Modular Cruising Catamaran

[ImaginaryNumber]

I am looking for an owner-buildable design for a 35’ (+/-) deck-bridge sailing cruising catamaran. My first constraint is that while I have plenty of room to build it where I currently live, I will have difficulty transporting a 20’ wide boat to a launching area short of using a helicopter. To solve this problem I’m wondering if it would be practical to build a modular catamaran? By this I mean that all the major sections of the catamaran would be built independent of each other, transported to a launch site, then lashed or bolted together in the final configuration. I want all the components to be truckable on standard roads without major hassle. A maximum width of 8-1/2 feet is ideal. 10 feet is okay. 12 feet wide is pushing it.

Another criteria is that the boat must be easy to manage by an older couple doing short-handed sailing. I’m looking for easy to build, easy and safe to sail, easy to maintain, easy to live in.

A third constraint is that I plan to sail in colder waters, which will require insulating and heating the living quarters. I don’t see that the three areas of a typical catamaran (two hulls plus bridgedeck) lend themselves to efficient heating. Too much surface area to insulate, plus temperature stratification between hulls and bridgedeck. So I’m exploring the idea of putting all the living space in a full-width bridge-deck, and using the hulls only for storage.

This configuration would have both pluses and minuses.

+Pluses include having all the living quarters all on one level (an advantage as one gets older)
+Easier to insulate and heat
+If the hulls will not be lived in perhaps that will allow a more hydrodynamically-efficient hull shape.

-Minuses include less privacy compared to a traditional catamaran. (not a major problem for me)
-Higher center of gravity, so less stable.
-Greater height, therefore probably more windage.
-If the bridgedeck was 16’-20’ long and 20’ wide it would have to be built in two or more pieces to meet my transportation requirements. I'm not sure how to join two bridgedeck section together, or how to join the bridgedeck ensemble to the hulls.

The ideas I’ve come up with for this last concern are:
=Split the bridgedeck transversely into two pieces, each perhaps 20’ wide by 9’long.
=Make the deck portion a plywood stress-skin panel perhaps 6” thick, with solid wood stringers, and foam in open spaces.
=Make the cabin(s) a lightweight bubble of 2”+ foam with fiberglass or thin plywood skins inside and out. (hope this pushes the COG lower)
=Place a free-standing mast in each hull, carrying either a split junk rig, cambered junk rig, or swing-wing junk rig. (These are relatively new variants of the “standard” junk rig, which have the same easy handling characteristics, but with improved windward performance.) Not using a shroud-supported mast on the deck might lessen the needed strength (AND weight) of the bridgedeck, and using two masts instead of one will help to lower the center of gravity.

I’m hoping the members of this forum would be willing to advise me whether this type of design is possible and prudent? Or what modifications could improve it? Are there similar boats already designed that I’ve missed?

Thanks for your thoughts,
i

[Squidly-Diddly]

"The Cat in the Box would be a 40' cat with 40' x 4' hulls connected by poles decked with either a tramp or some sort of solid removeable decking.

I'm thinking of a aft wishbone mast cutter rig with a third windsurfer type sail aft. I'd use spare sails to construct a 3 sided tent on deck.

In either boat I'd consider using the trailer frame as a aft wish bone mast. I'd even have provision for detaching the wheels and tires and mounting them on the flat on the deck as fenders so nothing would need to be left on shore.

I think it would be possible to carry the tow vehicle itself on the deck of a Cat in the Box, including ramps for on-off loading. The 'killer app' would be to tow the boat to the beach, launch the boat, expand the scissors (poles) to separtate the hulls, use the trailer as the mast, drive the tow vehicle up ramp (or pull up with winch) and sail away. Reverse at next land fall."



I'd also want it to be Containable with standard 40' x 8' box....while still on the trailer. No "standard boat yard operations" needed to launch or pack for shipping.

I'd want a generic simple way of connecting the hulls to the beams, so more hulls could be added, or even use 8' wide hulls. I figure once you are into towing one 40' trailer, another trip isn't a big deal.

I'm aiming at a 'system' that could go from a fast, bare bones cat with only accommodations in the two narrow hulls, to a "Fat Cat" with 8' wide hulls, to a 40' x 30(?)' flat platform onto which a 40' x 30' x 10' tent could be erected for massive temporary living space.

My target market would be everything from:

Weekenders wanting a big fast cat they can tow with normal big pickup and use without berthing fees,

to resort/special event operators who would like a modular shippable system with additional dedicated Head and Shower OR Kitchen and Dining hulls,

to work/business boats.

One BIG draw back would be no obvious built in pilot house or helm, as the deck would start off being flat across the beams, so this might not be good for cold weather.

[Squidly-Diddly]

able to be used as the center of a tri, possibly with the amas stowable inside the main hull for trailering/shipping.

Also, a single 4' wide hull could be used with same amas, and collapse down to 8' total with amas.

If the 8' wide hull could be trusted on its own, then turn the two amas into a 20' cat! I think stowing the amas inside an 8' hull is doable.

I also think their could be a market for 8' x 40' trailerable fuel efficient day cruiser for calm waters.

Mix and match.

For resort operators and floating hotels I'd want hulls to be able to be added or subtracted 'on the water', by slipping them under the deck, so refreshed bathroom and kitchen hulls could be exchanged without main boat heading for the docks.

[ImaginaryNumber]

Just my luck to have my thread hijacked first thing :(

[nero]

Why not look at a proa? There is one living area. Very easy to sail. Low cost build. www.harryproa.com

[Alan M.]

How about a "podcat" style of boat? Something like this: http://boboramdesign.wordpress.com/46-pod-cat-for-sale/

[bill broome]

look at woods designs, he has several with separate accommodation in a pod, and some are purpose designed for assembly at water's edge.

[catsketcher]

Every time I build a boat I have the same thought - My next boat is going to be square!

I have had this thought about a modular cat a few times. Hulls are good but hard to build accommodations into. Great for bunks (I know they are accommodations) and storage bins but a hassle to fair and finish. So I had a modular cat come into my head a while ago.

My 38footer basically has three bridgedeck sections

1- a full bridgedeck section containing the double berths
2- the bridgedeck cabin
3- the cockpit and aft deck

If I was to build this boat really easily I would build each section on a concrete floor and simple strongback. No section is longer than 8 foot from front to back. You build each section and then you put it away. Use a kitchen maker to cut out you square cabin fitments.

The hulls would be less essential for accommodation but could still be used for storage. As you need headroom I am guessing that this would only be useful on cats around 40ft.

In the end you would have 5 sections - two hulls and three rigid and strong bridgedeck sections. At the launch site you would bolt and glue all the sections together. If you were really clever you would use a simple moulding that is glassed in like a composite chainplate to hold the sections together so you could undo them if needed - but I bet the thing would stay together once made. Still I have wished I could have pulled my cat apart to work on it somewhere much cheaper than I am forced to got to. The beauty of the sectional method is that each section is a great torsion box on its own and can be built to take the typical cat loads with almost no design compromise.

I know people will say that a pull apart cat would "work" (move and squeak) but you could use the consistent strain from the rig to tighten the whole thing. If designed for it the rig tension would pull it all together so that she would move as little as a normal cat.

I would love to build a square boat that didn't look square. I also love the idea of working on each individual piece on the floor and then stowing it away. My mate paid $6000 bucks to launch his cat and it only had to go 5 kms.

Okay really pie in the sky stuff now - Make it so that you can put the whole thing in two containers - Darling lets go to the Pacific - pull it apart and then you fly over to the boat later.

cheers

Phil

[catsketcher]

Gday

I missed your points re the rig

I would not go the twin mast set up - as stated in the above post a normal rig will pre-stress the boat which is a good thing. Many thin and spidery trimarans are floppy without their rigs. Robin Chamberlin and John hitch used a pyramid style beam arrangement that actually used the down force of the rig to stiffen the cats - they were/are very stiff cats.

A twin rig set up is asking for slopping around in a seaway - the forces will act in many different directions - a normal rig will have consistent vectors that you can use to your advantage.

As to pitching - if you are not in marinas you can afford to lengthen the hulls if you make them only for flotation and storage. Hulls are easy to build - it is the fitting out that makes them slow. So lengthen the boat because long hulls will cost very little extra with no interior. You reduce pitching, increase speed, increase carrying capacity and make the boat better looking.

cheers

Phil

[Richard Woods]

As Bill Broome says, I have several designs that suit someone in your situation. For example, I live aboard and cruise my 34ft Romany design during the winters, and that would be a good option for you.

If you look at my Biography pages on my website you will see that it is possible to get a 20ft wide catamaran down a narrow Cornish lane if you try hard enough

Hope this helps, good luck with your boat hunt

Richard Woods of Woods Designs

www.sailingcatamarans.com

[ImaginaryNumber]

Nero:
I have looked at the HarryProa site before. What a clever and unusual boat! I have to admit that I've never felt that "spark" that one feels when falling in love with a particular boat or design.

Alan:
Oram’s PodCat is an interesting blend of catamaran and trimaran. I like that all the accommodations are kept in the pod, though it appears that the aft bunks are separated from the salon by the cockpit. I wish to keep all living quarters together for ease of heating and access in foul weather.

bill broome:
I have looked carefully at Richard Woods designs. In fact, it may have been from some of his designs that I got the idea of being able to build everything as components. I would be most interested if he were to design a fully segmented catamaran.

Phil:
You clearly understand the concept and appeal of a modular cat with all the accommodations in the bridgedeck! I think being able to build each section in a garage or outbuilding, then storing it outside while working on the next section, would be very appealing to many DIY-builders – particularly those who live in colder climates or those who have limited building facilities.

You make an interesting observation that a deck-mounted mast can be used to tighten the components of an otherwise flexible catamaran. I know of a few bi-masted catamarans with free-standing masts that have made significant blue-water voyages. Pete Hill’s junk-rigged China Moon made a number of Atlantic transits and sailed well into the Southern Ocean. Bertrand Fercot built a bi-masted Wharram Tiki 30 with Swing-Wing sails, with which he crossed the Atlantic. He liked it so much that his is now building a Tiki 46, again with free-standing masts and a swing-wing sail. I’ve not heard that either had problems with masts or hulls working, but maybe bridgedeck catamaran has different problems.

Bertrand Fercot www.themultihull.com/wharram2/bf9.htm
China Moon http://www.2hulls.com/usedcatamaran-2005/China%20Moon.html


Richard Woods:
Thank you for your kind wishes. Your Romany is very appealing to me. If my only quibble was difficulty of transporting from build site to launch site it would be less of a problem to solve than presented by your Cornish lane.

But I’m still concerned about heating three separate spaces in cold weather. When you say you winter aboard your Romany in the winter are you talking about Canada or Cancun? It’s Canadian-like winter weather that I need to feel comfortable in. Another disadvantage (to me) of a pod catamaran is that in foul weather one has to go outside to get between the pod and the hulls.

I would really appreciate feedback as to whether the concept of a modular catamaran even makes sense. Are there practical ways to sectionalize a bridgedeck? Are there practical ways to attach a bridgedeck to the hulls? What is the minimum size of the hulls to safely carry a standing-height bridgedeck? Will the extra weight of this type of construction create stability problems? I again emphasize that this would be a cruising boat. I’m willing to sacrifice speed, but not safety.

Thanks to all for your comments and ideas
John

[Richard Woods]

We bought our Romany last year when it was in Virginia. We sailed it to the Annapolis boat show in October and then started sailing south in late Oct/Nov.

We had no heater because I come from the UK and assumed that at a latitude similar to N Africa it would be warm and anyway we were on our way to the Bahamas. But it was cold!!! So we now have a little propane heater for the cuddy (where we tend to sleep when it is too cold for the hulls).

You will see on my Biography page of my website a photo of my first live aboard catamaran under 6in of snow, so I do know what cold is like when living on board!

Yes, you are right, a catamaran is harder to heat than a monohull, but in fact a cuddy catamaran makes it a bit easier as it has three "rooms" On a conventional bridgedeck cat the heat rises so it is hard to heat the hulls (and thus bunk cabins)

You are also right about having to go outside to get from hull bunks to saloon. But on the other hand, you do have a lot of privacy. And as I say on my website, the cuddy catamaran is a very efficient use of space.

I don't think it is a good idea to have hulls that are only used for storage on a cruising catamaran over about 25ft. You don't have THAT much stuff to take (our Romany has loads of empty lockers and underbunk space even though we were living on board for 6 months). And so you'll waste all that hull space. Basically you'd have the same accommodation as a trimaran.

The Flica 34 has very similar hulls to the Romany but has a full bridgedeck cabin. When I drew that boat I realised that many people would not be building near the water. So I drew it so that each hull plus part of the bridgedeck was built seperately. Then the middle section of the bridgedeck (about 6ft wide) was fitted during final assembly. You do need to spend some time by the water, but you can do a lot at home.

It isn't a good idea to make a joint on the boat CL, as that causes problems with, for example, the mast beam and king post. Equally not a good idea to make a joint on the inner bridgedeck/hull as that is where the most loads are. That is why I decided to make the joints midway across the bridgedeck floor.

Does that answer your questions??

Richard Woods of Woods Designs

www.sailingcatamarans.com

[ImaginaryNumber]

Richard,

I agree that if the hull shapes were left the same as a catamaran that had in-hull living quarters that there would be a lot of excess space. But if people weren’t living in the hull, perhaps the performance of even a cruising catamaran could be improved by making the hulls narrower (and longer?). Could you tell me if narrower hulls would imprudently reduce buoyancy or increase deck slapping?

My vision is to reserve the hull space for seldom-used items – like bicycles, a folding boat, and if weight allowed, a small motorcycle or two – and to have a full-width and a mostly full-height bridgedeck for the living space. That could give me living space that was perhaps 20’ wide by 16’- 18’ long. Having the living space all on one level and in a relatively compact shape would make it much easier to heat, and would also be easier for aging bodies to use.

Again, my concern is whether that would put too much weight too high, or whether the increased windage would make control of the boat unacceptably difficult?

You warned against making any connecting joints along either the centerline of the boat, or where the bridgedeck joins the hull. The idea I tried to describe in my first post was to have the bridgedeck sections each span the full width of the boat – from outer gunwale to outer gunwale. Catsketcher described it better than I did when he said:

1- a full bridgedeck section containing the double berths
2- the bridgedeck cabin
3- the cockpit and aft deck
…
In the end you would have 5 sections - two hulls and three rigid and strong bridgedeck sections. At the launch site you would bolt and glue all the sections together ... The beauty of the sectional method is that each section is a great torsion box on its own and can be built to take the typical cat loads with almost no design compromise.

So I’m still wondering if this modular idea for a cruising catamaran is worth further consideration, or whether there are fundamental engineering or aero- or hydrodynamic constraints that make this concept dead-on-arrival?

Thanks for your thoughts,
John

[rasorinc]

maybe this will generate an idea.http://www.seatrotter.com/

[Richard Woods]

First an aside


Okay really pie in the sky stuff now - Make it so that you can put the whole thing in two containers - Darling lets go to the Pacific - pull it apart and then you fly over to the boat later.


That is something similar to what I plan to do with my 10m Mustang design, only it would all fit in one 45ft highback container.
========================

So really what you are after is a trimaran with the main hull out of the water???

One of my customers recently emailed to ask "Can you design me a catamaran with only one hull?" Clearly he was getting bored with building the second hull

And as I said before, I think once you start building you will wonder "why not make this hull a few inches higher so I can get in it and USE it?" Adding even 12in of freeboard doesn't add much to weight (certainly less than a couple of motorbikes). And the extra freeboard and thus windage doesn't seem to slow boats down a great deal, especially when the hull freeboard breaks up the "boxy" main cabin.

Then you end up with, say, a Romany. Which otherwise has all the advantages you list. My 40ft version, the Rhea, has a big enough cuddy to fit in the heads/shower as well. One great advantage of the three compartment concept is the fact that there is lots of privacy. Another is that it is easy and safe to go forward as the side cabins act as bulwarks, whereas your proposal doesn't even have sidedecks (if I understand you right)

What you are proposing is nothing new. Eric Manners built several like that in the early 1960's, while Prouts built a 40ft boat, Phantom Wake, in the late 1970's (I think) with accommodation only in the central cuddy. I did the same with a 45ft cat in the mid 1980's (the hulls are made but it is still unfinished). The early CSK boats like the grp Polycon, still for sale in various places, were really very similar although you could get in the hulls.

Having said that it is clear that such a boat isn't a popular concept, so not quite DOA but close. It maybe your ideal boat, but I find most people come to sell even their "ideal" boat sooner or later and if the concept itself isn't popular then the chances of you selling your boat for anything like what you pay for it are slim. And that alone would be enough for me to advise against doing it.

Sorry to be so negative, but build it and prove me wrong.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[apex1]

Richard,

But if people weren’t living in the hull, perhaps the performance of even a cruising catamaran could be improved by making the hulls narrower (and longer?). Could you tell me if narrower hulls would imprudently reduce buoyancy or increase deck slapping?


You meant the other Richard I know. But let me say, if your hulls are narrower and longer (for the same displacement) they of course provide the same buoyancy. And the boat will be faster (much faster). It´ll be a topheavy boat, but that can be balanced with a appropriate design. It all depends on how sophisticated you can engineer the fixtures deck / hull.
In principle it can be done, and is´nt a too great task.

Regards
Richard

[Richard Woods]

Apex1

That is only true to an extent (as you well know). Top speeds might be higher, but at low speeds a long thin hull tends to be proportionately slower.

That is because of the extra wetted surface area. Imagine a coke can, unopened it holds, say, 500ml. Drink the contents and then flatten the can. You will get a long thin "hull" but it won't now hold as much coke. Or, putting it another way, for the same area of can (hull) a long thin shape cannot hold as much fluid (have as high a displacement) as a fatter one.

So those sailing in lightwind areas are often better off having a slightly fatter hull.

And a fine hull will sink quicker than a fatter hull as it is loaded. So that also means a cruising boat shouldn't have hulls that are too fine.

All you have to do is decide what "too fine" means!

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Ad Hoc]

"...Top speeds might be higher, but at low speeds a long thin hull tends to be proportionately slower...."

No true. The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too.

[Richard Woods]

Well all I can say is that isn't what I've found on the race course where, for example, my Strider design is faster than a Merlin in light winds but much slower in strong winds. The Strider has a fatter hull.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Ad Hoc]

Richard

I suspect that when you try and compare one against the other (Merlin v Strider), all the "facts" are not the same. So your observation whilst obvious when on board, the reasons for such, are not as clear cut as you image. Too many parameters affecting the observations.

Hydrodynamically, and nothing else, no wind, no sail area, AoA etc etc...the above statement is correct regarding long slender hulls and their lower length displacement ratios for a hull.

[rattus]

...and hydrodynamically, in low speed conditions (i.e. boat speed << hull speed), friction resistance dominates over that of wavemaking resistance for any hull size; therefore a long slim hull of equal displacement, and thus of greater wetted surface area to that of a shorter fatter one, will be slower at these speeds.

Taking that to an extreme, at infinitesimally slow speeds, a half-sphere would be the ideal hull shape.

Ad Hoc, you are what is known in engineering circles as an asshole. Richard(s), carry on with your conversation, most of us appreciate it!

Mike

[Rick Willoughby]

Well all I can say is that isn't what I've found on the race course where, for example, my Strider design is faster than a Merlin in light winds but much slower in strong winds. The Strider has a fatter hull.

Richard Woods of Woods Designs

www.sailingcatamarans.com

Richard
Slow for a sailing cat for me would be 4kts.

The lowest drag cat hull for this speed with a total ship displacement of 800kg will be 6.5m long, maximum beam of 700mm and draft of 280mm. How does your Strider hull compare with this. Length is the most important factor of course.

Rick W

[Ad Hoc]

"...Ad Hoc, you are what is known in engineering circles as an asshole..

Is that the engineering circle that prefers anecdotes to evidence?

I thought that was the school playground....oh yeah, that's where name calling usually occurs too.....silly me!

Such a mature non-engineering circle comment, thanks for the erudite contribution Mike :)

[bill broome]

ummm, btw: are you sure you don't want a trimaran?

[apex1]

.
Ad Hoc, you are what is known in engineering circles as an asshole.
Mike

Can we please stop this crap! Apart from being offensive, that statement was wrong. In the circle of real pro´s around on this Forum, he´s known as a real pro.

To topic:
At speeds where a cat has it´s advantages, wavemaking is the main factor we have to fight, so there is no doubt: the longer the better. period

Regards
Richard

[catsketcher]

To topic:
At speeds where a cat has it´s advantages, wavemaking is the main factor we have to fight, so there is no doubt: the longer the better. period


I don't agree on this for a cruising cat. Most cruisers get sailed at far below top speed after they reach say 8 or 9 knots, depending on conditions. As Richard says there are many other important considerations such as immersion rate, pitch resistance, dryness on deck, the livability of the hulls, access into the hulls etc, stern steps and very importantly tacking ability. I would not care if my cat never went above 15 knots if it got to 5 knots quickly - so you need fatter hulls than top speed calcs would suggest. As an ex racer I can sail our cat hard. We have averaged 10 knots over 16 hours for a family cruiser (Coffs to Southport) but our average on the GPS is 7 or 7.2 knots. Too fast and we all get tired. Better to have hulls around the 10 - 12:1 ratio and not get too extreme.

The advantages of a cruising cat are not always speed - increased livability, no roll at anchor in swell, no rolling on a square, real shoal draft, easy to set kites etc are also great advantages.

I would not like to cruise on a narrow hull cat unless it was very long and I don't like large cats for cruising (too big for fun) I would envisage this modular cat being max 42ft long with a displacement of 4000kg (pretty light) A 42footer with the room of your average 38 footer. You get headroom and still stay below some very scary loads that cost heaps in terms of rig size, winches, anchors and motors.

I understand Richard's point about going it alone and not being able to sell the boat. I have built 4 boats and I do see the incredible time that goes into the curved bits of interior. Hulls are easy to build - it is the interior that makes me cry. I have designed and built computer cut small cats that are fun but every time I build a boat I think about going square - not the hulls, but the superstructure. My friend spent about 3 months fairing the interior of his lovely Schionning. This is normal now. The level of fitout and work required has increased greatly just to be average. I would like someone (not me) to burst the bubble of increasing time needed to complete the interior of a cat. Compound curved roofs, curved dinettes, coves everywhere and two pack interiors are a recipe for less time cruising. A simple, flatter painted ply or similar interior can save many hundreds or thousands of hours and still get you to the same cruising grounds. How to achieve this whilst not compromising the rest of the structure is the issue.

cheers

Phil

[Richard Woods]

Once again I agree with Phil!

To Rick. The Strider WL beam is about 550mm, depth about 260mm. Disp in racing trim 800kgs, so 400kgs per hull. Merlin has approx 70mm narrower hulls.

700mm wide sounds like a trimaran main hull??

I would say 4 knots was the slow end of slow, 6 knots the fast end. Striders expect to sail in the 8-11 knot range much of the time. Easy to do high teens. Several people have done over 20 knots in flat water. I believe the max is 24 knots.

Merlin is quicker in more wind than a Strider.

To Ad Hoc.

I have sailed small multihulls for over 25 years and have owned one Gwahir, 7 (yes 7!) Striders, a Wizard and for the last 4 years sailed a Merlin. All these boats have been raced with some success. Eg I was European and UK National Micromultihull champion in 1987, 4th in the Europeans in 1994 and UK Champion in 1994.

So I reckon that if I say the Merlin is a faster boat than a Strider in more wind, and vice versa in less, than I am right.

So maybe you could outline your multihull sailing experience???

Personally since, in another thread, you implied that you would like to see ALL multihulls under 12m long banned, I suspect it isn't very much, if any.

Richard Woods of Woods Desiogns

www.sailingcatamarans.com

[Chris Ostlind]

Richard Woods,

Never fear... Our boy, Ad Hoc-inem will be along shortly to launch one of his famous, misdirection attacks on you personally, while completely ignoring the substance of the post you have so wonderfully phrased.

You'll have to pardon me while I am swept away by the vision of the festive Mexican Pinata with one wildly swinging party-goer well in over his head. There he is, flailing away, while the prize remains some distance from his grasp due to a non-existent set of on-the-water skills, in an otherwise featureless sea of cubicles. Don't you just love it when a "scientist" expounds on that with which he has little real life depth?

Of course, the fellow can always step out of the shadows and publicly proclaim his worldly sailing experience as accumulated under his real name...?

No, what's that... another pass at redirecting the issue...? You’re right, I really didn't think the function of honesty would be forthcoming.

Apex Richard... Just where did you get this character, anyway? Hey, you vouched for him, right? Why don't you provide the substantive info that brings his tired, mechanical diatribes into something that resembles a person we should respect? (as in: he has extensive sailing experience in a broad representation of craft of all sizes to back up this routine he chuffs on a regular basis) Until then, this guy is a wannabe sailor sitting on some store bought chair with too much time on his hands, pontificating about what it's like sailing boats that are appropriate for the typical reader on these pages.

Please guys, can’t you do better than this?

[Ad Hoc]

Richard

The discuss on one hull form or another has become blurred. Simply because your making reference to 'real world' attributes, such as "increased livability" or "dryness of deck". These decisions are all part of the "design spiral", ie a compromise. The debate, as i saw it, was purely one hull form against another. In which case one must compare apples with apples. The various parameters in the other boats are not all the same ergo one cannot make such a generalised statements about them 'hydrodynamically'. If the frame of reference is other than hydrodynamically then of course it is a different matter all together and when looking at "design" per se, is highly subjective. One just needs to rationalise what the 'debate is'....not what one 'thinks it is'.

"..Personally since, in another thread, you implied that you would like to see ALL multihulls under 12m long banned..."

I think you have me mistaken with someone else. Or, you have failed to understand what it was i was discussing.

"..So I reckon that if I say the Merlin is a faster boat than a Strider in more wind, and vice versa in less, than I am right...".
I cannot dispute your own observations, i don't doubt them, since that is your experience/opinion. However, i fail to see how this makes the observation "proof"... Unless of course you took detailed measurements of each hull you ever sailed against whilst competing and compared the L/D's, calculated the driving force, non dimensionalised the results and Rw's etc etc...so when you finished the race you could claim, eureka!

"...So maybe you could outline your multihull sailing experience???..
Shockingly poor, haven't done so for many years, not since a student. I'd be lucky to come in last..!!!

But since you claim that naval architects don't design boats only yacht designers do...why would you be surprised by this?!

[Ad Hoc]

Ahh..the metaphysical has popped up :)

[apex1]

May I remind you peers, that this:

Originally Posted by ImaginaryNumber View Post
Richard,

But if people weren’t living in the hull, perhaps the performance of even a cruising catamaran could be improved by making the hulls narrower (and longer?). Could you tell me if narrower hulls would imprudently reduce buoyancy or increase deck slapping?

was the question!

The only possible answer (apart from opinions and telltales) is YES, performance could be improved!
and:
NO, buoyancy is not decreased (if......see above).

So, what are we discussing here? The fivehundredseventytwo steps of a design spiral?

Thank you Mr. Ostlind for taking care of my character..........

Apex Richard... Just where did you get this character, anyway? Hey, you vouched for him, right? Why don't you provide the substantive info that brings his tired, mechanical diatribes into something that resembles a person we should respect?

But I feel nicer when people like you just ignore me! Your premature attacks do´nt really contribute to topic, they just show you have´nt understood how to discuss different points of view. And I do´nt feel responsible to provide any info about other members of the forum, nor do i vouch for any.


Regards
Richard

[Ad Hoc]

Apex/Richard

Nice to see someone else can understand and follow the topic/thrust of the thread, ie Richard's comments on narrow hulls. Everything else is well....unrelated.

[Richard Woods]

Mainly to Ad Hoc

I think you can agree that yacht designers design yachts - period (as Americans like to say). And that anyone can call themselves a yacht designer. Whereas a naval architect may be a stability expert or a propulsion specialist and not necessarily design vessels at all.

Almost certainly a naval architect will have had some formal training, but a yacht designer may not have done so.

Which leaves those of us who have yacht design qualifications in a dilemma. Do we call ourselves "naval architects", like Ed Dubois does, or yacht designers like "Bill Dixon" does? Both these highly regarded people did the same Yacht and Boat Design course as I did.

I suppose you could say a naval architect is akin to a scientist, whereas a yacht designer is like an engineer.

It is a very poor scientist who has a theory that he is not prepared to test in practice. And an even worse one who doesn't modify his theory when practice disagrees with theory.

I use my boats as floating experiments. So my Gwahir and Wizard each had two rigs, my Striders a total of five different rigs, I have had three rigs on my Merlin in 4 years. The basic hulls don't change, so any speed differences are the result of changes in the rig.

And although I could have just checked gps speeds when sailing the boat in isolation, I didn't. Instead I would race it against other similar multihulls (up to 50 other multihulls at times). So I could compare, say, a Strider's performance in certain winds against a Gwahir while using, say, a F24 as a benchmark.

When I say a Merlin is "much quicker" I don't mean by 1 or 2 knots, I mean by 0.1 knot. For those who race know that differences that small are major changes in speed.

A few years ago I raced an F31 against several sisterships. In the first race we kept the furled screecher up to windward. In the second race we took it down. We were "much" faster in the second race. Meaning that over a five mile beat, say 40 minutes, we were 100m nearer the competition.

That is what racers call "much" faster. No test tank or computer theory can predict that sort of speed difference.

I know that if it is a windy day I am more likely to win if I sail a Merlin than if I sail a Strider. Conversely, I also know, because I have done it, that a Strider can beat a fleet of Firebirds boat for boat in light winds, but be easily beaten by all of them in a blow.

Sorry this is way way off topic, and I won't comment again like this, but I want you to understand that I don't just make glib statements but rather back up considered opinions with proven full size data.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[Ad Hoc]

Richard
"..but I want you to understand that I don't just make glib statements.."

I'm not suggesting you did, plenty of hot air by others on this thread have done enough of that. I was just, as Richard/Apex was also doing, investigating the statement about narrow hulls.

As for yacht designers...well, this is all very subjective.

You're correct that yacht designers can be called that simply because that is their "field" (it is ostensibly a branch of naval architecture). But is is also true that anyone can call themselves a naval architect (certainly in the UK), without any formal qualifications. (I've just had a very interesting debate on this very subject with T.Blakley at RINA).

My best mate who is a yacht designer, whom you may probably know and maybe very well too, says i design straight lines (Im a NA), whereas i counter that he designs plastic bath tubs (He's a YD)..we've been ribbing ecah other about this for over 20 years...

A Naval Architect (a fully qualified & trained one I'm speaking about) can indeed be a fully fledged 'designer' (of boats/ships etc) or, as i know some who worked at VT, just designed ER brackets all day!!! Again, conversely a yacht designer may not have any formal training and simply "ohh, this is nice shape or idea", but does not know how to quantitatively "design it" to a professional standard and ensure its safety. (They often sub contract this out). So it works both ways.

Whatever we "design" requires training and education. But more importantly, recognising the implications, professionally, what we are doing and being able to support claims of the design, in one form or another and to make sure whatever is 'floating' is safe.

Again, slight digression too...sorry!

[catsketcher]

Gday guys

I should have made it clearer earlier about performance. I think this is a very nebulous concept and this is why I don't like super narrow hulls. A cruising boat must perform in may situations. It must tack, resist leeway, manouvre, resist pitching, carry variable loads, stay dry on deck, have people walk around without falling off etc etc. My high performance cat will not have one number - high speed - designating high performance.

My concept is a bit off key with "high performance cars" and the like where numbers such as top speed and horsepower designate performance. I probably should have a new phrase such as highly evolved or the like. This would at least try to convey that there are a myriad of competing issues involved in the design spiral.

A racer has only one object - to win. Performance can be easily determined by these easy and objective criteria. A high performance cruiser - whoa - that could be anything - it could be a really easy steerer, super comfortable in a seaway or a whole combination of facets.

The problem is that there are few numbers to help the buyer out here. Tacking ability, crew comfort, dryness, stiffness, noisiness, are more important to me that an extra 0.2 of a knot yet they have no numbers to show that my design is any better or worse so they fall out of the lexicon. We hear the same thing with economics - economists measure what they can and we try to show that this makes us happier or not. It is sometimes very hard to get numbers on the most important factors in a situation.

So I think we will agree to stand by our original points and I will muse on the inadequacies of models in describing the way our boats handle out at sea.

cheers

Phil

[masalai]

Build site costs are the least expense - have a look around, there must be a block of land where you could rent for a year, and on-sell the shed to the block owner or work out some arrangement with the owner?

I am renting an open ended shed, about 55ft x 32ft or something near that, with a very carefully levelled concrete floor, for AU$3800 for the year, including electricity, and the use of a "trailer" to deliver the boat about 3000 metres to the water... I drive daily 20km to the shed (not on Saturday or Sunday except for a strictly social visit - - no work on weekends as one needs a break)... See my thread on the build in the link below... the cat is 21ft x about 40ft...

[apex1]

Thank you Mas for coming back to topic. After throwing all the necessary compliments around, could we discuss the possibilities of building (and connecting) the bridge deck accommodation in segments? Any thoughts?

[marshmat]

Segmented bridge deck: Yes, it ought to be feasible.

An example: Chris White's "Explorer 44" trimaran. Each individual component (three hulls, plus fore and aft crossbeams) can be built independently and easily trucked to a final assembly site. At the final assembly site, the beams are bonded to the hulls and she's ready to launch.

Another example: Any of James Wharram's larger cats. These do not have a full bridgedeck, though- they have lashed crossbeams and, in some boats, cuddy-like deck pods that are structurally independent.

I can't think of any full-bridgedeck cat, though, that is demountable for piece-wise assembly. That's not to say it couldn't be done; I've done a lot of sketches myself trying to figure out how it might work. If you're OK with a "stack" of small bridgedeck segments, they become much easier to fit in a low-windage profile, much easier to fit on a truck, and I think less structurally complex as well. Perhaps a forward segment containing berths, a midships segment with dinette and nav/watch station, and a cockpit segment (its location in the "stack" depending on whether you want the cockpit ahead of or behind the deck house). At 8' thick each, three such segments, permanently joined together at the final assembly site, could form a bridgedeck comprising perhaps two-thirds of the boat's overall length.

I do think that at 35 feet, as the original poster suggests, it will be very difficult to come up with a full bridgedeck design that has sufficient bridgedeck clearance (a lot of designers seem to suggest about 3' minimum clearance for an ocean-going cruiser, while charter barges sometimes have as little as 1') while maintaining standing headroom. If you do achieve both, the likely result will be a very tall, high-windage profile, the cabin top being 10' or so above the water. It can be done, but I've never seen it done gracefully in anything 35' or less. How essential is it that we have an enormous area of standing headroom, especially in spaces (dinette, nav/watch) where we'd normally be sitting down?

[masalai]

ImaginaryNumber, It is not clear what your intention is as regards build in 12 ft wide components? is this a ONCE ONLY option required to transport cat to the launch site - - or - - is it to be a regular collapsible re-transport event... To my way of thinking, the latter option would be a right pain in the arse... in the former option, see my previous post build nearer to the launch site, as I am doing... 12 months build and anticipated launch cost around AU$300 ~ 350K... I hope:D:D:D:D

[apex1]

As far as I understood, the problem was to build at home and complete at shore.
If that is going to be a collapsable construct I would´nt like to be involved.
But lets make some sort of "book of requirements".
How much space is required at bridge deck level?
Can that living space be cleverly arranged to be divided into three sections?
What about the mimic to merry hulls and bridge? To join the segments should´nt be a problem.
Material?
When we have a rough idea how big this deck structure will come out, we can (endless) discuss the hull size and shape.

right?

[ImaginaryNumber]

Richard Woods:
Sorry to be so negative, but build it and prove me wrong

No need to apologize for being doubtful about my ideas. The purpose of my posting on this forum is to learn from those with far more experience than mine. At some point I will have to hire a designer/architect/engineer to convert an idea into buildable blueprints. Right now I gratefully relying on this forum’s expertise to see whether the concept is even worth pursuing.

http://www.multihull.de/flatcat/seiten/konzept.htm
English translation: http://tinyurl.com/nfu8eb
Here is a German website for a houseboat/catamaran which has nearly a full-width bridgedeck similar to what I am proposing. If you don’t read German (like me), Google provides a fair text translation. This is NOT the catamaran that I envision, but it does show the possibilities of having a single-level, full-width bridgedeck. To get from the FlatCat to my modular cat I would increase the clearance of the deck, replace the hulls with something sea-worthy, and make the superstructure shorter and more aerodynamic. The other big design difference is breaking up the cabin into three sections, with the two connecting joints running transversely, not longitudinally.

At the risk of hijacking my own thread, what are the pros and cons of an A-Frame type mast?

Richard Apex1:
if your hulls are narrower and longer (for the same displacement) they of course provide the same buoyancy.

I understand that the total buoyancy can be the same as for a shorter and fatter hull, but it is the distribution of the buoyancy that I am wondering about. It seems to me that in certain wave patterns a long skinny hull might “dig in” in a wave trough, and that it might also “high center” at the wave crest, causing deck slap. A shorter and fatter hull might be less apt to have these type of problems, but then pitch-poling could be an issue. So I’m trying to get a feel what relative length to breadth ratio a catamaran should have to counter the higher bridgedeck that I am proposing?

I see that both Richard Woods and Catsketcher are agreeing that 10:1 – 12:1 is a good proportion for a cruising cat. Thanks for the input.

Richard Apex1:
After throwing all the necessary compliments around, could we discuss the possibilities of building (and connecting) the bridge deck accommodation in segments?

Thank you, though I have also learned from some of the off-topic comments too!

Ad Hoc, if the specifications aren’t too ambiguous, could you suggest ways to solve the cabin segment to cabin segment connection problem, and also the bridgedeck to hull connection? Let’s say that the catamaran is 20’ wide, so each segment is 20’ wide and 8’ long. The three segments then have a combined length of 24’. Ideally (to me) the assembly process could be reversed. That would imply that everything was bolted or lashed (or ??) together. This is not a firm requirement, but it might be attractive to owners (me) when needing to haul-out when they don’t have ready access to travel lifts wide enough for a 20’-wide vessel. Lifting lugs might be incorporated into each segment that would allow it to be lifted on and off the hulls with a crane.

Matt Marsh:
If you do achieve both, the likely result will be a very tall, high-windage profile, the cabin top being 10' or so above the water. It can be done, but I've never seen it done gracefully in anything 35' or less. How essential is it that we have an enormous area of standing headroom, especially in spaces (dinette, nav/watch) where we'd normally be sitting down?

Yes, the windage has been a concern from the start. I don’t care about grace, but I do care about stability and controllability, and I’d like to keep the boat as small as is prudently possible. Standing room throughout the whole bridgedeck isn’t required. But since I plan to cruise for extended times in cooler climates I want enough standing room to help fight off claustrophobia when going outside isn’t inviting.

Thanks again for all the thoughtful suggestions,
John

[rayaldridge]

Can we please stop this crap! Apart from being offensive, that statement was wrong. In the circle of real pro´s around on this Forum, he´s known as a real pro.
Richard

I'm not any kind of pro, let alone a real one, but he's not known to me as anything but a guy who for some reason won't post under his own name. If Richard Woods isn't a "real pro" I don't know who is, and Richard doesn't seem to know who he is either. I have little patience with this sort of pointless coquetry, but maybe I'm just a grump. In any case, and this may be unfair, I can't bring myself to take seriously the statements of any person who isn't willing to stand by them under his own name and reputation. After all, this is not politics, and no one here is going to jail for saying the wrong thing.

As to the topic, it should be relatively easy to test the contention that a long thin hull will have less resistance under all conditions than a shorter fatter one of the same displacement. Freeship has a useful slender hull resistance module, contributed, as I understand it, by John Winters. If I get a chance this evening, I'll run a set of graphs. My expectation is that the fatter one will show less total resistance at low speeds, but I could be wrong.

The phrase "speeds where a cat has it´s advantages" seems a bit nonsensical to me. A cruising cat has to sail in all conditions, not just those where it has an "advantage." Light air is a fact of life. If the boat doesn't sail well in light air, evil consequences will ensue, such as overuse of engines.

[Ad Hoc]

rayaldridge

"...I can't bring myself to take seriously the statements of any person who isn't willing to stand by them under his own name and reputation..."

Well, that is the point that you and all those who are unable to comprehend. The post is not about me, nor who I am, nor anyone else, it is about the engineering/naval architectural facts to explore a concept.

The posts I make can easily be supported by endless text books, reference papers etc etc. I select not to go through the long process of detailing every little bit then finding out the person does not grasp some basic engineering concepts. So, to short circuit the debate, i present an abridged version, for clarity.

If your only way of learning or debating is by perosnally knowing who your debating with, rather than the topic at hand and the points/issued raised, your views shall always be subjective. Hence whenever you debate with a person, your views are biased towards whether you feel superior or inferior to the person, because you "know who they are", rather than can the technical claims be supported.

If any of my techincal statements i have made are incorrect or you feel require further explanation, please state so and we can debate. But if your only form of debate is a personal debate of what size my inside leg is, or how tall I am, or can i form big words or what type of tea i like (since this is what a personal debate is about, rather than a technical one) etc....it just demonstrates a lack of cognitive critiquing and comprehension. As such, there is no point reading your comments that are biased and subjective and have no value to the topic being debated.

[Ad Hoc]

ImaginaryNumber

As for your "concept". The engineering side can be done, it is not rocket since. But in order to achieve your objective, many compromises shall ahve to be made. During the life cycle of the design when presented which some of the compromises you shall be faced with, it shall slowly deviate from your original concept. In the end you may have to make so many comporises to satisfy your SOR, that you're not happy. However, you may find the some of the compromises are "I can live with that".

The first hurdle you have is two fold, hydrodynamically and structurally.

Addressing the structural first, may prove to be the wiser route. Since to have 3 modules, requires some serious connections and load paths to ensure the modules do not break free when out sailing.

So, the best way, is to sketch out the 3 modulus, and work out roughly what size for each, which you ahve roughly done, BUT, then see what you can reasonably fit in each and are you happy with it.

Once You have done that, then the task of establishing what the structural load cases are and then what structure is required to satisfy the load cases. After the first design spiral, you may find too much structure is required and compromises too much weight or space or both.

[apex1]

As to the topic, it should be relatively easy to test the contention that a long thin hull will have less resistance under all conditions than a shorter fatter one of the same displacement. Freeship has a useful slender hull resistance module, contributed, as I understand it, by John Winters. If I get a chance this evening, I'll run a set of graphs.
The phrase "speeds where a cat has it´s advantages" seems a bit nonsensical to me. A cruising cat has to sail in all conditions, not just those where it has an "advantage." Light air is a fact of life. If the boat doesn't sail well in light air, evil consequences will ensue, such as overuse of engines.

You may save your time testing well known properties of hull forms. And number crunching without the clue of what we are talking in terms of weight distribution is´nt worth the effort.
Every boat has to sail in (almost) all conditions, who does´nt know that? But when we talk cats, we auromatically focus on the upper end of the speed range. If not, there is little sense to build a cat with the specifications given by so far. (actually I do´nt see any, because ALL the requirements known by now, are better and easier to achieve in a mono, but thats builders choice)

I have little patience with this sort of pointless coquetry, but maybe I'm just a grump.
Well I have NO patience with this sort of comments! Far more than half of the forum members do´nt show their name! Who cares?




Richard Apex1:
Thank you, though I have also learned from some of the off-topic comments too!

There was´nt too much content worth to be learned.

ways to solve the cabin segment to cabin segment connection problem,

Thats no task, as long as you forget the idea of having the boat collapsable!
I doubt you find one professional (to use the term again), willing to make a design of a collapsable Cat in the 40´ range. The possibility to kill his reputation is not worth the pennies on his account! Think about that again, for your own sake.
The task are the beam / hull joints (even when permanent).

and I’d like to keep the boat as small as is prudently possible. Standing room throughout the whole bridgedeck isn’t required. But since I plan to cruise for extended times in cooler climates I want enough standing room to help fight off claustrophobia when going outside isn’t inviting.

So forget about the properties af hulls and decks and make a sketch of what you think is needed (forget to divide the structure to begin with), and lets start to make a SOR* or BOR*.

*Statement of Requirement: common in the commercial scene (shipbuilding)
*Book of Requirement: common in the Megayachtscene

***NIR: common in the yacht scene....................................No Idea about Requirement

Regards
Richard

[ImaginaryNumber]

Thats no task, as long as you forget the idea of having the boat collapsable!
I doubt you find one professional (to use the term again), willing to make a design of a collapsable Cat in the 40´ range. The possibility to kill his reputation is not worth the pennies on his account! Think about that again, for your own sake.
The task are the beam / hull joints (even when permanent).

I share your reluctance to design a "collapsible" boat. ;) Maybe the word "demountable" would be less evocative. Designing this catamaran to be demountable is lower in my priority list, and I'd be happy to have this group's suggestions pertaining just to a permanent attachment mechanism. But I'm not clear why the idea is anathema. Many catamarans are held together just with deck beams, including some rather large cats. So it seemed to me that these three proposed segments could be thought of, and designed as, very large, strong, and rigid deck beams.


So forget about the properties of hulls and decks and make a sketch of what you think is needed (forget to divide the structure to begin with), and lets start to make a SOR* or BOR*.

*Statement of Requirement: common in the commercial scene (shipbuilding)
*Book of Requirement: common in the Megayachtscene
***NIR: common in the yacht scene...No Idea about Requirement

A most helpful suggestion.

Can you suggest an on-line template that I could use for the SOR? That might save us all the frustration of my generating unnecessary or unhelpful specs.

Allow me to dispel any misconceptions: this isn't intended to be a BOR-type of project (at least for me)! :)

But I am grateful for those of you who are helping minimize my NIRs. :D

John

[masalai]

Start by identifying where you desire to cruise, for how long each "voyage", independent operation or regular calls to a marina for sleeps/shower restaurants etc., Is the region prone to sudden storms, are there lots of "safe" creeks etc where you may find shelter...

How many will sail with you? (are you running a hotel, or is this your "getaway" for peace & quiet with your partner, where you both will explore the region (gunk-holing, I have heard it called)...

Can you do without 'toys', can you adopt to a simple lifestyle... the technical stuff comes later...

[apex1]

I share your reluctance to design a "collapsible" boat. ;) Maybe the word "demountable" would be less evocative.
There is no difference, just forget it!


Many catamarans are held together just with deck beams, including some rather large cats. So it seemed to me that these three proposed segments could be thought of, and designed as, very large, strong, and rigid deck beams.
Of course, nothing else was my intention!

Can you suggest an on-line template that I could use for the SOR? That might save us all the frustration of my generating unnecessary or unhelpful specs.

Unfortunately not, every design is unique.

Allow me to dispel any misconceptions: this isn't intended to be a BOR-type of project (at least for me)! :)

Well that was a misconception! Yours will be a BOR not SOR! Ships have a SOR of some several hundred to several thousand pages. Yachts are fine with BOR of some dozen.

What I wanted to express was, do some legwork and draw a rough arrangement of your accommodation. There are hundreds of drawings and pictures on the net in exactly the size that might fit your needs.
When that is done, we can discuss the pro´s and con´s of your design and how it might be refined to provide one or the other advantage in one or the other situation.
But do´nt expect a drawing (sketches) from one of the pro´s here! When you show some serious effort done by yourself, you may be impressed how much additional work others are willing to give for free. But first your "legwork" please.

Regards
Richard

[marshmat]

Well, for starters, let me address the point made by several folks about The Requirements (whatever acronym you choose):

You need some!

And they need to be clear! And realistic!

And you need to understand your priorities- which requirements are firm, and which would be the first to go if it turns out you can't, in the end, afford the moon?

(And, if I may borrow some advice AdHoc gave me, write it all down! You may know, in your head, exactly what you need down to the finest detail. But no collaborators, designers, consultants or builders will have a clue what you're trying to do unless you write it down and talk it over. "No written SOR" only works if you are the designer, the engineer, the builder, the captain, and the only crewman. If anyone else is involved, the requirements have to be written out and discussed!)

So grab your notebook (or blackberry, or openoffice, or whatever) and start writing. There's no set format for a statement of requirements. You just write down how you want to use the boat, what features and characteristics you need, how you want it to perform, etc. Sometimes it's a paragraph, sometimes it's the size of a quantum physics textbook.

On to the boat: Yes, a big cat can be made to fit on a truck: http://cat2fold.com/
How do you do it? Brilliant engineers, plenty of cash, and plenty of compromises.

In any case, you can't disassemble a large multi-part cat in the water; no matter how you design it, the individual components still need to be hoisted, supported and stabilized somehow while it's being put together. Cat2Fold has a lot of complex engineering built in to stabilize everything as it expands and contracts. Most cats will need a crane of some kind to help.

If you really have to build inland, it's certainly possible to design for building in pieces that'll fit on trucks and stick it all together at the marina. But I wouldn't count on doing this any more than once in the boat's lifetime. Masalai's shop near the water is a dream to many of us....

[Ad Hoc]

I think everything regarding "requirements" and "a way forward" has been said :)

Excpt that so many people come onto this website with "I have an idea, what about.."...great we all have ideas. I would like to press a button and be teleported to my holiday destination, not waiting around at airports, sitting in a metal tube next to screaming kids etc. BUT, and it is a real BIG BUT, just having an idea and discussing the "idea" will get you nowhere and nowhere real fast.

You only have to read the contributions on this thread (and others very similar) by those who have no concept and cannot grasp this very simple fact.

Write it down and make it real, to paraphrase above. Once it is written down and sketched up, you'll be amazed what does or does not become clear very quickly. And half the questions you can asnwer yourself!

PS..nice to see the children dishing out negative points again...please don't stop. It is nice to know how immature and childish users on the website are, rather than having an enquirying and open mind, still its childs play, pressing a button, same on a computer program which one hasn't clue what it does :)

[rayaldridge]

You may save your time testing well known properties of hull forms. And number crunching without the clue of what we are talking in terms of weight distribution is´nt worth the effort.

No no no. You don't get to move the goalposts, just because you've scented danger. Ad Hoc stated baldly that "No true. The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too."

I ran the numbers on two hulls of identical concept, and they indicate that Ad Hoc has no idea what he's talking about.


The two hulls I ran started with a 20 foot dory-like hull that I've been working with for my last two designs. The hull displaces 12.072 cubic ft., has wetted surface of 39.4 sq. ft, and a waterline beam to length ratio of 10.4 to 1. I stretched and narrowed this hull to 25 feet. keeping displacement constant. The skinnier hull displaces 12.054 cubic feet, has wetted surface of 45 sq. ft, and a length/beam ratio of 17.9 to 1.

You don't even have to run both hulls through the KAPER module to see that Ad Hoc is completely wrong. I believe we picked 4 knots as the low end of the low speed spectrum. At 4 knots, skin friction on the 20 foot hull amounts to 5.374 lbs. Resistance due to wavemaking is .666 pounds. In other words, at this speed skin friction is almost 9 times as important as wavemaking resistance.

But wait, Let's look at the skinny hull to see if, as Ad Hoc asserts, the wavemaking resistance declines sufficiently to offset the greater skin friction brought in by the greater wetted surface of the long skinny hull. The 25 foot hull at 4 knots has 5.933 lbs. of resistance from skin friction, more, as you would expect. Does the decline in wavemaking resistance make up for it? Well it declines by half, to .312 lbs.

Unfortunately, at 4 knots, total resistance for the long skinny hull is 6.245. For the shorter, fatter hull, at 4 knots it's 6.040. It would appear that Richard Woods is probably correct in his assessment of the light-air performance of his own boats. Isn't that surprising?

The range for this exercise in number crunching was chosen to reflect the size of the hulls involved-- in light air, boats of this size may be happy to do 4 knots. For speeds under 4 knots, the disparity grows-- the shorter fatter hulls will be increasingly better at ghosting. For speeds over 4 knots the long skinny hull soon catches up. For a bigger boat, these relative values would pertain to substantially higher speeds.

[Rick Willoughby]

No no no. You don't get to move the goalposts, just because you've scented danger. Ad Hoc stated baldly that "No true. The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too."

I ran the numbers on two hulls of identical concept, and they indicate that Ad Hoc has no idea what he's talking about.


The two hulls I ran started with a 20 foot dory-like hull that I've been working with for my last two designs. The hull displaces 12.072 cubic ft., has wetted surface of 39.4 sq. ft, and a waterline beam to length ratio of 10.4 to 1. I stretched and narrowed this hull to 25 feet. keeping displacement constant. The skinnier hull displaces 12.054 cubic feet, has wetted surface of 45 sq. ft, and a length/beam ratio of 17.9 to 1.

You don't even have to run both hulls through the KAPER module to see that Ad Hoc is completely wrong. I believe we picked 4 knots as the low end of the low speed spectrum. At 4 knots, skin friction on the 20 foot hull amounts to 5.374 lbs. Resistance due to wavemaking is .666 pounds. In other words, at this speed skin friction is almost 9 times as important as wavemaking resistance.

But wait, Let's look at the skinny hull to see if, as Ad Hoc asserts, the wavemaking resistance declines sufficiently to offset the greater skin friction brought in by the greater wetted surface of the long skinny hull. The 25 foot hull at 4 knots has 5.933 lbs. of resistance from skin friction, more, as you would expect. Does the decline in wavemaking resistance make up for it? Well it declines by half, to .312 lbs.

Unfortunately, at 4 knots, total resistance for the long skinny hull is 6.245. For the shorter, fatter hull, at 4 knots it's 6.040. It would appear that Richard Woods is probably correct in his assessment of the light-air performance of his own boats. Isn't that surprising?

The range for this exercise in number crunching was chosen to reflect the size of the hulls involved-- in light air, boats of this size may be happy to do 4 knots. For speeds under 4 knots, the disparity grows-- the shorter fatter hulls will be increasingly better at ghosting. For speeds over 4 knots the long skinny hull soon catches up. For a bigger boat, these relative values would pertain to substantially higher speeds.

Ray
You are correct. There is an optimum length for the lowest drag hull for a given speed. There is a point where going longer will increase drag for exactly the reason you point out.

If you go back to post #22 I gave the basic dimensions for the lowest drag cat hulls with ship displacement of 800kg and speed of 4kts. It was not a wet finger in the air exercise. I analysed 17,284 hulls to arrive at that specific hull. Took almost 5 minutes.

Rick W

[marshmat]

Valid points, Rick and Ray.

There are several caveats that must be noted, though:
- KAPER is meant for canoes and kayaks; its estimates are not particularly accurate for any hulls that deviate from normal double-ender canoe/kayak shapes
- No resistance code can predict the drag on a hull to four significant digits. Most of the common methods will have the uncertainty estimate applied to the second significant digit.
- A set of estimates based on a numerical model of one particular hull at one speed does not necessarily reflect the properties of a different hull shape

[Ad Hoc]

RayD

Ok, so to take this further, where did those numbers come from
1) Published data on said hulls
2) Tank testing you ahve or just did
3) Computer program?

[rayaldridge]

RayD

Ok, so to take this further, where did those numbers come from
1) Published data on said hulls
2) Tank testing you ahve or just did
3) Computer program?

John Winter's KAPER module as implemented under Freeship.

Now it's your turn to support your assertion with actual data from any of those categories. I'm afraid you'll have to be specific.

Marshmat: your caveats are correct. The difference was 2 tenths of a pound, total resistance, so I feel fairly confident that it isn't just noise. That amounts to a 4 percent difference in drag-- significant to a racer, I suppose. At speeds under 4 knots, the difference grew. Every knowledgeable person with whom I've discussed this matter has confirmed that at low speeds, skin friction is far more important than wavemaking resistance. Which is why I found Ad Hoc's statement to be so strange. While it's true that different hulls will show different resistance characteristics, these were two hulls as alike in concept as I could make them, except for waterline length/beam ratio.

The point is that for any hull at low speeds, skin friction will be a much more important factor than wavemaking resistance.

As Rick pointed out, for any given speed, there will be an optimal length/beam ratio (optimal in the sense that resistance will be lowest.) Ocean greyhounds designed to be operated at high speed will have very fine hulls, since wavemaking resistance will be their main concern. A cruising boat that will have to deal with frequent light air will do better with fatter hulls, and besides, this is helpful in many other aspects of a cruising design.

[Ad Hoc]

RayD,

so, what are the caveats, or limitations of this KAPER program?

[rayaldridge]

RayD,

so, what are the caveats, or limitations of this KAPER program?

No, no. No more obfuscation. It's your turn to support your assertion. After all, you made it. Can you support it?

In case you've forgotten:

The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too.

[Ad Hoc]

RayD

I was giving you the opportunity to explore and understand naval architecture and hydrodynamics. But clearly you wish to remain ignorant in the subject and be a "I have a computer program, you can't tell me matey" type, of which proliferate on this website more than Spanish flu is currently doing.

So, just to scratch the surface (that's all since any more would be pointless that is clear), since you clearly have no desire nor understanding of anything other than superficial, the manual says thus:

"15.5.2 KAPER.
The KAPER resistance method is intended for canoes and kayaks. It was originally developed by John Winters, a naval architect now specializing in designing canoes and kayaks...It is based on statistical data obtained by model tests...
The range of valid parameters is:
● Prismatic coefficient 0.48-0.64
● Submerged transom ratio 0.0-0.04
● None of the other variables other than the waterline entrance angle me be zero."

So, without even getting in to aspects which are clearly beyond you as you are not a naval architect (nor choose to broaden your mind), for those who can read and comprehend, the program has extreme limitations.

In other words, if you have a hull outside the said parameters, the result can not be guaranteed, as they are beyond the limits.

But if that is how you wish to educate yourself on hydrodynamics using a very limited program and one "designed" for just canoes and kayaks, ...way to go matey...enjoy your limitations :)

[Rick Willoughby]

Valid points, Rick and Ray.

There are several caveats that must be noted, though:
- KAPER is meant for canoes and kayaks; its estimates are not particularly accurate for any hulls that deviate from normal double-ender canoe/kayak shapes
- No resistance code can predict the drag on a hull to four significant digits. Most of the common methods will have the uncertainty estimate applied to the second significant digit.
- A set of estimates based on a numerical model of one particular hull at one speed does not necessarily reflect the properties of a different hull shape

Mat
It does not matter what type of hull as long as you are comparing two hulls of the same type and using the same validated method of comparison. You will always find there is a finite length that will give the lowest drag for a finite speed.

Consider two slender hulls. One 50m long and the other 100m long. Identical draft of 1m, same displacement and same block coefficient. The beam of the long one is 0.5m and the beam of the short one 1m. Both have two square chines. One will have a wetted area approaching 150sg.m while the other will have a wetted area approaching 250sq.m. Bow and stern are not bluff but designed for streamline flow - like a canoe.

Now these two hulls are being towed through the water at 1 knot in calm water. Can you tell me which one will have the lower drag? (You are an engineer bound by the principles of physics. There is no magic Navil Architek wand that you can wave.)

Rick W

[masalai]

Then on those same hulls, which one will achieve the highest displacement velocity (before the power required starts to climb exponentially, the aft squats if pushed by a propeller at the stern or the hull tries to climb out and on top of the water, but at the point of any of those events commence occuring), then how much will the other hull require to achieve the same velocity?

Just looking at things from a different perspective and genuinely curious as to the answers... Thanks

[apex1]

[QUOTE]I ran the numbers on two hulls of identical concept, and they indicate that Ad Hoc has no idea what he's talking about.

In simpler words you played with your computer!


For speeds over 4 knots the long skinny hull soon catches up. For a bigger boat, these relative values would pertain to substantially higher speeds.

So now who said WE pick 4kn as a example? Did´nt I very clearly say "speed range where the Cat has advantage" ? And that is around 4kn???

Mr. Aldridge you show your lack of knowledge quite clear here, you play with numbers of completely unknown values to impress the amateur part of the Forum (Mr Willoughby likes that too). But when it comes to make a serious and valid step towards a design that fits the owners demand you have no idea!
Both of you have never been involved in Naval Architecture or Yacht design on a minimalist level, let alone on a professional one, but you claim the right to value proper advice. And to make it worse you reduce others reputation points, just because they contradict your playstation based statements. BTW others are able to play those instruments too, and probably to a further extend.
http://www.boatdesign.net/forums/design-software/step-step-design-your-boat-27900.html

As usual, you playstation engineers have no clue, no culture to discuss a different point of view and the only way to express your shabby self is the use of a anonymous rep. pointing system. Thanks for that!

Now before the thread is going to be completely hijacked by the nasty kids on the block, can we focus on the requirements again?
Speed (and hull shape) is not part of the list at present. It´s not possible to share the bears hide before we know where the forest is.

Your turn I N

[marshmat]

This is starting to remind me of that thread from a few months ago with a few of the same players...

remember, we were going to rename it "When Engineers Get Into Knife Fights"?

Now, let's all grab a beverage of our choice, sit back for a moment, and realize that we probably all agree on several key points:
- We love boats
- We're here because we like discussing boat stuff
- If we all approached problems the same way and came up with identical solutions, none of us would ever learn anything or make any progress

Now, we can probably also agree on the following:
- There are some speeds where skin friction drag is a bigger factor than wavemaking drag
- There are also some speeds where waves are more important than skin friction
- These speed ranges will not be the same for any two different boats, or even for the same boat with a different load

And, I think we'll also agree, if we go through and take a look at what the thread starter wanted, that:
- There is little point in worrying about the details of exactly how a hull will be proportioned until we have a clear idea of what the owner/builder wants to do with it
- What the original poster wanted was advice and discussion on the feasibility of building a boat in segments, inland, for later assembly at the shore, and whether a full-bridgedeck configuration would lend itself to this

[rayaldridge]

RayD
But if that is how you wish to educate yourself on hydrodynamics using a very limited program and one "designed" for just canoes and kayaks, ...way to go matey...enjoy your limitations :)

So you can't defend your remarks.

Good to know.

[rayaldridge]

In simpler words you played with your computer!



Just as you are doing now,... but without all that silly irrelevant stuff, like actual data. Maybe there's something wrong with me, but I like actual data. Don't you?

Why don't you take a stab at defending Ad Hoc's statement, since he has declined to do so? All you have to do is find something in the literature that supports his contention. Here it is again:

The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too.

For anyone who's wondering why I continue to poke at these silly folk... it's because I would hate to see the original poster take any bad advice from someone like Ad Hoc, who appears to be trolling. His statement above contradicts the stuff naval architects learn in their first classes. Therefore he is no naval architect (or if he is, he's deliberately spreading misinformation) and should not be relied upon for any advice.

I well remember the moment of disillusionment I suffered when as a design newbie infatuated with fast multihulls, I put forward the same notion-- the finer the hull, the less the drag, at all speeds. I actually believed this. It was Tom Speer who corrected me, and helped me to understand the very small role wavemaking resistance plays at low speeds.

It turns out that this is not rocket science.

[apex1]

Just as you are doing now,... but without all that silly irrelevant stuff, like actual data. Maybe there's something wrong with me, but I like actual data. Don't you?

Mr Aldridge we have no real data! Not even the questioner knows where his task will end (in terms of data).
And Mr Aldridge, I do not play with my electronic devices, I use them as tools when sensible! Whereas you make adventureous predictions of a completely unknown design. Unprofessional............

And Mr. Aldridge:

stop telling me what I have to do! You´re not qualified to do so.
John (Ad Hoc) can defend his position himself (and just to peeve you, on a professional level opposed to yours)

Can we find back now (all compliments are spread around I guess) to the topic, as Matt tried, unfortunately unsuccessfull?

Requirements?

[rayaldridge]

Mr Aldridge we have no real data! Not even the questioner knows where his task will end (in terms of data).


You're trying to move the goalposts again. Ad Hoc made a general statement pertaining to all hulls. I cited a specific example in which this general statement proved to be incorrect. Now it's up to you or him to cite an example in which his general statement is correct, or even the published statement of some well-regarded designer or naval architect which supports Ad Hoc's opinion. He was unable to do this, and now we see that you can't do it either.

This is actually a significant matter in terms of the original poster's purposes. As I understood the thinking, he wanted a boat with all accommodations in a modular center deck. This entailed the idea that he could make the hulls as fine as he wanted to, since they did not have any purpose that required ergonomic consideration. Those here who actually know what they're talking about pointed out that for a cruising cat, excessively fine hulls have disadvantages, and one of them is low speed drag. For some reason I can't understand, Ad Hoc decided to commit an act of pointless trollery and say that they were wrong. Deliberately misinforming someone who asks for advice is an ugly thing to do.

[apex1]

You're trying to move the goalposts again. Ad Hoc made a general statement pertaining to all hulls. I cited a specific example in which this general statement proved to be incorrect. Now it's up to you or him to cite an example in which his general statement is correct, or even the published statement of some well-regarded designer or naval architect which supports Ad Hoc's opinion. He was unable to do this, and now we see that you can't do it either.
T

Are you completely nuts? What have I to do with others statements ?

Prove my statements wrong coward or keep your mouth shut!

And who granted you permission to claim a answer within a few hours? Some are working to make their living! (do´nt try that, it´s for adults only)

[ImaginaryNumber]

Here is a tentative list of requirements for a modular catamaran. Probably many of the items on it could be debated ad infinitum. I’m open to suggestions. But the main point of posting this list is to aid those who might be willing to help address two questions:

Can a full-width bridgedeck catamaran be built in sections, then assembled at the launch site?

If accommodations are confined to a standing-room bridgedeck, can the resulting structure be designed to have an acceptable level of weight and windage as regarding boat control and stability?

Unfortunately, my drafting skills are negligible. I am trying to learn how to use Google Sketchup or Delftship, but could imagine that it will be awhile before I am able to produce something worth posting. So I’m hoping that my written description will provide enough of a description to address the above questions. Please ask more questions if my descriptions are inadequate. Thanks

Modular Catamaran Requirements

Where To Be Used:
Cruising SE Alaska and British Columbia (including winter), with capability of cruising to Mexico and Hawaii.
Water and air seasonally mild to cold. Winds light to very strong. Strong currents. Both sheltered bays and open coast.
High tides. Will often dry out.

How To Be Used:
Full-time liveaboard cruising for an older couple. When not sailing usually anchored; seldom at moorings or docks.
Infrequent access to major cities. Will regularly carry 6+ months provisions.

Accommodations:
Two double berths
Saloon: seating at least 6, convertible to bunk
Head: composting toilet, shower, sink
Galley: double sink, stove and oven, counters, food and cookware storage, refrigeration optional
Heater: diesel or kerosene (and maybe also a wood-burning heater)
Plenty of bookshelves
Chart table: full-sized with plenty of chart storage
Open space for working (sail repair, engine repair, hobbies, etc)
Cabin with 2”-4" foam insulation (or equivalent)
Helm in pilot house, or at least very sheltered (standing room)
Standing room in central portion of cabin, shower, galley, and helm

Catamaran Design and Construction:
Owner buildable, owner maintainable
(plywood, fiberglass, epoxy – have some experience with)
(foam composite – have no experience with)
(would prefer Strongall aluminum, but seems too heavy for this size boat – I can weld, but am not an expert)
Hulls and three-segment bridgedeck cabin 95% completed at building site, final assembly at launch site. All components less than 10’ wide
Hull length, ~36’
Hull waterline width, ~3’ to 3-1/2’ (12:1 – 10:1)
Overall Width, ~20’
Deck clearance ~3’
Net displacement 3000 lbs minimum (Net = Max – Racing)
Flat-bottom aft 2/3, then vee-bottom forward 1/3
Tough bottom to tolerate stress of drying out
LAR keels good for drying out?? Daggerboards better for performance
Rudders: skeg-supported transom-mounted
Self-Steering Windvane
Crossbeam between bows supporting anchor

Bridgedeck:
All accommodations in bridgedeck; hulls used only for storage
Bridgedeck assembled from three sections each ~20’ wide by 6’ to 10’ fore and aft
Forward Section: narrow foredeck, two berths in corners, passageway to foredeck hatch, access to hulls
Center Section: head, galley, saloon, workspace, access to hulls
Aft Section: helm station/pilot house, aftdeck, engine pod

Bridgedeck construction ideas (for each of three sections):
1) 6”(?) thick plywood stress-skin panel deck, 20’ wide by 8’long, spanning from outer hull to outer hull; main load-carrying structure.
Light weight, 2”-3” thick, composite panels for walls and roof of cabin; carries little load.
Very lightweight bulkheads supporting roof edges.

2) Deck, bulkheads, walls and roof of each section designed as a large composite box beam.
This might be preferred if typical Bermuda rig used

Hulls contain:
Batteries
Fuel
Water and wastewater
Food
Clothing
Extra sails, lines
Tools
Bicycles
Motorcycle(s)??
Folding dinghy and kayaks

Sails:
Biplane-rig: freestanding mast in each hull
Either split- or cambered-panel junk rig, or swing-wing sail
Each sail ~300 sq ft – total 600 sq ft
All lines leading to helm station

Engines:
Deck-mounted diesel with genset
OR
Two 9.9 outboards, and generator

Tenders:
Rigid dinghy on rear-deck davits
Folding kayak and/or folding dinghy stowed

Anchoring:
Two full-sized, plus at least two smaller secondary anchors
200’ chain, if weight can be tolerated
Nylon rode for all other anchors

Electrical - Electronics:
GPS
Computer
VHS radio
EPIRB
Depth sounder
Log
Cabin and running lights, LED or fluorescent where possible
Storage batteries
Solar Panels
Wind generator

[apex1]

Can a full-width bridgedeck catamaran be built in sections, then assembled at the launch site?

Yes, sure!

If accommodations are confined to a standing-room bridgedeck, can the resulting structure be designed to have an acceptable level of weight and windage as regarding boat control and stability?

Yes, sure!

I am trying to learn how to use Google Sketchup or Delftship,

Do´nt try Delftship! Thats a shipdesign software and it takes you months to learn even the basic functions! Make a sketch on a napkin and scan it!


Well done! Now we have something to start with.

Regards
Richard

[Ad Hoc]

Wow, woke up to a good laugh, since that is all one can do at such a narrow minded response.

It is very clear that RayD has the attention span and intelligence of a gnat. He feels that owning a program is all that there is to naval architecture. Since his one line replies reinforce the notion that he cannot comprehend anything other than a one liner. In response to the, ‘what are the limitations of the program’, he clearly doesn’t know and probably doesn’t care and/or doesn’t understand. He probably needs to buy a dictionary to see what “limitations” means, because ”it does not compute”!

He has no notion of simple things like the relationship between L/B, B/T, the length displacement ratio, the effect of Froude number and Reynolds number. Or simple sensitivity analysis like what happens if I make a mono but keeping the same volume and make it a multihull, or if I make the same volume in a long hull and another in a short hull…. not to mention laminar flow, separation and viscous/friction drag just to barely scratch the surface.

But this requires significant patience, reading, learning understanding and having an open enquiring mind. A button pusher has none of these attributes, again the above posts of evidence of this. Button pusher like RayD who have no training nor education in the fundamentals and principals of boat/naval architecture do not want to take the time to learn such things, “these” one liners are simply that. One line one button to press, it is simple. Don't waste my time explaining or trying to tell me otherwise, everything is so simple. So, can’t explain in one line, see…hopeless.

The next time I see my friend/colleague who is a Professor of Hydrodynamics at one of the universities that I occasionally lecture at, I’ll tell him his job is redundant. He no longer needs to teach hydrodynamics, of course he’ll ask why and I’ll tell him, that RayD knows it all. He has discovered the “holy grail” and it is a program by John Winters call KAPER. He can retire as can all the other Professors around the world doing valuable research…

Clearly I have wasted 7 years at university (and continuing) and a further 20 years designing boats. I consider myself to still be learning and shall until I die/retire. But no more!!. All I need is the KAPER program, simple. I shall now throw away all my books and research papers, including ones I’ve authored, and go and buy KAPER. I’ll tell my old Uni in the UK that they do not need to spend years learning/teaching too, just reduce the course to learn how to press buttons on a PC to drive KAPER...it is so simple, it is child’s play anyone can do it….oh, they already have! It has all the answers for all the hulls for all applications…wonderful.

That is the problem with button pushers and those with no patience and a mind tighter than a camel’s ass in a sand storm; they give professional yacht designers/naval architects a bad name. They perpetuate the notion that boats and all fields in it from design to building, are filled with amateurs that do not address small boat design seriously and with education and professionalism and so are just a waste of time and money. They go around proclaiming they know everything that there is no need to listen and learn and understand complex issue, because it is so simple, KAPER!

I was going to spend some time to copy and reference endless papers so you can read at your leisure and further your knowledge, but after the last posts, it is clear that it is a total waste of time. KAPER…the word is KAPER…no need for anything else.

Yes you read it here first. Today the world is in a new order…that order is KAPER! Don’t question it, don’t investigate the limitations, don’t think anything else matters, and don’t do anything other than trust it. KAPER!

Thanks for the comedy RayD. I’ll send you pictures of my Fahrenheit 451 moment in my garden.

Sorry ImaginaryNumber/Apex….lets get back to the thread and ignore those time wasting button pushers.

[Ad Hoc]

I.N.

"..Unfortunately, my drafting skills are negligible. I am trying to learn how to use Google Sketchup or Delftship,.."

As noted above, don't bother. As a first hit, just use a pen and paper and the paper to be lined graph paper. This way it is simple to scale. Don't worry if things look "boxy" to start with. This is the first step and nothing is exact nor accurate. But using simple graph paper helps you to get an appreciation of size and its limitations.

[rayaldridge]

Yes you read it here first. Today the world is in a new order…that order is KAPER! Don’t question it, don’t investigate the limitations, don’t think anything else matters, and don’t do anything other than trust it. KAPER!



You can't come up with even a single reference to prove your point? Really? That's a little sad.

Here's what you wrote, again, in case you've forgotten:

The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too.

Are you sure you don't want to back this statement up? No? Personally, I'd advise you to try. Otherwise, folks might start to wonder why a guy with your vast education, training, and experience can't do such a simple thing.

Here, let me show you how it's done, since you seem to be having so much trouble with the concept.

From:

Basic Ship Theory
By K. J. Rawson, E. C. Tupper

Given freedom of choice of length, keeping displacement sensibly constant, a designer will choose a short form for low speed ships, and a long, slender form for high speed ships. This is because an increase in length increases the wetted surface area and hence the skin frictional resistance. At low speed this will more than offset any reduction in wavemaking resistance...

You do see how that exactly and precisely contradicts what you said?

Now it's your turn. Of course, you could just continue with your clever strategy of calling me an idiot. In fact, I'm guessing that's exactly what you'll do, because that seems to be all you and your sock puppets have going for you. Don't disappoint me.

It seems odd to me that a guy who claims to be a naval architect didn't know this about resistance. It's really low-level stuff. Froude wrote about it over a hundred years ago. I'm starting to think you might just be a fraud.

[Ad Hoc]

Ah, see that's good you can copy and paste now too, you're evolving from just pushing a button. But as always with the button pushers, you look for one liners to satisfy your myopic world.
KAPER....
So are you now going to tell E.C.Tupper that his book is now redundant because of KAPER...it has it all....you have proved that, no one needs to know anything else...KAPER.

KAPER has no flaws, it tell you all need to know Don't question it...sounds like you're almost trying hard not to now though...

Oh for those that can read more than one line from his book:

"Form Parameters and Resistance:

There can be no absolutes in terms of optimum form. The designer must make many compromises. Even in terms of resistance one form may be better than another at one speed but inferior at another speed. Another complication is the interdependence of many form factors, including those chosen for discussion below. In that discussion only generalized comments are possible.

Frictional resistance is directly related to the wetted surface area and any reduction in this will reduce skin friction resistance. This is not, however, a parameter that can be changed in isolation from others. Other form changes are likely to have most affect on wave-making resistance but may also affect frictional resistance because of consequential changes in surface area and flow velocities around the hull."

But using parameters is a function of what a naval architect does....but that requires more than KAPER or pressing a button. So i doubt this is in a one-liner enough for you, too many words for you. Since hydrodynamics is a simple as KAPER and a one liner...great stuff, keep it up. This is much better than any comedy on TV right now. I look forward to seeing all you new theories on the bookshelves now...can i ahve a signed copy from the person that reinvented hydrodynamics overnight

I wonder what KAPER says about changing forms etc...oppss..can't don't ask, it is beyond it limitations and understanding that it is just a generic algorithm....suussshhhh. It is the answer to all our problems, don't upset the gate keeper to everything
:)

PS..forgot to add..that line from Tupper was written during the time of the big conflict in the UK MoD of Short fat ships versus Long thin ships. The short fatt ship lost.

PPS...if you believe this so much why is the only boat you have on your website long and thin..not short and stubby?..it is going very slowly..surely you practice what you preach?

[Ad Hoc]

I.N.

Sorry i'll keep to the post....button pushers are clogging up your thread.

[rayaldridge]

So are you now going to tell E.C.Tupper that his book is now redundant because of KAPER...it has it all....you have proved that, no one needs to know anything else...KAPER.

You're the one who disagrees with Tupper and Rawson. Didn't you understand that?

The stuff you quoted did not support your contention in the slightest. Where did it say anything that resembled what you said? It didn't. It was just a plate of copypasta, chosen to obfuscate the point under discussion, not to shed light on it.

What I quoted directly contradicted what you said, and what was so funny about it was that Tupper and Rawson used almost the same locution you attempted in your original assertion... except that they said the exact opposite of what you said.

I think you should immediately send a stern letter to Tupper and Rawson. Be sure to tell them what a prominent naval architect you are. I'm sure they'll take your word for it.

By the way, don't be afraid to use KAPER to prove me wrong. Even if you can't find anything in the literature to back you up, a guy of your stature ought to be able to draw a hull with a few magic bumps on it that will prove your assertion.

Here it is again, in case you've forgotten:

The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too.

Come on. Tell the truth. It's starting to sound a little dumb even to you, isn't it? The first sentence is redundant, and the last one is wrong. And you still haven't come up with a single reference to support it.

I guess I'll just have to assume you can't.

[Ad Hoc]

Oh dear Mr buttons is really now showing his ignorance of the subject by his cutting and pasting and not understanding them…oh wait…that is the same as KAPER, he is not aware and chooses to remain blissfully unaware of how it works.

So, finally for those who are being mislead by a non-naval architects who’s only source of learning is a limited program called KAPER, which he says is all anyone ever needs and cutting and pasting quotes without comprehending them…read on to understand more than just how to press buttons.

So, the quote is:

“The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too.”

So, what does that mean….well can’t ask KAPER I needs buttons pressed…oh how do we try to understand this then children?? Ok, lets explore what this means…..so taking a boat:

Well, lets take a boat say 10m long, beam 1m and draft 0.5m
So
L=10
B=1
T=0.5
Which has a displacement of around 2.82 tonnes

So the length displacement ratio is….?? Yup 7.07

So, lets tow this, and see what happens….we get a total resistance of X

Now, lets rotate the hull 90dgerees, so the B= the T and the T= B
Ie
B= 0.5
T=1

So what is the length displacement ratio…oh it is the same, no change, as is the length.

So, now lets tow this what happens??...oh…look a slightly different resistance, no, really, don’t believe it….yes children, around upto 10% different is the effects of normal B/T ratios. The resistance is now Y.

Ok, lets now rotate the hull about the midships, since according to Mr Buttons, the resistance will be much better, why, because it is shorter…ok children lets watch…


So
L=1
B=10
T=0.5
Displacement the same (same boat)

The displacement is still the same, so the length displacement ratio is now…yes children it is 0.707….!!...my my what a difference…even though nothing has changed all we have done is made it shorter on the waterline. (Mr Buttons says this is better..)

So, lets tow the boat now….what happens….gosh, look at those waves and disturbance….the resistance is very very different from the first two…really...hands up children who thinks this last run with the L=1 is much better than the first either “X” or “Y”,...oh ok... and hands up who thinks it is worse???

why is that children?? …What is different?....

yes Wiggins, at the back……”Length displacement ratio Sir”….well done, take a house point.

So what was the quote again Sir:
“The length displacement ratio is significantly better for long thin hulls compared to short fat ones and hence the wavemaking resistance is lower. This more than offsets the increase in frictional resistance at low speeds too…”

Oh, so is that what Tupper means when he said:

Frictional resistance is directly related to the wetted surface area and any reduction in this will reduce skin friction resistance. This is not, however, a parameter that can be changed in isolation from others. Other form changes are likely to have most affect on wave-making resistance but may also affect frictional resistance because of consequential changes in surface area and flow velocities around the hull."

Yes Wiggens, well done boy!….changing one parameter cannot be changed in isolation.

So, how many of you see VLCC’s which are slow, with long lengths are moving beam on to the sea…that is to say, the length is now the beam, and their beam is now the length?? Hands up…oh, no takers…what about a Cross Channel ferries have the length short…any takers, oh ok, what about yachts, surely there are yachts with very short lengths and wide beams because Mr Buttons and KAPER says this is better?...no takers??

Oh ok, well children, clearly you have an acute understanding of basic principals of hydrodynamics that you can understand something as simple as length displacement ratio and its affect on resistance.

For those wishing to explore further in more detail, try “Hydrodynamics in Ship Design” Volume 1, SNAME publication.

[catsketcher]

I can't follow Ad Hoc here. Maybe because what he and I say is fat, or slow are actually not quantified. Take one example

In dinghy sailing it is quite common for fast cats to absolutely blast the opposition in normal winds. In drifter conditions the cats can become "stuck" and fat boats like 470s and 505s of similar weight can go faster with the same sail and weight.

This is an empirical demonstration of the fallibilities of cats. Most dinghy designers (Frank Bethwaite is one) put cat's very poor drifting speed down to the increase in wetted surface they have with two long thin hulls (and rudders and boards although induced drag is debatable here). At least with boats of the same weight, with similar rigs, cats don't do well until wavemaking seems to be the issue. This tends to happen at about 5-7 knots wind speed although modern cats get going sooner.

In very light winds (low speeds) many dinghy sailers lean their boats over to get the more rounded (less wetted surface) shapes. Racing yachts do the same in light winds - getting crew forward in a drifter to raise the stern out of the water. In fact many of these techniques reduce the length of the boat - thereby increasing the displacement to length ratio - but it is a technique that works well and is proven every time that a group of dinghy sailors run our of wind.

The IOR style monos of the 70s and 80s were very much sailed this way. The big Farr type sterns had to have crew way forward - the boat did not have to lean more than if the crew stayed aft - they just had to get the big fat stern out. According to one theory it should have slowed the boat down because it was shorter and fatter but it didn't. Waterline was only important when the boat sped up.

In fact isn't that one of the fundamental principles of boat design, shown by the metre boats and any boat where LOA is not rated. Shorten the LWL for rating but put huge overhangs on it. So when the wind is light the fat hull is fine but when the wind comes up the overhang is immersed and the hull has less resistance.

For the boats Ray design I am sure that a fat - 6:1 or 8:1 hull shape is correct. Small boats have their length determined first and then they need cross sections determined by weight and therefore volume. For large cats that always move with engines the designs are different - LOA may be able to be changed and well developed hull ratios stayed with.

I maintain that a proper cruising cat should not have hulls thinner than 13:1 in less than 40ft for a cruiser. I base this on the fact that every thin hull cat I have seen cruising has it bum deeply immersed. An immersed bum is very slow and bad for tacking etc. In fact many cruising cats with even 11:1 hulls have immersed sterns. Then there is also how we sail. In 10000 miles of cruising my cat I got passed twice on passage - that's not much and both times by racing monos on delivery - not by fast cruising cats. That is because cruisers slow down in rough stuff. So to go back to the design here I would suggest that with all the stuff to go on board each hull has to have about 2500 litres volume. This is going to be pretty hard with very thin hulls of a semi-circular section. Do the spreadsheet and then add a heap more volume - say 10%. Every second cruising cat I have ever seen has had a stern extension because the designer, builder or owner got something wrong or more probably just forgot something.

cheers

Phil

[masalai]

The ones I have seen "overloaded" mainly because they "needed more stuff" than the design they bought/built should have been carrying so to carry that stuff a mould of a large oxy bottle was used to extend the bows and the stern was extended to allow the transom to be clear of the waterline.... Very stupid people... The design was the design not a supertanker... or a bulk cargo carrier... use what is there for what it is designed to carry/do - or buy a different boat more suited to your hoarding nature and desire for lots of heavy additional stuff...

A boat that can be readily disassembled cannot be called "seaworthy", for by its very structural form has weaknesses that are not necessary nor advisable in a boat - why compromise your safety with a design that is "engineered" to do something else? - - There are enough compromises in designing a well found boat, let alone requiring it to do and be something else...

[apex1]

that seems to be all you and your sock puppets have going for you. Don't disappoint me..

Stop that mate! You have crossed the line where delivering some compliments can be spicy! You are just offensive!

Your own private benchmarks and star ratings btw. show you as a unknown quantity! Even in your direct neighbourhood!

[Chris Ostlind]

Richard,

Perhaps the potential for fairness in your criticism is something to be pursued? Frankly speaking, I do not see any difference between Ray's comments and those of Ad Hoc in this matter. Yet, you have singled-out Ray.

To be honest, I'd rather see both of them chill with the invective and listen to each of their honest responses to the questions that have been asked rather than ignoring that which is obviously still without acknowledgement. Ray could simply say that yes, KAPER has its limitations and that some of the data as he supposes it, could be flawed in that regard. He could then go on to using another piece of software designed for the purpose and produce evidence that is more supportable. Ad's disdain for software in this regard is a Reddish sort of Herring as I'm sure that computer buttons are pushed all day long in that office of his.

Ad H, on the other hand, could very easily address the obvious here, rather than launch into a circuitous route that only avoids that which so many of us already know. What can one say? Many of us here have done a lot of actual sailing under a wide variety of conditions and purposes and the issues being "discussed" have long ago been sorted by the obvious results on the water. One can push numbers around all day, but the real deal happens out there where the boat is being used.

Failing that, perhaps it would be better to refrain from dosing Ray's commentary while letting Ad H present his own version exclusive of your distaste?

I know I speak for several of the guys who are reading this thread when I say that we long ago, as one of my esteemed friends has so ably put it, "Jumped the Shark", on this discussion thread. Apologies to those who do not know the expression. It can dosed here: http://en.wikipedia.org/wiki/Jumping_the_shark

Ad... Ray, it's time to let it go and get this back on the thread. You each have something valid to say, but I'm certain that it could be said in a whole lot more respectful fashion.

[M-Sasha]

Chris, I do not see Richards criticism unfair, the opposite. He was repeatedly attacked by Ray in a pretty stupid and premature manner for a statement Ad Hoc made!
For a man of his knowledge and expertise in boatbuilding it is unacceptable to be named a "sock puppet" by a tinker toy hobbyist, whos lack of knowledge is not substituted by playing inappropriate software.

Moreover despite of being attacked, Richard was the one here who tried several times to go back to topic, and to provide a helpful hand for the thread opener. Whereas Ray is out for fighting, and he has proven that on other threads.

As an aside, I have noticed your affectation to patronize people and repeatedly Richard. Knowing him personally for many years I can assure you, that man does not need to be spoon fed by anyone around here.

Sasha

[Chris Ostlind]

Sasha,

You can relax. I'm not patronizing Richard. I happen to like him and have enjoyed his posts a great deal. Both Ray and Ad can speak to their own motivations on these matters. They are both over the line, as far as reasonable decorum would indicate.

My take on Richard is that he's a reasoned and balanced dude. I'm just not seeing that here when he drops the hammer on Ray and not on Ad Hoc, as well. You can have any opinion you like, Sasha, but fairness is something that needs to be observed, or this whole thing will crumble quickly.

It matters not what experience, or letters, one has in hand if one acts in a way that is unnecessary. Trite phrasing, condescending sentence structure, the whole thing. If you think that Ad has not used that as a tool then go back, my friend and read his posts again. It's fairly easy, he's made 1500 of them since October. They are not all nice and a good deal of them are unprovoked.

I'm not saying anymore on this disturbance as there's a topic yet to be enjoyed. Surely you'd rather see a reasonable attitude expressed by all... as in everyone showing that kind of respect to one another...?

[apex1]

I'm just not seeing that here when he drops the hammer on Ray and not on Ad Hoc, as well.
?

If I may answer directly? That is very easy to understand Chris. this:


Why don't you take a stab at defending Ad Hoc's statement, since he has declined to do so?
For anyone who's wondering why I continue to poke at these silly folk... it's because I would hate to see the original poster take any bad advice


was just daft only. But:

You're trying to move the goalposts again. Ad Hoc made a general statement pertaining to all hulls............. Now it's up to you or him to cite an example ............................... He was unable to do this, and now we see that you can't do it either.


was barefaced and presumptious.

I call a person claiming that I have the obligation to either proof others statements or i´ll be named unable, a mentally disabled or simply a complete IDIOT!
But to retrieve the toy tinkerers'** honour, it has to be said that probably someone just left his kennel door open.

And as you can see it was Mr. Aldridge who attacked ME! Ad hoc did´nt. So why should I react on his posts?
but fairness is something that needs to be observed, or this whole thing will crumble quickly.

well, and where is your grave warning to Mr. Aldridge? Or was that a unilateral declaration valid only for the opponents of him?

Richard

**thank you Sasha well observed!

[Chris Ostlind]

Your points are taken and understood, Richard. I have not defended Ray. He's in this game as much as is Ad H and it has been stated as such. I've also had several bouts with Ray and they always go nowhere, so there's no point in pursuing that avenue and he knows it.

Ray was out of line for stepping into you that way. Agreed. You banged him around some for that and perhaps that could have been enough. When Ray references Ad Hoc's sock puppets, he's only trying to get you engaged again. If you refuse, he has nowhere to go with that line of debate.

Surely you see that Ad can be an unnecessarily contentious guy with little, to no provoking? When you side with him, you automatically get lumped in that pile and that's just human nature.

I'm getting emails from other members who say they find the topic interesting, but will not post here unless the BS comes to a halt. They find it a waste of time and see no reason to be subjected to the flame-outs by either of these guys.

Bring back your fair and reasoned approach and ask whatever party to stop when they are being excessive. Stay away from the feeding frenzy mode and seek a sense of order and respect.

With this said, I submit the following from my most recent post.

Danke sehr, Richard




I'm not saying anymore on this disturbance as there's a topic yet to be enjoyed...

[whoosh]

Your points are taken and understood, Richard. I have not defended Ray. He's in this game as much as is Ad H and it has been stated as such. I've also had several bouts with Ray and they always go nowhere, so there's no point in pursuing that avenue and he knows it.

Ray was out of line for stepping into you that way. Agreed. You banged him around some for that and perhaps that could have been enough. When Ray references Ad Hoc's sock puppets, he's only trying to get you engaged again. If you refuse, he has nowhere to go with that line of debate.

Surely you see that Ad can be an unnecessarily contentious guy with little, to no provoking? When you side with him, you automatically get lumped in that pile and that's just human nature.

I'm getting emails from other members who say they find the topic interesting, but will not post here unless the BS comes to a halt. They find it a waste of time and see no reason to be subjected to the flame-outs by either of these guys.

Bring back your fair and reasoned approach and ask whatever party to stop when they are being excessive. Stay away from the feeding frenzy mode and seek a sense of order and respect.

With this said, I submit the following from my most recent post.

Danke sehr, Richard

I agree with your balenced views Chris
You and I know that there are several other people who make their living from building, designing etc and those people will not come into a thread that is continually hijacked by individuals who will never ever credit anybody else or see anybody elses point of view
Anybody with a mediocre of knowledge of human behaviour, can see that these folk, scream for attention, perhaps because they have not achieved recognition, in a real life, but want that recognition in a virtual world
I do not have to name people here I promised the moderator that I would not, they know who they are if not whom they are

[rayaldridge]

For the boats Ray design I am sure that a fat - 6:1 or 8:1 hull shape is correct. Small boats have their length determined first and then they need cross sections determined by weight and therefore volume. For large cats that always move with engines the designs are different - LOA may be able to be changed and well developed hull ratios stayed with.

I maintain that a proper cruising cat should not have hulls thinner than 13:1 in less than 40ft for a cruiser. I base this on the fact that every thin hull cat I have seen cruising has it bum deeply immersed. An immersed bum is very slow and bad for tacking etc. In fact many cruising cats with even 11:1 hulls have immersed sterns. Then there is also how we sail. In 10000 miles of cruising my cat I got passed twice on passage - that's not much and both times by racing monos on delivery - not by fast cruising cats. That is because cruisers slow down in rough stuff. So to go back to the design here I would suggest that with all the stuff to go on board each hull has to have about 2500 litres volume. This is going to be pretty hard with very thin hulls of a semi-circular section. Do the spreadsheet and then add a heap more volume - say 10%. Every second cruising cat I have ever seen has had a stern extension because the designer, builder or owner got something wrong or more probably just forgot something.

cheers

Phil

Phil, actually, I wouldn't go less than 10 to 1 on any cat hull that hoped to exceed hull speed without fuss. In the two hulls I ran through KAPER, the fat hull was 10 to 1 and the skinny hull was 17 to 1.

Slider's hulls are a little better than 10 to 1, but I had to increase rocker in order to get enough displacement for two people and a modestly luxurious camping outfit, on less than a 15 foot waterline. I'm sure that slows her a little, but on the plus side, she tacks in a fairly snappy and uncatlike manner, so for a little boat with no pretension to speed, I think it all worked out okay. In any case, she slips easily through the hull speed barrier.

I'd agree that for cruising 13 or 14 to 1 is a good practical limit. I, alas, don't base this on any deep knowledge of hydrodynamics, since I'm only a slight step above a complete ignoramus, but having looked at an awful lot of designs over the last 30 years, the most successful designs by the best designers seem to stay under that 14 to 1 edge. I think if you graphed all the best live-aboard cruising designs, the average would come out around 12 to 1.

Everyone else: My apologies for giving any scope to Ad Hoc and his clownish games. It seems clear that he's a fraud and only here to massage his ego, and I regret helping him. I'll add him to my ignore list, presently occupied only (and recently) by German Richard-- I really don't think the appropriate response to polite disagreement is to call someone a coward and tell him to shut up. The internet is full of tough guys who'd be a whole lot meeker in person.

[apex1]

I'll add him to my ignore list, presently occupied only (and recently) by German Richard-- I really don't think the appropriate response to polite disagreement is to call someone a coward and tell him to shut up. .

Thank you! And the suffix "German" was the one to discover your intentions!!! fight...........
what a sad individual

[whoosh]

Thank you! And the suffix "German" was the one to discover your intentions!!! fight...........
what a sad individual

Richard
you hafta calm down, and walk away from what you do not like

you should not resort to personalities, I learnt that the hard way , frinstance there is a guy here, who is on abt 10 persons ignore list, thats his game to disagree, disrupt He remains anon. I,ll betcha thats his reply under, I,m just smiling , cos I can envisage what he writes
when I get peeved with someone, I offer to tallk it out by phone or some other way, same as I offered him early on
One man you guys ripped into, offered me the keys to his beach house

if I responded to every Turkey that posted nonsense or very Primer One Stuff abt my specialities, I would be a nervous wreck
Just today somebody gave me neg feed abt Frosty,s diesel post, yet I am a qualified diesel fitter getting to the stage where I post little, let the pics do the talking
Now go Hug a Mosque, mosquito? Turkish lady?

[Ad Hoc]

"..Just today somebody gave me neg feed abt Frosty,s diesel post, yet I am a qualified diesel fitter getting to the stage where I post little.."

That is the problem with fully open forums. Doesn't matter who or what you are, whether you post your real name or not...you shall always come across others that either:
1) Think they know more
2) Do know more
3) or simply not a clue what they are talking about either way

Either way, just because you do know more or don't know more...doesn't make them or you an expert. Just knowing a bit more or a bit less, that's all. In a normal world, debate is easy. There will always be disagreements.

But as noted on another thread and rightly said....what I write can be written with a smile or with a grimace...but they are just words...so how they are interpreted is all down to the person reading them. Since can they see me smile or frown when writing said words?

I have endless debates/arguments with my peers in my job. But it is a debate and a difference of opinion or exploring opinions, nothing more. We each enjoy it as fun too....there is no disrespect shown at all, quite the opposite extreme mutual respect.

But this is not the case on an open forums. Too many trying to look or sound knowledgeable and as such don't wish to be questioned or shown to be less than they portray. That is simply a personality disorder or education issue, nothing to do with the topic or the level of subject matter being discussed.. Why....go figure?

[masalai]

I get a feeling that this thread is starting to look like a "pissing contest" - - Lets start again, and try to point this bloke in the right direction???? If you reckon all the challenges in "Mission Impossible" were a cake walk, then continue with your original idea, and keep us posted with photographs and expenditures and test runs - I am sure many will delight at your exploits and adventures - - - - It does get boring herein occasionally... Otherwise build nearer to the ocean and build a well proven design with care and obey the designers instructions exactly and enjoy some good cruising...

[yellow cat]

John,
I am designing also a modular catamaran. I have to agree that if you build a cat or any boat or anything that is strange in the present world, you have to look at it as R & D and it's most likely that if it becomes a beginning of a new area design, chances are it will end up in museums or used as beach flower pot.
In architecture, with a white page in front of us (not copying any renaissance BS ...) , we are confronted with the famous form follows function or vise versa .(could be vice versa ...) .
The key here is what do you really want to do with your life at this stage of it.
Your program is similar to mine, in early 50's and retirering soon. Who wants to put his money into a fish hole (being in Canada on ice ... ) and then go to the super market and stare at the whooping 20% discount on toothpaste. Another fact , is who are you sharing the idea with ? If a boat cost you 50000 $ and 500000 $ divorce , you will not sell it with profit ...
Make sure your design will reflect your true minimal confort, safety (sped being safety up to a point) , flexibility, budget (unless you want to call it MS Virgin...) , etc.
If this can help, i list some major design criterias that i am working with.
1 - most injuries in a boat occur from falling, falling, falling. Either an object is falling on you or your falling on it. Especially with osteoporous ... should i say old (yes we are) age fragilities. This will greatly affect your finish and insulation decisions (floors, ceilings, walls)
2 - modularity : transportation, marina slip costs, repair ease, build ease, unsinkability, building costs (likely), to name these.
3 - materials : easy to find (plys, epoxies, etc) you may find motivating to go to Kurt Hughes multihulls web site. Most of his thoughts reach mine.
4 - nature's laws: vapor barriers, air-heads (for example) ... , fire (for example: would a sprinkler system be used as an AC and heating (with water storage))
5 - Center Of Gravity (COG) : This subject is complex. At the end of a sailing day , the COG of a cat is different from a Tri, Mono, Proa. It is also different in some ways (stability) between a motor cat and a saling cat. I know sometimes one likes to be on the wrong side ... but on a cat, the weight should be in the pontoons (amas) and as low as feasable possible in them.
An extreme cat is the "hydraplaneur mediatis" mr. Parlier's design criterias were extreme but it shows the "other side of the moon" . Motivation for innovation.
6 - Living : canadians have basements and the first thing my wife (i agree) told me was the she doesn't want to live in a basement, so the typical monos, and the live in tne pontoon is simply out of the question.
I have some more but i got to run.
"if it looks right it probably is "
Later
Mike

[daiquiri]

I get a feeling that this thread is starting to look like a "pissing contest" - - Lets start again, and try to point this bloke in the right direction????
I agree Mas. And I think that, although this is a free forum, the moderator should work a little bit more than he/she actually does.
I'm not talking about banning persons but simply about deleting messages which are not pertinent to the topic, being created simply to offend.

Freedom of speech should stop where insults begin, imho. Or otherwise we will end up with persons just chasing and punishing each other's mistakes on various topics, spreading their poisons through the whole forum.

We have a person here (ImaginaryNumber) who has asked for help about his idea to construct a modular cruising cat. He has also given us a pretty complete list of specifications, which can be read here:
http://www.boatdesign.net/forums/multihulls/modular-cruising-catamaran-28446-5.html#post288929

Couldn't we all (means - you guys :D ), from this point on, just go on with the technical discussion pertinent to his requests?
I think it is a pretty challenging list, and would love to see how will all the competent persons present here undertake this design challenge.

Cheers!

[yellow cat]

Imaginary Number
If that can be helpfull, i would order the dvd from Kurt Hughes Multihulls .com , he is in Seattle.
i did order it in vhs and in dvd ... it will give you an insight of work details with ply epoxy. I met a fella in Marina Gosselin on the Richelieu river in Quebec, his name was Michel (i misplaced his card) , this gentleman built a Kurt Hughes design cat, he could perhaps help you ou direct you.
So far, the closest best (i dont really know) place to buy boat DIY things is at Noah's boat supply in Ontario. The canadian dollar going up may change buying strategies.

Your requirements are similar to mine only in the modular aspect. I am pretty sure the two 9,9 hps will not be enough. Especially with windy conditions or currents conditions. I would consider minimum 2 x 40 hp (4 strk) with the most powerfull pitch you can get. If you plan to run aground at times, consider an aluminum prop or the carbon fiber sold at West Marine. I would avoid stainless, it gives little chance to the shaft on small hits, my neighbor learned it the hard way. I have seen and tried twin jet propulsion on a 45ft cruiser , he was also running aground at times in low tides (we all did) and he says he saved $$$ using jets turbines instead of props. . I don't know and i don't want to start discussions with my other neighbor who is a Seadoo engineer ... not yet anyway.

[masalai]

One thing not covered yet? but which in the end influenced my "individualistic plans" was RE-SALE-ABILITY... What happens if need is changed because of a stroke or whatever and one needs to sell your much loved ex-toy / pride-n-joy? If it looks "normal" it will find a buyer who may also appreciate some additional features - so long as they do not encumber the product with lots of caveats....

[Chris Ostlind]

Just yesterday, I posted this bit over at Sailing Anarchy, dealing with homebuilt boats and the business of resale value.

"If it's sweat equity that drives the equation, then forget about building your own and also buying new. Getting your hands on a fairly clean used boat where a good deal of all that has gone into it is amortized away as depreciation, is the way to go.

In this economy, especially, this is the single most cost effective method for getting out on the water as quickly as possible. This is about getting out on the water, is it not?

Building your own has to be mostly about the joy of doing it yourself and the inherent pride of ownership. Otherwise, after you pencil-out all the labor, as you mention, as well as the rent for the space to do the build and all the various costs for materials, etc., you're not doing yourself any favors. And yes... your personal garage has a square foot value as it is incurred in your house payment, overhead, etc. Whatever it was formerly used for before you start to build, you will not be using it that way until that multi-piece boat project gets out of the way.

All said in the interest of fairness, even though I provide plan sets for home builders. There's just no way around it. You simply gotta want to make your own boat more than the numbers say otherwise.

If your hobby build time is carefree and totally devoid of time/value consciousness, as a really good hobby should be... (In fact, a really good job should be that way, as well, but not many of us can make that claim) then you are off and running and can focus carefully on doing really good work, rather than really fast work. At that point, the whole vision of making your own boat for exciting, waterborne adventures comes fully into view and the calculated value of your time is a moot point. It's your boat, who's rushing you? OK, OK, don't answer that one, as someone is sure to tell you at some point to get the lead out and give back the garage... but you get the point. The looming question of needing to get your sweat back out should you sell the boat is also much further down the list, as it was already fulfilled during the joy of the build.

There's a larger question in all this that has to do with our societal "rules" regarding getting your value back on resale. For me... if I have to get all wound-up about how that coinage is coming back to me, if and when, I sell the boat... then I feel that I've done, or will be doing, the project for all the wrong reasons. We're talking personal, hobbiest, homebuilt stuff here and not a product that we produce for a profit that supports our style of life. Do any of you have the same concerns about the possible resale value of a tablesaw when you want to get a new one? Didn't think so... and the relative costs involved are virtually irrelevant to me, as I plan to keep whatever boat I do build for a long time.

Maybe it's just me, but this whole thing about the resale importance of a self-built boat is entirely overblown. You guys, of course, can make your own decisions on the issue as it presents itself in your lives."

Working in still photography for over 35 years, with a specialty in architectural imagery, I see a load of custom-built homes every year that have been modified by the owners after they move in. Some of these alterations run well into the hundreds of thousands of dollars and cover things like spiffy garage/shop mods, outrageous landscaping, etc. This stuff is done for the pleasure and purpose of the owner and quite often, they get nothing of value in return for the changes when and if they sell the house in the future. The dynamic variability of this process is too complex to get into right now, but suffice to say, there are many forces at work, globally, that can change your financial plans in a very short period of time.

I do recognize that there might be a cut-off point where the total cost of a boat is such that some inherent value, after the fact, could be substantial. For that kind of project, as it looks to apply to your current build, Masa, I do see the argument you present. For the types of projects that most of the rest of the guys here will engage, there has to be something quite different going on in the decision making process of spending say, $20-$50,000, for instance on a personal boat for pleasure.

If one of us were to spend that much on landscaping at our homes, there's no real expectation that it will come back in the form of a house sold at a higher value as reflected in the "improvements" we have made. It may help to sell the home as a perceived bit of curb appeal, but the new owners could just as likely tear it all out and put in a drought tolerant environment the day after you move out. So much for the $50K of expected returned value.

Value is a tricky thing, as most of us know. If nobody buys the thing in question, then it has no value. I don't care if it's made from aerospace modulus fibers, alien foam and satellite grade epoxy, no sale means no value... period. Just as the quick sale of a nicely built wooden boat indicates that it has all kinds of value, it is much more about who trundles along in the mood for what you've got and not about what that boat is made from.

My opinion is that it's much better to build it based on desire, use it in the same fashion and forget about how much might come back out of it, should it be sold for whatever reason. If the possible hit of a near zero sale is too much for the owner in question, then perhaps this person ought to not get strung-out in the process from the beginning. Boats and boat owners are fickle characters.

One look about in the real estate markets right now will teach one to never assume that the thing that you bought will be worth anything like your expectations when it comes time to sell.

[masalai]

daiquiri, No No No definitely not yes, Jeff has enough on his plate and leaving it run its course is the best.... Look at the stuff up governments make by interfering and "equalising"... Just don't read the dickhead posts - I don't even use the ignore option as sometimes there may be a very useful point that one could have otherwise read... :D:D:D:D

Chris, you are throwing a lot of new considerations into the light, and in the broader context very valid - I know some folk who consider "the build" their interest and some where the quality of the build is marginal to be polite, but only want to get out on the water as soon as possible and stay there... and millions of other flavours as well...

Most are content with the expected resale value of a cared for tool (here it is about 50%), but a boat that cost in excess of AU$350,000 is altogether different, and I would hope for at least materials and costs for a product built to a respected designers satisfaction/approval. and my boat is 39ft plus a bit...

In the decision making process all factors should be carefully assessed and do not let the dream be the controlling factor, just the gently directional guidance...

[apex1]

So, now where are all our Cat specialists? All the guys which have been so quickly responding to posts not convenient for them.

Where is your experience? Your advice, offered with a full mouth (too full I assume)?

This was from 26th of the past month:

Here is a tentative list of requirements for a modular catamaran. Probably many of the items on it could be debated ad infinitum. I’m open to suggestions. But the main point of posting this list is to aid those who might be willing to help address two questions:

Can a full-width bridgedeck catamaran be built in sections, then assembled at the launch site?

If accommodations are confined to a standing-room bridgedeck, can the resulting structure be designed to have an acceptable level of weight and windage as regarding boat control and stability?

Unfortunately, my drafting skills are negligible. I am trying to learn how to use Google Sketchup or Delftship, but could imagine that it will be awhile before I am able to produce something worth posting. So I’m hoping that my written description will provide enough of a description to address the above questions. Please ask more questions if my descriptions are inadequate. Thanks

Modular Catamaran Requirements

Where To Be Used:
Cruising SE Alaska and British Columbia (including winter), with capability of cruising to Mexico and Hawaii.
Water and air seasonally mild to cold. Winds light to very strong. Strong currents. Both sheltered bays and open coast.
High tides. Will often dry out.

How To Be Used:
Full-time liveaboard cruising for an older couple. When not sailing usually anchored; seldom at moorings or docks.
Infrequent access to major cities. Will regularly carry 6+ months provisions.

Accommodations:
Two double berths
Saloon: seating at least 6, convertible to bunk
Head: composting toilet, shower, sink
Galley: double sink, stove and oven, counters, food and cookware storage, refrigeration optional
Heater: diesel or kerosene (and maybe also a wood-burning heater)
Plenty of bookshelves
Chart table: full-sized with plenty of chart storage
Open space for working (sail repair, engine repair, hobbies, etc)
Cabin with 2”-4" foam insulation (or equivalent)
Helm in pilot house, or at least very sheltered (standing room)
Standing room in central portion of cabin, shower, galley, and helm

Catamaran Design and Construction:
Owner buildable, owner maintainable
(plywood, fiberglass, epoxy – have some experience with)
(foam composite – have no experience with)
(would prefer Strongall aluminum, but seems too heavy for this size boat – I can weld, but am not an expert)
Hulls and three-segment bridgedeck cabin 95% completed at building site, final assembly at launch site. All components less than 10’ wide
Hull length, ~36’
Hull waterline width, ~3’ to 3-1/2’ (12:1 – 10:1)
Overall Width, ~20’
Deck clearance ~3’
Net displacement 3000 lbs minimum (Net = Max – Racing)
Flat-bottom aft 2/3, then vee-bottom forward 1/3
Tough bottom to tolerate stress of drying out
LAR keels good for drying out?? Daggerboards better for performance
Rudders: skeg-supported transom-mounted
Self-Steering Windvane
Crossbeam between bows supporting anchor

Bridgedeck:
All accommodations in bridgedeck; hulls used only for storage
Bridgedeck assembled from three sections each ~20’ wide by 6’ to 10’ fore and aft
Forward Section: narrow foredeck, two berths in corners, passageway to foredeck hatch, access to hulls
Center Section: head, galley, saloon, workspace, access to hulls
Aft Section: helm station/pilot house, aftdeck, engine pod

Bridgedeck construction ideas (for each of three sections):
1) 6”(?) thick plywood stress-skin panel deck, 20’ wide by 8’long, spanning from outer hull to outer hull; main load-carrying structure.
Light weight, 2”-3” thick, composite panels for walls and roof of cabin; carries little load.
Very lightweight bulkheads supporting roof edges.

2) Deck, bulkheads, walls and roof of each section designed as a large composite box beam.
This might be preferred if typical Bermuda rig used

Hulls contain:
Batteries
Fuel
Water and wastewater
Food
Clothing
Extra sails, lines
Tools
Bicycles
Motorcycle(s)??
Folding dinghy and kayaks

Sails:
Biplane-rig: freestanding mast in each hull
Either split- or cambered-panel junk rig, or swing-wing sail
Each sail ~300 sq ft – total 600 sq ft
All lines leading to helm station

Engines:
Deck-mounted diesel with genset
OR
Two 9.9 outboards, and generator

Tenders:
Rigid dinghy on rear-deck davits
Folding kayak and/or folding dinghy stowed

Anchoring:
Two full-sized, plus at least two smaller secondary anchors
200’ chain, if weight can be tolerated
Nylon rode for all other anchors

Electrical - Electronics:
GPS
Computer
VHS radio
EPIRB
Depth sounder
Log
Cabin and running lights, LED or fluorescent where possible
Storage batteries
Solar Panels
Wind generator

There has one being argueing here when a reply did´nt come within 24 hrs. Where are YOU now?

So, get your legs up guys............

[masalai]

Don,t be so impatient, and I am no "expert", some things are achievable without too much difficulty...

My build could be done in halves and joined elsewhere then final painting and rigging,,, but I would not recommend it as some serious engineering and how to join effectively to distribute loads would have to be worked out... Got lots of spare money could be done I guess, but the cheaper option would be to buy / rent a shed and build nearer launch point... Building in epoxy (and probably other glues) has difficulties in cold climates so a heated shed may be appropriate - (It is a right shit when the epoxy does not go off - just a very difficult and painful task to remove all evidence)

So my suggestion, seeing how the project is being done by "older people" may be to build further south where there is no need to heat the shed, and sail up the coast (in the fair weather season) to get to your cruising ground...

If you must have a collapsible boat get a proven design as the engineering loads are significant and complex... some of your boat specifications are too complex for older people cruising... The bi-rigged schoinning came in a burst of publicity but seemed to fade - leads one to speculate on some handling issues? for the older to handle.... Your cruising range alone will present some problems - heating and cooling (read money and weight of unused part and fuel) - 6inch thick plywood - are you nuts or is that a typo? as a box girder - go find a competent marine (CATAMARAN) engineer... Aluminium comes into its own around 40 ft and overlaps with DuFLEX which is good even for the dingy - have a look here http://www.duflex.com.au/duflex/amateur

To carry 6 months stores look at nearer 40 ft and (5500kg = 12125pounds) 5000 to 6000kg minimum displacement ready to cruise, so long as you can live sparsely and frugally... decide galley up or down... Forward or aft cockpit (for sail handling, including reefing and battening down in the event of some failure) - I am using a hitch-hiker rig of 2 genoas only on roller reefing/furling - NO MAIN...
List all the stuff and WEIGH it can you live happily with that?... Electric anchor winch?... Paper charts... Mag compass... Genset location will be a problem... Jibeing is a shit of an idea for oldies... What do you want 2 sinks for?... You have too many different fuels!... how much will you carry? A full size chart table???... mini-keels are OK if you are not racing and will "protect" rudders & screws... Windvane steering NO - reliable electric/hydraulic autopilot... I will carry 2 x 30M2 sails (about 645 sq ft) and weigh 4500kg... Bookshelves (books are too heavy) a stacked shopping trolly gets close to 2000 pounds.... Go and look on the web at as many layouts you can find and realise your limitations... You need a freezer... your stove can be 2 burner but that means carrying gas bottles as well, (fire-extinguishers) - do lots of homework, count and record the food you use over the next 12 months, what stuff you need to have and weigh it... Start another post in 6 months time or buy a well found boat - - - GET A RELIABLE SURVEYOR TO CHECK IT THOROUGHLY... money well spent...

[Richard Woods]

I just got back from sailing my catamaran here in hot and sunny BC, so missed a few pages of this thread.

I see Imaginarynumber wants to use his boat in the PNW.

I was talking yesterday to someone who lived on board his 38ft Horstman trimaran in BC for 8 years. He was telling me about the time he was iced in up Tod Inlet.

He is a member of the BCMS. Maybe joining that association would help you contact cruisers with the experience of multihull sailing that you are seeking.

You may also like to contact Garret Hennigan (time for a catamaran adventure . com) who, with his wife, home built his modular 28ft Gypsy and cruised the same area as you plan to. He did overload his boat though with lots of "goodies" and later agreed he would have been better starting with a 34ft Romany.

As I wrote before, you CAN build a bridgedeck catamaran in sections. What I think would be a mistake is not using the hulls for accommodation but only for storage.

Using your graph paper sketch a boat 35ft long with 4ft freeboard. (The hull sole will be about 12in below the WL, so that would give you 5ft headroom in the hulls. Clearly if you have any more than 5ft you will definitely be using the hulls for accommodation.

Then draw a line for the bridgedeck clearance at say 18in about the WL (2ft would be better though)

Then draw a line 6ft 6in above that to give you standing headroom in the central cabin. Then try and make it not look like a box. I think you'll find it will look much better if you raise the freeboard, or add a step in the cabin side or have a raised topside.

And thus you'll probably see why people don't actually draw the boat that you would like.

Hope this helps

Richard Woods of Woods Designs

www.sailingcatamarans.com

[ImaginaryNumber]

Hello All:
That was a bit of a blow we just had. :rolleyes: Thanks to all who weathered the storm and still wish to continue sailing towards the original destination. Thanks for all the helpful posts. I’ll comment on some of them below, but I hope that there will be more discussion on my two basic questions – a modular catamaran with bridgedeck-only accommodations.

Richard Apex and Ad Hoc:
I’ll save learning Delftship for when I have a year or two to spare. It appears that Sketchup is more tractable.

Yellow Cat:
You’ve mentioned a number of interesting points.
Falling: One reason for a flatter-sailing catamaran. However, a large, open bridgedeck can also be a problem in rough seas. I’d like a large open work area, yet also recognize that narrow, confining passageways can reduce injuries.
COG: Yes, having as much weight as possible in the hulls is best, so putting all the accommodations in the bridgedeck is working against stability.
Divorce: Not in the list of requirements, and, hopefully, not one of the inevitable compromises. :)
Noah boat supply: I’ve purchased plywood from them. IIRC, they have both US and Canadian distribution addresses.
Outboards: After I posted “9.9 outboards” I realized that they would likely be too small. Good ideas regarding aluminum or carbon props, or a jets. Please feel free to share more of your modular catamaran design ideas.

Masalai and Chris Ostlind:
Resale value, and build vs. buy, are good questions. In my case, building is intrinsically pleasant. In addition, I’ve not seen a boat with the particular specifications I desire.

Masalai:
Deck NOT 6” thick plywood. I meant to suggest the possibility of making a 6”-thick stress-skin panel for the main load-carrying member. I’m open to suggestions for other options. Also, after I posted my requirements list, I realized that the NET displacement needs to be significantly higher than what I specified, as you correctly pointed out.

Richard Woods:
Thanks for the BCMS and the time-for-a-catamaran-adventure.com suggestions. I also appreciate your designs suggestions. If I could work out a reasonable way to transport a non-modular catamaran from my building site to launch site I would certainly consider your designs.

Thanks all,
John

[ImaginaryNumber]

Here’s a crude Sketchup rendition of an idea for a modular catamaran. The following dimensions are for reference only – everything is subject to change. I don’t present this as a ready-to-build blueprint, but because some thought I should get down on paper at least a crude concept – both to make things clearer to me, as well as to better explain my concept to others. It’s the implementation of the engineering details that I’m hoping you folks will help me with.

LOA 36’
Catamaran Width 20’
Hull Width 3’+ at waterline
Hull height 5-1/2’
Draft 1-1/2’, keels not included (I don’t really know what the draft will be)
Masts 32’ above deck
Deck clearance 2-1/2’
Cabin height 7’ (outside dims)
Cabin bury in hulls 1-1/2’
Length of Fore-module 8’ (including foredeck)
Length of Center-module 8’
Length of Aft-module/aft deck 5’

My two primary questions are:

If all the accommodations are in the full-width bridgedeck can the superstructure be designed to have not too high a COG, and can it be aerodynamically designed to not have problematic windage?

Can the bridgedeck be designed to be built in three transverse modules, with most of the work of building the modules and the hulls being done away from the launch site? I think this last feature (not necessarily considering the bridgedeck-only accommodations) might be of interest to catamaran designers whose clientele might appreciate being able to mostly build away from the launch site.

[Richard Woods]

I should also have said (as I think others have also done) that I would not recommend the bi plane rig, nor the lack of headsails.

You should think about how easy it will be to get forward, maybe at night and in a big sea??

Also getting on board from a dinghy, from the side when docked, and from bow or stern when "Med moored" (which you will do in the PNW)

Also you want to be able to see both bows and both sterns from the helm station(s)

Richard Woods of Woods Designs

www.sailingcatamarans.com

[masalai]

Long, long, learning curve - a bathtub toy, as buoyancy is not there (reminds me a little of my first drawing effort... I used dozens of sheets of A3 graph paper... hehehe)... GIVE UP on the "idea" of joining, far too risky... The structural box girders on my build are everywhere and all different sizes... Spend LOTS OF TIME looking at existing boats and plans, and talking to builders and owners - asking all the dumb questions you thought you should not ask, it is accepted by all, (but the arrogant arseholes you can ignore as they would like of you), as part of the learning process and most will be delighted to introduce you to their view... - - - You are not ready yet... look around, go on daysails, make friends, supply a slab (carton) or 6pack of beer as a "sociable lubricant during a sail and enjoy the gathering of knowledge"...

[Ad Hoc]

I.N.

As I noted before, if you use simple graph paper, then the lines become a simple scale. Measure items from your own house or better still go into a friends boat, measure the size of "typical" room and items, the head, bedrooms etc. Assuming you're happy with the size of the "typical" rooms, then draw these up on your graph paper. Once you have drawn up the "room's" you think you require, or would like, you'll see how small or how large the boat shall be, just as a first hit. Then you can ascertain the deck layout and from that select the hull best suited. Once you ahve have gone through that and you're satisfied all "looks" ok, get nice detailed weights for everything. Do a simple CoG check, to see where the CoG is, and then you can see, from your selected hull, is she floats, floats up right and at a waterline/trim you hope/expect.

Until you've done this simple procedure, you'll constantly be going around in circles and doing "what if's". Once drawn up, many things become obvious...

[apex1]

Na also, geht doch!:D

[ImaginaryNumber]

I would not recommend the bi plane rig, nor the lack of headsails.

You should think about how easy it will be to get forward?

Also you want to be able to see both bows and both sterns from the helm station(s)

Richard Woods, I’d like to better understand why you don’t recommend bi-plane rigs? The two links I gave in a previous post were both for bi-plane cruising catamarans. Pete Hill is a very accomplished sailor, and he sailed the junk-rigged China Moon mostly single-handed thousands of miles over the course of a few years. Bertrand Fercot liked his bi-plane 30’ Wharram Tiki well enough that he is now building a larger 46’ Wharram bi-plane with Swing-Wing sails (which have some similarity to junk sails). I don’t particularly care whether I have a bi-plane rig or not. What I do want is the ease of sail handling that comes with the newer versions of the junk sail. Junk sails typically are used on free-standing masts, and I’m not sure how to mount such a mast on a catamaran’s deck – thus the choice to go with a bi-plane rig.

To gain access to the foredeck I am exploring the idea of a hatch of some sort at the front end of the cabin. I’m not sure how to do that. I know that some of the larger catamarans have front cockpits, so they have solved the problem of a forward passageway. But I don’t know the details, and don’t know if I can use that for my size boat. The problems I see are having a hatch that can withstand the force a wave breaking over the bow, and also allowing dry passage through it during a heavy rain. Because junk sails are so easy to tend I don’t expect to regularly need to go on the foredecks during heavy weather. I suppose if a forward hatch is not practical I can always go up and over the roof, or down into the hulls and back up through a hull hatch – but these are not my preferred solutions.

I also left off any details of a helm station on my drawing. Some sort of doghouse on the roof comes to mind, but that puts a small piece of the superstructure even higher. :confused:


asking all the dumb questions you thought you should not ask, it is accepted by all

Long, long, learning curve - a bathtub toy, as buoyancy is not there

Masalai, Thanks for inviting me to ask dumb questions. I’m doing my best not to disappoint. :) There is nothing I would like better than to not have a long learning curve. I’d prefer not to be doing any designing, but rather look through the existing designs, pick one that fits my needs, and start building. My reluctance to go with any of the designs I’ve found thus far resulted from my desire for an easily-heated cabin (low surface area for high interior volume; i.e. a single cabin), and a modular structure that could be mostly built away from the launch site.

As I noted before, if you use simple graph paper, then the lines become a simple scale

Ad Hoc, The Sketchup model is to scale, though from the perspective shown in the above model the length may appear foreshortened. It really is amazing how fast one can learn the basics of Sketchup, though I am having particular trouble with intersecting curves for the hulls. Eventually I gave up and resorted to crude approximations with large triangles and rectangles.

Your suggestions of laying out floor plans and calculating CoG’s are appreciated, but as I noted to Masalai I’d rather be building than designing. The primary living quarters are in the front two modules. Together their floor space is roughly 20’ wide by 14’ long, call it 250 sq ft. Considering all the storage space that is still available in the hulls I believe that there would be plenty of space for our needs, and the big, open bridgedeck could accommodate any number of acceptable layouts.

The primary reason I’ve come to this forum for help is to see whether a couple of specific problems could be solved by the generous designers and engineers here. I know that many problems are complex, and one apparent solution may turn out to be inappropriate when other constraints are introduced. But I think enough has now been specified so that a first-approximation design can be made, if folks are interested in doing so. The stresses on the bridgedeck are not going to be appreciable different whether the berths are placed forward or aft. Nor is the windage going to change much according to where the galley is put.

[ImaginaryNumber]

Perhaps I’m asking too many questions at once? I’ve made another sketch of just the hulls (a bit narrower and deeper than before), with a simple, flat, three-piece deck. The forward deck has a triangular deckbeam, and the aft deck has a rectangular deckbeam. The decks are ~6” thick by ~20’ wide, and the beams are 1-1/2’ high. The fore deck and middle deck are 8’ long, and the aft deck is 5’ long.

Would anyone care to suggest a design whereby the decks are built independent of each other and the hulls, are strong enough to carry the expected loads, and can be fastened to the hulls as a secondary operation?

Thank you,
John

[Ad Hoc]

I.N.

"..I’d rather be building than designing..."
I'm sure you would, but if you don't do the basics first, you'll be on this website again, in about 1 year, asking such questions why this and that is happening and how do I cure it. Which will just point to the fact a simple CoG analysis would have shown prior to any build. As I've always said to the draughtsman and naval architects I've trained up, an extra 'hour' spent in the design office, can save endless manhours or even days/weeks in production hours, not to mention money later on. But if you choose not to do so, that is your prerogative.

"...Would anyone care to suggest a design whereby the decks are built independent of each other and the hulls, are strong enough to carry the expected loads, and can be fastened to the hulls as a secondary operation?.."

I've design several catamarans in the past, (commercial) where the two hulls ahve been bolted together via box beams. It is not a difficult task in the engineering sense. All you need to do, is calculate your full/max load and then establish the sea conditions and hence the applied loads that shall be experienced. From this, you can design the structure to be "bolt-able", or any other quick means of fastening, having the ability to "take out" and sherk the applied loads to the surrounding structure. It is all about the applied loads, the rest is child's play after that.

[Rick Willoughby]

Some random thoughts - hopefully of value:

1. You should be able to master Delftship in about half the time as it has taken you to get to grips with Sketch-up. Once you come to grips with the idea of surface modeling it is very easy to use. It has more capability than Sketch-up for boat rendering and design data. Cannot remember if Shecth-up has layers but this adds tremendously as you get further into the design process to easily get weights of the main components.

2. What you are aiming to build is more like a pontoon boat. Accommodation separate to the hulls. You may get design and construction cues from these.

3. Joining cat hulls requires structurally competent beams. I would look to separate these from the accommodation, at least in the first instance. So the boat would be like a big beach cat until the accommodation pod was added. This gets large structural loads out of the accommodation pods. Large beams could be socketed into the hull on tapers. Pulled up for assembly and jacked off for disassembly.

4. Constructability on an engineering project usually follows the design. It IS iterative but the method of construction does not dictate the outcome. I would look for the boat that came closest to suit the needs then look at constructability. If there are simple design changes that made it easier to build then these are incorporated.

5. The design effort that goes into a complete boat of these proportions from scratch is significant. The more you can take from an existing design the less work involved. If you know of a boat that has the basic proportions then this might be a better starting point. A NA will charge around $100/hr and you do not get a lot of design for a days work. You can make your own estimates but taking your ideas and getting detail design for a completely new boat would be say 10 weeks work at a guess. So before you start building you have spent $40k on a unique design. Can you save this on the construction?

Rick W

[ImaginaryNumber]

Here is a pint-sized version of the style of catamaran I am wanting - sans modularity. Large single cabin, free-standing masts, easily managed sails, fun to use. It doesn't have to be car-toppable! Don't any of you catamaran designers see the same vision that I see?

http://turtleislands.net/mc/default.html

[masalai]

Scaling up is not really successful, the diagonal twisting forces are the killer... - - why does it cost a lot less to build 4 boats 20 ft by 10 ft than one boat 40 ft by 20 ft? the same reason the 4 boats weigh less than the one... I can't be bothered, DO SOME practical RESEARCH... GO SAILING... Try boats about the size you want... WHY reinvent the wheel - it probably has been done and found not to be very successful at the size / scale you have expressed interest....

Have a look at this sailing rig, It is called a "Hitch-hiker" rig after John Hitch... if you want an easily handled sailplan - - NO forward or any-where else work all done from within...

[Inquisitor]

Then draw a line for the bridgedeck clearance at say 18in about the WL (2ft would be better though)


Would it be too much to ask for you to elaborate on bridge deck clearance? I’ve probably read about every word you have on your website and know the reasons for bridge deck clearance... wave pounding the underside. Obviously there is always going to be a point where pounding occurs even at 3+ feet clearance and I understand why hulls wider apart need even more clearance.

To the discussion at hand… say ImaginaryNumber’s size 36’x 20’. What would the differences be that you would recommend based on mission (costal cruiser, racer, blue water)? And with your recommendation for blue water, what has been your experience of how much you have still experienced pounding?

[Inquisitor]

Hello All:
I’ll save learning Delftship for when I have a year or two to spare. It appears that Sketchup is more tractable.

I don’t have any credentials… (I’m an amateur) but I’ve found that Delftship is very easy to learn as long as you don’t ask it to go beyond doing the hull shape. Forget using it for interior structure and bridge deck. You can export the hull bottom using File/Export/DXF 3D Mesh… This is easily imported into Google SketchUp. I’ve found building with it to be a lot easier. However, I would not want to try building the hull in SketchUp.

e.g. – Building a 90 degree staircase on the back of a Cat hull took nearly a half week with Delfship. Doing the same thing with Sketup takes less than 5 minutes.

But, for the stage you’re in now… throwing boxes around… you’re doing fine.

[masalai]

http://freeship-plus.pisem.su/indexEN.html is the Russian version, I used it and mostly sorted and satisfactory within 6 months, Delftship is the European ? version and has an upgrade path to its commercial stuff. If you are not brain dead or afflicted by encroaching Alzhimer's then either path is the way to go as the others cannot give displacement and weight analysis which is necessary to determine if the stuff you want aboard will fit (space wise as well as weight carrying ability) DO NOT WORRY ABOUT bridgedeck refinements yet... Until you realise what is achievable and realistic in cost benefit analysis, the technical stuff can wait... Then sort out the structural engineering issues, then and only then, bridgedeck clearance and hull lines for cruising efficiency...

Berths in the hulls aft will give the most comfortable movement for anchored up at night - feet aft/head forward... Toilet and shower in the forward end of one of the hulls, washing machine in the "toilet space" in the other hull... consider hitch-hiker option (no main and all the controls associated with it and no head banging boom for 'old farts' to worry about / forget is there - - OUCH)...

Got that? sensible layout first

Engineering issues (split and join) next

Cruising design on hulls and bridgedeck clearance

Find an existing design that meets most of your needs / desires and buy build that - saying, "So close to what I am after, why re-invent the wheel"

A well trod, tried and proven path...

Sailing wing on wing (both sails set outside) is bloody silly as a minor change in wind or whilst climbing some swell could force a catastrophic jibe... Never do that, and cats are better tacking downwind (better VMG) That is also why windvane autopilots are stupid, cats often make their own wind (the apparent wind seems to come from more foreward than the true wind) so windvanes fail to do anything useful... (windvanes seem to work beautifly on those heavier canoe stern cruising mono's happily holding a steady 4 knots through the water)

[Richard Woods]

Like everything in yacht design, bridgedeck height is a compromise. Higher is better, but adds to windage and overall boat weight. A wider hull spacing does not mean the bridgedeck needs to be higher. It is best to start the bridgedeck as far aft as possible and have a gently sloping front. Don't carry the deck low aft. That is because as the boat pitches the aft end of the bridgedeck can hit the water. Furthermore, the wave interactions between the hulls usually mean there is a high wave under the cockpit.

I write more on my website, but as I said, as a starter try for 18in - 24in clearance.

Just because one sailor used a bi plane junk rig doesn't make it a good efficient rig. I have seen Badger sailing to windward in the Caribbean. It was pitiful to watch.

As I understand it, the Chinese developed the junk rig because they only had woven bamboo for sail cloth. A material that couldn't take a load. Hence the full battens.

A 35ft catamaran with a modern full battened mainsail fitted with lazyjacks and singleline reefing with good deck gear can be reefed single handed in a minute or less. I doubt if a junk rig can be reefed quicker. But the fully battened sail will get the boat to windward far better otherwise race boats (and indeed the vast majority of cruising boats) wouldn't use a conventional rig.

Do you base your junk rig comments on personal experience, or just from your reading?? If the latter I strongly advise that you try a junk rig, or a biplane rig yourself before deciding.

it is quite possible to have a centrally mounted unstayed mast on a bridgedeck catamaran.

If you sail in the PNW you need lots of sailarea and an efficient rig. The average wind speed is about 5 knots (in the UK it is 13 knots). Believe me, I have sailed in the PNW for the last 5 years and not yet had to reef.

(I am late replying to this thread as I've just come back from a few days cruising, despite the rain.)

Hope this helps the debate

Richard Woods of Woods Designs

www.sailingcatamarans.com

[rayaldridge]

Bertrand Fercot's Pha is not junk-rigged in the conventional sense. The biplane rig is a sort of soft wing sail, with the shape of the sail defined by sets of doubled battens, the mast running up inside the battens. I don't know what sort of performance he gets to windward, though he did sail the boat across the Atlantic from west to east. He's an accessible guy, if you want to ask him. His Tiki 30 looks as though it were built more for comfort than speed, with a big pilot house on the center deck. It could be his standards for performance are more relaxed than some. On the other hand, he likes Pha well enough that he's building a Tiki 46 with a similar biplane rig.

There are a couple of junk-rigged Wharrams here:

http://wharrambuilders.ning.com/group/junkrigged/forum/topics/wharram-cats-rigged-with-one

I'm a big fan of junk rig, and have some experience with it, though only in monohulls. Windward performance has traditionally been a problem for the rig, but in late years much experimentation has been done to improve this, with cambered panels and gurney flaps. In fact, I'm such a fan of the rig that I've put it on unsuitable boats, like this 11 foot dinghy:

http://slidercat.com/blog/wordpress/wp-content/uploads/2008/09/nesterjunk.jpg

However, I don't think that it is a good idea for a cat with any pretense to speed, though I could be wrong. A real naval architect once told me that he'd sailed on several junk-rigged Wharrams, and he called them death traps. I don't know if I'd go that far, but there are definite problems. Because fast boats are generally operating with apparent wind well forward, it behooves the rig to be weatherly. The weight aloft is another problem. Even monohulls will need a stout stick if it's unstayed, and because of the great initial stability of cats, rigs must be much stronger than similar monohull rigs. It's not just the stick-- the battens, sheetlets, euphroes, and so forth add up to a considerable weight up high, and this weight exacerbates the tendency of fine hulls to pitch. And because of the balanced nature of a junk rig, tacking is not as crisp as with a rig where all the mainsail is behind the mast, and cats sometimes are a bit sluggish to tack, anyway.

I'm even more dubious about biplane rig than junk rig. Thomas Firth Jones built a cat with two sticks and sailed her for three years in increasing dissatisfaction, finally replacing the rig with a conventional fractional sloop rig. Even the high-priced versions, like the Radical Bay have not been entirely successful. On the other hand, there's Tony Bigras' Miss Cindy, a nanocat which just completed a successful voyage of substantial length. His ideas for sheeting the rig (which appears to be more of a battened lug than a junk) are very interesting. Again Tony is an accessible guy, so you could talk to him about your ideas and see what he says.

All that said, I'd love to be proven wrong, because junk rig is such a pleasure to use, and the biplane rig is simple to engineer.

[Richard Woods]

A slight update.

There should be no need to go on the foredeck, or even out of the cockpit, to do any sail handling on a well designed cruising catamaran except to hoist/lower the spinnaker. And maybe a sea anchor/parachute when you will sure want to get to the bows in safety.

However you WILL spend a lot of time on the foredeck when coming alongside, anchoring etc. And chances are that at some stage you will need to get there FAST

To add to Ray's comment. James Wharram was a great advocate of junk rigs. He tried one on his Tehini. It lasted a year, then he took it off and replaced it with a conventional ketch rig.

And as an aside. It seems that many people here think that a computer designs good boats.

It doesn't.

All it is is a glorified pencil. And to continue the analogy, some people are asking how to sharpen their pencil.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[daiquiri]

I'm even more dubious about biplane rig than junk rig. Thomas Firth Jones built a cat with two sticks and sailed her for three years in increasing dissatisfaction, finally replacing the rig with a conventional fractional sloop rig. Even the high-priced versions, like the Radical Bay have not been entirely successful.
Just because one sailor used a bi plane junk rig doesn't make it a good efficient rig. I have seen Badger sailing to windward in the Caribbean. It was pitiful to watch.
Biplane rigs are less efficient when compared to a single-masted rig. It is their inherent characteristics, can't do nothing to change it.
For a same total surface and aspect-ratio, a biplane rig's height is 70% of it's single-masted correspondant. It means that it can catch less airflow (the wind speed increases with height above water surface) and therefore will produce less thrust.
Furthermore, two sails means two sources of induced drag, which again directly decrease the overall rig performance, and the VMG in particular.
Less thrust, more drag. Make your own conclusions.
And then, there are the obvious constructive and handling complications...

[rayaldridge]

I think Richard was probably referring to the Badger owned by Annie Hill and her then-husband Pete Hill, which is a junk-rigged monohull dory yacht designed by Benford. Because of Annie Hill's terrific books, it's one of the more famous junks. In her books, she sort of glances over the issue of windward performance, which supports Richard's observation.

Back to biplane rig, Thomas Firth Jones sailed with one on his Dandy for 3 years before finally giving up on it. He cited the usual lee blanketing issues, that biplane rigs are prone to, and said that the rig was both slow as well as disappointing to windward. H also pointed out that reefing could be a trial, since the leeward sail was further out over the water than it would be in the skinniest of monohulls.

But then there's Tony Bigras, who overcame the efficiency issue by putting a lot of area into his rig. 200 sq. ft. of sail is a lot for a 16 foot cruising cat with a beam of 8 feet. He says he solved the lee blanketing issue when reaching by sheeting the windward boom to the bow, hauling the clew forward of the mast-- in effect, converting two sails into one foil. He could do this because Miss indy has an unstayed rig, whereas Jones' Dandy was stayed.

I remain unconvinced but it's hard to argue with Miss Cindy.

[ImaginaryNumber]

I've design several catamarans in the past, (commercial) where the two hulls have been bolted together via box beams. It is not a difficult task in the engineering sense. All you need to do, is calculate your full/max load and then establish the sea conditions and hence the applied loads that shall be experienced. From this, you can design the structure to be "bolt-able", or any other quick means of fastening, having the ability to "take out" and sherk the applied loads to the surrounding structure.
Ad Hoc

I’m not an engineer. Would you be willing to guide me through a back-of-an-envelope calculation for determining the full/max load, establishing the sea conditions, and then designing a quick-assembly structure? We could pick a pre-existing catamaran about 36’ long so that we wouldn’t have to spend time on construction details, except as it applies to the hull-connecting structures.

You should be able to master Delftship in about half the time as it has taken you to get to grips with Sketch-up. Rick W.

I’ve found that Delftship is very easy to learn as long as you don’t ask it to go beyond doing the hull shape. Forget using it for interior structure and bridge deck. Inquisitor

I’m encouraged to try Delftship. What CAD software do commercial designers of catamarans use that allows them to design both the hulls as well as bridgedecks and interiors?

Joining cat hulls requires structurally competent beams. I would look to separate these from the accommodation, at least in the first instance. So the boat would be like a big beach cat until the accommodation pod was added. This gets large structural loads out of the accommodation pods. Large beams could be socketed into the hull on tapers. Pulled up for assembly and jacked off for disassembly. Rick W

I’m open to either the beams being separate from the accommodations, or the accommodations being directly incorporated into what are in effect very large deck beams. Can you point me in the direction of a design that uses sockets and tapers for attaching the beams to the hulls?

The design effort that goes into a complete boat of these proportions from scratch is significant. The more you can take from an existing design the less work involved. Rick W

Yes, much, much easier. I don’t have the resources to hire a naval architect to design from scratch. One of my hopes in starting this thread was to find out if I had overlooked a design that was close to what I wanted. Although some of the respondents have also indicated an interest in a modular catamaran, no actual design has been presented. FlatCat and Miss Cindy have the single interior space. Wharrams (and others) build their hulls independent of each other, then assemble latter. There are a number of monos and multis having free-standing masts, some using junk rigs. I see most of the pieces of what I want already developed. They just aren’t configured together quite like I want them.

It is called a "Hitch-hiker" rig after John Hitch... if you want an easily handled sailplan - - NO forward or any-where else work all done from within. Masalai

That does look like an interesting sail plan. Can you give me a link to a description of how it is configured, and what its sailing characteristics are?

It is quite possible to have a centrally mounted unstayed mast on a bridgedeck catamaran. Richard Woods

Could one of your designs, say the Romany 34 or the Flicka 34, readily be converted to support a free-standing wood mast?

Biplane rigs are less efficient when compared to a single-masted rig. daiquiri

I agree, though they do have the advantage of lowering the center of effort, which some cruisers appreciate. And junk rigs, because they are squarish, lower the CoE even further.

[ImaginaryNumber]

Just because one sailor used a bi plane junk rig doesn't make it a good efficient rig. I have seen Badger sailing to windward in the Caribbean. It was pitiful to watch.

A 35ft catamaran with a modern full battened mainsail fitted with lazyjacks and singleline reefing with good deck gear can be reefed single handed in a minute or less. I doubt if a junk rig can be reefed quicker. But the fully battened sail will get the boat to windward far better (otherwise race boats and indeed the vast majority of cruising boats) wouldn't use a conventional rig. Richard Woods

I think the Hills would agree that Badger, with its flat-panel junk sails, didn’t sail well to windward. When Pete built the junk-rigged China Moon catamaran he attempted to address that shortcoming by using articulated battens that allowed a limited amount camber in the sail. I don’t know if he was pleased with that design or not, but he has continued experimenting with jointed battens on a subsequent boat, Shanti.

However, the newer camber-panel and split junk rigs appear to be competitive with Bermuda rigs to windward, while still retaining the junk’s easy manners. The camber-panel rig is similar to a flat-panel rig, except that a “bulge” is cut into the top and bottom of each panel (or, alternately, a “shelf” is sewn into the top and bottom of each panel). This allows the panels to form a camber, giving a better aerodynamic shape. The split junk rig, designed by Slieve McGalliard, is very similar to the camber-panel, except that the sail is “split” vertically at the mast, allowing the sail to be free of the mast on either tack.

Below is an exchange on the Yahoo junkrig group describing a Slieve’s experience in last year’s annual race around the Isle of Wight using the split junk rig.


Posted by: Slieve, Sat Nov 8, 2008
Hi Wally
The report on the Split Junk gives the basic details, but not the race result. We were in the top third of the handicap fleet of over 800 boats, but that does not tell the story. Turning onto the last beat we found the boat dead in the water, and discovered that the bilge water was up to the floor boards, so we pulled out into the adverse tidal stream to get elbow room to pump out and look for the source of the problem. We didn't find it so returned to racing and achieved the published result. In practice, from earlier calculations and from examination of the log on the plotter after the race it was clear that we had lost over 40 minutes, and that was not counting the time lost carrying an extra half ton of water. If we subtract 40 minutes from our finishing time we would have been in the top 10% of the fleet, and possibly in the prizes.

The real point of the exercise was to compare the rig against a range of boats and the results seem to indicate that the split junk rig, even in its undeveloped form can outperform the average Bermudan cruiser without the crew having to work hard. We tacked 36 times and gibed twice and changed reef twice, yet we only adjusted the halyard and downhauls twice and the main sheet 4 times during the whole 50 miles of the race, and that was with a force 5 to force 6. Add in the fact that we only left the cockpit for domestic reasons and that we did not suffer from water over the deck and it becomes clear (to me) that the rig seem to have every advantage over the more conventional boat.

Since then I have sailed at the Stavanger Rally and the performance of the boats with Arne's sails confirm that the modern junk rig is a real contender.

Two days ago I did a delivery on a rundown Bermudan sloop. The fully battened main sail stuck in the mast track so we had to sail under genoa alone. The engine lost all its oil so we had to beat into a narrow estuary in a light wind. The baby stay caught the clew of the sail each time we tacked so it was difficult to sheet in quickly after each tack. After beating a couple of miles up the narrow river I was exhausted, especially when aware that it would have been a pleasure to sail the same trip with my split junk rig. I really cannot see why anyone would want anything other than a good cambered junk or wing sail.

Cheers,
Slieve.

Posted by: Jon
I am interested to read Slieve's account of his performance in this years Round the Island race. Normally I sail a 28' Sunbird and find it an excellent rig. In this years race however I was crewing on a Bermudan rigged Westerly Konsort. I was amazed at how tiring the sailing was. Every tack took 3 people's full effort (there were only 3 of us), and even when not tacking we had to post one crew member on lookout who had to peer out under the Genoa and call to the helmsman whether to stand on or give way. Quite terrifying under the windy and very busy circumstances.

However my favourite memory of the day was when we were halfway between Needles and St. Catherines point - enjoying a fast beam reach. I looked behind and saw Poppy with her beautiful white Junk rig just coming around the Needles. She flew through the pack and within 20 minutes had overtaken us, and everyone else it seemed. 20 mins later she had disappeared into the distance ahead. It seemed that no-one could touch her for speed on that leg. We caught up with her much later in the day - and now I know why- but she still crossed the line well ahead of us.

Jon

Posted by: Slieve
Thanks for the chat on the 'phone this evening Jon. I also spoke to Colin, the owner of the Konsort and he agreed that we overtook you on the last beat when we started racing again.

For the record, I was concerned that the Konsort was ahead of us at the end of the first 13.5 mile beat at the Needles, but you were able to tell me that you started at 07:30 where our start was at 07:40. Even ignoring the handicaps used in the race as you didn't (couldn't in the conditions) use your spinnaker and using the WOA handicap which would make my boat 1% faster, on elapse time you took 9:45:50 and we took 9:28:27. Subtract the conservative estimate of 40 minutes we lost pumping out and checking for leaks and I think a corrected time of 8:48:27 suggests that we took about 10% less time for the 50 mile course.

Apart from the difference in time, we were not tired at the end and went out for a meal before the (60+ year old) boys drove over 70 miles home. (Our combined age for the 3 of us was over 190 years)

The reason for labouring these points is to show that a good home made Junk rig can beat an equivalent cruising Bermudan rig when sailed on equal terms without too much effort on the part of the crew.

Cheers,
Slieve

[Ad Hoc]

I.N.

Sure no problems. If you can just sketch up, that is pen on paper, back of a fag-packet type of sketch, the basic arrangement, we can take it form there. Since we need the layout, ie length, beam of each hull and overall, displacement, distance between CL's.

[Richard Woods]

The Flica would be a better choice for a free standing mast, but I have done it on a cuddy cat like the Romany.

One structural advantage of the free standing mast is that there are no real compression loads so you don't need a deep mastbeam.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[masalai]

I was with John Hitch yesterday and posted some stuff on my build site (links in my "signature area" of all my posts), That is what I am putting on my build - I am 65 and retired, so desire something easy to manage... The mast will be raked some 10 to 15 degrees aft. The mini-keels will be set about in line with the CofE for the sails... (only three sails, a pair of fairly flat cut genoas (John has "star cut") and a small blade /storm sail running up from half way between the line of the bows and the mast base, also no roller reefing.... Do NOT use the heavy "coloured" sail protector, but use something light, (that you can easily replace?) as the sail gets too distorted when partially roller-reefed, and would be too heavy in light airs... You are cruising? - so being able to perform in "drifting situations" is an advantage, and all sail work can be done from either a forward of the mast or aft cockpit - both sheltered from the weather (sun or sleet).... John is sailing up North (inside the Barrier reef, Queensland), to return around Xmas and may drop in for another visit then... and I will get some more images for myself (and post some also)... XIT is balsa cored with hand layup of grp as preglassed panels were not available then...

Check out the ATL site carefully http://www.duflex.com.au/duflex/amateur/projects/oram_44_c_cruising_catamaran is the bigger model (44-47 ft loa & 23 - 25 beam) - mine is in my "Bob Oram link" in my signature area.... I would strongly advise, that you find a build site nearer to a launch location avoid cold and rainy areas as it is not nice to work with epoxy as the hardners need to be adjusted for ambient climate... Don't take my word, check the advice from the professionals at ATL, they deliver, and 3 boats and more will fit inside a container for a group build (mutual support and bulk discounts on other items).... Working 5 days a week project should be launched within a year with 2 novices working on the build, or about 5 years "part-time as in http://scrumbleproject.wordpress.com/table-of-contents/ .... Neil who is building by himself and occasional casual help, will build his 44C in about 14 months of 5 day week work... He will launch April 1 2010 (Neil & I are "racing" each other to get on the water first:D:D:D)

Why all this determination for free-standing masts and bi-pole rigs? Not a good choice, go and sail one and you will understand and remember the forces are multiplied as sixe gets scaled up.... so expect scantlings for that choice to include a one off pair of carbon fibre masts.....

[ImaginaryNumber]

Ad Hoc and all,

Attached are sketches of a plan and profile for a 36’ catamaran, with the hulls connected by box beams. Most of the dimensions are for reference only – anything can be changed as needed. I’ve stuck a shortened mast on the forward main beam. I’m not sure whether I want two free-standing masts in the hulls (my original plan), or one free-standing mast on the beam/bridgedeck. I would appreciate your walking me through the basic method of determining the expected stress on this catamaran, and then giving me some ideas of how to design appropriate beams that can be quickly fastened to the hulls.

Thank you,
i

P.S.
Fully loaded displacement is ~11,000 lbs

[Ad Hoc]

I.N.

What is the approx full laod displacement?

[ImaginaryNumber]

Fully loaded displacement is ~11,000 lbs

i

[marshmat]

sqrt(-1),

The classification society known as "Bureau Veritas" makes their yacht rules freely available: http://erules.veristar.com/dy/app/bootstrap.html
There's also a thread on this site in which those rules are discussed:
http://www.boatdesign.net/forums/classification/bureau-veritas-rules-download-23030.html

The BV rule is by no means the be-all and end-all of design requirements, but it does include a reasonably good, easy to follow section on the load cases to which a sea-going yacht might be subjected, including catamaran-specific loads (in sec. B.4, B.6 and B.7). As you've probably noticed by now, catamarans are subject to incredible stresses in the rig and crossbeam structure, and the calculations to deal with them are not trivial. But it will give you some idea of how the boat might be stressed.

[Ad Hoc]

I.N.

Thanks for the data.
Ok, the first thing is that you have 3 transverse beams. In terms of taking transverse pitch connecting moment loads, ie twisting, only 2 are doing the work, the other is just adding weight. So, which two do you want/need?

The fwd most is doing the most work, so it sounds sensible to keep this. However you need to support the mast. If you keep the beam to support the mast and this beam ends up being as stiff as the fwd most beam, then you're in trouble. Because the beam supporting the mast and its loads will attract the main transverse loads owing to it stiffness, yet not be designed for this torsional load.

Therefore, it is best to ignore the beam up fwd and use the beam for the mast as the fwd beam and the aft beam, as the main beams to take the torsional loads.

Do you concur this is ok, unless you ahve some other function for the fwd most beam?

[ImaginaryNumber]

sqrt(-1) :)
marshmat
Thanks for the Bureau Veritas link. That will take awhile to digest!


Thanks for the data.
Ad Hoc
No, Thank You! I appreciate the explaination you gave for how the beams are loaded and where they can do the most good. The forwardmost beam I showed smaller because I imagined it's primary function to be supporting an anchor, trampoline, and perhaps a boarding ramp. Perhaps it could be retained, but sort of free-floating, taking minimal loads. So I agree with you that the mast beam and the aft beam should be the primary load carriers.

i

[Ad Hoc]

I.N.

Ok, understood...i'll put something togther later today, assuming wife doesn't hassle me too much, and we can take it from there.

[tspeer]

Would it be too much to ask for you to elaborate on bridge deck clearance? I’ve probably read about every word you have on your website and know the reasons for bridge deck clearance... wave pounding the underside. Obviously there is always going to be a point where pounding occurs even at 3+ feet clearance and I understand why hulls wider apart need even more clearance. ...

Here's one way to think about it. Consider a wave that has a wavelength larger than twice the beam, and the boat is straddling the crest. The wider the boat, the higher the crest will be above the waterplane of the hulls. For a very narrow catamaran, the curvature of the crest will not be very important. But very wide cat, the curvature is definitely a factor.

So there are really two ways for the wave to impact the bridge deck. One is for the boat to be immersed in the wave crest, especially at the bow, by the amount of the bridgedeck clearance. This would be the same for both narrow and wide catamarans. This case would be most relevant to hitting a wave crest head on, so the crest passed from bow to stern.

The other way is for the waterline on each hull to be near its normal position, but for the wave to mound up between the hulls. The wider catamaran needs more physical bridgedeck clearance to handle this case. This would be most relevant to a beam sea, with the wave crest running parallel to the boat. In reality, of course, waves from all directions are present and the sea is composed of a lot of lumps instead of being pure ridges. But the same principle would apply to the lumps.

This argues for a lower limit to the aspect ratio of the tunnel (under deck, between hulls) as well as a minimum height to the tunnel. The height of the tunnel is commonly cited, but I've not heard anyone talk about the aspect ratio of the tunnel.

[Autodafe]

Hi I.M., interesting thread,

My reluctance to go with any of the designs I’ve found thus far resulted from my desire for an easily-heated cabin (low surface area for high interior volume; i.e. a single cabin), and a modular structure that could be mostly built away from the launch site.

Hear Hear! I have been on the lookout for some years for a cruising oriented "Pod cat" design. I am now also in the process of (slowly) designing my own, and quite enjoying the task, but it would be much simpler if some stock designs were already out there.

In regards to bridgedeck clearance, the maximum slope of non-breaking waves is typically regarded as 1:7, but I have seen transient peaks in confused swell that look much steeper than that. The required height is also affected by boat inertia (translational and rotational), hull immersion rate and reserve buoyancy. My own conclusion is that the problem is too complex for a feasible solution, and rules of thumb vary significantly between designers. On the bright side, with a modular design it may well be possible to change the clearance retrospectively if required by modifying just the cross beams.


Daiquiri,
On the subject of a biplane rig, I'm no expert, but one simple point always seems to me to be lacking from debates on this topic: multiple masts allow a boat (of given righting moment) to carry more sail area in safety. (Given a fixed sail aspect ratio, twice as many sails means ~40% more sail area to the same heeling moment). A single sail is certainly the pinnacle of efficiency, but as a cruiser (untroubled by sail area handicaps and rating rules) I can live with a less "efficient" boat that sails faster and more safely.

You make a very valid point about air draft however - for an area where very light winds were the prevailing feature a shorter rig is at a definite disadvantage.

[masalai]

Autodafe, the lower the sail the less wind available as power especially in light wind situations... I consider it is more significant to have a robust pair of hulls (for a cat - as a tri has different engineering issues that I have not even looked at)... - - Warram designs - in traditional form allow a fair amount of flex between the hulls, - - mine has some flex - but not much, - - in the overall structure, the John Hitch X-IT is as stiff as all get-out, the hulls could be called wave piercing as only 2 ft wl beam - images in a recent post on "my little piece of peace" thread... I am not in favour of trying to make a silk purse out of a sows ear, or, scaling up from a toy or little day sail "lake" boat - it just does not work from an engineering point of view....

[Autodafe]

Hi Mas,
I agree windshear is a consideration against low sailplans, but by the same token it favors sails such as gaffs and junks which get more of the sail near the top of the mast.
It would be great to get some more info on windshear, if anyone has it, perhaps a series of windspeed vs height for a variety of weather conditions.
The data I have seen suggest that the difference between 5m and 10 is more significant than that between 10 and 20m. But I'm prepared to be corrected on that one.

Loved the pics of X-IT too, it is much along the lines of what I would like, but I think I'm too lazy to go for a highly streamlined bridgedeck, as I plan to build in plywood.

My personal preference is for a stiff structure - it simplifies the calculations, and also prevents shock loads due to "flexible" joints reaching the end of their travel, but it is less important with an unstayed rig.

[Richard Woods]

You may find my comments on bridgedeck slamming, unstayed rigs and crossbeam design on my FAQ's page useful

Richard Woods of Woods Designs

www.sailingcatamarans.com

[masalai]

Easy to do yourself - a pole and a wind speed thingy and a means to hoist it up and down, then sit below and measure the variance whilst sitting at the foot of the pole reading the instruments - Those tactic ones have self powered wind info senders - a good project for you....

[Autodafe]

Not a bad idea Mas, I'll see if I can overcome my chronic lazyness to do it some time - first to find someone with a 20+ meter mast who'll let me borrow their boat :D
I have found this handy wind gradient page, with formula and spreadsheet:
http://www.onemetre.net/Design/Gradient/Gradient.htm
There's quite a strong surface roughness component, so light winds and big seas is the worst case for short masts.

[Ad Hoc]

I.N.

Ok..sorry for the delay…had a 400km round trip yesterday and got caught up in a 45km traffic jam…long story!

So, attached is a simple diagram of the main loadings on a catamaran beam….as you can see three main load cases. I looked at GL,BV and DNV and compared to simple first principals. I didn’t bother with LR, since I’m familiar with these when compared to DNV’s. The DNV are the most easiest and consistent (based upon very simple first principal calculations too). Which is no surprise, since I’ve been happy with using DNV for the past 20+years. BV were odd that increasing the wavelength of wave encountered increased the loading. Which at first seems sensible, but if a wave of 300m is encountered, you’re not going to get this type of loading, only when the waves are near unity. Ignoring the mast loads for now, lets focus upon the main beams.

The transverse bending moment roughly 52kNm
The pitch connection moment is roughly 81kNm
The torsional moment is roughly 72kNm

There is also the combination loads to consider, such as 100% transverse bending and roughly 70% pitch connecting moment.

Assuming the bolted connection what are the vertical reaction loads?

Well, looking at the worse case and the combo loads, the reaction is 33kN.

Allowing for growth and being over weight add 50%, and, since this is a simplistic calculation, one needs to consider fatigue too, so a roughly FoS of 5 and then sea water environment another FoS of roughly 2. Therefore 33x1.5x5x2 = 495kN.

The connection of your box beams, via bolts, needs to take some 500kN. So, what does this mean, well, an M25 area = 490mm2. Assuming simple mild steel bolt, yield 235MPa, the number of bolts at each connect is 4.3, or 5 bolts.

The box beams must extend to the outboard beam and be connected at the outboard beam and inboard beam location. The beam being the demihull.

The structure that is supporting the beams and is being bolted, needs sufficient shear paths to take this load into the surrounding structure. But that is another detail.

So, once you have considered this, and if this is possible for you, we can look at the stiffness of the beams to take these moments/loads.

[masalai]

The nasty one (and I do not see it illustrated? is when in effect the diagonally opposite corners are suspended (2 waves) and the other corners have bouncing (panicking) weights (crew/passengers)....

[Ad Hoc]

that is the pitch connecting moment load case, or nasty case as you call it

[Autodafe]

Excellent summary on catamaran load cases AdHoc.

It is worth noting if unstayed masts are to be mounted in the hulls there is an additional case where the heeling moment generated by the sails and rudders has to be transmitted to the crossbeams. This appears as a moment between the inboard and outboard beam bolts.

Say,
max RM = 250kNm, hull beam = 1m, Total FoS = 10, then both inboard and outboard bolt groups require 2.5MN, or ~25 bolts each.
This force will be split between both beams, but still requires 25 bolts per joint.

Depending on the sail area and flexibility of the mast it may be reasonable to assume less than total righting moment on each mast, which would reduce this to perhaps half.

Alternatively, if the two masts are to be mounted on the cross beam directly this does not apply.

[Ad Hoc]

Autodafe

Thanks for the comments :)

Agreed, the sail loads have yet to be included. Since this is his first time, i can only go through the steps bit by bit, so first, the basic hydrodynamic loads from the hull displacement in a sea way...otherwise way way too much information to digest.

I haven't even gone through the stiffness requirements of the beams yet too..., whether with or without a mast, as noted.

So, as always in design, looking at every load case/scenario, and then see which is the worse case, never assume there is just one and its magnitude, must be 'proven' first.

[masalai]

316 to 346 is all the reward I can offer to you for your understanding, patience and compassion

[Ad Hoc]

masalai

That's jolly decent of you :)

Makes a pleasant change from the usual personal tirade and ad hominem attacks i get..

[masalai]

If a person makes a post that I reckon is praise-worthy, I give points, that is just the neighbourly thing to do, that does not mean I do not type cheeky responses if the cap seems to fit:D:D:D Personal attacks just display an immature and insecure personality, from someone who may feel you have got pretty close to the truth and made them feel very inferior... hehehe - think of that next time "personal insults" fly... :D:P:D:P:D:P

[Ad Hoc]

Indeed, and right neighbourly of you...well we are also in the same time-zone, just about, just different hemispheres!!

Yes i know how close i ahve gotten to the truth, and am happy to take all those immature hits just so the orginal poster can appreciate a different point of view and not a myopic one! :P :cool: :D

[masalai]

How is the land of the rising sun? seems out of recession officially announced.... - I am just waiting to see what the second wave of shit from the USA brings, how is the economic world from your perspective? perhaps you could post http://www.boatdesign.net/forums/open-discussion/global-economic-situation-liveaboard-cruising-yachties-26558-63.html instead of continuing this "piracy"...

[ImaginaryNumber]

Ad Hoc,

Like you, I was (am still am) on the road, so my responses are at times sluggish.

I understand the concepts depicted in your very helpful diagrams. I'm not sure what GL, BV, DNV and LR mean. I will try and look them up later, but I suspect they are some sort of engineering protocol that I don't need to know. As far as the numbers -- because I don't know engineering, I will certainly accept what ever you say, and hope that more knowledgeable forum members will catch any mistakes.

If what Autodafe is correct, I would like the calculations to include free-standing mast(s).

Is the process you used to calculate all the moments too complex also include here on the forum? I am grateful for whatever you wish to share, but am curious if I can follow the step-by-step math. It might then allow me to experiment with different size hulls, beams, sea states, etc.

Onward and forward!
i

[Ad Hoc]

I.N.

You need to decide whether you want free standing or not..otherwise lots of calculations for no reasons, other than, hmmm..just an idea. Hence you really need to decide what it is your boat shall be and what you want. Going around in circles of what if's...does just that, goes around in circles and no convergence is achieved.

Since if you want free standing masts, a shed load more work is required in your design before we can address the structural loadings..since where do these loads come from...yup..the free standing mast arrangement. Where is best place for the mast and what size sail plan etc etc..all these must be done first before we to get the structural loads....see my point?

DNV= Det Norske Vertias...these are all Classification societies.

[yipster]

here attached a rough idea for a triangular cat framing spaceframe, could be modular too i guess
any thoughts on it? any reason why frames are not used triangular or sawtooth wise?

[marshmat]

Yipster,
I see no reason to reject a spaceframe as a possible solution for a cat.
I think the main reasons we don't see them often is that it is very difficult to design a spaceframe that doesn't intrude into the living spaces. Structurally, it is a perfectly sound concept.

I.N.,

The idea behind the "design spiral" is that, with each analysis of the idea and subsequent revision, you get closer and closer to what you want, making ever-smaller changes, working on more intricate details, until you have something that meets the requirements you set out for it.

At this point, we're still fairly early in your design spiral. Although it's certainly a good idea at this point to do a few back-of-the-envelope calculations to get a rough idea of the structural challenges involved, the detailed design of the structure simply can't be done until the general arrangement of the design has been decided on.

That's not to say that you shouldn't be considering structural issues, seeing as this will be one of the main challenges with a transportable, inland-buildable boat designed for modular assembly. But for the moment, I'd look at it in terms of "where are these stresses going to go", rather than "how big does this beam need to be"- a question which is impossible to answer now, but relatively straightforward once the layout, geometry and weights are known.

The freestanding vs. stayed mast is a case in point. Both are possible and feasible, but the engineering concept is very different in each case. One needs to handle huge compression loads on the mast step, the other has to resolve huge bending moments. The decision should be made based on the performance and handling characteristics you want. Then- and only then- the engineering should be done to satisfy those desired characteristics.

Of course, at some point we will also have to think about the hull shape itself. Perhaps that is a subject for another thread, though, leaving this thread for discussions on the modularity idea.

I've been tossing around some ideas for a year or so now about an inland-buildable, ocean-going cat of 50' or so. I'm convinced that there do not need to be any compromises in strength or performance to facilitate modular inland building and near-water final assembly. Any such project for me is still a decade or two away, but I'm following this thread with interest to see how this works out.

[Ad Hoc]

Matt

You pretty much summed up my last, but rather more, succinct reply, thanks.

[yipster]

Yipster,
I see no reason to reject a spaceframe as a possible solution for a cat.
I think the main reasons we don't see them often is that it is very difficult to design a spaceframe that doesn't intrude into the living spaces. Structurally, it is a perfectly sound concept.

thanks for the reply mat, finding the right web and 3d path's is indeed intricate
maybe that projection thing is the reason behind square, instaed of zigzag framing as well

[ImaginaryNumber]

Thank you, Ad Hoc and marshmat, for helping me to better understand the design process. I definitely want some variant of a junk rig, so that requires a free-standing mast. Of the five catamarans that I'm aware of which use a junk rig or a junk-rig-like sail, all are bi-masted. I'm not partial to bi-masts, just going with what others have apparently found works for them.

I'd encourage any others who are following this thread who are particularly interested in the modularity concept to make your interests known. If there are many potential catamaran builders who are interested in a build-it-inland cat, it may encourage the professional designers on this forum to consider this style of design a commercial opportunity. :)

Looking forward to learning more,
i

[rayaldridge]

The well-known designer, Tom Colvin, uses stayed masts on his junk rigs, so unstayed masts are not a hard-and-fast requirement for the rig.

Chris White, who is probably one of the best multihull designers now working, tried unstayed masts on his 60 foot tri Juniper. He recounts his experience in his book, which I recommend. In brief, after several years, he replaced the rig with a stayed rig. He found that he was unable to adequately control sail shape in heavy air.

Bear in mind that unstayed masts for a cat must have much heavier scantlings than the equivalent sized rig for a monohull, because of the enormous initial stability of the cat.

[Ad Hoc]

I.N.

"...Looking forward to learning more,.."

If you wish to learn more, perhaps you should ask all those who think they know better and whom have never designed anything for their advice, since they think they are such experts, but of course making a comment leaves one open to scrutiny. Hey great idea, lets see what words of wisdom these "anonymous" posters come out with....surely they must be able to contribute, otherwise how would they know a good comment from a bad one to hit neg points??...:D:D

[rayaldridge]

do have respect to knowlegde but slightly uncertain if spoken to as adhoc generalizes "I see the uneducated, immature and ignorant are out again"
i'm just an amatuer too and get doubts over mentioned spaceframe, sure plating and framing goes together, space and zigzag frames no good?

Yipster, I don't think he was talking about you.

I think I've seen space frames, or at least triangulated reinforcements, used on racing multis, though I don't remember the details.

[Richard Woods]

I agree with others that your design spiral is getting really skewed. You don't need to think about the structure for a long time yet. And it is curious, to me at least, that you haven't yet published an outline accommodation or deck layout for discussion.

On space frames. Remember the Bugatti "bird cage" racing cars of the 1950's? Later used as a concept by IOR boats "The skin just keeps the water out, bulkheads and frames provide the strength"

Both quickly supeceded by monocoque construction.

Speaking as one who has personally taken a 20ft wide catamaran down a 14ft wide Cornish country road and who has designed modular boats, like the Gypsy for example - one of which was built in three different countries!!! I still think you'll find that you don't really need to follow the route you are taking.

Having said that, have you considered making the complete central section of the boat and adding bows and sterns to it?? So you'd have an accommodation block 10ft 6in (say) wide (on the trailer, obviously 10ft 6in long on the boat) by 20ft long (or 20ft beam on the boat).

I am guessing that 10ft 6in is the max trailing width you are planning on, but different countries have different regulations. In the UK the max legal trailer width is 7ft 6in, but you can have an load that overhangs 12in each side, so you can tow 9ft 6in without a police escort. You can tow up to 14ft wide and 16ft high (I think) with a free police escort. Bigger loads than that are feasible, but I believe they require that the Queen walks in front carrying a red flag.

Richard Woods of Woods Designs

www.sailingcatamarans.com

PS thank you masalai for the note on reputations and where to find comments. Like yipster I'd always wondered what "rep" meant.

[downunder]

Dereck Kessal has several modular designs and is desining most of his range now for modular construction - the < ma range> in 3 sections 2 hulls and bridgedeck. he is currently in the USA according to his website

http://www.kelsall.com/sailcat.htm


http://www.kelsall.com/kisskat/index.html

[marshmat]

Not sure what it's like in other jurisdictions, but around here an oversize load permit for up to around 10' wide is just a matter of a few hours and a few dollars. It's when you start to get into over-height, or seriously over-wide, that costs start to skyrocket- calling the utility to temporarily prop up overhead wires, that sort of thing.

[rattus]

Richard, the "birdcage" cars were Maseratis; the original's complexity appears to be somewhat greater than what Yipster had envisioned ;-) : (nice model of the chassis)

http://www.classicdriver.com/uk/magazine/3200.asp?id=12506

John Shuttleworth also did an interesting analysis of a spaceframe bulkhead engineered for the loads of an Aerorig:

http://www.john-shuttleworth.com/Articles/52AeroDesign.html

See Figure 10 for the spaceframe detail. Interesting stuff!

Mike

[masalai]

Royal and Yipster, nothing directed at you folk, It is the usual bunfight that erupts when some ignoramus feels his bluff has been called and the only recourse is a petulant childish attempt to get even by anonymously giving negative rep points.... It is just a wankers' need to be told every so often to sit quietly in a corner, take their meds and see their shrink/counsellor...

I am sure it would all be resolved if negative rep was disabled and / or ALL who give any "rep points", was identified.... - such is life - :D:D:D:D:D

[Ad Hoc]

"...I am sure it would all be resolved if negative rep was disabled and / or ALL who give any "rep points", was identified...."

Fully concur

[yipster]

yah, no way to use that spanner also from japan (http://www.boatdesign.net/forums/open-discussion/boat-jokes-we-need-few-laughs-14472-171.html#post294391) and i for one promise to try to use the rep's in a good manner

thanks for all the ideas on modular spaceframes and for a one off i was thinking its easy'r than a splitted monocoque
with foam sandwich the water can be kept out and enables working bigger skin sizes

[Fanie]

Hello ImaginaryNumber,

I apologise if this was suggested in between all the bickering loke old wiemen earlier in this thread, I just couldn't read through it all.

I have the same problem you have, getting the boat to water, although in my case it's much worse, I live 450km from the nearest coast :( and apart from that it is too darn expensive to leave a boat in a marina.

I have decided to make my boat foldable, to some extent like cat2fold did.
Since you want a full bridgedeck I am sure it can be placed once the hulls are on the water.

The hulls can be trailed. If you want wider hulls the trafic guys could assist with a once off trip to the water, but it would still fit on a road.

The cabin can be made to fit, taken off and again fitted back in it's place. The cabin can be transported also on a trailer on it's rear and sideways, It should fit on a flat bed.

Since you are going to transport it only once, you could also use solid beams and not hinged ones. With a bit of carefull design when assembled the parts could fit together while supporting each other to maintain position, which would make final assembling / glassing possible even on the water.

Nothing is impossible and yes, it is always more difficult than anticipated at first :D

[ThomD]

"In brief, after several years, he replaced the rig with a stayed rig. He found that he was unable to adequately control sail shape in heavy air."

It isn't as though he replaced the rig with a nice simple pole and triangular sail like his freestanding rig, then declared victory because it was so much more controlable, he went to a pretty nearly opposite level of tech that was more comtrolable, and a lot of other things to boot. You have well related his remarlks, just some context for the heck of it.

"Bear in mind that unstayed masts for a cat must have much heavier scantlings than the equivalent sized rig for a monohull, because of the enormous initial stability of the cat."

Keeping also in mind that if it is split between two hulls that would reduce the requirements somewhat, if for two spars.

[rob denney]

"In brief, after several years, he replaced the rig with a stayed rig. He found that he was unable to adequately control sail shape in heavy air."

It isn't as though he replaced the rig with a nice simple pole and triangular sail like his freestanding rig, then declared victory because it was so much more controlable, he went to a pretty nearly opposite level of tech that was more comtrolable, and a lot of other things to boot. You have well related his remarlks, just some context for the heck of it.

"Bear in mind that unstayed masts for a cat must have much heavier scantlings than the equivalent sized rig for a monohull, because of the enormous initial stability of the cat."

Keeping also in mind that if it is split between two hulls that would reduce the requirements somewhat, if for two spars.

G'day,

Too much nonsense on this thread to read it all, so apologies if this has been said.

The unstayed mast option for a cruising cat is by far the most sensible option. Cheaper, lighter overall and with a lower centre of gravity it is also much safer to sail and to operate. The scantlings are actually far lighter than for a stayed rig as they are more localised. They are also in directions (tension and compression) suitable for easy application rather than in inefficient bending.

The 15m/50' boat in the video at http://www.youtube.com/watch?v=8chR6DAFjGA has an unstayed mast which weighs the same as the alloy mast and rigging of a cat with the same righting moment and sail area. The boat is also modular. The beams, hulls and bridgedeck all fit together without bolts or fastenings. Put the windward hull on it's side and it is 2.7m/9' high.

regards,

Rob

[masalai]

ONLY for a proa...

[rob denney]

ONLY for a proa...

Why ONLY in a proa? Why won't it work in a cat, either in one hull (the easiest option) or in the middle where the conventional mast is located.

rob.

[masalai]

That debate has occurred on another thread and I am not qualified to further pursue the matter.... It was a consideration in research for my build...

[rob denney]

That debate has occurred on another thread and I am not qualified to further pursue the matter.... It was a consideration in research for my build...

Could you tell us where this thread is, please, as I don't recall any threads where the suitability of an unstayed rig for a proa vs a cat was discussed. As there is no reason for them not to work on a cat as well as they do on a proa, I suspect it would be a very short thread.

'Search' bought up a few threads about unstayed rigs, but apart from someone having trouble sailing backwards out of an anchorage without a jib, and some wild, unproven gossip about a carbon mast exploding in a shower of red hot razor sharps shards in a lightning strike, there don't seem to be any reasons why an unstayed rig would not suit a cruising cat.

Again, this is not a surprise as there are no reasons which come close to outweighing the benefits.

Perhaps you could also tell us why you decided against it, and whether "it" was an unstayed ballestron, biplane or una rig.

Ta

[masalai]

Somewhere? 'unstayed masts' were debated quite a while ago but I am not sure in the thread title... There was no serious debate, just a few posts in favour and against mainly experiential comment... which left me with the view that there would be no advantage in looking at unstayed, as too difficult to implement - I think it related to a wishbone type setup????

[rob denney]

Somewhere? 'unstayed masts' were debated quite a while ago but I am not sure in the thread title... There was no serious debate, just a few posts in favour and against mainly experiential comment... which left me with the view that there would be no advantage in looking at unstayed, as too difficult to implement - I think it related to a wishbone type setup????

I have no idea what it was related to as a wishbone works extremely well on the unstayed Wylie cat rigs. Bob Oram (your designer, I think?) is a big fan of unstayed rigs and there is far less work involved in designing and building a boat for an unstayed rig than for a stayed one. There is also far less ongoing work and cost as there is no maintenance and no need to inspect the rigging daily and replace it every few years. All of which are good reasons to use one, but pretty insignificant compared to the ease of use.

I strongly recommend some "serious debate" and perhaps a revision of your view.

I am now living on the Gold Coast. I believe you are in Brisbane? If so and you ever get down this way, drop in and take my 25' proa and it's unstayed rig for a sail. May give you an appreciation of what you are missing out on.

regards,

rob

[Fanie]

I am in favour of unstayed masts as well. If I one day get there, my cat would have two unstayed masts if I still go sail boat by then. The stays clutter a boat consderably (imo) and will eliminate the clanking noise in the wind as well especially at anchor.

The little experience I had with stand alone masts was good up to now, they just have to be made stiff. Yeah yeah I know what to add :D

[rayaldridge]

One issue is cost. For the smaller boats I'm interested in, a stayed mast can be built from timber fairly cheaply, and not everyone can afford a carbon spar. Another issue that concerned me when I was considering an unstayed mast for my little open bridgedeck cat was how to support it out on the beam. I considered struts, which worked well on the model. But eventually I concluded that in order to have a sufficiently strong timber spar, it would mean a lot more weight aloft than the stayed rig I finally decided on.

[rob denney]

One issue is cost. For the smaller boats I'm interested in, a stayed mast can be built from timber fairly cheaply, and not everyone can afford a carbon spar. Another issue that concerned me when I was considering an unstayed mast for my little open bridgedeck cat was how to support it out on the beam. I considered struts, which worked well on the model. But eventually I concluded that in order to have a sufficiently strong timber spar, it would mean a lot more weight aloft than the stayed rig I finally decided on.

G'day,

How deep is your beam, and how long is your mast? We put an unstayed mast on a heavy 37' open bridgedeck cat. 13m mast had 750mm between the bearings. Works well. http://www.harryproa.com/MASTS/Taywun/Taywun.htm

Do you have the costs for the wooden mast and all the gear (shrouds, turnbuckles, chainplates, additional beefing up, etc) required to hold it up? Be interesting to compare it to the cost of the unstayed carbon tube on my Elementarry or a similar boat. What is the righting moment, sail area and mast height for your boat?

What weight did you get for the unstayed wooden mast? Was it hollow?

regards,

rob

[rayaldridge]

Rob, I fear we're working at completely different edges of the technical spectrum.

http://slidercat.com/blog/wordpress/wp-content/gallery/slider1/sailjul2.jpg


This picture will probably tell you everything you need to know. Total cost was under $200 for the whole rig. The mast, for example, cost less than $15, as it was laminated from a couple of carefully-selected construction grade 2X4s.

This design was an attempt to come up with a multihull version of the many small simple open monohull cruisers-- something that a relatively poor person could afford to build.-- a kind of entry-level catamaran for those who might like to experiment with the many virtues of multis. (Obviously, performance was not a priority.) There aren't any similar cats available, so far as I know, which was why I drew it instead of buying plans from a real designer.

[rob denney]

Rob, I fear we're working at completely different edges of the technical spectrum.

http://slidercat.com/blog/wordpress/wp-content/gallery/slider1/sailjul2.jpg


This picture will probably tell you everything you need to know. Total cost was under $200 for the whole rig. The mast, for example, cost less than $15, as it was laminated from a couple of carefully-selected construction grade 2X4s.

This design was an attempt to come up with a multihull version of the many small simple open monohull cruisers-- something that a relatively poor person could afford to build.-- a kind of entry-level catamaran for those who might like to experiment with the many virtues of multis. (Obviously, performance was not a priority.) There aren't any similar cats available, so far as I know, which was why I drew it instead of buying plans from a real designer.

G'day,

Perhaps at different ends of the tech spec, but we are both trying to build boats as cheaply as possible. Yours to cruise/fish/have fun in, mine to go fast/be easy to sail.

The set up you have would be hard to emulate in an unstayed rig, nearest would be a second hand laser/OK dinghy/Finn/windsurfer rig mounted in each hull.

$200 is a cheap rig. Comparatively, the materials for the mast and boom on my Elementarry (lighter boat, similar sail area) cost $Aus600/$US480. A large percentage difference, but not so much more money to pay if you want all the advantages of an unstayed rig. Having said which, if I wanted a boat for me and my kid to fish, cruise, learn boats and mess about in, the Slider rig would be much more suitable than an unstayed rig.

Look forward to seeing the next one in the series.

regards,

Rob

[rayaldridge]

Rob, I appreciate the kind words. As I'm sure you know, being a contrarian isn't always fun, but it has its rewards.

The cartop cat I'm building now is going to be a lot cheaper than Slider was-- almost no hardware, except for blocks, rudder gudgeons and pintles, and a few cleats. Rig's another stayed sprit, held up by cheap Dyneema cord. It's aimed at the same functional niche as a PD racer, though it'll cost a bit more than that. You might say I'm devolving.

But after that, I'd like to draw a fast trailerable cruising cat, just to avoid falling into a rut.

[BigCat]

A lot of the ideas being discussed in this thread are ideas that went into the BigCat design at http://bigcatcatamarans.com - A boat to be built in pieces that are to be transported without any wide loads, an unstayed biplane rig with reefing and furling wingsails, etc.

The calculations have all been done to the satisfaction of the USCG for a passenger boat capable of legally carrying 149 day passengers in US waters, plus crew. I sailed across the Pacific Ocean in a boat with unstayed masts, and would never go back if I could possibly help it.

My mast design isn't the lightest available, but it is easy to build- two half masts made in a female mold with an overlap to be bonded together with commercially made epoxy putty. The vertical uni is carbon fiber, the +45-45 for torquing strains is e-glass, and the resin is vinylester.

I have never seen anyone remark on this fact, but the biplane rig placement of the masts greatly increases the boat's stability by increasing its roll moment of inertia, per the findings after the Fastnet debacle. :o