden air”? I don’t mean to be flip, but they operate in the same environment. Operating temperatures are hot enough in both to vaporize any water that they may encounter – though there shouldn’t be any liquid water in the engine space. As for using air – let’s agree that the amount of combustion air needed is equal, then the difference is solely in the volume of cooling air needed to be run over the heat exchanger(s) and exhausted from the engine space. I will concede that there could be residue left behind from moist sea air as it is heated as it passes the heat exchanger. But why wouldn’t one include in the maintenance schedule taking the shrouds off and inspecting/cleaning the heat exchanger?

Perhaps the concern is the volume of air necessary for proper cooling and how that volume would affect other ancillary equipment normally found within the engine space. The simple answer then is segregate the engine and its need for large volumes of air from the rest of the equipment space, therefore minimizing any contamination of said auxiliary equipment.

Portager continued: “air cooled engines need to make certain compromises, such as lower compression ratios to prevent premature combustion due to hot spots.”

OK, I’ll concede that is one compromise, but is that necessarily that bad? I think that may be a judgment call on each individual’s part.

But to suggest that one can’t have a hot shower because one engine is water cooled and one is air cooled is a misleading notion. Either engine is very capable of driving a high-output alternator charging a high capacity battery bank – and will if the boat is to be independent of marina’s – and therefore a small electric hot water heater will provide those showers just as easily as a heat exchanger off a liquid cooling system would. And if one wants to stick with the heat exchanger concept, circulate the engine oil through an oil to oil exchanger and the route the secondary oil through a water storage tank. Doing an oil/oil exchange will preclude any possibility of water contaminating the engine oil. I’d probably want to use a Gulf States external oil filter system anyway, so including a heat exchanger in that external loop wouldn’t be that big of a deal, IMO of course, and YMMV as always.

Portager continued: “lower efficiency which is the bane of long range power boats.”

Very true, but when comparing fuel efficiency we must of necessity take into consideration exactly how much power is actually being used. For example, the Deutz specifications for the F3L2011 engine specify 218 grams of fuel per kWh of output. This engine has a 34kW sustained output, but I doubt whether we’d cruise with the engine running its maximum, so for arguments sake let’s halve that and say we’ll run it at 17kW. So if I do the math correctly, that means that the engine will burn 3706 grams of fuel per hour. That translates into about 130 ounces and that translates into just a smidgeon over 1 gallon per hour.

So if we can produce a hull that will travel ‘x’ miles on that 17kW(~23hp) then we’ve got an x efficient boat. It’s my understanding that at least three factors contribute in a major way to how efficient the hull can be propelled, total displacement, waterline length and Cp.

Let’s say we do the hull design really well and the total displacement is a light as practical and that 23hp will shove the boat along at 6 knots. Then we’ll be getting 6nm/gal. Let’s say we’ve done an even better job of optimizing the hull shape and that 23hp shoves us along at 8 knots. Then we’re achieving 8nm/gal. But maybe these numbers are just SWAG’s and aren’t realistic. Dunno.

But let’s get really crazy – try this one - http://dieselducks.com/Troller%2050.html - scroll down to the very bottom of the page – for ~7 knots @ 13hp. So doing the math conversions (13hp = ~9.7kW = ~2115 grams of fuel/hour = 75 ounces/hour = .585 gal/hour) means this particular boat MAY get almost 12 nm/gal @ 7 knots. Using the widely accepted .06 gallons of diesel per horsepower hour figures out to .78 gallons per hour to produce that 13hp – so that equals just shy of 9 nm/gal. Regardless of what figure you choose, that prediction ain’t too shabby for a 50’ boat displacing about 32 tonnes!

And as Buehler says, “Here's figures my computer developed. Please keep in mind they refer to calm conditions which means no tide or wind. In real life you're generally pushing against something but just the same, they give a good reference and in one case, we found the 38' DUCK actually surpassing what the computer said she could do.”

So to answer Fast Fred’s recent query, it doesn’t appear that long and skinny is the only prerequisite to decent fuel efficiency.

Portager continued: “First diesel is intrinsically safer than gasoline.”

No question about that. But just because it is does not mean that one has to rule out a gasoline powered outboard. If >I< (YMMV) were going to power a boat with an inboard engine it would be a diesel. But if the design worked well with an outboard, then a 4-stoke of appropriate size couldn’t be ruled out.

Gasoline tanks can be built and placed in accordance with Coast Guard and ABYC safety regulations and be safe for usage.

As for 4-stroke reliability… as others have said: if I were only cruising close to the coast or on rivers and lakes and if the design worked well with an outboard, I wouldn’t be hesitant about choosing that direction. As always, YMMV.

Finally Portager’s comments about ply/epoxy and aluminum. All valid and something to be taken into consideration. But Ilan Voyager expresses my sentiments exactly. He said, “I do like aluminum but I think that all the work and cost of the insulation annihilates any advantage in small boats; a metal hull without a thick insulation under the tropics, no thanks.”

As for the Parker Dory and its flat bottom. Again as several folks have said, it’s all a personal choice.

Phil Bolger has lots of designs that utilize flat bottoms – whether sharpies or dory style hulls. He’s apparently well aware of the pounding that occurs and has designed a couple of solutions. One I’ve seen is nothing more than a flat disc that intersects the waterline forward. This eliminates the acute angle between the water and hull, thus reducing the irritating slapping of small wavelets when anchored.

In dealing with larger waves he has designed a ‘cut-water’ for several of his designs. This appendage acts much like a traditional bow shape and does not allow the waves to see a flat bottom forward and therefore greatly reduces any pounding usually associated with a flat bottom meeting an oncoming wave while keeping the inherent ease of building a flat bottom boat.

If, like Mike, your concept is for a transportable boat, then the choices available seem to narrow. But if you’re not limited by height and width restrictions, then the choices are much more numerous.

The point of starting this thread was to solicit ideas and discussion on what choices are available for those of us that want to be able to transport our boats to different cruising grounds each season. 10miles/gal fuel mileage would be great when on water, but that same fuel mileage on land at 60 mph is even better!

I’d like to suggest that no one person has all the answers. They >might< have some that are appropriate for their personal circumstances, but to learn and consider viable alternatives we must keep an open mind and not reject out of hand ideas that don’t fit our preconceived notions of what is right and proper.

My personal progression is but one example. A few months ago I rejected Bolger’s designs out of hand because I simply disliked the boxy shapes that many of his designs employ. In his boxy designs form follows function without regard for conventional aesthetics. Because I didn’t >>CHOOSE<< to look beyond the (to me) ugly square-ness, I completely missed the brilliance of the underlying engineering.

In July I took a trip to the coast with Chuck Leinweber of Duckworks Magazine (http://www.duckworksmagazine.com) to see a wooden Diesel Duck being built (pictures of this particular boat and discussion of Buehler’s designs available here - http://groups.yahoo.com/group/BackyardBoatbuilding2). The discussion during that trip caused great pause in my “conventional” thinking. I started looking at alternatives that would allow me to achieve the goals and requirements of my retirement boat.

I’ll be so bold as to suggest that if one wants to learn about some alternative marine engineering, look at two of Bolger’s boats – the Tahiti and the Sitka Explorer.

The complete treatise on the Tahiti can be found in the magazine Messing About In Boats (MAIB) volume 17, no’s 12, 13 & 14 from November and December 1999. An update is in volume 19, no 22 from April 2002. Apparently this design is afloat in the Florida Keys and is nearing completion.

Sitka Explorer is described in MAIB volume 20, no. 6 from August 2002. Apparently someone has commissioned the full design and it will be complete sometime this winter.

MAIB can be reached at 978-774-0906. I have NO CONNECTION whatsoever with MAIB and mention this only as a community service.

The point? Think outside the conventional box. There may be good and valid reasons for >>NOT<< doing something too unconventional. But that doesn’t mean that we should accept at face value the ‘conventional wisdom’ of the industry.

Progress – whether incremental or by leaps and bounds – is only made when someone has an epiphany or questions the status quo.

So I sincerely hope that we’ll continue to explore alternatives in this conversation.

Best,

Leo

[Portager]

I agree with most of Ilan Voyager ‘s comments with the following exceptions.

That explains why I prefer a multihull configuration with a preference for trimaran (one engine only) for a slim boat. A small monohull with a ratio of 8/1 would be dangerous.

I beg to differ with that miraculous conclusion. A monohull can support an 8:1 L/B, it all depends on the center of gravity to center of buoyancy height. If you don’t get the height out of proportion to the beam it won’t require too much ballast. Besides this is a lot of comparing apples to oranges. Multihulls have a less efficient structure and higher wetted surface area. In addition when you scale a multihull down you risk pounding on the wave tops. I prefer monohulls because years of research revealed that they are susceptible to structural torsion in beam seas and they have high inverted stability (turtle).

I do like aluminium but I think that all the work and cost of the insulation annihilates any advantage in small boats; a metal hull without a thick insulation under the tropics, no thanks.

I do agree that Aluminum boats must be insulated, but I didn’t realize that installing insulation was so costly and complex! To think that I was lead to believe that was the easy part.

Lightning is not a concern if you take the precautions needed whatever the hull material.

I guess I shouldn’t mention the mass of empirical evidence to the contrary.

What’s the difference between a marine-ised diesel and an industrial diesel in this regard? Does the marine-ised diesel have some special air filter that precludes it from “sucking salt laden air”?

I took a closer look at the Duetz engine. It really isn’t air cooled it is oil cooled. You could probably make it work by using an oil plate cooler or keel cooled. You could also use an oil to water heat exchanger to heat water. You don’t need to worry about water leaking into the oil through the heat exchanger since there is solid metal separating the liquids.

And as Buehler says, “Here's figures my computer developed.

I checked Buehler’s calculations and they don’t agree with Conch’s equation or Dave Gerr’s equations. I’ll do some more calculations tomorrow, but I don’t believe a Duck with a 44’ 7.5” LWL, 15’ beam and displacing 69,668 lb is going to provide 12 nm/gal @ 7 knots. Portager is an efficient design but with a weight of 32,000 lbs light, LWL 46.75 feet, beam 12 feet it only does 4.5 nm/gal @ 8 knots.

Finally Portager’s comments about ply/epoxy and aluminum. All valid and something to be taken into consideration. But Ilan Voyager expresses my sentiments exactly. He said, “I do like aluminum but I think that all the work and cost of the insulation annihilates any advantage in small boats; a metal hull without a thick insulation under the tropics, no thanks.”

Why not try thinking outside the box once in awhile? Open your mind to new possibilities they might surprise you. :D

Regards;
Mike Schooley

[CDBarry]

You should be able to borrow it through inter library loan, or perhaps it will be at a university library nearby - it is widely held. Also, send an email to publications at RINA and just ask. Finally, there is always Amazon, eBay and the various used book online sources. Finally, a significant amount of the information is exerpted in SNAME's PNA.

[FAST FRED]

Good fuel milage at slow fat boat speeds are EZ .
Our 33ft cutter is a Maurice Griffiths design (Lone Gull II, blown from 24lwl to 28lwl 33loa).

With over 4000 hours of engine operation since the mid 70's the fuel consumption is 3/4 gal per hour at 6- 6.5K normal cruise.
Volvo Md3B 1 to 1.91 reductiohn with 19X13 TWO blade propellor.

The two blade is more efficent under power , and quite easy to index and lock behind the deadwood. DL 333, Bwl 10.6 at cruising 17000lb displacement.

A fat, not light boat, but restricted by the beam from ever going more than 7.2 or so , even with a gale blowing.

The question is how can I doubble the cruise speeds on the same fuel?

I think its impossible , but to doubble the speed to 12 or 13K on 3gph may be doable.

The low & hull profile if an early Commuter with 8 to 1 lb ratio or better, along with a very light simple interior should take care of the boat part.

For the engine & drive the problem becomes one of maximizing the output.

Certainly 2 engines , one of 70 hp run at about 50 should be in the 2 1/2 to 3 gph burn for long range work and a second high power at what ever is affordable would allow splendid top speed when required.

There are multiple engine drives from LST and other military surpluss sources so the price would not be out of line.

But carring a large engine for very rare use doesn't make loads of efficency.

My concept is to use a truck transmission for the multiple speeds.
YES they are cont duty rated .

An very fresh truck engine/tranny of 250 hp is quite inexpensive , and the exhaust manifold is OTS.(Off The Shelf)

By setting the boat to run at top speed in a lower reduction gear , the tranny could be shifted up to increase the loading at low (1200 to 1500RPM) distance cruise .

Egt gage and the mfg fuel map would be required.

The semi submerged prop system looks ideal for ease of onboard repair and efficency.One of the nicest concepts of the propsed surface drive would be the ability to take the ground with out damage.

The largest compromise for speed / efficency would be the need to use a 2 or 3 chine hull to lower building costs & time.

FAST FRED



Bus coach conversions , the orig insulation is tossed and spray foam is used.
Relativly cheap , and the interior is faired using a body shop "Jitterbug" (air file) with very little effort .
BUT one HECK of a lot of dust to vacume up!

The foam selected should be non burning , and a simple wall finish is simply glued on, or pop riveted to framing.

[Portager]

The problem with surface piercing propellers for this application is they are very inefficient at low hull speeds, which is where your high efficiency drive would operate. I believe a controllable pitch propeller (CPP) would be a better application because they provide high efficiency over a wide speed range. Note: a variable pitch propeller (which is a propeller with a constant pitch that varies with radius from the hub) would provide higher peak efficiency but the CPP provides high efficiency over a broader range.

If your interest is high efficiency at moderate speed like 6 to 8 knots, but the ability to also achieve higher speed such as 10 to 12 knots, then a semi-displacement hull and a CPP will provide that capability. This could be done with a length of 36 to 64 feet. To achieve IMO offshore stability with minimum weight, i.e. nearly zero ballast would require a beam of ~10 feet, so the L/B would be 3.6:1 to 6.4:1.

On the other hand if your desire is to obtain the highest possible efficiency at 10 to 12 knots, then I believe a long skinny design is required. To be highly efficient at 10 knots will require a V/SQRT(L) of 10 which equates to a LWL of 100 feet. Again the minimum beam for minimum ballast weight would be ~10’ so the L/B is 10:1. At this L/B your structural efficiency will suffer so it might save weight to increase the beam to ~12’.

From a transportability standpoint, a 100’ length would be very difficult to transport. Even though you could get an over length permit, you would need to hire pilot cars in many areas and it would be difficult to negotiate corners. You would probably need steering on the trailer axels, which increases cost, complexity, …

A good compromise between transportability and cruise efficiency would be to keep the LOA below 65’ and the beam below 12’. This would be transportable without pilot cars except on some two lane highways. The L/B would be 5.4:1 and the efficient cruise speed would be about 8 knots. With a semi-displacement hull and light weight design maximum speed could be 12 to 16 knots depending on maximum power.

To increase maximum speed much over 16 knots would require a planning hull and massive engines instead of a semi-displacement hull, which would be detrimental to cruise efficiency and sea keeping in rough seas.

Regards;
Mike Schooley

[Ilan Voyager]

That's becoming interesting more and more...

1/ Nothing at RINA. Visibly the internet archives begin with the year 1990. I made a search in internet and I've found a few informative pages on displacement boats with a small illustration of NPL series hulls..
www.nautica.it/superyacht/497/tecnica/bottom.htm
www.nautica.it/superyacht/490/tecnica/bottom.htm
www.nautica.it/superyacht/485/tecnica/bottom.htm

http://books.nap.edu/catalog/5870.html (a bit arid...maths)

I did not made a search in http://www.nationalacademies.org/ where you can find a lot of treasures after digging a lot, the naval libray is impressive.

A few words about NPL series hulls: these hulls are a shape that can be simplified in triple chine without a great loss of efficiency.

Surely RINA will sell the doc it against some good english pounds.

2/SAQuestor post

**The ciphers given in http://dieselducks.com/Troller%2050.html are totally false.

There are the ciphers I've roughly estimated in hurry:

ratio length/width at LWL 3.41 meters; it's normal, nothing slim.
At displacement 31.63 metric tons;

V/L .. Knots ..... HP claimed Rough HP
1 ..... 6.96.... . 12.9 96
1.1.... 7.65...... 19.8 116
1.15.. .8.0....... 24.3 126
1.20... 8.35...... 31.5 138
1.25... 8.70...... 42.4 149
Following; out of limit of hull speed at 32 tons
1.30... 9.04...... 57.3 161
1.35... 9.39...... 77.9 174

The induced skeg loss factor of the propeller, correction of hull speed and correction of shape are not included.

The max hull speed counting the displacement and shape is 8.5 knots at best. With the old 100 HP this boat was running at about 6.0 knots, a common speed for fishing boats a few decades ago.

I estimate, by smelling this boat with my engineer's nose, that it needs at least 200 HP, gearbox 5/1 and a propeller of diameter pratically 2 feet to move at 7.0-7.4 knots cruising speed. Navigating in dangerous places as North Brittany (France) with tide currents and strong winds I would put 300 HP to be sure to arrive at the harbour.

A lot of internet sites give false infos, or unbelievable claims...Dynacam engine and Bugatti boats (poor Ettore, he must cry in his grave) which with its pics of old russian WIGs and other stupidities attain the level of the total fake are a few examples among dozens of other.

That shows that everyone must have a very critical eye, and to check the veracity of the claims.

** Whatever you shall do, a flat boat will pound. For me, the V is easier to build and stronger in chine building: the triangle is the lone geometric figure that cannot be deformed and you have a strong keel instead of a floppy flat pannel. Flat boats are acceptable only in very small boats, or in lakes and calm rivers.

2/ Fast Fred post

The facts are stubborn, and hydrodynamics applies to all thing going on water:
so I do totally agree with the searchers of the english DERA, the engineers's pool of the french DCN, some PhD guys of the La Haye Naval Institute plus a bunch of australian and neozelandese designers of the fastest ferries of the world, who think all together, after an extensive and costly research, that the most energy efficient ship for some applications is a slim hull with a ratio around 8 to 10 and thet the best configuration with slim hulls is the TRIMARAN.

With so innovative designs, progress are cautious and slow as the finantial risk is great; the success of the campaign of validation and evaluation of the RV Triton will probably speed up the process. Various navies are now very interested by trimaran frigates.

I agree also with Nigel Irens, one of the best naval architects of the world, plus Mrs Morelli and Melvin, who are among the top cream of the yacht design. They have access to all needed data and have experimented hydrodynamicians to give them a little help.

The 4.8 nm/gallon average at 8.93 knots of Yanmar Endeavour (only 40 feet long) was made while crossing The Pacific, thus the boat was fully loaded at the beginning of the trip. It may be improved as this boat was powered by 2 small (27HP) diesel outboards: small fast revving (4500 RPM) diesel and small fast spinning propellers are not the best combination for efficiency. The 12 knots top speed is gotten fully loaded. These ciphers are not computer calcs but true facts coming from the use in sea.

The most interesting fact is that these results are obtained by very simple means; a hull, 2 outriggers, common engines and a lot of strong thinking.

3/ Portager Post

First I remind we are discussing about 35-60 feet slim power boats.

As I'm not christian, I refuse the word miraculous about my assertion "A small monohull with a ratio of 8/1 would be dangerous". It is the result of simple arithmetic; take a 40 feet hull, so 40/8= 5 feet at the LWL. Try to add the accommodations. Everybody with some experience will think immediately: dangerous.I guess that the medium term in a small monohull boat is about 5/1.

There are 8 to 10/1 monohulls (I've sailed on them in the Navy) but these boats have a very huge difference in size.

The wetted surface and structure unefficiency doesn't seem to bother the modern sail and power multihulls (I do not speak about a Arthur Pivert tri, or some crappy cat of the 60's) for going fast and to be efficient; you have just to sail on one of these boats to be convinced, and to see the results obtained.

Structural enginnering problems are solved since 15 years and the pounding is known only by badly designed multis. Ask the Australian which use 20 feet power cats in rough sea.

About inverted turtle position, I prefer to stay in a inverted multi, whose design had foreseen this eventuality and organised the survival, with food, water, radio etc that to be on a rubber life boat with the monohull being one mile under my feet. A french multihull joke says; "while capsized, multihulls float inverted, monohulls sink upright".

I shall add that power monohulls may float also inverted, and a part some specially designed rescue boats I do not know self-righting power monohulls. It seems you're mixing power and sail boats stability facts.

The facts are there, the remainder is an old academic discussion, which seems to be closed long time ago at least for europeans and australians.

I understand perfectly that you do prefer monohulls and it's your own right that you have not to justify or rationalize.

About metal boat insulation cost and time: just make a excel sheet of the cost (work even free it's spent time, and materials) of foaming, paneling and finishing the inside with marine standards of a 50 feet metal boat. calculate also the (heavy) weight. You'll be astonished. Finishing is the hardest and longest part of boat building. The hull is no more than 25% of materials cost and time of a living aboard boat. I have a (too, my beard is white now) long experience of this fact.

About lightning: many mine sweepers are in fiberglass now, with a lot a fragile electronics. Lightning should be a big concern but it is not a problem with the normal protection technics. I maintain that "Lightning is not a concern if you take the precautions needed whatever the hull material". I won't detail here the very well known technics of lightning protection of a boat. It's probably be a good thread subject.

About Deutz engine; you're right and I was mistaken. I thought it was the common air and oil cooled engine. I've downloaded the PDF and truly it's an interesting engine for a small boat. Worth to be marinized. So the noise and corrosion concern have to be thrown in the garbage.

About Duck boat. We agree together that the given ciphers in the internet page are impossible.

The last; Portager is a nice boat, even if I prefer multihulls.

3/ Fast Fred second post

A truck transmission: Why not? I have seen and tried a 45 feet shrimp boat in Senegal fitted with a truck transmission and engine. They changed of gear with the boat stopped. It worked very well, and the boat was a good one. On a such boat, size and weight were not a problem, but truck engine and transmission are truly bulky and heavy.

The nicest feature of this boat that this boat has been conceived with the help of an engineer of the Arsenal de Dakar by local fishermen and built on the beach between 2 coco trees by local artisans...

4/ Portager second Post

As surface piercing props come from competition, they are perceived as designed only for fast boats. The surface props found in the american market are designed only for fast boats with "fast" propellers.

But surface props work very well also on slow boats if designed for this purpose:
Mr Sholz ( www.levidrive.com/ ) makes very efficient surface props, designed by Sonny Levi, for small fishing boats in Malaysia.
The harbour captain's service boat of the Vieux Port at Marseille (France) uses 2 surface props...it pushs like a tug and it's used sometimes as tug.
Mr Dorado, naval architect in the south of France has designed successfull working boats with surface propellers.
The nice feature of surface props is when too charged, they slip instead of cavitating, and thus give like a kind of automatic gear box effect. The other advantages have been already said.

Pitch controlled propellers are very expensive, and I'm afraid, on small boat, of the reliability.

I agree with the analysis which follows in your post for monohulls (we are far of the 8 or 10/1 monohull...)

To end this too long and surely boring post, I think that for a 2 persons a 40 feet live aboard is enough, with possibily for 4 during short period. My personal tastes go to a 40 feet trimaran, maybe foldable with a 90 or 100 HP engine. With small boats, small problems...

Best regards to all.

[SAQuestor]

That's becoming interesting more and more...


2/SAQuestor post

**The ciphers given in http://dieselducks.com/Troller%2050.html are totally false.



OK - I've never built one. But...

"The main propeller is NiBral, 30" x 21" with a 3 to 1 gear reduction. The saildrive prop is a folding, geared, bronze 15" x 10". At 1400 rpm the main engine drives her about 6 knots and uses approximately 1 ½ gph. The sail drive unit can move her about 3 mph."

http://www.rusty-duck.com/construction/specs.html
http://dieselducks.com/Duck48study.html

Another...

"A very interesting trip From Zhuhai to Yokosuka Japan via Hong Kong. All told the trip took 9 days 22 hrs and 15 minutes for the trip including 2 hours dead in the water. Thats an averag of 7.34 kts. All in all, not too bad."

Unfortunately Don doesn't give fuel usage, but the engine is a small 4cyl. Cat. Didn't take the time to look through his entire web site to see if he mentioned the exact size.

http://_gaijin.homestead.com/index.html

Another...

"John Deere 4045 135 hp low pressure Turbo diesel marine diesel with ZF Hurth 2.78:1 marine transmission."

Since these folks live in Hong Kong they don't have any long voyages to report on.

http://www.cadwell.net/Makena.htm

Another...

"ENGINE:

I chose a 78-hp Perkins M80T turbo diesel, identical to the Volvo TMD22. Not just because I got a good deal on this engine, but the lively 2 liter motor of the newer generation will do for sure 20,000 hrs. of service without critical, expensive, technical hick-ups, as long as the engine gets its oil and filter changes and the changing of the timing belt once awhile. Being designed for the automotive and farm equipment use, it has a self bleeding Bosch diesel fuel system and a 400 hr. oil change period. The 4,000 Perkins network outlets in 160 countries and the countless Volvo outlets are providing rapid supply of spare parts and responsive one-stop servicing on all factory specifications.

Nowadays diesel motor technology is changing fast. I wanted to go away from the heavy weight, slow turning, not responsive, but fuel gulping iron brute of the dinosaur age. This motor, with the 2.74 Hurth gearbox, coupled with an Aqua Drive to a 40 mm (prox. 1-1/2") prop shaft of a 20" CP Propeller System, from West Mekan (Konrad Skibenes) will propel "Diesel Duck" just fine without killing our wallet when paying the fuel bill."

http://www.msdieselduck.com/

I point out these links and quotes not to be argumenative per se, but rather to show that perhaps the traditional calculations aren't always as accurate as we'd like.

Since Mr. Buehler isn't one to exaggerate, I respectfully suggest that your figures of needing ~6x more HP - 19.8 vs. 116 is too far off to be true either.

1.1.... 7.65...... 19.8 116

116*.06=6.96 GPH and a total range of .... Well he didn't spec the fuel tank size on the troller, but if we look at a similar boat of Buehler's, http://dieselducks.com/Duck48study.html the fuel tanks there are spec'd at 900 gallons.

The speed at V/L 1.1 is similar - 1.1..... 7.44.... 13.7 for a range of 8147 miles.

So let's take (for approximations sake) the same ratio and thus 13.7hp becomes 80hp using your calculations. Using the 80hp figure and the range drops to a palty ~1400 miles, a ~6750 mile loss.

Perhaps George's calc's aren't exact, but I'll also suggest that he'd not sell any plans and no one would build an ocean crossing power boat that had a range of less than 1400 miles on 900 gallons of fuel.

Please, before you dismiss this as hog-wash, spend the time to do the research on Buehler's built boats and you'll find that more than several have indeed crossed oceans putting along happily at ~6.75-7.25 knots and burning about 1 gallon per hour (depending on conditions of course.)

Regards,

Leo

[Ilan Voyager]

SAQuestor,

I have worked on the design (alone or in a team in the Navy) and/or built something like 143 boats if my archives are good in about 33 years. Actually I'm working on the number 144 a 35 feet diving boat. This variety goes from the prelimanary sketches of one aircraft carrier to a sailing dinghy of 3.2m, passing by fast patrol boats, duty boats, tugs, power yachts, fishing boats ( 35 built from 8 to 50 m), racing multihulls and so on.

While working for a client, I'm able to calculate the speed of a work boat if the shape is well known within 1/10 of knot, and estimate the consumption at 1 liter hour, as these results are guaranteed by contract with heavy penalties if the intended speed and consumption requirements are not fulfilled within a certain very small percentage. Ask to any naval architect or engineer working in this field and he will tell you the same thing.

That I guess is that Mr Buehler confused the ciphers of the 50 feet with another boat (38 feet I do not remember) he was talking about in the same internet page.
I didn't said that Mr Buehler was a hustler. I've simply said and Portager will agree that the ciphers were impossible, as the boat weights about 31683 kg for less than 14m of LWL.

The Gerr formula without any correction of shape (double ender, skeg etc as I have not the hull's coefficients) gives a max hull speed of about 8.75 knots.

The other examples you give are from different boats and we do not know exatly the hull shapes and coefficients (As I have seen without paying attention to details the shape is very different; look at the sterns).

A good semi displacement fishing boat of 15 meters of LWL weighting 32 metric tons can make easily 7 knots with 100 HP and 9.9 knots with 200 HP, but need only 51 HP to get 5 knots... but it's not and old double ender in transverse bottom plaking style; a such boat creates an enormous drag while tempting to approach the 7 knots because of the stern and the drag penalty of keel and skeg shape.

I'll follow your advise and I'm going to discover the Mr Buehler's boats in detail. I'm going also to look in my old books about power calculations of true displacement boats, it's good to read again the old classics...

My statement about some internet sites (look at the "bugatti" site and you'll understand) remains valid.

[SAQuestor]

SAQuestor,

I have worked on the design (alone or in a team in the Navy) and/or built something like 143 boats if my archives are good in about 33 years.

I've snipped a good bit.

I'll not dispute your knowledge and experience, and bow to your long career.

Besides, this discussion has taken a turn away from how to get a long skinny monohull power boat to be its most efficient.

If possible, I'd like to see the discussion get back on that course.

Best,

Leo

[Ilan Voyager]

It would be very sad to start a dispute while we are here for our pleasure, to meet interesting people, and to exchange ideas.

Surely, there are always subjects of disagreement as esthetics, monohull versus multihull, marinisation of engines etc but that never has to come to dispute.

As anyone can make mistakes, I'm going as I said in a former post to re-read some old books about the displacement boats of Mr Buehler's style.

For example the ciphers given by http://www.rusty-duck.com/construction/specs.html
are consistent. The hull has a wide stern: a very rough calculation gives a hull speed of 8.8-9.2 knots, a speed of 2.7 knots with 18 HP (close to the about 3 knots), the "about" (that can be somewhere between 5.6 to 5.9 knots...) 6 knots at 1400 RPM of a torquey slow revving N.A. Lugger 105 HP with a 3/1 gearbox and a 30" x 21" propeller (a good combination with such a boat) is "normal" and within the range of the engine.
We are far of the 6.96 knots with 12.9 HP of the troller 2050...

We'll be back to the subject of this thread. If you feel I have been rude, please accept my excuses, I did not wanted to be rough.

Best,

Ilan

[Tad]

Excellent, very nice discussion.

And Ilan is to be congratulated on pointing out mistakes where he sees them. Take everything you read not as gospel, but as one side of the story. Check technical assertions against your own experience and with other published references.

This paper includes some lines from one of the NPL hull series. NPL Hull (http://www.rina.org.uk/rfiles/IJME/A3-2003/Discuss/millward.pdf)
The form is close to where I ended up when creating my Passagemaker Lite series of hulls. This particular NPL form is very fine forward; the PL hulls are slightly fuller. I would love to compare seakeeping of the two with tank or software.

I include some writing I did a while back on comparing the efficiency of various hull forms. This was in reply to Harry Bryan's article in WoodenBoat # 170 on fuel efficient displacement hulls. I would like to get some trimaran data to include.

-------------------------------------------------------------------------

The comparison of MPG without regard to either load (displacement/weight), or time (speed), seems an incomplete discussion. There is a very useful comparison of speed/power/weight called transport efficiency (Et ). With this coefficient, plotted against a dimensionless speed, we can compare the efficiency of displacement, semi-displacement, and planning hulls.

Transport Efficiency takes into account not just the power required (in effect MPG), but also the weight (displacement in the case of a boat) being moved, and the time required to move that weight (speed).

Et = W * v / Pd * 550

W is operating displacement, in pounds.
v is speed in feet per second, (knots * 1.6889).
Pd is the horsepower required for the above v.

For Rambler I guessed at a cruising weight of 1600 pounds.
6 miles per hour is 5.2 knots is 8.798 feet per second.
I took the power as your stated 3.2 HP.

Et = 1600 * 8.798 / 3.2 * 550
Et = 7.998

Plot this against Volume Froude Number, (see WoodenBoat # 137)

FNv = v / (g * disp.^.666)^.5

v is speed in feet per second.
g is acceleration due to gravity, (32.2)
disp. Is displacement, this time in cubic feet.

FNv for Rambler is .53 . This is about mid-range for displacement boats. Displacement hulls operate at a FNv of 1.3 or less, semi-displacement hulls at FNv of from 1.0 to 3.0, and planning hulls at FNv of 2.3 or more. (This is certainly open to debate!!)

Piquant, designed by Francis Herreshoff and W.J. Strawbridge in 1950 was close to the ultimate in performance for a displacement hull. She was 47’ by 6’6” and double ended, displacement was 6700 pounds. Twin 35 HP gas engines burned 3 gallons of gas per hour for a cruising speed of 16 knots. Top speed was 20 knots. I calculate her top speed Et at 5.88 and FNv at 1.26. A fairly high speed is possible if the boat is very light.

In the early 1970’s Bill Garden designed Clam, which he termed a doomsday cruiser. She is 42’ by 8’ and of very simple vee-bottom plywood form. Her power was a Gray 4-69 gas engine, developing 15 HP @ 1800 RPM. Cruising displacement would be about 9300 pounds and she has bunks for 4, an enclosed head, and galley. Mr. Garden calculated a cruising speed of 6 knots using 10 HP, 1575 RPM, using one gallon of gas per hour. I calculate an Et of 17.13 at a FNv of .34. A big boat going very slow can be very efficient.

Another efficient hull is Phil Bolger’s Slicer, 29’ by 5’2”, a plywood vee-bottom hull of very light construction. Her displacement is about 1700 pounds and she achieved 18 knots with a 15 HP outboard. This is an Et of 6.26 but at a FNv of 1.79, which is well up into semi-displacement territory.

Just for fun I ran the calculations on a typical SUV to see how it would come out. A 5000 pound SUV gets 25 MPG on the highway, we’ll call that cruising speed. Working backwards I calculate about 56 HP is required to maintain 65 MPH. That gives me an Et of 13.9 at a FNv of 3.92. This is a transport efficiency far better than the best planning hulls. Regarding the effort required to move a land vehicle as opposed to a waterborne one, I think you missed the difference between the force required to accelerate a mass and that required to maintain a mass in motion.

Running through the published figures for the Hinckley 29 I come up with an Et of 1.81 at a FNv of 2.11. This is below the efficiency of the best planning boats and also below the performance of her big sister, the 37’ Picnic Boat. This probably reflects the smaller boat’s higher beam/length ratio.

Looking at your performance figures (37 mph for 200 HP) and guessing a weight of 5000 pounds for the Parker 23 gives some interesting results. I get an Et of 2.46 at a FNv of 2.23. This is better than the Hinckley and is probably a reflection of the greater propulsive efficiency from the outboard as compared to the waterjet.

The ultimate Et is a moving target as improvements are made in hull form and propulsive efficiency. I’m sure all the vessels above could exhibit improved Et with better underbody fairing, different propellers/gearboxes, and optimized forms.

Thanks for adding fuel to the debate and opening the discussion.

My best to all, Tad.

[SAQuestor]

Excellent, very nice discussion.

[Lots of snip]

Just for fun I ran the calculations on a typical SUV to see how it would come out. A 5000 pound SUV gets 25 MPG on the highway,

Tad,

Thanks for the enlightenment on Transport Efficiency. Excellent.

The point I quoted above is just a quibble - but I've not seen any 2 1/2 ton SUV achieve 25mpg. Take 3/5ths of that number - 15mpg and I'll not quibble.

I just don't think giant SUV's are all that efficient on their own.

And as always, YMMV (Your Mileage May Vary) :D

Best,

Leo

Going back to the boat discussion.

[Ilan Voyager]

I'm too busy today for to write a long answer. I'll make a synthetic excel sheet (imperial and metric units) which, I hope, will help everybody for the calculations, and as always I shall bother all you with my ratiocinations.

Regards,

Ilan

[Portager]

I promised to check of George Buehler’s Troller 50 calculations, but first I wanted to give George an opportunity to check his calculations. George must be too busy, so here are my calculations.

First here is George Buehler’s data:

LOD: 50'
LWL: 44' 7-1/2"
Beam: 15'
WL Beam: 13' 9-1/2"
Draft at DWL: 6' 6"

The displacement is interesting because it changes rapidly depending on the loading. Here's de figures....

Displacement at DWL = 69,668 lb
floating 3” high = 61,42 (yes there is a digit missing here, use your imagination)
at 4” high = 59,497
at 3” LOW = 77,572
at 4” low = 80,074
at 5” low = 82,829

V/L .. Knots .... HP
1 ...... 6.96...... 12.9
1.1.... 7.65...... 19.8
1.15.. .8.0........ 24.3
1.20... 8.35...... 31.5
1.25... 8.70...... 42.4
1.30... 9.04....... 57.3
1.35... 9.39....... 77.9

First I noted that the V/L does not equate. The square root of 44.625 is not 6.96 so I determined that George must be using a LWL of 48.44’ instead of 44.625?

Next I started with Dave Gerr’s equations as follows:

Eq #1: D/L=(weight/2240)/(0.01 * LWL)^3

Where D/L is displacement/length ratio
Weight is weight in pounds
LWL = Length at Water Line in feet

Eq #2: S/L = 8.26/(D/L)^0.311

Where: S/L is the maximum displacement speed/(length)^1/2

Eq #3: Hullspeed = S/L * LWL^0.5

Eq #4: SHP = D/(10.665 / (S/L))^3

Where D = displacement in pounds

Plugging these equations into Excel and using a LWL of 48.44 I get the following:

V/L Gerr Speed Buehler
HP Knots HP
D=69,668
1 57.43 6.96 12.9
1.1 76.44 7.65 19.8
1.15 87.35 8.0 24.3
1.2 99.24 8.35 31.5
1.25 112.17 8.70 42.4
1.3 126.18 9.04 57.3
1.35 141.3 9.39 77.9

Note these calculations do not provide for waves, wind, current, skeg losses, shape corrections, … i.e. to are what George claimed. I consider these numbers optimistic predictions that you will probably never achieve in real life. Another significant point is the calculations assume good propeller efficiency, so if you are using a fixed propeller you will only approach these values at your design point and at any other speed propeller efficiency will drop off so power requirements will be higher and fuel efficiency will be lower. With all that said I would put more faith in Ilan Voyagers numbers than mine.

Now that we have an equation to estimate power requirements, it is a simple mater to estimate fuel consumption, provided we know the brake specific fuel consumption (BSFC) for the target engine. Engine manufactures will provide a curve for BSFC versus engine speed and it is usually a shallow bath tube shaped curve with a minimum point between 50% and 80% power. This curve assumes that the engine load or torque is optimized for that speed (rpm). If you compare the engines optimum power curve and a fixed propeller power demand curve, the propeller power demand curve is much steeper than the engines optimum power curve. Since you never want the propeller power demand curve to exceed the engines optimum power curve by more than a few percent (this would equate to overloading the engine, which is not a good thing) the propeller can only be optimized for the maximum speed you wish to achieve plus a few percent. At any speed less than the propeller design speed, the engine will be under loaded and BSFC will be less than ideal. To determine actual fuel consumption, you need to get a BSFC chart from the engine manufacturer that shows a family of curves of BSFC versus speed for different torque levels (they all have this data because they use the optimum point on each curve to determine the BSFC curve versus speed), but manufacturers are reluctant to give this data out and (unless you can get it in an electronic format) it is cumbersome to work with. In addition if you are in the process of selecting an engine from multiple candidates, evaluating each engine can be exhausting. Since the BSFC curve is a very shallow curve, the variation in BSFC is small over a typical operating range, therefore designers typically use an approximation of 0.055 (David Gerr’s recommendation) to 0.06 gallons/HP/hr (the marketing departments recommendation) for diesel fuel and 0.1 gallons/HP/hr for gasoline. Another factor that can impact range is BSPF ratings are usually in mass/power/time and we measure fuel in gallons or liters. There is significant variability in the density of fuel which will directly impact your range. As they say, your mileage may vary.

Getting back to the equations, multiplying SHP by the BSFC provides fuel consumption rate.

Fuel consumption rate = SHP * BSFC

And dividing speed by fuel consumption rate provides mileage

Mileage (NMi/gal) = Speed / Fuel consumption rate = speed / SHP * BSFC

Using 0.06 for the BSFC and substituting Eq #4 produces:

Eq #5 Mileage (NMi/gal) = Speed / 0.06* D/(10.665 / (S/L))^3
= Speed * (10.665 / (S/L))^3 / 0.06* D

At first glance it appears that the way to increase mileage is to increase speed, however since power requirements increase faster than speed so we know the to increase mileage we must reduce speed. See that attachment I provided for a graphical representation of this. Additionally, we see that mileage is inversely proportional to displacement, so the most direct way to increase mileage is to reduce weight. This is illustrated in the attachment by the Idlewild curve. Idlewild is another George Buehler design as documented at http://dieselducks.com/Idelwild.html . At less than half the displacement of the steel hull Troller 50’ and only 8% longer LWL than the Troller 50’, Idlewild provides a significant increase in mileage at a given speed. As you can see, reducing displacement is the best way to improve fuel efficiency.

On the subject of Idlewild, note that she is built in Aluminum. George says, “Personally, I think plywood is better because it’s considerably cheaper unless you’re hiring the labor of course; aluminum is fast to work so paying for labor is a much better deal than paying for a wood builder.” To me this means if you don’t put any value on your time plywood is cheaper, however if you value your time Aluminum may be a better option. In addition Aluminum will certainly be lighter, which improves fuel economy. Finally, as Ilan Voyager points out, wood/epoxy can be made durable provided you use enough epoxy and glass matt. However if you skimp a little too much, even in a small area, it creates a potential leak and a place for rot to start, conversely if you go overboard it adds weight. Finally, how well you build is a big unknown for potential buyers if you ever decide to sell, which is why home built wood/epoxy boats has much lower resale value.

Now you are probably saying that this a supposed to be the long/skinny boat thread, but beam isn’t part of the mileage equation. Well, actually beam is a key part of the equation but it is hidden in the displacement. Since displacement (in the nautical usage) is equal to the weight of water that the boat displaces,

D = LWL * BWL * draft * 3DPC * density of sea water
Where D is displacement
LWL is the length at the water line
BWL is the beam at the water line
3DPC is the 3 dimensional prismatic coefficient

Since we know we want to increase LWL to reduce the speed/LWL^.5 term, then we must reduce the beam, draft and/or prismatic coefficient to reduce the displacement. Lets leave changing the prismatic coefficient for now and just discuss reducing the beam and draft. The problem is if we reduce beam and/or draft we will loose stability. To accommodate reducing the beam, we need to lower the center of gravity. We could lower the center of gravity by adding ballast, but that would increase displacement and reduce mileage, therefore we need to reduce the center of gravity without adding weight. We can do that by reducing height and lowering height of high density items such as the engine, batteries, tanks, … As you can see, the draft of the hull actually helps reduce the center of gravity because it allows us to locate high density items lower than we could with a flatter bottom. If the hull is deep enough, then the equipment can be located below the floor of the living spaces allowing maximum living space without increasing the overall height too much.

Reducing the prismatic coefficient is basically going to a multihull configuration. By increasing the beam and pushing the displacement out to the sides we can increase stability and minimize displacement. However multihulls are difficult to make trailerable, although not impossible.

Well that is enough for now. I’m donning the asbestos underwear and wait for the fireworks.

Regards;
Mike Schooley

[Ilan Voyager]

Before going to bed, I made a little jump to see the thread.

Portager, take out the abestos underwear (abestos is bad for the lungs): I have just read your post: everything looks fine and I agree with the method of calculations (how I wouldn't? Dave Gerr knows his job...).

The difference of HP comes from I've used an different equation I had under hand (It's why I said; rough calculations). Probably the true ciphers are somewhere between our ciphers, plus the corrections. To know the exact ciphers has finally no importance; the important is to know that Mr Buehler ciphers are impossible.

I'm bothered by such big discrepancies, so I'm reading some old books as I want to find the other methods used on old displacement hulls.

I wouldn't said better about the corrections to make and about the importance of the propeller, gear ratio. I agree totally that the principal penalty is weight; a boat must be as light as possible without sacrifying reliability and on small boats you have to make choices about accommodations and amenities.

The method of consumption evaluations is perfectly exposed: there is a also a method by taking the best torque RPM of the engine (it's almost always where the engines have the best specific consumption and are the most efficient) and calculate the gear and propeller for the best cruising speed at this RPM. That sacrifies generally top speed but gives the best mileage at the best cruising speed. The perfect propeller is the variable pitch one as you can adjust perfectly the load of the engine whatever the sea conditions.

The lone assertion I do not agree it's about low prismatic coefficients of multihulls.

It's easy to give a high prismatic coefficient to a power slim hull: entry curves are smooth and are only a small fraction of the hull, the central part (where prismatic coefficient is close to one) is the longuest fraction of the hull , and the stern when wide (about 75 % of the max beam) with a good keel curve has also a fairly high prismatic coefficient. A PM of 0.65 is not difficult to obtain with a slim NPL hull or an elliptic sections hull.

That which may change a lot is the block coefficient: The block coefficient represents the cargo capacity if a hull in a given length, and for example a NPL hull, with its close to V sections, has not a very high block coefficient.

I think that some illustrations will be needed, so these 2 notions will be better understood. I'll work on that. Now I have to get some sleeping hours.

Best regards

Ilan

[Portager]

I wanted to see how accurate Dave Gerr’s 0.055 gal/HPhr rule of thumb was and if that approximation was causing me to over or under estimate mileage and range. Since I plan to use either a Steyr Model 164 or a Yanmar 4LHA-DTP, I downloaded the Steyr Model 164 performance curves from http://www.steyr-motors.com/products/products0006.htm and measured power and brake specific fuel consumption (BSFC) versus engine speed. I then plotted BSFC versus power, as shown is the first attachment. Dave Gerr’s rule of thumb appears a little conservative over the middle power range (i.e. from 25 HP to 150 HP, but it is overly optimistic at the ends of the power curve. Next I added a trend line, shown by the dashed line, and used trial and error to find the best fit. As you can see a 6th order polynomial provides a good curve fit. The error between the curve fit equation and the measured data ranges from -1.42% to +1.39%, but by leaving out the last two points that are outside the range of the curve fit, the error ranges from -0.82% to +0.55% which I think is good enough. Note: if you attempt to utilize this curve fitting technique, make sure that you increase the number of significant digits on the text box of the equation or the round off error will cause erroneous results.

Now that I have an equation for the Steyr Model 164 BSFC versus power, I can calculate the BSFC based on the power requirement and then multiply by the power to determine the fuel consumption rate. The second attachment shows the mileage prediction versus speed for Portager using the BSFC curve fit and using Dave Gerr’s 0.055 gal/HPhr rule of thumb. To Dave Gerr’s credit, I notice that the curves are very close, however his rule of thumb is slightly optimistic below 6 to 7 knots and a little pessimistic above. It should be noted that these predictions are accurate for controllable pitch propellers, however if you are using a fixed pitch propeller it would only be accurate at the weight and speed that the propeller is designed for.

The third attachment, range versus speed, shows a similar characteristic although the difference is slightly more pronounced. Range improvement at speeds above 6 to 7 knots if a welcome benefit. The reduction in range is above 2,600 NMi (light) and 2,300 NMi (loaded), which is greater than my maximum design range of 2,200 NMi (Los Angeles to Hawaii) so it is doubtful I’ll ever operate in this speed regime. To better illustrate the difference between the BSFC curve fit and Dave Gerr’s rule of thumb, I plotted the difference in range versus speed in the fourth attachment which shows a 200 to 240 NMi improvement in range between 9 and 10 knots. The fifth attachment shows the percentile difference which shows up to a17% improvement is range between 9 and 10 knots.

I hope this is helpful. If you would like a copy of my spreadsheet, send me an email and I’ll send it to you, but keep in mind it if a roung engineering spreadsheet with no comments.

Regards;
Mike Schooley

[FAST FRED]

For an early look at Long efficent boats , Yachts In a Hurry , C. Philip Moore ,W.W.Norton & Co. is great!

Of course the 20's era was using 300 to 500 hp gasolene engines that weighed 3000lor more each!

Although every attempt was made for lightweight construction & outfitting , these boats were HEAVY!(at least by todays standards.)

There were in the ball parek on LB ratios , from the many examples given:

45x10...56x11...75x12'10...68x12'6...60x16...46x9...72x14..

From the list begining with the A's

Seems today we should be able to construct a modern foam GRP or aluminum vessel that would be seaworthy and fast , while being cheap to run.


Does anyone have a concept for the fuel milage at cruise speed , say 12K+ that could be obtained?

From my playing with the simple graphs avilable to me , I feel 5 NMPG would be barely atainable with an optimised design.


Any way to better that? or?

FAST FRED

[Portager]

If you want 10 NMi/gal at 12 knots, then the fuel consumption rate will be 1.2 gallons per hour. Using a brake specific Fuel Consumption (BSFC) of 0.050 gal/HPhr, then the power level must be 21.82 HP. Solving the power equation for displacement allows you to compute the maximum displacement to achieve the desired 12 knots speed. The attachment shows the combinations of length and displacement that provide 10 NMi/gal at 12 knots.

Some data points are at;
Length Maximum
Waterline Weight
Ft lbs
70 8,970
100 15,316
125 21,405
150 28,138
175 35,454

These weights seam quite low to me, but maybe it is possible. If it were accomplished it would be so light that I would worry about it bouncing around like a cork if it encounter heavy seas.

One idea that comes to mind is a smaller vessel with inflatable sections between the bow, mid and stern sections. When the inflatable sections were inflated the total length would increase to the required cruising length. Once the vessel arrived at its destination or conditions became too rough, the vessel could be deflated and the rigid sections reconnected.

Regards;
Mike Schooley
Designing "Portager" a 48' transportable trawler

[FAST FRED]

A 70 ft boat that was only 9000lbs would be quite an achievement , considering the minimum engine weight , fuel & water & supplies , necessary weights like ground tackel .

Doubble that , say 18,000lbs would be far easier , and would not need exotic construction or titanium anchors.

AS a past multihuller (45 Nicol Voyager) there is little hassle with being ON the water , rather than being IN the water, although the motion is different , its hardly bad.

What does your computer say about a 18,000 lb boat optimized for long range passages at speed?

Thanks

FAST FRED

[Portager]

You set an aggressive performance goal; therefore it stands to reason it would require an aggressive weight reduction effort.

On the plus side, you only need 22 HP, so the engine weight will be the least of your concerns. Unless you also want to be able to go faster than 12 knots, which would require additional power and thus additional weight.

If you double the weight, then you double the required power and fuel consumption rate, which cuts your mileage in half.

Regards;
Mike Schooley

[8knots]

Portager, Your in the wrong biz there my man, I envy tour skill at crunching numbers.
Well Im not sure what we are considering "long and skinny" but one of my many concept doodles I will attach, she has a wl length 77' with a beam of 18' draft 2'9" my rough numbers give me 112,000 disp DL of 110 and a BL of 4.27. I cant remember all the particulars but seems to me I had figured on a pair of 170hp will drive her to SL 1.5 or about 13kts. I think she is a little beamy for the long skinney concept but I think she needs it considering the top hamper factor. In my opinion it is still a good compromise in length and usable space. with good speed performance with but modest HP. I'm still fidling with the idea of the "Seabright" box keel Gerr is so fond of. I think you could drive her to SL 2.0 before fuel consumption gets out of control. A pair of 700hp Luggers will drive her to SL 2.5 (apx 21kts) drinking about 28gph @WOT 2100rpm ease her back to 1700-1800 and yor cruising @ a reasonable clip without breaking the bank. Keep in mind she is an "able coastal cruiser"
Some time ago there was an article in PMM titled "Passagmaker lite" By a Tad Roberts. I'm guessing it is our own Tad that posts here from time to time.
It is a good read and a great overview of what you folks are trying to do.

[Oldfart]

I just stumbled on your discussion but have been interested in long skinny boats for some time. I haven't read thru everything so forgive me if I am redundant. On of the best examples I have seen is Bill garden's Tlingit, a 62 foot "ferry launch" with a 7'6" beam built from lumberyard 2x4's and plywood. It was built mainly as a carrier for an old 20 HP (463 cubic inch!) Easthope engine with which it could run 10.2 knots. It is detailed in Bill Garden's "Yacht Designs". Another boat you might be interested in is Phil Bolger's Breakdown Schooner from "Boats with and Open Mind". Also there was the Energy 48, basically and Alden ocean shell scaled up to 48'. If fuel prices keep going up these boats will come back.

[FAST FRED]

"If you double the weight, then you double the required power and fuel consumption rate, which cuts your mileage in half."


Of course different programs will have different output , but when I use

http://www.users.globalnet.co.uk/~fsinc/yachts/spreads/fred.htm

doubling just the weight does NOT double the thrust required to go the same speed.

Also the very tiny diesels seem to be mostly rated for pleasure boat , not 24/7 work as the more industrial engines are.

The Yanmar would probably last at about 600lbs or so for 100 Hp max. and 20-50hp for the long pulls.

The newest common rail tech would be great as its more efficent ,and vastly quieter , BUT the lack of get home operation would be really scary in a lightning storm.

HAS anyone come across a mechanical injection timed diesel , that gives modern fuel consumption, and 24/7 realistic service?

FAST FRED

[Portager]

Coincidentally number crunching is also a prerequisite for engineering.

I like your Seaka 75. I crunched the numbers on her and to do a S/L of 1.5, 13.16 Knots, she needs 311.6 HP. I calculate her “Hull Speed” using Dave Gerr’s equations of S/L = 1.92 or 16.82 Knots, which requires 650.76 ponies. At S/L = 2 power requirements are 738.63 HP. S/L of 2.5 requires 1442.63 HP or 721 per engine. Fuel consumption would be 79.345 gph (see attached graph) using a BSFC of 0.055 gal/HPhr. To get 700 HP at 28 gph would require a BSFC of 0.04 gal/HP hr. All in all I’d say your memory is pretty good, but I’ll have to look up the BSFC of the Luggers, 0.04 is quite impressive.

Fast Fred try looking at Kubota Super 03 series http://www.frontierequip.com/kubota/kubota.htm#Super3 you can also get Kubota engines under the Beta lable http://www.rhby.com/betaengines.html and from Nanni(SP?) amoung many others. These are high efficiency long life water cooled diesel engines.

Regards;
Mike Schooley

[8knots]

Yep, I blew it on the fuel consumption of 28gph. But im glad you agree with the lower SL HP requirements. Gives me a little faith that I am learning.
here is the link for the Luggers
http://www.lugger.com/northern-lights/PDF/L6140AL2.pdf
She would be a head turner at speed I think, So long as you were in flat water.
Thanks for your time mathing her out!
8knots

[Portager]

Fast Fred;

I forgot to mention I could not use the calculator at http://www.users.globalnet.co.uk/~fsinc/yachts/spreads/fred.htm . Perhaps I have stale Java?

Anyway, I thought we were discussing monohulls. The hull resistance calculator is based on the equations and formulae in chapter 3 of "21st Century Multihulls" by Joseph Norwood Jr. I question it applicability to monohulls and I do not know if its predictions have been validated in practice. Just out of curiosity, when you double the displacement (not just the weight) how much does the power requirement increase?

Regards;
Mike Schooley

[Dr.khani]

i want some articles about this title.

[fcfc]

Look at http://www.setsail.com/dashew/do_PARADIGM.html

This is an interesting technical thread, but I fear you forget the economic/psychologic side.

There was an article by Tom Fexas, designer of the "midnight lace" series, narrow and light boats. He was explaining why the new series are heavier and wider and yes less efficient.

Look at GB classical series. They now have 2*400 up to 2*800 hp for semi disp hull because the owner of a 1 M$ boat want some speed and does not give a **** to the fuel bill, be it 1000 or 5000 $. And putting 2*115 hp as the initial design have no meaning, because you will reduce the cost only from 1M$ to 900K $, but you will cut the speed more than half.
You are at price level where this is unacceptable.
And with a heavy use of a leisure craft at 300 hours / year, in both cases, the fuel bill will be insignificant for the owner. (marina fees, insurance, electronic maintenace etc ...)

Even on nordhavn site, they explained why they switched from canoe transom for the first series (46 -62) to wide transom for all the newer. They simply said that the owner of such a boat does not care if the boat burn 1.5 or 2 gph, provided he has enough range with bigger tanks, and more importantly, sligthly higher cruise speed and more interior space.

[FAST FRED]

"Anyway, I thought we were discussing monohulls. The hull resistance calculator is based on the equations and formulae in chapter 3 of "21st Century Multihulls" by Joseph Norwood Jr. "


Thje AYRS (site owner for the computer) is mostly a speed under sail group.
They hope eventually to hit 50 K under sail , with 80K as untimate goal.(46K now)

Their work is either for the main hull of a Tri or twin hulls of a Cat.

The minimum drag form of the hull from them would seem ideal for a single hull cruiser.

Stability could come from Form alone , Tri configuration ,Flopper Stoppers or powered gyro from Mitsubishi.

A semi circular hull form would be really rolly , but should have a better softer motion than a chined boat.
The numbers generated seem good enough for comparing LB ratios and weight changes on the same hull.And assesing the ability of a hull to get 5 to 10 mpg at speed.

We head south in a week , I will attempt to post the Numbers for different weight sets previously generated ,after the US election.

FAST FRED

[SAQuestor]

Look at http://www.setsail.com/dashew/do_PARADIGM.html

This is an interesting technical thread, but I fear you forget the economic/psychologic side.

There was an article by Tom Fexas, designer of the "midnight lace" series, narrow and light boats. He was explaining why the new series are heavier and wider and yes less efficient.

Ok. But you're referring to folks that have made a zillion bucks someplace/how and don't care a whit what their total costs are - at least as long as they can afford the total bill. I fear that those sorts of folks - except for the Dashew's and others of similar thought - care more about looks and 'how many she sleep' sorts of concerns than being efficient. And there is enough anecdotal evidence (and perhaps some surveys or studies?) that support the idea that the guy wants the boat to show off his "manliness" and his mate wants a floating apartment.

I started this thread because I'm not one of those zillion buck guys and I want a boat that can be safe and efficient while providing more than a modicum of comfort and still be affordable, both to build and run on slightly more than a Social Security budget.

Look at GB classical series. They now have 2*400 up to 2*800 hp for semi disp hull because the owner of a 1 M$ boat want some speed and does not give a **** to the fuel bill, be it 1000 or 5000 $. And putting 2*115 hp as the initial design have no meaning, because you will reduce the cost only from 1M$ to 900K $, but you will cut the speed more than half.
You are at price level where this is unacceptable.

Agree completely. But again you are speaking of $1 million boats. Not something that 'average Joe's' can afford to purchase or run.

And with a heavy use of a leisure craft at 300 hours / year, in both cases, the fuel bill will be insignificant for the owner. (marina fees, insurance, electronic maintenace etc ...)
(snip) They simply said that the owner of such a boat does not care if the boat burn 1.5 or 2 gph, provided he has enough range with bigger tanks, and more importantly, sligthly higher cruise speed and more interior space.

Again, I agree completely. But that sort of boat purchaser isn't going to be here reading about what criteria makes a boat efficient. That person is going to go buy a boat that compensates for any masculine lack and he's going to look real good with that drink in hand having his dock tied to the boat.

It's my opinion that this discussion is not about how much space one can get in a mega-horsepower semi-planning boat where the owner doesn't have a need to consider efficiency.

Rather this discussion started out - and still should be focused - on how to achieve reasonable safety and comfort in an efficient hull package. And though those of us that have participated in this discussion may disagree on the particulars, I think we all agree that a long - skinny boat is way more efficient (in terms of movement and usage of dwindling resources) than the plastic fantastic million dollar dock warmers that are the current rage for those folks that don't care about design, but rather buy and have a boat to show off their wealth.

Your opinion may of course vary.

Best,

Leo

[fcfc]

I just simply was saying that recipe for fuel efficient boats are know for decades, if not centuries.
And such boats does not exists, it is that fuel efficiency is not on top priority for boats owners.

Look at http://www.andrewsyacht.com/andrws52.htm Remove the ballast and rig and you will get a 52 ft 8000 lbs boat fully equiped with curent engine. Strong enough to cross ocean (and to resist to ballast rigthing moment). You can even narrow it a bit. say 11/12 ft beam.

Remove the auxiliry prop system. Put a new aluminum euro diesel 3 cyl 70-80 cid, with 24000 psi electronic injection pump and 28 psi turbo. This will give you about 50 -60 hp sipping a misery. Drive a 40" prop with a 5:1 or 6:1 redrive.

And you will get at end a very fuel efficient boat with today technology. (All is available for at least 5 years). Nothing fancy.

But there is not a single boat like this on earth.
There must be some strong reasons. That s all what I wanted to show you.

[SAQuestor]

I just simply was saying that recipe for fuel efficient boats are know for decades, if not centuries.
And such boats does not exists, it is that fuel efficiency is not on top priority for boats owners.

Let's be real clear - RICH boat owners don't (may not) care if it is a priority or not. The folks that I chat with constantly talk about and bemoan the cost of fuel, especially at marinas.

Long - skinny efficient boats don't current exist because we are just at the end of an era where exploiting the oil riches of the earth made energy extremely inexpensive. There hasn't been any demand because energy has been very cheap. These next few years may show us to be at the beginning of a major paradigm shift. Since we don't have crystal balls to tell the future, we'll see in 10, 15 or 20 years. Maybe by then boats will truly be the exclusive playtoys of the ultra-rich.

Look at http://www.andrewsyacht.com/andrws52.htm Remove the ballast and rig and you will get a 52 ft 8000 lbs boat fully equiped with curent engine. Strong enough to cross ocean (and to resist to ballast rigthing moment). You can even narrow it a bit. say 11/12 ft beam.

Remove the auxiliry prop system. Put a new aluminum euro diesel 3 cyl 70-80 cid, with 24000 psi electronic injection pump and 28 psi turbo. This will give you about 50 -60 hp sipping a misery. Drive a 40" prop with a 5:1 or 6:1 redrive.

And you will get at end a very fuel efficient boat with today technology. (All is available for at least 5 years). Nothing fancy.

And why on earth would anyone want a power boat (a converted racing sail boat no less) with a 10.5 ft (3.2m) draft? They'd have to be daft!

But there is not a single boat like this on earth.

Thanks be to your diety of choice!

There must be some strong reasons. That s all what I wanted to show you.

And all this thread is about is thinking outside the current short and fat, dock tied to the boat, drinkmobile that you see in every marina all over the world. There are indeed many strong reasons. Several of which I enumerated in my previous post.

But let's be realistic here. The price of crude is over $54/bbl. Do you really think that the price will go down anytime in the next decade - and I don't mean downward fluxuations of up to $10/bbl?

Not likely, IMO. So if I or anyone that IS NOT a millionaire wants to have a efficient power boat that means that we need to think outside the box.

Portager has a great concept in being able to transport his boat from sea to shining sea and get the best of the various cruising grounds.

So what if 99% of the boats aren't like this? The time for a long - skinny fuel efficient boat may soon be upon us, especially if it's one that doesn't have to sit in a marina sucking up $10-$15 per foot per month. If that long - skinny boat can be cruised efficiently and then trailered off to the next cruising grounds or even just hauled onto the hard until the next cruise, there very well may be a market that develops for a commercially produced boat. A long- skinny efficient boat that has the required systems to avoid marinas and be able to anchor out 95% of the time and safely go from 1) the Baltic to Med via the canals or 2)from the NE to Florida and the Bahamas via the intercoastal or 3) from the Puget Sound to Alaska and then on a trailer to Baja may well fit into the retirement plans of lots of folks that can't afford to have that 600hp diesel sucking masculinity compensating $1 million dollar yacht.

That's all I wanted to show you.

[Tad]

fc,

You are correct, fuel consumption is not a factor to the average Joe buying a boat, he will probably only run at cruising speed for 15-20 hours per year. While lots of folks think they want to cross an ocean in their "PassageMaker", very, very few people do so. Yes, I know some will do it if gathered together and run across under close supervision. That was the lesson PAE learned, they have also learned that people who do live aboard (which is their customer base) want to carry every toy imaginable. Thus bigger butts.

But yacht designers can learn lessons about what could be from what is. Right now the buying public are being offered various versions of fuel hogs. This cannot last. So where do we go from here?

Your comments about a converted TP52 are great, but I think you forgot a couple of things. I don't know what the fuel capacity of a TP might be, perhaps 20 gallons? Certainly not enough to get very far. Taking a TP across an ocean is busy and hard work, no time to get bored. But a powered version would offer none of that sailing distraction, so the power voyager carries along a bunch of diversions. Books, movies, toys to play with, a decent dinghy. These all drive the weight up.

I think powered versions of high-performance sailing types have been around for a long time. LF Herreshoff's Marco Polo was designed around the end of WWII. She is 55' by 10', she has a short sailing rig and weighs about 42,000 pounds ready for sea, with 15,000 pound in ballast. She was designed to travel at 10 knots around the clock, at the time an unheard of level of performance while ocean cruising. She carried 1000 gallons of fuel and her behavior in a sea is, in the words of Phil Bolger, "Like that of a hooked Swordfish".

The next long skinny powerboat I would draw your attention to is Jim Hawkins. She was designed and built in 1969 by two racing sailors, Avard Fuller and Bob Derecktor. She is aluminum, 61' by 13', weighing about 47,000 pounds and twin 64 HP engines would drive her at 9.5 knots. Her range at 210 miles per day, burning 100 gallons of fuel per day, is 1500 miles.

Why didn't these types become popular? First off because they were never built and offered to the public at a reasonable price. By all acounts there is considerable interest in Phil Bolgers Tennessee design. She is a long skinny flat bottomed plywood skiff, well suited to flat water cruising. Length is 30' and beam 6'2". With a 15 HP outboard she will cruise at 10 MPH. The problem for the marketing people is that there is no room for windfall profit in building such a cheap looking boat.

I do think that the next 10 years will see a real market develop for boats that use less everything, and are of reasonable cost. It will take some vision to get there.

All the best, Tad

[8knots]

My Opinion on the long skinny is this! You have two real groups of buyers
1) The guy who is loaded and can afford to feed 3412 cats and go fast
2) the majority of us who have a good job and can afford a moderate sized production boat and afford reasonable sized fuel bills for the 6 weekends a season we use it.
most folk in group 2 only have one boat and probably work up to and top out at 40 or so feet. He has 2 kids and a wife. he more than likely has the 9-5 job so he has the week end to get his boating in. to him differance between a $40 dollar or $200 fuel bill is of little consequence.
You would have a hard time trying to sell "long skinny" to group 2. $160 bucks is not worth all the sacrifices you have to make to get a good family cruiser. We all know people want and buy the "condo on jon-boat" style. ads in any mag prove this.

Ina nutshell we are group 2.5 the weirdo's who know just enough about boat design to push for true performance and buck the cookie cutter production boat mold.
Gotta run Wifes working on kid number two... another 2.5 :p
enjoy your weekend 8

[fcfc]

20 years ago:
http://www.reducostall.com/HTML/pages/Elfbridge11_gif.htm
Atlantic crossing both way without refueling.

Nine years ago:
http://www.francisdesign.com/yachts/motor/uldb.htm

ULDB sail boat are know for years. Yet there is not a single production ULDB powerboat.

[FAST FRED]

I'm not sure that the box boats are built with no concern for fuel , there more concerned with overall cost.

AS the boats usually sit in a marina , where LOA is the $$$ detirminant , the choice of a box boat 3 or 4 stories high maximizes the cottages room and allows some privacy, at the lowest cost.
If the box takes 30GPh its of no concern with only a few hundred hours (if that ) per year.
Even the "trawlers" sold by folks that claim passagemaking ability , are usually top heavy and vastly overpowered for distance cruising.

So far , ONLY the "Long Skinney boat" seems to have the ability to do any distance , at a good speed 10K+.

This leaves us with the need for a custom designed (or early design , modified )to seaworthy scantlings and with 24/7 engineering for engine & equippment.

My experience camping in a Greyhound Bus conversion 35 X 8 is very posative , it is enough room for 2 , but crossing an ocean is far easier with 4 total.

3 hours on 6 off , skipper on call 24/7 , and filling in with the cooking and dishwashing has worked fine on a couple of sail trips to the Carribean for the winter in a 33ft sail boat.

I'm with Portager in the concept of a trailerably hull , but the cost of an extra long tow does not get as expensive as an oversized hight or extra wide haul.

I think a very fine & comfortable design could be 12ft beam and 65 ft long.

The Air draft would be limited to under 9ft for the Euro canals , and to get her down to 13.5 on the trailer.

Using the Computer on the AYRS site allows me to think that 5MPG should be possable at 12 to 15K .This I think is within the realm of a normal persons pocketbook.

With Aluminum construction , the use of a marinized truck engine & tranny (to obtain efficency at low RPM), I believe such a boat could be built (to work boat interior specs) for under 100K.

FAST FRED

[fcfc]

Can you give a weigth estimate (empty/loaded)for your 65*12 proposal ?

Thanks.

[fcfc]

BTW, the price range of the dashew Beowulf series, similar to the FPB 83 * 17 is 4M$. 40 times what you suggest for a 65*12 boat.

What can be had for 3 times your amount is LOA 41 * B 13 and 76 hp. See http://www.kastenmarine.com/coaster40.htm
(price http://www.irbs.com/lists/trawlerworld/0201/0844.html)

M. Kasten also tries light and slender boats : http://www.kastenmarine.com/moxie.htm

Regards.

[Tad]

There are at least two threads going here, an economy coastal/inland cruiser, and an economy ocean cruiser. The two should really be split as the original question concerned an economy coastal/inland cruiser.



FF,

An aluminum boat 65' by 12' might be about 37,000 pounds light ship. The raw aluminum might be about 11,000 pounds * $2.00. Nesting, cutting, shipping, and welding materials will be another $1 /pound minimum. So material cost for the shell will be 1/3 of your budget, paying nothing for labour perhaps you could do it.

A professionally built aluminum boat, 54' by 11', bare bones (mostly empty) with minimum birch ply interior, no paint, and 65 HP Kubota engine is currently & locally about $350k CAD.

A complete Kasten Coaster 40' in aluminum with no exterior paint, generator, stabilizers, bow thruster, or autopilot is currently $572k CAD. These are real numbers, not hopeful quotes.

fc,

At 31000 pounds the Kasten boat will just manage 8 knots with 65 HP. At 10 knots she will stand on her tail and you will see nothing but foredeck from the wheelhouse. It will also require twice the 65 HP.

Tad

[tspeer]

Steve Dashew has taken the sail-boat-hull-as-powerboat idea and developed it into his FPB: http://www.setsail.com/dashew/FPB_Milestone.html
http://www.setsail.com/dashew/images/intro_2.jpg

On a smaller scale, right next to my trimaran in the dry storage lot is a boat belonging to Seattle NA Paul Bieker. This is a powerboat conversion of an Ultimate 30 sailboat hull. At the stern you can still see where the hiking racks mounted. But he's added a cuddy cabin, cockpit seats, and raised the aft skin (I find it hard to call it a deck since it's not flat) to hold the fuel tanks, etc. It's a fast, efficient powerboat for Puget Sound. I'm sure he picked up the hull for a song, so it's a cheap solution, too.

He's told me it's the way he thinks powerboat design is going to go in the future - light and fuel efficient. I think he's right.

[fcfc]

The only problem of the FPB (other than the guessed 4M$ price) is that the concept is not really downsizeable.
If you divide all by 2, you get a 41 ft LOA, 9 Beam, 6.5 BWL and 12500 lbs displacement.
The closest I have found is this :
http://www.rangeboat.com/galerie-exterieur9.html
Nigel Irens design, 3.5 nautical per gallon at 12 kts.
Although a bit wider than pure scale (11 ft beam), the stability, loading capacity and space only allow this design to be a picnic / day boat.

Or this : http://www.motorboating.com/motorboat/seatrials/article/0,12696,553628,00.html
http://www.tofinou.com/gamme/index.php?bateau=AND12&chglg=en#
. A bit less efficient, (2 nmpg), but cruise 15 kts with twin engines.

Just for info, these slender boats are only at a slighly lower (15-30%) price range of a great harbour 37. http://www.mirage-mfg.com/html/body_gh37.html who can go about the same efficiency if you don't want to go beyond 6-7 knots. (range 1475 nm with 500 gals incl 10%reserve at 6.6 kts).
The living space is in another world.

[FAST FRED]

The concept of the hull/deck in aluminum at 1/3 the budget ($100,000US) cost would work just fine.

If commercial assembly brought it to 50% that would work very well.

Welding aluminum is a very straight foward process , with the correct gear.

So budget wise that would work just fine.
Here in CT with welders being released from Electric Boat , that come with their weight in certification , 2 @ $20.00 per hour EACH should make short work of a few thousand feet of welding.

I had estimated the all up weight at 25,000 lbs , about doubble the hull weight.

With fairly inexpensive interior construction (work boat not Yachty) the overall weight CAN be held down .This I would prefer to do, not contract.

The "need for speed " at least 12K+ ocean cruise cuts down on the required supplies and crew .
If you can transit in 10 days rather than 20 -25 , the ability of the weather guessers to allow a good weather window increases too.

The detirminant of suitability for offshore is the hull & deck integraty ,and suitable machinery instalation not mere internal volume.

As many circumnavigations have been made with 30ft sailboats , the volume and lifestyle from a 65X 12 (-8BWL)should be grand .AS would be the living conditions while at anchor.

FAST FRED

[fcfc]

65 LWL, 35000 lbs, 12 kts. That gives on my sheet nearly 100 hp.

3000 nautic at 12 kts = 250 hours.
100 hp for 250 hours = 1500 gals. No reserve and always good weather.

1500 gals = about 9000 lbs.

So the boat, empty @ 25 000 lbs, will start cruise @ 40 000 lbs, and arrive @ 30 000 lbs (some fuel, water, crew and gear still aboard).

That leave a 15 000 lbs variation for an empty weigh of 25 000 lbs.

Assuming a waterplane coeff of .7, waterplane is 65*8*.7 = 364 sqft.
That means 8 inches flotation variation.

LWL 65, Disp 35000. Cp assumed of .63 That means a immerged cross section (dont know the us:english term for that) of 13.3 sq ft.
BWL = 8 , S = 13.3. assume section coef of .7 that means 2 ft 4 in canoe draft.

Now, you want to reach some offshore stability criteria with a boat about 8 ft BWL, and hull depth between 2 ft empty 2ft 8 in fully loaded. How do you plan it ?

[Portager]

I agree with Tad, there are really two threads here. It might be less confusing for Fast Fred to start a new thread for a fast economical Passagemaker.

The Dashew FPB could be scaled down to a 12’ beam (66%) and 65’ length (78%) but I’m not sure they have the right hull form for this application. They are operating in the semi-displacement speed range (S/SQRT(L)=1.55) so I think they would benefit from a slightly broader stern, Fast Fred’s Fast Passagemaker (FP) will operate at 1.512 which is also best served by a semi-displacement hull IMHO.

I ran some numbers for the FP 65 assuming a light ship weight of 25 Klbs. At 12 knots she requires 71.22 HP and consumes 3.561 gph providing 3.37 NMi/gal. To make a passage of 2,200 NMi with a 12% fuel reserve (this is the longest passage required to circumnavigate) I figure she needs 900 gallons of fuel.

Adding the weight 900 gallons of diesel at 7.11 lbs/gal and 1,600 lbs for crew, gear and supplies. I get an optomistic fully loaded weight of 32,000 lbs. At her fully loaded weight she requires 94 HP and consumes 4.7 gph providing 2.55 NMi/gal.

Calculating fuel consumption and resultant weight on an hourly basis she achieves a range of 2,208 NMi in 184 hours (7.67 days) at 12 knots having consumed 784.44 gallons or 87.16% of her original 900 gallons.

I think this is a significant accomplishment. Portager has to slow to 7 knots to achieve this range so she requires 13 days and 528 gallons to make the same voyage. So am I going to stretch Portager to 65’? Probably not. First, at 65’ the FP 65 will be a pain to transport although the fuel efficiency and higher speed potential are hard to pass-up. This is a compromise that requires additional thought. At 32 Klb fully loaded she can not carry enough weight for the accommodations that the Admirable and I want. Fast Fred has a good point that shorter passages allow you to reduce supplies, but what about emergency supplies encase of a breakdown? Meals ready to eat? Also if we are going to live aboard Portager after retirement, the Admirable wants a dishwasher, washer & dryer, air conditioning, … and I want an air compressor for my SCUBA tanks, …

Regards;
Mike Schooley

[FAST FRED]

Having lived aboard for over 22 years , I'm delighted to use a sail bag , rather than washer , drier et all.
The power requirements are far far beyond the amount of gen set noise that would be needed on the hook.And to go voyaging quickly & cheaply , weight has to be a dirty word.

Air cond (rooftop RV 15,000btu ,14A @120V ,90lbs) off a DC genset with a trace 2440 Inverter would work fine , as would a microwave .

There is not a problem with sinking 8 or 10- inches into the water at full load , as the boat would STILL be quite light interms of DL ratio..

Only disadvantage would be the USCG stops boats (with extra wide waterline) as part of their Zero Tolerance policy , so the simple interior might get smashed to bits (at owners expense) on occasion.A very open plan would solve this.

When doing a work sheet of costs , after the hull ,opening ports or Mfd exterior doors are the next highest item.

Simple solution would be to select fine (for US$ ) inexpensive commercial vessel Canadian opening ports and cut the holes to fit.
BUT install lexan over the holes as fixed ports untill the $1000 for a fixture or two can be justified.

Many systems can be done for very little money, baseboard heat is cheap to install and operate from main eng or genset underway.

As in most boats the fridge freezer would be biggest long term power draw, fairly EZ with a large volume hull to find 6in for insulation arround the boxes and the fine Danfoss DC units can run from 2 solar panels fairly well. Not cheap stuff , but Salsa dip , chips and cold BEER is a Religion to some.

FAST FRED

[Portager]

I think the issue that fcfc is pointing out is that when you are riding 8" high it will be precariously unstable. This is why most long range passagemakers require ballast. i.e. to maintain stability as they expend fuel.

I think the problem can be solved by using saltwater ballast. Since you have plenty of internal volume, what if you provide salt water ballast tanks below the waterline with a weight capacity equal to your fuel capacity. As you consume fuel you place an equivalent mass of salt water in the ballast tanks, thus maintaining a constant waterline and stability. This allows you to maintain stability as you consume fuel without increasing your fully loaded weight as fixed ballast would require. In favorable conditions you may be able to off load some of the salt water ballast and reduce power requirements, but, since the tanks are below the waterline, you would always have the ability to take on weight as conditions require.

Regards;
Mike Schooley

[fcfc]

I fear that you need to assert stability boat minimum load and maximum load. On minimum load, tanks are empty and ballast are filled per operating manual. On maximul load, from what I have understood, all tanks that are fillable are filled up, including ballast tanks.

Another point, if you have 6000 lbs of fuel, 6000 lbs of water from a 25000 lbs boat, you already have filled more than half of the space under the waterline. (fuel density < 1). And you need to add also the engine, batteries, fresh water tank, grey tank, black tank etc ...

Also has FF checked price of prop and shaft ? He needs 100 hp continuous, so he will probably in the 150 -200 hp range. He wants high efficiency, so he will rather have a big prop (in the 40" ) turning slowly (< 500 rpm). That means at least 20 ft shaft, 2.5 - 3 in dia if he wants an engine about weigth centered

Going 12 kts has a high price.
Slowing to 10 kts, with same weight, same LWL only needs half the power. You will cross in 12 days instead of 10, but you wil use only 60% of the fuel.

BTW all theses figures need the same power for 12 kts
LWL disp
40 16 000
45 18 500
52 22 500
65 30 000
90 55 000
120 98 000

And my raw formulae for power uses disp and LWL as input, but not the beam.

[FAST FRED]

Most small boats do nor have balast tanks as ships do,

The fuel on many passagemakers is ONLY filled for offshore cruising , so with costal work much less weight is carried.
Todays practice does NOT put much fuel in bilge tanks , as the loss of stability empty/coastal cruising would be unsetteling.

Instead the fuel is usually carried in twin or more sets of P&S tanks which extend from low in the boat almost up to deck level.Perhaps 6 or 8 ft tall(Located near the CG) but narrow enough that free surface area will not effect the vessels stability.
If more than one set is required , the unused sets are left full till the first tanks are empty.Full the ultimate stability may be reduced slightly , but the weight makes for a slower roll.

"He wants high efficiency, so he will rather have a big prop (in the 40" ) turning slowly "

Although efficency is the name of the game , some sacrifices must be made for a normal draft , so a 30 inch prop would be more desirable than 40 inches.

A cruising boat MUST be able to "take the ground" as she certainly will on occasion.

With very lightweight diesel , my engine location preference would be in the first 15ft of lwl.An absolutly horrible place for people , but fine for the iron.

The shaft would be simple truck drive shafting with intermedate bearings. This can easily run 40 ft a very low cost , little noise or vibration. Trucks regularly run over 500HP thru the same shafts after tranny reduction so they would be very underloaded.

Of course a Thrust bearing would be required on the actual prop shaft , but the Variable pitch props (Hundstat)or simple surface drives (others have sugested) provide for this .

"And my raw formulae for power uses disp and LWL as input, but not the beam."

Using the AYRS drag tables (referenced)my numbers (which are for weight and do include beam) I figgure 2 1/2 gal to 3 gal per hour at 12 to 14K.

The reason for a long skinney boat (with all the needed compromises) is the low fuel requitements ,needed at what is still simple displacement speeds.

Most formulas are for 3 or 4-1 LB boats , when you get up to 8-1 or 10-1 , the wavemaking is very reduced.

FAST FRED

[fcfc]

It is know for a long time that the foreplace is not a comfortable one, so why very few builders put the engine there ?

And 2.5 / 3 gph means you will get about 50 to 60 hp. Going 12 - 14 kts in a boat with four people, their gears for 10 days, and 800 gallons of fuel with that power seems IMHO a bit optimistic.

[8knots]

My guess would me the long shaft lengths. This to me means a fairly complex set of pillow blocks and modifications to your transverse framing to allow removal/service of a multi piece shaft. Your cabin sole will need to be removable "as it should be" I imagine you will need a thrust bearing to carry the load (prop thrust) on the first length the rest can just "float" Ahhh just dawned on me........It would prove difficult to maintain watertight integrity between bulkheads. fuel vapor and exhaust runs will need to be considered also. I dont think it is a detriment...just costs more for a production builder thats why we dont see it more often. I think a added plus of a long shaft is the reduced shaft angle. I dont know how much...I think I read in Gerr's Propeller handbook that 0-15 degs not much efficiency is lost but logic tells me closer to 0 is better.
Just some thoughts....8Knots

[Portager]

Putting the engine in the forpeak has been tried and for MOST applications it has been discarded. The problem is a combination of the long shaft length and the detremental affect on the pitch moment of inertia.

Long shafts, especially shafts with joints have a tendency to become unstable in torsion. Think of the shaft as a rotary spring and the drag on the blades as a variable load which has a feedback loop to the engine. The weaker the spring force or the lower the tosional stiffness the lower the natural frequency of the dynamic system. Since an internal combustion engine provides varying torsional loads, when the natural frequency of the drive shaft is equal to the forcing frequency, the system becomes unstable and the results are not pretty. Thus your maximum engine speed determines the stuffness requirements for the drive shaft. If you add joints to the drive shaft then this effectively lowers the spring rate and reduces the natural frequency. As a mechanical engineer I believe the truck drive shaft with multiple U joints will only work at very low shaft speeds (i.e. hundreds of RPM as opposed to thousands of RPM).

The problem with putting the main engine in the forpeak has to do with the pitch moment of inertia. The moment of inertia about any axis is the sum of each unit of mass times its distance from the center of mass (AKA center of gravity) along the axis squared divided by the total mass. Putting large masses like the engine a long distance from the boats center of mass, i.e. the forpeak, increases the pitch moment of inertia and slows the vessels response to waves. Every vessel in heavy seas will need to slow down for the conditions, however one with a higher pitch moment of inertia will need to slow down more than one with a lower pitch moment of inertia. You could argue that since you are going to use a very small engine the impact on the moment of inertia would be minimal however since it is also a very long vessel and the distance to the center of mass is squared (30^2=900) this factor will overwhelm the reduction in engine mass. If your boat were only intended to operate in sheltered conditions or coastal cruising you could get away with putting the engine in the bow, but for a passage maker it is a bad idea IMHO.

Regards;
Mike Schooley

[Ross Adams,]

wow great info thanks

[announcer]

I don’t know why I involve myself in these threads, I was just searching for more options on cylinder molding for long hulls for better passage making with lower fuel costs. But hear is my point. William Garden when he designed Tlingit designed the boat around antique gasoline engine that was not very efficient. Later in life he told me that if a boat such a Tlingit were built to around one hundred feet with a twin vee drives setup (better for maneuvering in small dock areas) with fuel efficient engines the boat would be very fast with no wake and extremely miserly with fuel. Four people could go eight thousand miles on less than six hundred gallons of fuel even considering in bad weather in very comfortable conditions.

I also had a chance to speak with one of the grandsons of the original owner of Tlingit ( pronounced Klincket for the Eskimo tribe who built the kayaks that Garden used as a base design for Tlingit) and he said that he and his brother enjoyed their grandfathers boat very much and were very sad after his death that the boat was sold and moved to the east coast.

Had the design process evolved Garden would have shown how a long narrow boat cold have quikly covered long distances with les fuel and a better ride than the pigs that pose as yachts today in modern boating magazines. I have been trying to contact the man who now hs control over all of William Garden’s designs at a well known east coast boating institute. Making contact with this man unless your name is Vanderbilt or Rockefeller is impossible like most east coat institutes. Luckily Garden laid out in his books that the Tlingit design was just formed upon the mount of 2X4 lumber and plywood sheets his friend he was designing the boat for what had available. Although the boat was built at a boatyard that is now a waterfront park. The once great yacht yards are now just condo’s and bicycle paths and finding space to rent to build a boat would cost more than the material used to make the boat.

Had this been in Portsmouth or Barr Harbor it would have been declared a national treasure. But we must realize that the east coast is the only place where real ships were built. Just ask any snotty so and so that runs one of their maritime museums. Gloucester, Swampscott, New Bedford and Bristol to them are the only places that good boats and their plans should remain. Even if the author of those plans was from the pacific northwest. Sorry about the rant but I cannot see the point in Mr. Garden’s plans residing in an east coast institute that makes common folk like myself jump through fiery hoops to buy a set of his plans.

One good thing is that Bill Garden left us the formula by telling us that Tlingit was built from 2”X4”’s and plywood. Even if a boat similar we built cold molded and then Laminated all the large dead wood its back would be strong and the waves be Damned. She would carry enough in tankage and room for four people to live in a comfortable manner and be able to cross an ocean. Even George Buehler has a very light version of a boat like this called the Pilgrim but it is only a few feet longer than forty. His version is for a young man filled with wander lust and very little cash. George calls him a Hamburger Flipper but the money saved pushing a light hull over a long distance could make a small grub steak go a long way.

How I wish I was twenty one again and know what I know now. But a longboat I would have with a narrow beam and a few sails along with my motor to make my fuel last even longer.

[Richard Petersen]

Yacht designers do not get upset or respond! All ships that can not say "screw it" to the marine insurance companies, have have pretty much picked on hulls of super tankers, air craft carriers, converted WW I & WW II ocean liners. Commerical owners do not believe, short, wide and tall, is the most value or safety for their non-living cargos. The fact is all wealthy yachtsmen have their boats CARRIED across the ocean on large freighters to Cannes, then step aboard .

[SailDesign]

Announcer, which "well known East Coast institute are you referring to?

[announcer]

Dear Sail Design,

Unfortunately I must inform you that the well known East Coast institute that keeps Bill Garden's special plans under lock and key is Mystic Seaport. The Man who is in charge of said plans also works for Wooden Boat Magazine and his name is Maynard Bray and he is the gate keeper of the plans. The Man is very illusive and has proved very hard to contact since I have been unable so far to make contact. All I want is a set of plans to Tlingit or a boat of similar design. I have a large lake I live on now called upper Klamath Lake.

I would like a long narrow boat to test the abilities of the design since the lake has frequent high winds and is over thirty nine miles long witch corresponds to the town of Klamath falls at the lower end and at the upper end my home at Modoc Point. During times of the year the narrow road along the lake has frequent land slides so the main route into town is blocked and an alternative form of transportation with low cost fuel consumption would be a pleasant alternative to hours of waiting for the road to open.

My column in a few boatbuilding magazines has gained immensely from my home being so close to such a perfect water supply here in Oregon. A Tlingit design or the one Garden talked about with twin vee drives with up to date power plants and one hundred feet long would be super testing ground until it could be moved too the Ocean and run to Mexico a few times.

So if anyone has any influence with Mystic Seaport or Maynard Bray of Wooden Boat Magazine who works also at Mystic Seaport please let him know that a writer, columnist and disabled boat builder would like the chance to build one of Gardens best designs. I could wing it and either make a boat only its mother could love and it’s an orphan or really make an inspired boat using all the many drawings I have and the building experience I have to make a very rough duplicate of an inspired design.

I don’t really have that much faith in myself to build a Garden Design without plans. If Bill were not so old and in need of his privacy in the golden years of his life I would travel to his Island in the San Juan’s and try to get his help. I respect the man and his genius to much to intrude upon him. Lets see what help I can get by this forum in contacting Maynard Bray. I have been on the phone to Mystic Seaport more times than my wife’s telephone bill hiding from her can be worth. That is why I have such a negative attitude about these institutions that control the wealth of designs and always ask for more money but don’t provide the stored knowledge and resources that boat lovers want and need. That is where the disparity comes in.

In my opinion west coast museums and historic societies have a much more useful and helpful way of dealing with the public. I was born on the East Coast and moved to Oregon where in my town everyone says hello or thank you for opening door. Try to find that in New York or Boston. Well I was harsh and I take back my complaints about Mystic Seaport and Maynard Bray. They probably have a work load that would bury me in seconds. We really do need more access to Bill Garden plans and if there is something I could do to help please use me.

John Cupp

[FAST FRED]

A really light boat will have a very variable displacement , but this should NOT be a problem if the tanks are built for the boat.

Instead of Diesel tanks filling the bilge (where empty./full will vary the stability ) its simple to build the tanks vertically , somewhere near the CG.
AS the tank empties the stability Increases a bit , so light boat is not a hassle.

Small diameter and 6 or 7 ft deep will have little free surface area , and 4 tanks could be managed so there either chock full or empty , with only a gravity feed day tank to slosh a bit.

Remember Dorys can carry & handle loads of huge proportions with little loss in performance.

Todays engines are so small and light , the proposed Deutz oil cooled engine is 170hp at about 1100lbs, not much for the bulbous bow to hold up.

Drive shafts are Off The Shelf from any box truck and are cheap and easy to maintain. at the Price of needing a thrust bearing at the stern, no biggie.

With low enough weight and a tranny that can load the engine well at lower speeds , I think 4 NM per gallon or even 5mpg should be doable.

The only variable seems to be how fast one can go at that speed.

AS a long time sailor , we have no need for the complexities of washer driers , bread ovens , and any of the "needs" of the modern water campers.

Think of a simple interior that would have worked well in 1930 , (but with central heat) and you get the idea , painted ply , wood trim.

Comments?

FAST FRED

[Richard Petersen]

I am a member of the Antique Boat Museum in Clayton, N Y and our volunteers love to help any walkin to the library. What kind of goofball management does Mystic have to allow that. Have you notified the Director or the Chief Curator?----------If that fails. There are hundreds of other museums.

[FAST FRED]

Would the table of offsets be enough , or do you need the entire plan set?

FAST FRED

[announcer]

Fast Fred,


I do have a table of offsets that were in one of Garden's design books. What transpired since that was printed is when the owner of the boat died Garden bought back the boat and added in new design features like a get home sail plan and a new keel that made the bow not slap the flat bottom anymore. According to someone close to Garden he also made offsets for an 80’ and 100’ boat in the same paperwork.. This might be pure speculation except it came from close source to Garden and with Garden’s attention to detail there could very well be a new set for both new sizes.

Since he did remodel the boat after buying it from the estate I think this is the only way to see the way he wanted the boat to look after and for all new copies that people would be compelled to build. He was quoted in his book as saying with the vee drives and longer hull with sleeping quarters added it would be the closest thing to the sound of sailing in a motor boat anyone could get With a new turbo small diesel combined with vee drives and very wet exhaust sitting behind the pilot station forty feet you could sneek around anywhere. I think it would be a great canal cruiser in Europe and also be able to make the coastal hops to the next set of canales much better than the long boats of Europe that sit so high.

With an even longer water line the hull speed would be very high and probably could be pushed there by a small diesel just barley above idle to give it some turbo boost and good oil pressure but most of all very miserly fuel use. With enough tankage and a clear hole in the weather it could give people on fixed incomes the ability to cross an ocean without renting space on a freighter and the ensuing insurance costs with the terrible fees for boats over forty feet..

An amusing side note to this is, I was the manager of an Algae harvest company and I built a 110 foot Algae harvest boat. Since both owners of the company were felons ( yes I did not work there long after watching the drug use) I registered the boat in my name and myself as the builder, a very true statement since none of them had ever built any boats at all.. Very soon I had motor yacht magazines subscriptions coming in almost every day and tickets to a big yacht show on the French Riviera where they wanted me to take my creations and show them to the beautiful people of the world. I guess registering a boat over one hundred feet puts you in some kind of club I knew nothing about.

How I wish I could have taken my twin hulled Algae harvester over there complete with a crew streamline travel trailer for sleeping bolted ten feet off the deck and the 12-71 gen set roaring at full throttle with the forty by thirty Algae screen sitting out over the bows. What an entrance, they would have had to get the French navy to sink it before it bumped any of the precious French floating cream puffs could be damaged..

To bad all the big boats I have built so far where for fishing and work. BTW I did also design the algae harvester. It is still working out on Klamath lake and selling pond scum to people that don’t have enough sense not to pay $600.00 an once to eat the stuff.

[Skippy]

To the Riviera, that's hilarious..... Please post pix if you're ever able to. :)

[FAST FRED]

OEM status is precious if you are planning on building another boat.


Discounts from list of 50%+10% are NOT to be sneezed at!

Wish engine mfg were as generous as hardware hawkers .

FAST FRED

[Packeteer]

good to see that somebody has already mentioned the Dashew boat

nice boat and very efficient!

[safewalrus]

Welllllll, I've waded through all the stuff in this thread for some reason I can't figure - the question was I believe about the viability of a l-o-n-g slim motor boat! As the man at the start said 'depends what you want it for?'

From experience - back in the 60's we (the lot I was with at the time) had occasion to come across several vessels of that type - long slim canoes with ginormous great outboards on the back, used I believe for smuggling cigarettes (light payload!) around the Malay and Indonesian islands. When we first saw them we chased 'em they just opened up the throttle and were gone like **** of a shovel - the only thing we could catch 'em with was that stuff which comes out of the front of a gun! and with the speed aiming was pretty awkward! So yeah they do work! (we wern't really interested in that particular commodity at the time so didn't push it to much).

Interesting to note that certain UK Special Forces now have a couple of the same style of vessels (only more sophisticated build) which have the same style of movement - bloody fast in calm water - depends what you want it for?!? As a yacht? to get you there and back in time for tea, OK but for comfort? Try a hotel - or sleeping bag in the bilge?

well that's my pennyworth! of use?

[yacht371]

I'm a late comer to this thread, but I have read through all of the posts. I think that we could come up with the true cost of yacht ownership in a formula. Don't ever tell your spouse!

Recently I bought a new car. I didn't lease but I did evaluate lease rates. Interestingly, the best lease rate offered was on a BMW 3 series, cheaper than on several other makes that cost less to buy. Why? Extraordinarily high resale value!

A major part of boat ownership costs is what you can sell it for when you are done. I know from bitter experience that even the finest custom yacht drops about half its value on launch day. Home builts are even worse. Popular production boats with inboard diesel power depreciate the least.

So the true cost of the boat equals:
((B-S)+F+M+P)/y

Where:
B is the cost of buying or building the boat including taxes (don't forget to value your time properly if you build her)
S is the net selling price after brokerage etc.
F is the money spent on fuel during the time of ownership
M is maintenance costs during that time
P is port charges, moorage, shore power and other such charges
y is the number of years owned if you would like to put costs on anannual basis

Now plug in some real numbers. I happen to have owned a lot of boats and I have those figures handy, but I'm reluctant to publish them in case my wife reads this...:D

These are based on real world numbers, the first a benehuntalina 35 and the second a custom built wood/epoxy boat of the same general size. This was done much earlier so the actual dollars look similar in purchase, but in reality bought at the same time the custom boat would cost about double. I used sailboats because that is what I have numbers for.

Benehuntalina 35
((152000-122000)+600+12000+15000))/3=19200 P.A.

Custom Wood/epoxy 35
((120000-39000)+950+36000+18000)/6=22658 P.A.

The better resale value of the production boat, and possibly lower maintenance more than makes up for the longer ownership time of the custom boat. All figures rounded for clarity, but it makes very little difference.

I make a good bit of my living designing custom boats but I always tell the clients what they are getting into. If they are rich enough, or plan to keep the boat so long depreciation is not a factor, they may still go ahead. Many say "thanks for the info" and go buy a production boat.

You will note that changing fuel prices would have little influence on the above equations. With a power boat the fuel numbers will be bigger, but depreciation will still be the major factor.

That said, a well made fuel efficient production power boat will have low depreciation. Price out used Nordhavns...might as well buy a new one!

For a fuel efficient production boat see the MC27 at www.aviadesign.com
This has twin hulls of B/L ratio 14:1 and overall beam of 8'-6" so trailerable. It isn't designed as an ocean voyager but as an economical coastal cruiser but we are in the planning stages of a trans-atlantic voyage in a diesel version.

[flipper08]

When we discuss the design of long and slim hulls it might be worthy to consider a couple of very important considerations. First; weight always plays a big part in the overall picture because weight equals displacement, and more displacement always costs something; speed or fuel. Within the hull of any boat, space is always a major consideration but there can always be a balance between space and structural strength. "Space frames" have not been widely used in boats but they should be considered because of the tremendous advantages in terms of their weight to strength ratio.

[FAST FRED]

""Space frames" have not been widely used in boats but they should be considered because of the tremendous advantages in terms of their weight to strength ratio.'

With modern cored construction a very strong hull can easily be done almost as a tea cup, no framing at all inside.

For speed a looong hull and a D/L of under 100 seems to be the best answer.

How cheaply the vessel can be constructed very light is a different consideration.

FF

[moTthediesel]

Very glad to see this thread revived, it's one of my all time favorites!

Interesting to see what changes have come about since it was started. Four years ago we were fretting about oil prices of $54/bl. Who would have guessed then that it would double in that time? Makes you wonder what things will be like in 2012 doesn't it :?:

moT

[Tad]

My latest "long and skinny" is 39' by 7'. Construction is plywood. Weight is less than 5000 pounds, power is a 50 or 60 Hp outboard in a well. D/L is about 52 thus she will eaily run up to S/L of 2.4, a little less than 15 knots. At 12 knots her S/L is 2, reqired power is 22HP and around 1.8 gph for 6.5 mpg.

Of course the accomodation is that of a boat 10-15' shorter, but the speed and motion in a sea will be far superior to shorter boats.

The form is based on Garden's Tlingit, I call it a Motor Canoe.

20172

20173

20175

[Chris Ostlind]

I really like that boat, Tad.

My take on this genre is a bit different.

Four person utility transport with style.
30' LOA
3' BWL
2800 lbs. displacement
Beam in passenger compartment 4.5'

Folding amas for dry storage and trailering.

30 hp four stroke gives 16.5 knots with a 12 knot cruise at half throttle. It coulda been optimally skinnier, but I wanted the trailer length to be something manageable on a regular basis.

[charmc]

Chris,

I like the concept, but 3' BWL doesn't seem enough for side by side seating, unless there is a lot of flare that I didn't see. I'm neither a giant nor a body builder, but my shoulder width is a good bit more than 18". I think 4' would be a minimum for comfortable seating.

The look is neat, very original for a power launch.

[charmc]

Very nice, Tad. That bow is a work of art.

[Chris Ostlind]

Chris,

I like the concept, but 3' BWL doesn't seem enough for side by side seating, unless there is a lot of flare that I didn't see. I'm neither a giant nor a body builder, but my shoulder width is a good bit more than 18". I think 4' would be a minimum for comfortable seating.

The look is neat, very original for a power launch.


Thanks for the comments.

The overall beam of the vaka hull is 4.5', allowing for plenty of room for a side by side seating arrangement. There is a nice spray chine detail running from the bow to transom, that kick starts the small bit of flare in the upper hull panel. All this gives the boat a very slender hull in the water while still presenting a comfortable seating setup in the passenger compartment.

The fairly high Cp amas remain very slender, yet have sufficient buoyancy for the times when they will contact the water. During the design process, it came up that this design, while principally created for short hop coastal cruising, would also make for a very interesting harbor launch. Something along the lines of a classic car being used for double dates for dinner.

All we need now are 50's style diners at water's edge with carhops cruising out with the cheeseburgers and cherry cokes.

[charmc]

Thanks for the comments.

The overall beam of the vaka hull is 4.5', allowing for plenty of room for a side by side seating arrangement. There is a nice spray chine detail running from the bow to transom, that kick starts the small bit of flare in the upper hull panel. All this gives the boat a very slender hull in the water while still presenting a comfortable seating setup in the passenger compartment.

The fairly high Cp amas remain very slender, yet have sufficient buoyancy for the times when they will contact the water. During the design process, it came up that this design, while principally created for short hop coastal cruising, would also make for a very interesting harbor launch. Something along the lines of a classic car being used for double dates for dinner.

All we need now are 50's style diners at water's edge with carhops cruising out with the cheeseburgers and cherry cokes.

OK, the bow on view you added to #88 illustrates that nicely. She just might fit in with grilled salmon and a dry Chardonnay, too. :)

[big-boss]

Tad, that is beautiful. Will it be plans you have for sale? Company going to produce them? Very nice. Any more info would be appriciated.

[paulewill]

long and skinny with a flat flat bottom.

does it have trouble turning?

[dobsong]

[QUOTE=Tad;195795]My latest "long and skinny" is 39' by 7'. Construction is plywood. Weight is less than 5000 pounds, power is a 50 or 60 Hp outboard in a well. D/L is about 52 thus she will eaily run up to S/L of 2.4, a little less than 15 knots. At 12 knots her S/L is 2, reqired power is 22HP and around 1.8 gph for 6.5 mpg.

Of course the accomodation is that of a boat 10-15' shorter, but the speed and motion in a sea will be far superior to shorter boats.

The form is based on Garden's Tlingit, I call it a Motor Canoe.

Hi Tad just wondering if this design got built or perhaps it has evolved?

I'm searching for a design around 40', hopefully an inboard that can cruise at 14-15 knots and has a range of more than 600 nm. I usually go out alone and sometimes with one or two friends so don't need a lot of berths etc. love the look of the downeast lobster boats especially the long lean ones with a nice simple pilot house....

Currently I have a 24'x9'x2'6" clinker Halverson built in 1961 in Sydney. Love it but it lacks range and the 318 Chrylser loves a drink. so looking to upgrade for my retirement.

Love to hear whats happened with the Motor Canoe..... any other suggested designs 9or designers or builders) welcomed

[Guest625101138]

I have been working on a retirement project for a solar boat. Something suitable for coastal hops. I started out with the idea of a long slender hull but it had certain limitations.

I have been working on a concept (provided by a forum member), which I have called a faux-tri. It is really a stabilised monohull. It behaves like a slender monohull from powering perspective, has the initial stability of a narrow trimaran, is self-righting and has the cabin of a decent size monohull.

I have done the hull shape to check power requirements and have a rough rendering of the proposed design per attached.

If I ever build it, it will be built very light with modern materials, probably carbon fibre on Corecell, in flatpack construction. With the target displacement of 500kg it will do 8kts with 900W in calm conditions. The electric motor I have is rated at 4.5kW on 48V and this should get it to 14kts in calm conditions.

I am really pushing the limits of efficiency to get the best from solar power but the concept could be applied to a conventionally powered vessel that would give good speed at very good economy.

I am in the process of building a 1/5th scale model to see if it has any vices in a seaway that are not obvious.

There are similar boats around so the idea is not new but it looks very good.

Rick W

[Boston]

so whats the magic formula to calculate long skinny hull speed
Im not after 1.34x the square root of lwl
that one is kinda broad for what Im interested in
Im after hull drag mostly and what it takes to get something up to a certain speed

http://img.nauticexpo.com/images_ne/photo-g/power-trimaran-motor-yacht-197569.jpg

this things got three long skinny hulls rather than one fat one
should go a lot faster but
whats the math to figure that out from
one of you folks is bound to have it right off the top of your head
or at least know where to find it

something tells me its more a mater of surface friction in a long skinny hull than wave resistance
so there must be an average coefficient of friction for say marine paint
resistance goes up as a square of speed if I remember
seems like it would have been mentioned in the thread somewhere but I didnt see it
thanks folks
B

never mind
I just found a hull resistance calculator
interesting thread though
was a good read
cheers

[Ad Hoc]

"...so whats the magic formula to calculate long skinny hull speed..."

There isn't one.

You'll get empirical data from 'similar' boats and their hp/ton giving certain S/L ratios..but that's it.

Just do like the rest of us, tank test to get proper results...otherwise, use lots of fudge factors from your 'basic' calculator!

[Guest625101138]

so whats the magic formula to calculate long skinny hull speed
............
something tells me its more a mater of surface friction in a long skinny hull than wave resistance
...

Boston
Your gut feel is correct. The wave drag for the lowest drag hull for any given speed will be around 5% of the total drag if you do not have a length constraint.

The best examples are rowing sculls. Have a look at the wake they leave.

There is a friction formula based on empirical measurement termed the ITTC friction line. You will need to determine the Reynolds number to apply it.

Sadly Michlet is no longer freely available but it will give you drag within 2% of actual in calm water conditions. If you want the underwater shape for the lowest drag hull for your particular parameters then I can do it for you.

The faux-tri concept looks good to me. I have not been able to arrive at anything with lower drag with adequate stability.

I keep evolving the idea. My latest variation requires 750W to do 8kts. Should get to 15kts with the 4.5kW motor I have.

Rick W

[Boston]

750 watts is like one horse power
you could have the kids swim behind and push if you wanted
that pretty bloody incredible Rick

I been copying stuff like a mad man into a file called boat building tips and I got a whole section on calculating the Reynolds number
its slow going but Ill get a decent design outline eventually

I looked for MIchlet a while ago when I saw it mentioned in several places
was a futile endeavor
drove me nuts
thanks for the tip but I could have used it about three months ago :-)

Ive always kinda liked that thing Rick ( Faux Tri )
I think you may have a salable item there if you smooth it out some and it looks like your aiming in that direction

I found this groovy hull resistance calculator
http://www.google.com/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fuk.geocities.com%2Ffnsnclr%40btinternet.com%2Fyachts%2Fspreads%2Ffred.htm&ei=vkIvSvawKJy6tgO1rbzbCA&rct=j&q=hull+resistance+calculator+&usg=AFQjCNFtbYdRzR9iZsjrFpF4lDnxsce0yg&sig2=-ya2ruFoHI9vBRMp1D68eg
you guys probably all have it but I thought Ild throw it up just so you could see which one I found

its kinda odd but it does tell me the hull resistance in lbs pr knot
so its a good comparison tool for different weights and beams on my 60' project

I like wood
and Im loving steam
Im limiting power to 250 hp max 80 hp cruise
I want some of those Vawt generators for my passive power regeneration
( you can keep solar cells a simple cost analysis places VAWT generators way out ahead of the curve )
now I want a decent hull form
Ill worry about getting the look back once I establish the form

so whats better
box keel type or trimeran in the say 15 knot range or whatever I can get out of 80 hp and 1000 rpm

and whats that formula
ITTC friction line

Add man
Ill definitely be tank testing something eventually I just want to math out as much as possible
my skills are rusty but they're coming back little by little
been building to long I guess
and all the engineering that goes into a house is canned
no there was little opportunity to practice
this naval engineering is a bit overwhelming ( has this nasty intuition component to it that took some getting used to ) but I got time
the tank will come in handy eventually but for now
its all going to be done on paper till I can get to the point were I need to hire someone to make sure Im not just building an expensive coffin

[Ad Hoc]

"...The wave drag for the lowest drag hull for any given speed will be around 5% of the total drag.."

Yet another baseless statement from the none naval architect.

At slow speeds the resistance is wholly viscous, as speed increase it affects the total resistance, since the frictional resistance varies at the power of V^1.825. As the speed increases a series of 'humps' and hollows' in the energy system of the waves occur. This increases the overall resistance, and is known as residuary resistance. The total resistance is a summation of the two.

[Guest625101138]

Boston
The lines of my faux-tri are simply for the next stage before I front my friendly local NA to make it look pretty and determine constructability.

I will set GODZILLA to produce the the lowest drag monohull for 15kts and a displacement of 5t. It will be quite long. This forms the basis of a faux-tri because the amas just skim the water surface and offer little drag. It will give you an idea of the feasibility and a starting point for design iteration.

Rick W

[Boston]

nice
well make it happen cause on flat water that thing is going to be a step ahead in boating from what I can see so far

why is is more beneficial to not submerge the amas and make em carry a share of the weight
seems like
oh
wait dumb question
the volume is more efficiently held with the least surface area by one submerged and the others just balancing

how do you prevent sponson walking type instabilities at speed
wouldnt you have to submerge the sponsons at least enough to accommodate people moving around topsides

I still need to look up box keels

[Ad Hoc]

Boston

"...Ill definitely be tank testing something eventually.." Hope you have a cheap local place??

"..why is is more beneficial to not submerge the amas and make em carry a share of the weight.." Resistance!

"..how do you prevent sponson walking type instabilities at speed.."
The constant motion of the boat when being exposed to waves will cause a slight roll moment, to either port or stbd. Depending upon how you have designed your ama's, and where you have placed them, will dictate whether the restoring force of one ama is enough to right itself or not, and whether there is sufficient dampening to prevent oscillations.

"..wouldnt you have to submerge the sponsons at least enough to accommodate people moving around topsides.."
Basically, yes, you can design your ama's to be 'kissing' the water at DWL, rather than being fully submerged. For example, you can have your ama's "Y" shaped. So a thin section is constantly submerged. Only the fatter part of the Y comes into to play at larger heel angles..

[Guest625101138]

Boston
Attached shows the lowest drag hull for the set parameters of 5t and 15kts.

The hull is 29.5m long, 870mm beam and 365mm draft.

It requires 14kW on the hull to do 15kts.

Now if you think 100ft is too long you need to suggest a maximum length for the next iteration. Constraining the length to something around 80ft should not cause a huge increase in power. The other option is to set a lower cruising speed and accept the penalty running at higher speed. Normayll the drag would be minimised for the target cruising speed.

Rick W

[Boston]

my design limit is 60' and 4200 lbs disp
the calc Im playing with shows serious advantages to even the slightest weight savings

I like the look of the trihull configuration ( that big huge I could never afford it red thing I posted earlier )
but am curious about the box keel
something tells me the two are mutually exclusive

funny thing is when I consider elongated multihulls what I get is two cruise speeds
with neither being planing

for a 60' 14' beam 4200 lb vessel split into two 7' 2100 lb sponsons I get an initial extremely efficient movement up to 8 knots and then energy use skyrockets to about 140 hp in the 14 knot area
then falls again to about 110 hp at about 25 knots
you would think that would equate to planing but at no point does the wave resistance part of the graph show any disturbance
it just steadily rises
so I dont think this thing shows planing even at a hypothetical 25 knots

Add
so the gull wing kinda configuration of the sponsons kinda want to keep em balanced at speed
works for air planes should work for boats
ok
so whats that ITTC equation

[Ad Hoc]

18m weighing some 2 tonne all up....with a 250hp engine, fuel, outfitting etc etc...hmmm...have you done a real proper weight estimate yet?!!

[Boston]

so thats why the tri's are more efficient than the cats
the tri's concentrate the bulk of the displacement and ballance a long skinny hull form between two dynamically stabilized amas
and the cats have to have a greater proportion of surface area to displacement cause they are forced to sit on two hulls evenly
interesting
soo
how does the box keel get such good mileage

[Boston]

18m weighing some 2 tonne all up....with a 250hp engine, fuel, outfitting etc etc...hmmm...have you done a real proper weight estimate yet?!!

I may have misquoted
my weight is 42000 lbs
thats 21 short tons

ya I just went back and saw I had left off a zero

[Ad Hoc]

ITTC...in a nut shell:
A standardised frictional correlation method was needed for estimating the powering between model data and ship. This was established in 1957 in Madrid. It is a simple formula

The frictional coefficient is thus 0.075/(logRn-2)^2

Rn = Reynolds number.

[Ad Hoc]

".,..so thats why the tri's are more efficient than the cats ..."

You need to be careful with carte blanch statements like this. Each design is different. The main influencing factor depends upon the length displacement ratio, which is affected by the speed you wish to travel at and the payload you want etc etc...design is a series of compromises. Whatever boat/configuration you choose.

Since at higher Fn, say in the 0.8~1.2 range a slender cat is more efficient than an equivalent mono....so, everything in its place. You must compare apples with apples.

[Boston]

there should be a direct comparison between length, displacement ratio, speed and beam

why is beam left out or are there actually a number of mitigating parameters and beam is just one of em
speaking of which some one some where has bound to have made a formula for that to

oh and I was thinking of vessels of the same length and disp

[Boston]

so back to the original question
which is going to be better ( faster ) in the 60',14'beam,42000lb range powered by a max 250 hp and 80 hp cruise power supply
a trihull or a box keel
in open water

this new calculator is a gas
ok so if I keep the fuel load to 4 tons my disp is 36000 lbs
on a 60' cat hull with 5 beam sponsons and a 14 beam overall Ild be burning 100 hp to get 23 knots cruising speed
with resistance leaping from zilch to that 100 ponies between 5 and 12 knots
I got to be doing something wrong
according to this that hull is capable of 50+ kts with 250 hp
cant be right

[Ad Hoc]

better and faster are two very different design parameters. Better is subjective and deals with cost, outfitting, quality, accessibility etc etc.

Faster is just a simple matter of power requirement for the hull. Based upon drag of the hull at varying speeds.

Yes, i know these sound like vague replies, but you need to pin down and begin to define in real terms what the principal dimensions and characteristics of your boat really is to fully answer. Since then a comparisons with equivalents and non-equivalents can be made. Then you'll see where the compromises have been made and which, if any, you are prepared to make.

Naval Architecture is not an exact science, despite what many believe. The main elements such as hydrodynamics, structures etc are pretty much an exact science, but the "whole design" is greater than the sum of each individual "part".

This si why you need to pin down your SOR into a spec, weight estimate and GA, then review and see if it is feasible.

Just talking "numbers" without anything 'concrete' is a waste of time and will tie you up in knots!

[Boston]

well ive limited it to 60' length 14' beam 4.5 draft 42000 lb and 250 hp with a cruise of 80 hp
in that range I would like to cruise at about 15 kts or there abouts
and Im just starting to look at hull forms
thought after speaking with several folks that I would take a look at trihulls and box keels first

[Guest625101138]

Boston
The attached shows what the lowest drag 5t, 15kts 18m max length hull looks like.

It has a draft of 460mm and a beam of 960mm. Power on the hull lifts to 16.2kW.

The idea with the faux-tri is to get a usefully wide cabin structure on an efficient underwater form. It means you reduce the required power by a significant amount. There is corresponding weight reductions. This reduces loads and you can build a lighter boat.

You have to iterate with the basic concept to meet your ultimate requirements.

Costs usually correlate to weight although if you need to build extremely light you can pay a premium. At 60ft and a target speed around 12kts you are in a good range to get the best from the idea but you have to think in terms of low weight. Weight and efficiency do not fit well.

Rick W

[Ad Hoc]

Well, you need to draw up a GA...then and only then can you establish what the weight will be. You cannot say 42,000lbs without drawing up how the boat will be arranged and certainly not without even knowing what hull form you have selected.

You need to start at the beginning..not the end. With respect, that is the amateurs way or the i have a computer prgram so i'll tap out numbers way of designing. They focus on the wrong bits and in detail too when you need to establish the basics first, not last.

[Boston]

Boston
The attached shows what the lowest drag 5t, 15kts 18m max length hull looks like.

It has a draft of 460mm and a beam of 960mm. Power on the hull lifts to 16.2kW.

The idea with the faux-tri is to get a usefully wide cabin structure on an efficient underwater form. It means you reduce the required power by a significant amount. There is corresponding weight reductions. This reduces loads and you can build a lighter boat.

You have to iterate with the basic concept to meet your ultimate requirements.

Costs usually correlate to weight although if you need to build extremely light you can pay a premium. At 60ft and a target speed around 12kts you are in a good range to get the best from the idea but you have to think in terms of low weight. Weight and efficiency do not fit well.

Rick W

does that 5t represent 5 short tons or what is that
42000 lbs = 19050 kilos if that helps

concept is basically to make it look like that old elco and still get through the water like I know we can today rather than a hundred years ago
that big red trimaran is really nice looking in its hull configuration
I could make that hull work for me I think
but I need to figure out its performance against say a box keel type hull
on the other hand if the tri has adequate performance I might just go with it as I just hate flat bottoms on a boat
my interior lay out is flexible to some degree

I thought Ild mentioned my design criteria over on another page
so was hesitant to repeat it
basically
I want a live aboard that is transoceanic
the hardest run Ill be making is across from Newfoundland to the Irish coast
I need to be able to have a reliable satellite hook up
and I want accommodations for 2 couples including myself and the girl
Im a huge fan of large enough spaces that Im not always cracking my head on something
and I hate cramped spaces so one large pilot house with an office area and kitchenette, one huge master berth with at least one smaller double berth a nice bath and tons of stowage
fuel is pellets 64 cu/ft pr ton at 350 miles per ton considering for the old elco hull
max fuel load is 7 tons to get me across the pond
wood build
vawt generators
electric auxiliary engine with three gorilla batteries
I know exactly how I want the rooms layed out but its not relevant yet

[Ad Hoc]

5t = 5 tonne or 5000kg

It has no relevance to your design SOR whatsoever..it is just a series of numbers plucked out of a program. Since your fuel load is 4t..!!..see my point, just meaningless numbers

As I've said above, you need to draw a GA then establish a real weight estimate based upon your GA...then and only then can you look at powering and see if you get what you thought...

[Boston]

Well, you need to draw up a GA...then and only then can you establish what the weight will be. You cannot say 42,000lbs without drawing up how the boat will be arranged and certainly not without even knowing what hull form you have selected.

You need to start at the beginning..not the end. With respect, that is the amateurs way or the i have a computer prgram so i'll tap out numbers way of designing. They focus on the wrong bits and in detail too when you need to establish the basics first, not last.

the weight was based on the original hull configuration of the boat I started with
it may not apply once I get the hull reconfigured and is only good for a target weight max
so I been using it for the sake of argument

I sorta started all over the place having not tried my hand at boat design before
my plan is to take it as far as I can while I have time to play with it and then when I think Ive made some good decisions go find myself a competent NA and let him do a cost analysis
see were I am

original weight of that vessel was 42000 lbs so thats my max target weight
I calculated the weight based on the original scantlings and planking type and thickness decking bla bla bla and determined how much of that ttl was in the frame and how much was in the Finnish
I then increased the scantlings to bring the boat up to blue water standards although the exorcise was academic given that the configuration of the vessel was not blue water capable
it was however a place to start
or
one place to start

Im sure 42000 lbs fully loaded is on the heavy side of close enough for now
36000 with a 4 tone fuel load
28000 lbs empty weight
thing is once or twice a year Ill load it down with fuel
rest of the time it will be floating at the dock like most other boats

[Ad Hoc]

so your requirements need to be 'drawn' up...otherwise it is a list...just a wish list. You need the list, your SOR, to be made into a concept that some basics can be established...so you need to draw up the layout, does it fit, do u need a longer hull..do u need a catamaran..do u need a tri...too many what if's...you can only draw up what u want....you ahve to start somewhere....you're at the point where if you don't....it'll just remain a dream in words rather than reality.

[Ad Hoc]

"...I think Ive made some good decisions go find myself a competent NA and let him do a cost analysis.."

A shipyard will give you cost.

A competent NA will just scrutinise your work and then tell you if it will work, not pay lips service to your wants. If you're serious, you need to get the basics with a NA now, not later.

[Boston]

Ill know what I want when I figure out what works best
and Ill be a whole lot happier figuring it out by consensus in a group setting than going on one mans opinion
no shipyard brother
if its anything like home building
most of those guys look like they just got out of prison and I wouldn't trust em to build an outhouse
no thanks I am fully capable of building it with my own crew under the supervision of the NA

thing I always hated about clients I was designing a house for was that they were generally clueless about how things go together and they tended to want mutually exclusive design concepts
Victorian porch elements on a post modern house for instance or a multi story house that had 9' ceilings and looked like a single story from the outside or that you couldnt see from a mile away

my deal with designing the boat is to strugle out the various components and get an idea as to what I want
basically if yacht design is going to be a no right answer science
then some of these decisions will be made by consensus of opinion in a place like this were the opinions are generally informed ones
generally
not sure if you have been over to the climate thread yet
now that is one seriously misguided group of people

point is that each design element has made itself self evident the more I got into it
this one will as well
box keels are supposed to be pretty dam efficient
tri hulls are supposed to be pretty dam efficient
one will be better in the open sea than the other
one will get better millage
bla bla bla
so I thought Ild start with the millage
soooo
whats the deal

two boats of the same length and weight
one a box keel
one a tri hull
given the same power plant
who wins for fuel efficiency at the same speed
and
whats the speed
Ild like to see say 15 kts

[Guest625101138]

does that 5t represent 5 short tons or what is that
42000 lbs = 19050 kilos if that helps

.....

Boston
You have to iterate with this. You need to set out the requirements such as cruising speed, range, accommodation, amenities, tankage etc.

Taking 19t as the upper limit the lowest drag 18m hull form gets quite unrealistic. It has a draft of 1.9m and beam of 720mm. The power on the hull has now gone up to 64kW.

If the draft was constrained the power will go up again.

The important thing is to set out the things you want from the boat and go from there. The problem with this concept is that you are starting from scratch so there are no readily available examples that you can take data from.

Rick W

[Ad Hoc]

"...my deal with designing the boat is to strugle out the various components and get an idea as to what I want.."

Well, you have a basic SOR. But you need to progress from this, otherwise you be like "..clueless about how things go together and they tended to want mutually exclusive design concepts.."

Because design is just one big compromise. Until you decide what is important, and list them in order of merit, ahve them drawn up on a general arrangement that satisfies your basic concept of what you want, you shall be clueless too, to why the reply is as it is. You're going around in circles.

Hence, draw it up yourself, or get someone to do it for you, but you MUST get it drawn up before talking any details and making any radical changes/decisions based upon, what...er...um...another idea that's unproven for your boat!

I cannot give any more advise, until you get your boat drawn up....it is meaningless to do so...

[Boston]

ya that hull doesnt look like its going to work at all
there is a solution in there somewhere just got to find it

speed should be 15 knt
range should be 2000 miles
fuel load is 7 tons to make that 2000 miles
4 people in two dbl berths
4 people need to to 7.5 days food and water so call it 1500~2000 lb of supplies
that makes about 8 tons of cargo including fuel
so there is about 26000 lbs of boat involved
assuming 42000 ttl

lets just stick to the basic comparison to hull efficiencies for the moment and Ill see how its incorporates once it is determined what is best under what conditions

what happens if you make that hull wider
say enough to get the draft up to about 1 meter
then reduce the primary hull to only carry say 75% of the ttl disp

think Ild want the primary hull in the trimaran configuration to hold say 75% of the weight
so that 42000 becomes 31500 and the two outer amas hold about 5350 lbs each
in a 60' vessel thats still going to be a pretty long skinny hull
each one is long and skinny in itself so although Im paying in surface friction Im saving in pressure of depth

[Ad Hoc]

"...lets just stick to the basic comparison to hull efficiencies for the moment..."

well, you can discuss with Mr.Numbers and get hull forms that displace 5t when your fuel requirements is 7t...or you can forget efficiencies fro now and focus on what is required first.

As I said before, amaterur designers, non-naval architects and those that tap away into programs on their PC will talk about efficiency until the cows come home..why.??..because they have never designed a real boat before and have no frame of reference other than a series of numbers.

It is your choice if you wish to continue discussing numbers, that is your prerogative. But I gave you credit from your post about building for others etc that you understood this concept. Perhaps i'm mistaken....my bad!

[Boston]

I got the concept
had I been designing a house for the first time I would have gone through the same basic process
learn a few things
then go talk to someone
Im still learning a few things draw up some sketches
which I have
thing is its time to get a hull under these numbers and as you yourself said
this is an inexact science
what the sciences do when they have an inexact conclusion is derive a percentage of confidence from a consensus
thats what Im after on this hull issue
some folks will explain what hull they like and why what they do best and where
so on and on
those are the folks Im looking for
I think you underestimate Rick
he doesnt just seem like a pencil pusher to me as he's got more screwy designs he's worked through to floating than a lot of folks in here
thing is being as how this is an inexact science a conglomeration of opinions is going to paint a better picture than just one
should I go bother 10 designers into some kind of design contest
or should I just join a design group and learn a few things before Im ready to rock and roll
besides
this is a great way to interview possible NA's for the task
got some great folks hiding behind this computer screen
one of em just might end up making a few bucks off me who knows
I got lots of time before im ready to move back to the coast and start building

thanks though
I appreciate the help
that hull resistance formula will come in handy

comparing basic hull configurations
say long skinny hulls
is what this thread is all about though isnt it
seems like an excellent educational tool that might just allow me to make a better decision in the end
so I do appreciate the help
B

[Guest625101138]

ya that hull doesnt look like its going to work at all
there is a solution in there somewhere just got to find it

speed should be 15 knt
range should be 2000 miles
fuel load is 7 tons to make that 2000 miles
4 people in two dbl berths
4 people need to to 7.5 days food and water so call it 1500~2000 lb of supplies
that makes about 8 tons of cargo including fuel
so there is about 26000 lbs of boat involved
assuming 42000 ttl

lets just stick to the basic comparison to hull efficiencies for the moment and Ill see how its incorporates once it is determined what is best under what conditions

what happens if you make that hull wider
say enough to get the draft up to about 1 meter
then reduce the primary hull to only carry say 75% of the ttl disp

think Ild want the primary hull in the trimaran configuration to hold say 75% of the weight
so that 42000 becomes 31500 and the two outer amas hold about 5350 lbs each
in a 60' vessel thats still going to be a pretty long skinny hull
each one is long and skinny in itself so although Im paying in surface friction Im saving in pressure of depth

Boston
Once you start getting up in weight there is advantage spreading the load across more hulls for a length constrained vessel. This is something that Matt Marsh arrived at when he developed the faux-tri concept for his needs. Although his ended up as a conventional trimaran.

If you reduce the power requirement then the fuel load comes down accordingly.

It is useful to set up a spreadsheet that sets out your requirements. This way you can link dependencies. Displacement is an important requirement to narrow down. Some things will not change through the iterative process as they are set and independent of other factors. Others will. A hull that is easily driven will have lower forces on the propulsion system so mountings get lighter. The engine will be lighter. You will need less fuel.

At some point you need a complete list of all the items in the boat to build an estimate. Right now their weight is the data required.

Rick W

[Boston]

the original numbers are all for that old elco
so my thinking is that by optimizing the hull the fuel load and weight can only come down compared to a hundred year old design

[yipster]

i'm trying to attend a session and this tread was on top, anyone "in" here
Nigel Irens http://www.proboat.com/ June 10, 1 pm US EDT and Live: Designing Fuel-Efficient Powerboats
i keep gettin "your allready registerd for this" but cant get in
so what am i doing wrong how to get in later up to 90 day's after..
anyway, here the masters filosofie on LDL http://www.nigelirens.com/

[Guest625101138]

the original numbers are all for that old elco
so my thinking is that by optimizing the hull the fuel load and weight can only come down compared to a hundred year old design

Boston
Do you intend to build the boat yourself?

Is unsheathed wood your material of choice?

Are you wedded to the steam propulsion?

If these are criteria for the boat then they need to be included in the design requirements.

Rick W

[Guest625101138]

i'm trying to attend a session and this tread was on top, anyone "in" here
Nigel Irens http://www.proboat.com/ June 10, 1 pm US EDT and Live: Designing Fuel-Efficient Powerboats
i keep gettin "your allready registerd for this" but cant get in
so what am i doing wrong how to get in later up to 90 day's after..
anyway, here the masters filosofie on LDL http://www.nigelirens.com/

The first link just loops. I have no idea why some sites do this.

The nigelirons link has some nice concepts. The little clip at the beginning of one of the LDL designs looks good.

I like the way the LDL vessels slice through the water. I have recollections of beamier boats slamming into even moderate seas no more than 1 to 2m high. Absolutely bone jarring. I expect the same conditions in these fast LDL hulls would be less severe.

Rick W

[Boston]

Boston
Do you intend to build the boat yourself?

Is unsheathed wood your material of choice?

Are you wedded to the steam propulsion?

If these are criteria for the boat then they need to be included in the design requirements.

Rick W

most definitely
I just won a contract to do a black lacquer front entry on one of the old Victorians down town. I had to talk em out of a black lacquer hand rail around the deck and they are talking about doing the deck in black walnut although my vote is for baked poplar, its cheaper and better in this application. Ill be hand turning the rail components and the spindles in the same material. I think Im capable of building just about anything and have from highrises to antique English conservatories, my skills are not the issue its the vagaries of yacht construction that will require I hire a decent yard manager/NA to oversea each aspect of the build and double check my work similar to the inspection process Im used to as a builder. I have no intention of winging it nor do I plan on ignoring the advice of folks who do this for a living. I will also not be pressured to begin or throw my hat in with anyone until I am comfortable that I clearly understand the entire process and why each decision is what it is, which is pretty much why I joined this site.

I have no decisions set in stone and believe that this process needs to be an organic one that is allowed to grow the more I learn

steam propulsion is a strong contender but not the only one Im considering
so far its main draw backs are the mass of the fuel and the blazing fire in the bottom of what amounts to my life raft
course each fuel type has its draw backs

I am glued to the idea that I will not start anything untill I have all the funds fully available, no bank, cash on hand
which means I earn it off my trade account ( I had a stellar day by the way )

Im all about low embodied energy
wood meets that need
if another material can be shown to be as easily reparable as readily acquired and as comparably cheep then I will consider it

I plan on using natural glues wherever possible and only encapsulating the last layer of the double diagonal planking in epoxy under paint and copper bottom
Im however pretty well set on it not exceeding 60' length 4.5' draft and 14'beam although a little smaller is ok
I prefer to remain flexible throughout the process in order to incorporate the best of all worlds

[Guest625101138]

Boston
Your strategy is sound apart from the day trading aspect. You might get lucky and actually be one of the few that make money.

I started with pedal boats to learn about efficient hull design and propulsion at a scale that is fun to use. After I sold my last yacht I began building model boats but i did not find them highly rewarding. Playing with pedal boats has taken me in unanticipated directions. Not a lot of new stuff but ideas and knowledge that are not widely known.

Rick W

[Boston]

Im actually kicking its ass day trading
I posted my day in real time over on the global economic conditions for live aboard yachties thread
if your curious go check it out
my final post in the series Ill quote here as it was a good synopses of the day
it was a series rather than one after close post because I wanted the times on the posts to correspond with actual market positions thus corroborating my buys and sells
I figured people might want to actually see for themselves I was in fact keeping step with the market motions with my positions on the day

I ended up having a great day but obviously could not have known that at the start
I just wanted to honestly represent the uncertainties in real time

my last post in the series was an effort to explain my reasoning and its results

this morning is a great example
the open was high
well above the close of the previous day
above the 7 day trend but not above the anomalous high on the fifth ( which resulted in a drop from that opening high back to within trend )
so I was thinking it was not so far off to be fully outside of trend and given that, I bet it would drop like a rock ( as it had before ) back to average at least for the 7 day period which was down around 940.0
I got in early at 954.2 with a strong conviction it was going to drop
it did
but bounced a little more than I wanted to see and so I got out missing some additional gains but still
taking a tidy profit
then it fell some more, I could have flipped my trade and gone sds but by that time it was in average territory and predicting its next move was not so easy, so I waited, it bounced off the average trend line as it had a few times before over the previous 7 sessions
so I got back in on the bounce and then out again when the bounce fizzled out ( that was my smallest gain on the day )
at which point there were no clear indicators as to where to go from there, so I waited again
it fell
and fell
and fell ( lots of missed profit there but hey I was not sure which way it was going to go so I just watched and waited )
it crashed all the way to my predicted low from a few days ago
at which point I expected a bounce so I got back in with sso funds
it shot upwards and landed me another nice profit
I got out a few minutes before close with all indicators favoring a continued upward movement right up till the end

day trading is about the only way Ive managed to survive since the contracting biz fell flat on its face over the last few
surprisingly, when so many people told me not to even think about it
turns out Im good at it
I think it just might pay for the yacht cause contracting sure isn't

cheers
B

[Tad]

Boston...

What the ........ does your day trading bs have to do with long skinny powerboats?

Thread drift I understand....intentionally adding posts with no bearing at all on the subject makes no sense!

[Boston]

Rick had mentioned something about financing the project with day trading
so I threw him some bs about day trading
which turns out will likely finance a long skinny hull just fine

sorry if it didnt make any sense
cheers
B

pertinant question then
Im working on my math skills
submerged area, 60' hull 6' beam 2.75' draft
when I crunch the numbers I get 2500 lbs of thrust to reach 20 knots
or 100 hp
Im sure you have a hull efficiency calculator in there somewhere
whats it say when you input those numbers
Im curious if Im close
thanks
B

[Guest625101138]

Boston
Here is a test on one of my slender boats with a small motor operating at 200W. The motor is rated at 600W. It went to 10kph (5.4kts).
http://www.boatdesign.net/gallery/data/500/V11JE_10kph.wmv

I intend to use this motor on the 1/5th scale model faux-tri but it will be minus the big gear ratio.

One of the sailors looking on could not imagine that a tiny motor could move me at that speed. The motor weighs 149 grams and is 40mm diameter I have a 12:1 overall gear reduction.

Anyhow it demonstrates how little power a long slender hull needs.

Rick W

[eponodyne]

no can view on a Mac, sorry.

[Guest625101138]

no can view on a Mac, sorry.

Can you view YouTube:
http://www.youtube.com/watch?v=GJedBprmSkk

There is nothing particularly great about the video. The impressive bit is the little 140 gram motor pushing a person on a boat it 10kph.

There is a little program called Flip4Mac that enable Quicktime to view wmv files.

I use Mac for email and web viewing so it is handy to have.

Rick W

[eponodyne]

oh holy crap that sounds like a dentist drill moving the gates of doom into place. Sure, that's a dandy little powerful motor. Annoying as f*ck.

Better you than me, buddy. I'm glad you're wiling to do the research and put up with it, because it would drive me to world domination or some **** like that.

[Guest625101138]

oh holy crap that sounds like a dentist drill moving the gates of doom into place. Sure, that's a dandy little powerful motor. Annoying as f*ck.

Better you than me, buddy. I'm glad you're wiling to do the research and put up with it, because it would drive me to world domination or some **** like that.

The camera seems to amplify the sound quite a lot. It is not anywhere as noticeable on the boat. My son also found it very annoying when I first viewed the video at home.

My main issue during the test was lack of a third hand and fear of losing the remote control while filming. I was trying to run directly with the waves so it would stop the jerky roll before I tried full power. I later found I had collected some weed in that run and was able to nudge just over 10kph with a clean prop.

When you compare noise with the equivalent ICE used for model planes it is silent.

Rick W

[Boston]

ya as a kid we used to play with those RC planes a lot and dam
they scream
ok well then I guess my numbers may be at least close then cause I took a big guess at the wave resistance and assumed it was half at 20 knots
basically I only figured for the fluid resistance and doubled it to get to 20 kts at 160 hp for a 32000 trihull with one 60x6x2.75 and two 40x1.5x2 sponsons
the sponsons work out to 30 hp each at 4000 lbs disp and the primary hull works out to 100 hp at 32000 lb displacement
or 160 hp to hit 20 kts
so the 250 hp Im planing on should be more than enough to keep me ahead of weather

funny part is at 8 knots
it seems to work out to about 16 hp
cant be right
which Is why I was hoping some one would check my numbers

[Boston]

oh
video played fine on my mac
but I already have flip for mac installed

[Tad]

Rick....

What is the length, beam, and weight(total with you aboard), of the boat in the video?

Thanks...that's interesting work.

[Guest625101138]

Boston
The lowest drag hull for 15kts with max length of 18m, max beam of 4m and max draft of 1.4m is a mono. The beam of the hull is 0.8m. The wetted surface area is 62sq.m.

It requires 66kW for 15kts and 115kW for 20kts.

A catamaran requires 80kW and 153kW.

A trimaran with a 1t minimum displacement amas requires 71kw and 132kW.

So the best option from a powering perspective for these constraints is still the faux-tri.

Rick W

[Guest625101138]

Rick....

What is the length, beam, and weight(total with you aboard), of the boat in the video?

Thanks...that's interesting work.
Tad

Around 110kg total. LWL = 7.2m, BWL = 225mm, draft a little over 100mm.

The two little VRLA batteries are 12Ah and weigh 7kg combined. I have done full discharge test on these and they give about 1 hour operation at 7A. The 12Ah is based on 20h discharge rate. These batteries die if you try to pull 12A. That is where the lithium batteries win out. With a 5Ah lithium battery you can pull 70A and they still hold voltage. A 1kg battery will allow me to get full power from the motor - not for very long though.

I know it was cold so there has to be some motivation. I am truly impressed with these modern motors and controllers. They are very well engineered and do not cost much.

Rick W

[Willallison]

Rick,
What I want to know, is what on earth posessed you to go out in a pair of shorts on a cold Melbourne winter's day !?!;)

[Guest625101138]

Rick,
What I want to know, is what on earth posessed you to go out in a pair of shorts on a cold Melbourne winter's day !?!;)

That is my normal attire for pedalling when it is not sunny. Once I start pedalling I enjoy the fresh air. No pedalling was very cold. I was shivering it was so cold. All for the sake of scientific enquiry.

With hindsight I should have set up the pedals so I could have got warmed up.

Rick

[Boston]

the appropriate response Rick would have been

if you had legs like these
you wouldn't cover em either
( and then the questioning look )

you got to work on your pithy comebacks mate
if for nothing else than for the laughs at the pub

cheers
B

[Ad Hoc]

Oh dear, silly season again.
I must say, the anonymous spineless weakamateur, who left the delightful message "..dogmatic rubbish..", for my post #127, has just proved my point once again. QED.

I think you need to return to school to re-take your English comprehension and science classes again. Oh, wait...can't do that....you prefer to remain ignorant. silly me :P:P

That is some 70 neg hits I've had this week....i must be really pissing-off those, "i have a dream"..ooops., no wait..."i have a computer" types :)
As can be evident by the large numbers of real boats they have designed on show for all to see, to demonstrate their professionalism, experience and maturity!

PS...No wait, another,....yup another spineless comment. "..thuggish rubbish. More concise.."
gesssss...some poeple just don't like being told some hard truths !!!
One must feel so superior and smug behind that anonymity and experience....:P:P

PPS..and another!!!...but blank this time...awe..pity, i like the immature comments!

If those of you that come onto this website and would like to learn or understand or even educate others, it is very difficult when you have not got the courage to post publicly. Posting publicly expose one to ridicule and scrutiny and also highlights any ignorance by being so open. But that is the point isn't it...hence the anonymous posting and not wishing to engage in a debate to establish the limits of ones knowledge to either further that limit (or even educate others), or as it seems many prefer, to simply hide and throw stones from a distance like all cowards. Why do you come onto the website then if that is your MO??...very very sad. Still, I'm sure it helps give you kicks in your sad world :)

[Jenny Giles]

That is some 70 neg hits I've had this week....


HTFU, Nancy! This is boatdesign.net, not your "Dear Diary everyone hates me" MySpace blog.

[Willallison]

"HTFU".....
the last two letters I can figure out, but what are the 1st two short for?

[Submarine Tom]

Ad Hoc,

What are you talking about, your post #127 you refer to was five months

ago...

Do you get bored and go looking for conflict?

How long will you be stuck in your unhappy situation in Japan?

Tom

[Johnnylee]

Thanks for sharing

[Ad Hoc]

Tom

I only just got the hit, I may have written it months ago, but a saddo wishes to sit behind a sofa and throw stones. Just thought i would highlight their sad behaviour, that's all.

What is funny, these "saddo's" come on for advice/guidance, but only want to hear what they want to hear, and not come with an open mind or willing to listen. I find it very ironic and amusing...so i thought i would share :)

[Frosty]

70 negative rep points in one week is some kind of record, well done!!.

[Ad Hoc]

Thanks frosty, but it is now approx 100, in just a few days...this is great stuff. I'm doing well...
I think i'll open a nice bottle of Pinot Noir to celebrate :)

Update, more than 100 this week now....:):):)

[Frosty]

Why don't you pop down town and get some sushi and an old slitty eyed slapper in one of those cheap hotels, a bit of suki saki will help take your mind of it.

Hey you could do a bit of karoke afterwords, if you can still walk.

You'lle be alright in the morning, trust me, im an expert.

[Ad Hoc]

Domo arigato :)

[Frosty]

Douitashimashite.

[Boston]

Douitashimashite.

I give up
whats it mean Frosty

[Ad Hoc]

In simple form：

Thank you = domo arigato or どもありがと

and the much used reply, in western cultures is:

You're welcome = do itashimashite or どういたしまして

[Ad Hoc]

"...Ruined a good thread with off-topic rubbish.."

And your worth while intelligent contribution is what..???...er....um.....yeah, just like your anonymous neg hits.....worthless!

If this is your thread????... if so, say so and say get back on topic, if not, what right do you ahve to lecture to anyone else on this thread...none...to demand so, from behind your "veil of anonymity," is even more pathetic and spineless!

If you have something to say, say it publicly, otherwise stay hidden behind the sofa whimpering because you saw a shadow.....gessss, such immature behaviour!

If everyone debate issues like you and the others, we'd still be in the dark ages....ignorance is bliss!

Ahhh...and another person wishing to contribute by neg hits, all because they do not have the intelligence to debate a simple concept in public, in full view exposing their true thoughts and knowledge and 'experience' yet have the arrogance that they feel it is THIER thread when they have actually contributed diddly squat. Well, what can one expect from someone who shall never achieve anything in life with such petty immature narrow minded attitudes, other than self flagellation in secret.

Wow, that makes 120 neg hits from last monday to this monday....i must be really rattling the cages of those that wish to hide and seek...hahahaha :P:P
"..Infantile tantrum ruining a thread..