Catamaran vs Trimaran

[Maciek188]

Hello everyone !
I was always wonder if to compare racing catamaran and trimaran of the same size, for example Formula 40, which one out of two will have better performance, it means speed in the same weather condition? I am talking of typical racing boats without any accommodation for crew, build very light and simple, like beach cats, only larger, just for speed, not comfort!
Since we plan to get one of those any input will be highly appreciated. So far the only answer to my question was from Tornado sailor and Olympic medalist.
Hi said: "Why to carry 3 hulls if you use only 2 at a time?" And than he added: "Always easier to fly 1 hull than 2", lol.
Maciek

[Skippy]

Depends on the wind. The answer to the question is that ideally, you only want to use one hull, not even two. In light air, most of the boat's displacement will be taken by the main hull, whereas the cat will have both hulls well in the water. The tri then has less wetted surface. In stronger wind, the leeward float of the tri will go in quite a bit, whereas the windward hull of the cat will start to pull out. If you can fly the windward hull of a cat (heavy wind) or, on a small tri anyway, fly both floats in a light breeze, then the wetted surface is even lower. So favor tris for light wind, cats for heavier.

[CT 249]

The trimarans dominated Formula 40 in the end.

[Doug Lord]

I think-for now - trs's get the nod:A) In light air they have less wetted surface and because of "B" they carry more SA.,B) If the tri is designed to fly the main hull(and because of "C") then it will more than likely have more RM than a cat and C) because of the probablility that the tri will have substantially more beam than a cat it will make better use of "banana board" type hydrofoils.
The premier example of Open 60 multi's is Frank Cammas "Groupama" with canting mast(more than other ORMA 60's) and "tighter" banana boards for more lift area and a trim tab on the main daggerboard.

[rob denney]

G'day,

Assuming you want to go as fast as possible, then there is another alternative; a proa. Think of a trimaran without a windward hull, the rig in the (double ended) leeward hull and only one third or less of the central hull.

How does it work? Check out http://www.harryproa.com/Elementarry/SailingPhotos_4.htm for a 7.5m/25' version. Has the same righting moment and sail area as a Tornado, but less windage, longer waterline and weighs 100 kgs vs 160.

If you are looking for a bigger boat, then I am designing a 15m/50'er for the '08 and '09 Single handed TransAtlantic races. Weighs 1250 kgs/1.25 tons ready to race. Seems pretty light, but we have just launched a 50 foot cruiser which weighs 2 tonnes in sailing trim. This for a cedar strip boat with 2 huge double bunks, ice box, toilet shower, galley and covered cockpit for 8 people. Launching photos and details at http://www.harryproa.com/BlindDate/Jan_9.htm and previous pages.

Of course, if you really want to clean up you could try the proa at http://www.harryproa.com/Texel/texel.htm A 10.5m balls to the wall racer is being built to this design at the moment.

As well as fast, these boats are low cost. Less materials and smarter use of them enable the builder to build his own carbon components (mast, beams, rudders and fittings) from low cost carbon tow, at prices lower than buying the alloy equivalents.

Regards,

Rob
www.harryproa.com

[yipster]

.....tri's have a better rightning curve than cats.....

[mackid068]

Tris seem to dominate racing...for now. More stable by virtue of three hulls, more sail area can be carried...........

[Dan Ward]

Most experts acknowledge that compairing a cat to a tri of the same length the nod goes to the tri. However tri's are more expensive to build, so on a performance per $ basis the cat gets the nod.

[mackid068]

Maybe so, but it hasn't been determined if money is a factor for this.

[DSmith]

It is however interesting that cats have held the round-the-world records for a long time.

Dave

[Doug Lord]

Now,now: lets not forget Ellen's recent round the world record in a big tri!

[Skippy]

Derek Kelsall has an article comparing cats & tris for offshore racing (http://www.kelsall.com/CatvTri.htm), which I agree with entirely. His claim is that tris dominated racing back in the day when they just weren't as fast, so most of the displacement was taken by the main hull. With a lot more speed out there these days, he asks, if you expect to fly the main hull anyway, then what's the point of having it in the first place? I have no idea why a wide cat wouldn't outperform an equivalent tri given enough wind.

[Doug Lord]

Yves Parlier's ORMA 60 cat was a shot in the direction of the tri's. With the stepped hulls and assuming that their light air variable geometry system worked I would have thought he had a chance. I think that, maybe, his lack of success (so far) may have more to do with the lack of efficiency of the twin side to side rigs as compared to the tall square top canting rigs on the tris.
I think that if you built a cat as wide as a tri and used twin retractable fore and aft rotating foils instead of a conventional rudder and board that you might make up for any slowness in tacking but there is still that pesky problem of light air wetted surface since the cat(though it would probably be lighter) would still have a bit more wetted surface and would be using the same rig as the tri's. The twinfoils could be molded in an "l" shape giving the boat the same potential hydrofoil lift benefit the tri's get from
banana boards.The disadvantage would be that the hydrofoil portion of the rotating foil could not be retracted like the banana boards can be. There would also be no need need for a main daggerboard like the tris have or the three rudders-saving more weight.
So I think a cat could have real potential in most conditions if the new ideas were incorporated to solve some of the old problems.

[yipster]

only speedread Derek Kensall's site but... if you expect to fly the main hull anyway, then what's the point of having it in the first place?seems easy to me, who does not like to have sail and weight on the right side?

[Doug Lord]

On a cat like the one Kelsall designed or like the Lake Garda one designs the boat has -for lack of a better term-a virtual hull in the middle of the boat to take some of the loads-it's like a hull but doesn't touch the water. As best I can tell if you built an ORMA cat as wide as a tri using the same type rig the CG would be in nearly the same place but the cat might be a bit lighter. Lighter for the same beam means less power to carry sail but it would probably be a hell of a race at least in hull flying conditions.

[yipster]

http://www.john-shuttleworth.com/Images/NESF2.GIF
Doug, above graph from http://www.john-shuttleworth.com/Articles/NESTalk.html who has articles on the subject also.
the tri's beam is wider tho and not toutching all the cats merrits i'd say a tri is and behaves different than a cat in many ways.

[DSmith]

A trimaran may also be faster in drift (<5 knots) conditions as the boat is healed slightly allowing the sails to fall into a nicely aerodynamic and twisted shape. These days with heavily battoned sails it may not be such an issue.

Dave

[Doug Lord]

I think, as time goes by, the most important criterion for high speed multies will be : what is the best configuration to maximize the use of hydrofoils? And I believe the trimaran probably wins that hands down.

[yipster]

I think, as time goes by, the most important criterion for high speed multies will be : what is the best configuration to maximize the use of hydrofoils? And I believe the trimaran probably wins than hands down. looking out the window here i'm thinking hydrofoils for cars, what a summer, its pooring! orange blosom road winibago time? hell, i can be like this there too! yes, think your rite, cats are great, tri's even harder/higher on foils

[CORMERAN]

Re: Racing cat or tri.

An issue that seems to be forgotten is the stress on the crossbeams.

Given: - that the mast is being driven through the center of the main
crossbeam of a cat and this beam is also trying to hold the boat together.
It follows: - that said beam has to be pretty substantial.
So: - if you were to have as wide a boat as a tri - your crossbeam
will need to be HUGE.......and heavy.
Where as: - the centre hull on a tri absorbs the downward force of the
mast(s) much more easily - with less weight.

Also as a tri's main hull - is in line with the forestay loads - it is proberly
resisting these loads better than a cat's crossbeam does. So are we not also going to get a tighter forestay on the tri? A factor in windward performance.

[cleblanc]

Weight is a very important factor in the speed of a multihull and a catamaran can be made lighter than a trimaran and the structure is much more simple to design and to optimize

However, with the use of more expensive building technology and better FEA simulation, a trimaran can be made almost as light as a catamaran and it will be faster in many conditions.

Open 40 is a interesting example because there was a 1800kg minimum weight and the class was dominated by catamaran at first because they were able to meet the minimum weight requirement. With the improvement in the building techniques, the trimaran were also able to meet the minimum weight requirement and they started to dominate.

As far as the new giant multihull, again, the class is dominated by the catamaran because they are simpler to design and are cheaper to build. There is one competitive trimaran however, it doesn't have the latest advances from the Open60 series like foils, canting rigs and amas steering capability.

[CORMERAN]

Yes, CLEBLANC, the Formula 40 results were interesting.

- And yes, the three most important design considerations for designing
multi - hulls is weight, weight and weight!

However: I think it is an open question as to which is lighter.

I keep going back to the crossbeams - that are INHERENTLY less
stressed with a tri.
( Except - perhaps - when brave people insist on flying 2 of their 3 hulls.)

- If, LORSAIL, you made a cat as wide as a tri, the weight of the crossbeams
will start to enter the zone of diminishing returns.
For if, lets say, you DO have a weight advantage in your cat - the extra
weight incurred as the beams grow outward - will eventualy bring you
up somewhat even.
( Remember the loads increase, at least, as a square root multiplier.)
A lot of effort too get to the same place as the tri - but now you have
even worse light air performance than you had before you grew wider.

- Frankly, this is an discussion that has gone on for years - and I dont see the debate ending - anytime soon.

- Suffice to say: I have witnessed catastrophic failure of the
hull / crossbeam connections on a cat. A sobering sight !
Luckily, I was close to shore, at the time.
- Also, I'm aware of this happening, historicaly - with other vessels.

- Help me out here, sailors with long memories,re:
- A list of the Structual Failure of cats Offshore.

I hasten to state:
I wont suggest that trimarans haven't had there share of troubles.
( Witness the sad legacy of Mr. Piver)

However, before you build that super - wide cat......let's see what our
informal survey says.

[frosh]

I have to largely agree with Cormeran on his thoughts about going much wider than 2 to1 on the cat. The loading increase on crossbeams is already well known and more strength plus more length equals a lot more weight. Heavily loaded cat hulls are slow!
Further, manouverability of a very wide cat would be worse (especially tacking) than a regular width cat which is already worse than a tri.
This is not an opinion that cats or tris are generally better, although I personally like the aesthetic and design solutions afforded by tris. :)

[CORMERAN]

Thank you FROSH,

for your support - re: racing multi - hulls.

Like you, I lean towards trimarans. Almost to prejudical level.
However, outside of ocean racing - they tend to be a hard sell.

All that wonderfull beam we've been talking about - becomes a decided
negative - when you are trying to find a slip in a crowded marina.
Or selling a your concept - Super Tri Cruiser - to an Investment Banker........

[Redsky]

i have this long narrow mono hull im currently working on as a working boat...though in order to keep the design it may need to become a trimirian
and iv always liked trimirans...so perhaps if people regularly see a tri as a working ship instead of just a racer ,specialty pleasure craft, they will start gettng around...and perhaps a open mooring spot is better and cheaper.

[CORMERAN]

To Redsky:

As a WORKING boat - are you refering to - a SAIL or POWER boat ?

If we are talking power only - my research indicates - that your options
are more flexible than you might realize.

We have done a lot of work, specificaly, in respect to commercial
Tri - Hulls. So we can be of practical assistance.

Send us an E - Mail with a bit more information and we will see how we
can help you.

Cheers !

[Eric Sponberg]

Dick Newick is one of this country's foremost multihull designers, with specialty in trimaran design. He's mostly retired now and living in California, but I thought his opinion, printed in the March 1988 issue of SAILING WORLD, is worthwhile and to the point: I quote:

"I've predicted all along that a good trimaran will beat a good catamaran almost every time. For an all-around multihull racer-cruiser, I would suggest that tris have the following advantages: They have more stability because they are wider for a given length. They have more maneuverability because when they turn, they are dragging two long slender hulls cross-ways around an imaginary point in the middle--they have one long slender hull pivoting around the same point with the amas largely out of the water. They have an easier motion at sea; they don't have a quick jerky motion; they don't pitch anywehre near as much going to windward. With a smaller-size cruising boat you can get more useful accommodation without excessive freeboard since it's down in the hull instead of on a platform several feet above the water. And, because of the trimaran's easier motion, it is much easier on its, rig, so it doesn't need a heavy one. Lastly, you are stepping your mast in a hull, instead of someplace out over the blue water, and therefore your engineering problems are fewer.

"In really light weather the trimaran has a very big advantage in less wetted surface. When you can't fly a hull in a catamaran, you're just stuck in the water. As soon as you're sailing practically, you're flying the weather hull on a trimaran. Other than that I think catamarans are fine."

Eric

[rayaldridge]

Newick is a great designer, and many of his points are valid.

However, in my opinion, catamarans are superior as cruising boats.

Trimarans are generally faster over the usual range of conditions, the engineering problems are easier in terms of rigging, you have accomodations in a central hull that can be more open and well-integrated in function, the boat is more maneuverable, and so on.

But one great advantage of the cat is that unlike the tri, it does not heel appreciably. You have to expoerience this advantage over the length of a cruise for the wonderfulness of it to truly sink in. You can set your drink down on the deck, go below and check the chart, come back on deck, and your drink will still be right where you put it. I know, it doesn't sound like a big deal, but it really is. It's much safer, for one thing. The leading cause of death at sea is man overboard. Your crew is much less likely to fall off a flat stable deck. It's also much less tiring than sailing on a slant and you will be better rested and better able to make good judgements.

The other huge advantage of a cat (or at least an open deck cat) is the vast acreage of deck. Most folks, when cruising, spend the majority of their time at anchor. With a nice awning and some deck chairs, a folding table, a chaise lounge or two, you have a space aboard that can't really be duplicated on a monohull or trimaran. It's like a terrace on the water-- ultimately luxurious.

Ray

[CORMERAN]

Newick is - with no question - an authority on Trimarans.

Also he is quoted or paraphased all the time by myself - and others to
our prospective clients:

" YOU CAN HAVE A FAST BOAT, SIR .............
YOU CAN HAVE A LUXURIOUS BOAT.............
YOU CAN HAVE A CHEAP BOAT....................
......... BUT YOU CAN NOT HAVE ALL THREE !"

[Chris Ostlind]

Gosh, Ray, doesn't all that substantiation of the cruising cat-over-tri argument, really depend upon the design details of the tri?

For example, if the tri amas are designed to just kiss the water surface at design load, there is very little heeling going on when the sails are engaged and the ama is pressed to equilibrium. Any gusts beyond the norm would cause both boats to experience a degree of enhanced heel and that comfy notion that a martini will sit still in a seaway goes right out the door.

There are other scenarios where the supposed advantages in cruising are not what they seem, but I won't address them now.

What really sets the cat apart as a cruising machine is the aircraft carrier style deck space that can be utilized aong with huge, below decks stowage. That kind of room is just not up to luxury cruising standards on a tri until you get to the 40'+ LOA designs and really throw down some serious money. (assuming all appointment levels are nearly equal)

It is really hard to compete with one of the performance oriented cruising cats like the Gunboat, for example, if you want speed, accomodations and pure stroke on the waterfront.

[frosh]

Chris, I would like to point out that almost all tris nowadays are designed so that when one float is slightly immersed the other is well clear of the water.
This means that the tri will sail at a slight angle of heel in light winds and allows a slightly lower wetted surface than a similar size cat.
Interesting that Ian Farrier in an interview in "multihull magazine" explained that accomodations were superior in a tri over a cat in sizes up to 40 feet and this was largely why all his designs up to about 12 months ago were tris. (Note his speciality has been folding ama tris between 22 and 36 feet). His biggest production boat design was being featured which was 41 feet, and interestingly a cat, and he explained how this had a relatively huge amount of interior space. This argument seems the opposite to yours.

[Chris Ostlind]

Chris, I would like to point out that almost all tris nowadays are designed so that when one float is slightly immersed the other is well clear of the water. This means that the tri will sail at a slight angle of heel in light winds and allows a slightly lower wetted surface than a similar size cat.


Did I say something different from that?


Interesting that Ian Farrier in an interview in "multihull magazine" explained that accommodations were superior in a tri over a cat in sizes up to 40 feet and this was largely why all his designs up to about 12 months ago were tris


I believe that the F-41 cruising cat was designed in 1998.


... and he explained how this had a relatively huge amount of interior space. This argument seems the opposite to yours.

What I said was this, "That kind of room is just not up to luxury cruising standards on a tri until you get to the 40'+ LOA designs" The key here is cruising standards and I take that line of thinking from the huge numbers of boats in the marketplace. While Ian has had a nice run of success with his F-boat tris since their inception, the total sales of under 40' cruising multihulls are easily dominated by cats. There's a very good reason for that. They have more livable area for the dollar invested.

Virtually all cruising appointed multihulls of 40'+ LOA have serious room available. It is my take that the vaka hull of trimarans generally does not have the same amount of interior volume, as does a cat in the smaller sizes as discussed. Without knowing how Ian is arriving at his comparison stats, it is impossible to argue the point. Perhaps Ian is counting the tramp surface of his boats as part of the space?

I have designed a 6.5-meter folding tri with a cabin, as well as a 21' cruising cat with a trailer legal beam. These boats have nominal dimensions for their type. The tri has a vaka hull volume of 90 cu ft. and the cat’s volume is 100 cu. ft. Please see the attached renderings.

This isn’t the end of the discussion, as you can probably find examples of designs that reverse the relationship. It’s my experience that the references I have provided are fairly representative.

[Chris Ostlind]

Faulty attachment routine apparently

[rayaldridge]

"Gosh, Ray, doesn't all that substantiation of the cruising cat-over-tri argument, really depend upon the design details of the tri?"

No, I don't think so, if we're talking about modern designs.

"For example, if the tri amas are designed to just kiss the water surface at design load, there is very little heeling going on when the sails are engaged and the ama is pressed to equilibrium. Any gusts beyond the norm would cause both boats to experience a degree of enhanced heel and that comfy notion that a martini will sit still in a seaway goes right out the door."


The tri ama does have to sink a little to reach equilibrium, which translates into heeling. Maybe I don't understand what you're saying, but to me, heeling is deviation from level. A cruising cat will rarely heel as much as 5 degrees even in a big puff. A cruising tri will often heel 10-15 degrees. Makes a fairly big difference in the MSQ (martini spillage quotient.) Of course, the other side of that is tris give more warning when hard-pressed than cats, but I'm talking about cruising boats, where flying a hull is pretty unlikely, for the prudent sailor. It's just physics, it seems to me. A tri ama will always have less buoyancy than a cat hull for boats of similar displacement. So the same forces will depress the tri ama more than the cat hull-- and that disregards the fact that the lever arm will usually be longer on a tri, because of its greater overall beam.

At anchor, crew out on the side decks of a tri will depress the ama and the deck will develop a definite and less-than-comfortable slant, unless it's an enormous tri. The cat won't. Also, modern tris at anchor have a terribly annoying habit of walking back and forth, first dipping one ama and then the other. Cats don't.

As the former owner of a 27' cruising cat, I can tell you that the no-spillage thing is not hyperbole, or even a "comfy notion." It's entirely true. (Though in my case it was a lot likelier to be beer than martinis.) Anyway, the extraordinary stability of cats in a seaway is definitely not just a hopeful marketing ploy. As an extreme demonstration, I came in Destin's East pass one day in high winds and a strong following sea, in my old cat, with wind against tide. The seas were breaking heavily in the pass, and like an idiot I still had the main up. I broached to on a 10' breaker, surfed at a high rate of speed toward the jetty, and recovered just in time. I had guests with me who'd never been sailing before, and when I screeched "Hang on!" they set their beers down on the deck to cling to something. After it was over and we were inside, they just picked their beers up, and they didn't know enough about sailing to understand how remarkable that was.

We're having a pretty old argument, but in my opinion tris are the better go-fast platforms (due to lower wetted surface and greater sail-carrying stability) and cats are the better cruising platforms. The existence of monsters like Playstation makes for some ambiguity on the first assertion, but I regard the second as pretty much settled.

Ray

[Chris Ostlind]

5 degrees...that's all, really?

I guess that would mean I've been pushing too hard with my boats in the past.

All silliness aside, the following seas story so totally explains your perception.

Beer has a much lower center of gravity than does the typical martini. That is especially true if the beers in question were dark and German.

Here's the pre-requisite 5 degree heel I prefer...

[rayaldridge]

5 degrees...that's all, really?

I guess that would mean I've been pushing too hard with my boats in the past.

All silliness aside, the following seas story so totally explains your perception.

Beer has a much lower center of gravity than does the typical martini. That is especially true if the beers in question were dark and German.

Here's the pre-requisite 5 degree heel I prefer...


Yep.

It's easy to work out with graph paper and protractor. Assume a 35' cat with 15' beam and 18" draft. By the time the windward hull is clear of the water (NOT an excellent idea in a cruising cat) and the leeward hull is depressed 6" you're only at 6 or 7 degrees of heel. Most folks will never see that much heel on a cruising cat, unless they're beam-on to a big steep sea, and then it would be worse aboard a tri or monohull.

I'll quote Thomas Firth Jones on this: "It may seem niggling then, to say that Carol and I prefer the motion of a cat. It goes to windward at only 3 to 4 degrees of heel, where a tri may heel 10 to 15 degrees in gusts." ...from Multihull Voyaging.

This is not to claim an unvarnished benefit for cats-- the downside of all that stability is that the mast and rigging of a cat must sustain much higher shock loads... because why? Because, of course, a cat does not heel in gusts.

But I like your theory about the CoG of consumable liquids.

Ray

[Chris Ostlind]

Ray, you're getting way too serious for the topic. (for me anyway) You already made those points, all in attendance got it and the last letter from me was to put the whole thing in perspective by taking the humor from the subject and making it the focal point.

Essentially, it's an endless argument, though I suppose that if you'd like to press-on, we can always find some obscure stuff to toss on the fire. There's always quotes from one guru or another to fan the flames if you want, so whad'ya say it just goes away?

Besides, it's really hot here, I'm kinda tired from being in the boat shop all day fashioning a carbon cockpit rim for my new canoe/trimaran and my wife wants to go to the movies. Now there's a loaded list for which you'll never have the better answer.

[rayaldridge]

Sorry, Chris. When you said, above, that:

"For example, if the tri amas are designed to just kiss the water surface at design load, there is very little heeling going on when the sails are engaged and the ama is pressed to equilibrium. Any gusts beyond the norm would cause both boats to experience a degree of enhanced heel and that comfy notion that a martini will sit still in a seaway goes right out the door."

...I thought you were seriously putting forward the idea that there was little substantive difference between the heeling characteristics of tris and cats. Needless to say, I found this inexplicable, considering how knowledgeable I find you to be on the subject of multihulls in general.

I like this discussion. In laying out the differences between two hulls and three, a lot of light is shed on the differences between one hull and more than one hull. Interesting stuff, to me.

Hot here, too, and I'm putting a new roof on the old homestead. I'd rather be boatbuilding.


Ray

[RMG]

After reading through the many posts I was surprised to see that nobody has brought up the Lake Leman multihulls used in the Bol d'Or regatta and other various lake events in Switzerland. Following the 2003 Bol d'Or, the Lake Class box rule, which limits overall length to 19.6 meters, waterline length to 12.5 meters, and height to 24.5 meters, was scrapped due to escalating costs and was replaced with the Decision 35 class, which was based off of the Alinghi Catamaran that dominated the scene from its launch in 2000 through 2003.

Throughout the 1990s, trimarans won a majority of the lake regattas in Switzerland. Prior to the commission of the Alinghi Catamaran, Ernesto Bertarelli was sailing a yellow Gino Morrelli designed trimaran also named Alinghi. In 1999 Ernesto Bertarelli asked Sebastien Schmidt & Jo Richards, Gino Morrelli, and Van Peteghem & Lauriot Prevost to propose a new multihull design under the Lake Class box rule. The commission ended up going to Schmidt and Richards.

What I found so interesting was Schmidt and Richard’s design process. They first started out by designing the most optimal sailplan that best suited the tricky winds of Lake Leman often ranging 360 degrees from 0-30 knots, without taking into consideration the rig, beams, or hulls. Computer tests were then run using the already designed sailplan on optimum tri and cat platforms. They found that in light air, the difference in wetted surface area favors the tri only if sailing on the central hull, which is not possible. The tri goes through an increase in wetted surface area until flying on one hull. To fly two hulls, the tri will be heeling at the very minimum of10 degrees. The wetted surface area of a cat only decreases with heel. The cat has a weight advantage of 400kg in this case, 1200kg compared to 1600kg. The cat only needs 3.5 degrees of heel to fly on one hull. What about righting moment? Obviously a tri is going to have much more righting moment than a cat. This was solved with 320 liters of water ballast and six crewmembers on racks. This extra weight is movable unlike on a tri.

On this 1.2 ton boat, 23.7 tons of mast compression was calculated, similar to that of AC boats. An innovative carbon truss/tie rod structure was used to solve the compression and torsional deformation problems prone to cats. Two carbon trusses spaced 4 meters apart on the rear beam meet at the mast base and continue forward as a single truss to form the bowsprit. The structure looks like an upside down Y. A complex system of PBO rigging was used to support the trusses attached by tie rods.

This catamaran was untouchable. None of the trimarans under the same rule came close to beating the Alinghi Catamaran. I think that this is a perfect example of how a catamaran platform is more optimal than a trimaran platform. It would be interesting to see this concept applied to larger racing catamarans. (Attached is an article from seahorse written by Sebastien Schmidt on the Alinghi Catamaran that I got most of my information from.)

[jam007]

Some thought on tris and cats.
Background:
Maximum traverse righting moment determines the maximum sideforce from the sails and depends on weight and beam. Maximum longitudal righting moment depends on length, weight and shape of the hulls. Maximum speed possible depends on longitudal stability since it is the driving force that has to be maximized.
Sideforce is greater than driving force for relative wind angles up to ca 50 degrees, for larger angles the sideforce rapidly gets smaller.

I would then guess that a tri can use a large beam more effective than a cat since the longitudal stability of the large central hull and one side hull is higher than for one cat hull. In other words: the risk of pitchpoling when coming off the wind is higher for a catamaran than a timaran of the same length to beam ratio.

If the above is correct it would lead to the following:
For very high performance boats that seldom sails with a relative wind angle above ca 50 degrees a beamy cat should be the fastest in all but the lightest winds as the central hull of a tri will fly anyway.
With lowering performance the tri will start to be advantageous due to it´s higher maximum speed off the wind (smaller wetted area and high longitudal stability) and in light winds.

Comments anyone?

Anders

[frosh]

Hi Jam007, No argument with your conclusions from me. In a way the discussion applies more to racing craft as in cruising multihulls it is more about ease of handling, liveability and so on. Speed is a much lower priority, however inevitably it will be considerably more than a similar size monohull.

The Volvo Extreme 40 catamaran is relative to almost all other multihulls overpowered to an extent that longitudinal stability is as fragile as tendency to heel in even light winds. See this link with some good photos:
http://www.catsailor.com/Stories_Temp/VolvoExt_UK-Day2.htm

[jam007]

When it comes to cruising boats i think Ian Farrier (referenced above and also here: http://www.f-boat.com/pages/catamarans/index.html) have a convincing argumentation for choosing tri or cat.

Anders

[jam007]

Found this post from Tom Speer about multihull stability:
http://boatdesign.net/forums/showpost.php?p=15588&postcount=15

Some other thought about cats and tris:
Is there not a built in conflic for catamarans. To lower the wetted area you want to fly one hull in as low windspeed as possible. But that must mean that you have a low maximum sideforce. If you make a wide catamaran you get a high max righting moment but also a high "flying" windspeed and will have a large wetted area in light winds. A trimaran can be as wide as you want and still have a small wetted area in light winds. Again the difference is small if the boats have high enough performance to be limited by sideforce and minimum relative wind angle in all but the very lowest windspeeds.

A note on longitudal stability. When iceboating you can actually lift the front runner when releasing the sheet when traveling at high speed as the drag is almost only from the rigg and hull. There is never any high net forward momentum even when traveling at maximum speed for the same reason. A similar effect should be possible for boats with very low hydrodynamical drag reducing the need for longitudal stability. (And giving us spectacular pitchpole capzises when something goes wrong:)

There is also a scaling effect. With increasing size the righting moment and longitudal stability grows much faster (forth power) and wheight (third power) than the wetted surface (squared) this would make cats superior when it comes to very large boats as a cat can be made lighter than a tri of the same size.
In a way tris are occupying a (shrinking?) part of the high performance size spectrum between skiffs and cats.

Anders

[Doug Lord]

I don't think you can look at longitdinal stability(pitch resistance) or roll stability on high performance multi's these days without considering the effect of the use of foils whether it's rudder t-foils to aid pitch stability or a combination of rudder and lifting foils to not only aid pitch stability but reduce wetted surface at high speed.
Orma 60's have proved the viability of lifting foils on the ama's as well -on some of them- as the combination of lifting foils and rudder t-foils. Parlier's planing cat relies on rudder t-foils to keep the stepped planing hulls at the right attitude.Steve Clark has experimented with the combination on a C class cat and at least one production beach cat comes with rudder t-foils. The Catri trimaran uses foils advantageously as well.
I think the careful application of foils in high performance multihull design can allow shapes that would not be possible w/o foils and lead to better handling, higher speed and greater safety.
------------------
edit: I'm referring to the use of "foil assist" hydrofoils not full flying hydrofoil systems.

[jam007]

oh no Doug Lord...
I will not take up that glove but stop foiling every thread or someone will stick one in you...

Anders

[Doug Lord]

Sorry Anders, but in case you hadn't noticed foils are intrinsic parts of the design of many
modern high performance cats and tris.
Anders, the use of foils on cats and tri's, as I mentioned in my last post, allows for very different hull shapes, increased pitch stability and represents state of the art today. You don't think it should be discussed?
===============
edit--Ander's I've participated in this thread since it started in 2005 with a guy asking about the advantages of an equal sized high performance cat vs a high performance tri-it was not about cruising multihulls! You simply can't look at a high performance multihull today without, at least, considering the application of hydrofoils in one form or another with the ORMA tri's being the best example.
====================
Post #1 in this thread
================
Hello everyone !
I was always wonder if to compare racing catamaran and trimaran of the same size, for example Formula 40, which one out of two will have better performance, it means speed in the same weather condition? I am talking of typical racing boats without any accommodation for crew, build very light and simple, like beach cats, only larger, just for speed, not comfort!
Since we plan to get one of those any input will be highly appreciated. So far the only answer to my question was from Tornado sailor and Olympic medalist.
Hi said: "Why to carry 3 hulls if you use only 2 at a time?" And than he added: "Always easier to fly 1 hull than 2", lol.
Maciek

[Chris Ostlind]

Hey Anders,

This is the same disease that you will see on many other, Doug Lord postings around this forum... that being that foils designed to lift a boat above the water are the Messianic solution to all that is wrong with the boating industry, especially the racing part of the boating world.

It's perfectly appropriate that the initial posting to this thread (way back in July of 2005) suggested the paradigm that is being followed by the Volvo 40 catamarans. Maciek188 asked about the comparison of trimarans and catamarans of the type and extended his query to include racing boats of the type that are built for speed and not comfort. He specifically did not ask about lifting foil equipped boats of the type so incessantly mentioned by Mr. Lord.

Here's his original query from July 2005:

Hello everyone !
I was always wonder if to compare racing catamaran and trimaran of the same size, for example Formula 40, which one out of two will have better performance, it means speed in the same weather condition? I am talking of typical racing boats without any accommodation for crew, build very light and simple, like beach cats, only larger, just for speed, not comfort!
Since we plan to get one of those any input will be highly appreciated. So far the only answer to my question was from Tornado sailor and Olympic medalist.
Hi said: "Why to carry 3 hulls if you use only 2 at a time?" And than he added: "Always easier to fly 1 hull than 2", lol.
Maciek


Like almost all boats that go fast for a living, they do have foils in the form of rudders and daggerboards. This is not the type of foils which Mr. Lord wishes to lecture you about, however. He's into the lifting variety that push the entire boat out of the water where it becomes a flying object, much more than it behaves as a traditional boat that you may have come to know and enjoy.

This flying foil thing is Mr. Lord's particular disease.

Let it be known that boats do not need to fly above the water to be considered appropriate for the genre. Mr. Lord has it in his head, in a most peculiar way, that this methodology is necessary to feed the need to always be at the state-of-the-art position on design issues. First of all, this is not state of the art, as it has been going on for a very long time as an adjunct science at the extreme periphery of traditional boating. By far and away, the rest of the boating community does not share his position and you should not feel the need to get the newest and most complex stuff in order to feel as a part of the game.

In short, your instincts are correct, as were the original thread position statements about cats and tris of the Volvo 40 type.

If the conversation were to be confined to that idiom, then eventually, even Mr. Lord will have to sit down with his relentless, self-serving and... some would even say, overly processed, attitude about lifting foils and flying boats.

Every year, there are literally, hundreds of new boats introduced that advance the craft without the use of foils to lift the hull from the water's surface. Comparatively, there are perhaps two or three new boats each year of the foiling variety. The foilers suffer from overly complex mechanisms to get them to fly and nonsensical power to weight ratios that severely limit their usefulness. Their susceptibility to "stuff in the water" being wrapped around the lifting surface, which can instantly ruin the lifting function of the foils, if not damage them beyond repair and functionality, is on the record. Ask Mr. Lord about the French boat, L'Hydroptere, in which it went out for a speed run and had a foil literally slammed right off the end of the ama while at speed due to a foreign object in the water which destroyed the foil. Ask him how fast the boat was after it returned to a waterborne state. Yes, State-Of-The-Art is a really cool place to be. I wonder if it would be so cool if it were your wife, girlfriend or family on the boat when the lifting foil were slammed into oblivion?

You'll be amazed at the answers as given by Mr. Lord as to the frail qualities of foiling boats in general.

Ask Mr. Lord how many commercial, foil-borne craft are still in operation worldwide compared to the numbers once introduced. Ask him about the business of substituting high technology for grounded and measured advancements in the "State-Of-The-Art", as are taking place all over the planet as we speak.

You see, Anders, this is a guy who wants to take the short cuts in life. He doesn't like hard work, sacrifice and painstaking, incremental discovery. He just assumes the feeling that he has the right to jump to the front of the line without doing any of the work associated with the transition. Now to be perfectly fair about all this… I don’t like the hard work either, but I long ago realized that it’s the soundest methodology for a well-developed product. Short-cuts only lead to dead-ends from my experience.

Make your own conclusions as to whether the style of Mr. Lord's behavior in these matters is appropriate.

[Doug Lord]

Mr. Anders, in the previous post Mr. Ostlund 100% mischaracterized my postings particularly the one you responded to earlier. I did not suggest the use of full flying foil systems; in fact I added an edit to make that abundantly clear when I first wrote the post.( #44)
The foil application that is most widespread and that will probably have the most profound effect on high performance multihulls is FOIL ASISST not full flying hydrofoil systems.
It is particularly applicable in the area of pitch stability as I earlier pointed out.
Foil Assist has an important and growing place in high performance multies-not discussing it won't make it go away. If you were to look at the idea seriously you might find not only performance enchancement but safety improvement as well- in reducing pitch pole.
===================
POST # 44

I don't think you can look at longitdinal stability(pitch resistance) or roll stability on high performance multi's these days without considering the effect of the use of foils whether it's rudder t-foils to aid pitch stability or a combination of rudder and lifting foils to not only aid pitch stability but reduce wetted surface at high speed.
Orma 60's have proved the viability of lifting foils on the ama's as well -on some of them- as the combination of lifting foils and rudder t-foils. Parlier's planing cat relies on rudder t-foils to keep the stepped planing hulls at the right attitude.Steve Clark has experimented with the combination on a C class cat and at least one production beach cat comes with rudder t-foils. The Catri trimaran uses foils advantageously as well.
I think the careful application of foils in high performance multihull design can allow shapes that would not be possible w/o foils and lead to better handling, higher speed and greater safety.
------------------
edit: I'm referring to the use of "foil assist" hydrofoils not full flying hydrofoil systems.

[Chris Ostlind]

What did I tell ya, guys? Not 35 minutes goes by and Mr. Lord is busy issuing non-denial, denials.

And he says he never reads, nor answers my postings...

Very funny stuff, and oh so transparent in its desperation to be regarded as substantial.

[Dan S]

[quote=Chris Ostlind]What did I tell ya, guys? Not 35 minutes goes by and Mr. Lord is busy issuing non-denial, denials.
quote]

All some people do is sit on forums and post all day long, most often they are called TROLLS.

[jam007]

Sorry all. I have woken the bear.

Doug Lord:
I don't think you can look at longitdinal stability(pitch resistance) or roll stability on high performance multi's these days without considering the effect of the use of foils whether it's rudder t-foils to aid pitch stability or a combination of rudder and lifting foils to not only aid pitch stability but reduce wetted surface at high speed.
Orma 60's have proved the viability of lifting foils on the ama's as well -on
...
I think the careful application of foils in high performance multihull design can allow shapes that would not be possible w/o foils and lead to better handling, higher speed and greater safety.

I find the original question on tri and cat performace very interesting without arguments about how nice it will be when evering is lifted (oops, assisted) by foils.
How does foils used on TODAYS COMMON racing boats affect the roll and pitch stability and how does that affect the choice between a high performance tri and cat Doug Lord?

Anders M

[Doug Lord]

Anders,I don't believe foils used as "foil assist" appreciably affect roll stabilty* but they certainly affect pitch stability. I think that because the application of "foil assist" is relatively simple on most catamarans that the choice particulary in small "common" boats would be to lean toward a cat whose performance could be markedly improved relatively inexpensively using-at least-rudder t-foils. In one off designs of any size or in larger multihulls designed from scratch I think the tri would have the edge if "foil assist" was designed in from the begining.
--------------------
About the Stealth Marine F16
" The t-foil rudders enable more sailing power with the same amount of square meters of sail".
Cathouse Import en verkoop van Stealth Marine Catamarans
Address:http://www.cat-house.nl/Engels/f16.htm Changed:6:55 AM on Saturday, July 30, 2005

-----
From the F14 forum "..and with every "pitch" that the non-t-foiled cat made the t-foiled one stepped just slightly ahead. "
". The t-foiled F14 gave the F18 a head start and caught up by the bottom mark every time"
Catsailor.com: "T" foils on F14
Address:http://www.catsailor.com/forums/showflat.php?Cat=0&Board=forum14&Number=77606&page=0&fpart=all
-----------------
*Production proa where foil assist is used specifically for roll stability:
http://www.hydrovisions.com
-----------------
More on T-foils on "common" high performance cats and pictures:
Catsailor.com: T foils
Address:[url]http://www.catsailor.com/forums/showflat.php?Cat=0&Board=Fleet45&Number=84517&page=0&fpart=2[/url

[Dave Higgins]

Interesting discussion.

I believe that foils for lifting multihulls (or even monohulls like the Moth) completely out of the water are a terrific idea but one with very limited market appeal. This is because they usually require complex control systems, they often require a lot of skill to use, they add a great deal of expense to the boats that use them, and the boats that use them have limited appeal when they are not foil borne. A great example is the Hobie trifoiler. Terrific performance on the foils, but how many have sold?

A few years ago, Rod Johnstone of J-Boats did some market research and determined there was a need for a high performance, car toppable sailboat that was easy to learn to sail (unlike the windsurfer). He approach foil specialist, John Slattebo, with the design brief. John's answer was a foil stabilized outrigger. The design was introduced recently as the Raptor 16. (www.hydrovisions.com) What is unique about the design is that it is very simple AND the boat can be paddled easily without the foil, can be sailed without the foil in light winds, and can be sailed without the foil in higher winds with ballast in the "sidecar." There is a single moving part patented foil system that counteracts roll and that retracts and stows away with a tug on a lanyard.

The Raptor was just listed in Sail Magazine as one of the year's best new boats, and it is a candidate for the 2007 Sailing World Boat of the Year.

Foils can do a lot of things, not just convert a conventional sailing vessel into a flying machine.

Dave

[frosh]

After two attempts to get Mr Lord banned from this forum but to no avail, I finally decided that it was stupid in the extreme for me to quit just because he happens to exist, and he haunts this forum a bit like "Jack the Ripper", but without the carving knife.
I will just refuse to engage with him from now on. I love the pure design and technical aspects that 95% of guys on this forum want to discuss, and I want to be part of it, and I also believe that I have something useful to offer.
As far as the cat vs. tri argument, there is no better multihull. Both have so many fine attributes albiet a little different from each other that both forms have enormous validity and probably on balance greater application than monohulls, in sailing craft.
Any discussions about which type of multi is better, ultimately has no real answer. It depends on the exact purpose of the boat, many other practical matters such as berthing, accomodations, budget, and most of all individual passion of a prospective owner for one or the other.
Personally I prefer the aesthetics of the tri, but would never claim it to better than a cat.
Hey, it feels good to be back. :)

[CORMERAN]

Thankyou frosh,

for saying what some of us might be too
timid to say..............!

Also, you MUST be an most intelligent and capable fellow
- as you share my view on many things.

Like the back and forth on Cats and Trimarans.
It all depends on what the end use is............
As it is with all vessels.

Cheers !

[frosh]

Hi CORMERAN, Thanks for your kind and generous comments. Your last posting makes me feel that I made the right decision to come back. All power to you and Chris, and the many other sane and considerate members of this forum! :)

[rayaldridge]

Any discussions about which type of multi is better, ultimately has no real answer. It depends on the exact purpose of the boat, many other practical matters such as berthing, accomodations, budget, and most of all individual passion of a prospective owner for one or the other.
Personally I prefer the aesthetics of the tri, but would never claim it to better than a cat.
Hey, it feels good to be back. :)

I think you can cite advantages for both. The trouble is that if you say, for example, that a cat is better for cruising, some tri fanatic will be offended, and if you say tris are faster over the usual range of wind speeds, then some cat fanatic will be offended.

[llamalookout]

I recently purchased a Windrider 17 Tri based on the priority list below. Previously I owned a Hobie 16, which was great fun but was rather unstable and very wet - now with a family I need something dryer and safer and more suitable for day adventuring around our harbour & coast:


Desire.......WR 17......Hobie 16.....Best
Multihull.....yes..........yes...........Multihulls are best for speed
<$10k US...yes...........yes..........Hobie 2nd hand cheaper
Low draft...yes..........yes...........Both ideal for my tidal harbour
Fast..........yes..........yes...........Hobie is faster
Trailable.....yes..........yes...........Both trailer OK
Dry............yes..........no...........Windrider windward hull out of water
Friends.......yes..........no...........Windrider takes 4 children & 3 adults
Motor.........yes..........no............Windrider has 50cc 2hp outboard
Easy tack....yes..........no............Windrider never gets caught in irons
Dry storage...yes.........no..........Windrider has dry hatches to store all gear
Safe.............yes.........no..........Windrider _very_ hard to capsize
Relaxing........yes.........no..........WR has central skippers seat, no jumping from side to side required
Main adjust...yes.........no...........Windrider has easy halyard to reef or drop main
(My Hobie halyard latched at mast top so return to shore was required)

see www.windrider.com for info on this fun boat

[Doug Lord]

Thanks! I've been interested in hearing a first hand account of this boat and your comparison is excellent and informative. How about the workmanship on the Windrider-did/does everything fit and work well? Have you tried the bimini?

[ActionPotential]

The original question was 'for racing' and the jury is in.
Off the beach it is cats. For bigger stuff it is tris. F40 proved it.
The big RTW boats are cats cos you can get a bigger boat for your money and a bigger cat beats a smaller tri but a same size tri beats a same size cat.
Theorise why all you like, the proof is in the (race) results

[llamalookout]

Glad to hear tris are fastest for their size - I love those ORMA60 boats they are a thing of great beauty.

Hi Doug, the Windrider 17 is very well designed and constructed (I haven't got a bimini). I have it moored down on our mud flats and other than a bit of weed growing it is coping well. Its great to have the boat on the water with mast up with the gib roller reefed. The draft is very low, which means that I have about 3/4 of the tidal range available for sailing (compare that to the fat, heavy & slow old stub keel monohulls on the next moorings!) The keel protects the perminant rudder - so all I need to do to go sailing is padle out in my old canoe, chuck the hatch covers into the canoe, pull the boom & sail out of the centre hull, and sailings on.

For me it was always the time consuming rigging and derigging of racing boats that spoiled the fun, especially after getting back cold and tired.

Doug, I am very interested in your comments on foil assisted stability. The one thing missing from the Windrider 17 (and the hobie 16 for that matter) is a foil to give good pointing ability. If I'm out adventuring, or burning off other cruising craft, then I want to be able to make headway into the wind as good as possible. So I am designing some bolt on foils to give me this ability. While I'm at it I want to angle these inward from the amas at 45 angle so they contribute to both the pointing ability and to lateral stability. On the Windrider the amas have a much shorter water line length than the main hull, so they must add a lot of drag as they get buried. In my head I can see the leeward ama skimming the water with the foil assist, me sitting on the windward ama to do my bit there, and the vaka slicing through the water like a very narrow, but very stable, monohull.

So far the sites I have found to assist with this mission are:

Catri 24, performance foil assisted tri - http://www.ahoy-boats.info/big/speed5-bsk.htm

Small volume carbon foil manufacturer -
http://www.philsfoils.com/

Next I need to decide on the foil size & shape.

Regards
Mike

[Doug Lord]

Mike, you might consider contacting John Slattebo at Hydrovisions. He builds a neat little proa that uses a foil stability system. They may or may not be suitable for your application but are guaranteed to be the closest on the market to what you could use. They are "L" shaped so that the lateral resistance and lift functions are separate and if you used two you might have a good solution. I'm not sure he'll sell them separately but I am sure that he's a first class guy with whom I've had great conversations. Here's his website:
Hydrovisions Innovative High-Performance Watercraft Design
Address:http://www.hydrovisions.com/ Changed:5:55 PM on Friday, May 5, 2006
Let me know how it goes....

[bilbobaggins]

I was always lead to believe that the tri configuration permitted a stiffer rig and a much stiffer forestay - leading to an efficient headsail, and hence more speed.

Readers might care to view the attached photos of 'DaddyLongLegs' - a one-off ( rotating ) foiler presently sailing at the UK Sailing Academy, Weymouth, Dorset - the site of the next Sailing Olympics. It will be seen that a centreline beam is used to mount the mast, distributing the compression loads between the two carbon crossbeams. This would appear to have some merit.

I'm personally interested in this configuration, and whether I can 'borrow' the carbon beam-end 'lugs and pins' arrangement, and make it so for the alu crossbeams I already have.

Would any structural engineers/sailors care to comment?

[Doug Lord]

The Decision 35 has a similar structure for the same reason:
Décision 35 Challenge Julius Baer Course trimaran, Course catamaran
Address:http://www.challengejuliusbaer.ch/pages/decision35/concept.lbl?lang=en Changed:9:27 PM on Monday, October 9, 2006

[bilbobaggins]

Thanks for that pointer, Doug Lord.

Folks *may* be interested to see the boat being rigged for its first sail of the year, just a couple of weeks before the AYRS 'Weymouth Speed Week'......

I'm not a 'fundamentalist' about foils, but this was a fascinating example of the guys' R&D. And, yes, they actually are rocket scientists!!!

http://http://i33.photobucket.com/albums/d78/bilbobaggins1946/IMG_0861b.jpg

[bilbobaggins]

Thanks for that pointer, Doug Lord.

Folks *may* be interested to see the boat being rigged for its first sail of the year, just a couple of weeks before the AYRS 'Weymouth Speed Week'......

I'm not a 'fundamentalist' about foils, but this was a fascinating example of the guys' R&D. And, yes, they actually are rocket scientists!!!

[Doug Lord]

B, is Doug Culnane involved in that project? He tried a "diamond foil" similar to the forward foils on the cat on a Moth monofoiler.

[CORMERAN]

To bilbobaggins:

Re: Beam Design.

One reason a Tri, generaly, will have a stiffer forestay is
because a beams resistance to bending goes up by
the sq.

i.e. 2 two x fours, side by side will be twice as strong as
a single two x four.
However, a SINGLE two x six will ALSO be twice as
strong as a single two x four.

- And, most important for multi - hull designers,
a single two x six is - obviously - going to be
significantly LIGHTER, than 2 two x fours.

So it follows:
With most cruising tris - the center hull ( as a beam ) will have
more resistance to bending, than a cruising cat can sustain
( of the same displacement ), as the center hull will - most likely
- be significantly deeper - than one of the cat's single hulls.
Especialy, if you includ the cabin stucture, as part of said beam.

Therefore:
The force that can be applied to a typical tri's forestay,
backstay AND mast - without making a ' banana ' out of the
vessel is, almost always, going to be greater than can be
applied to a cat of similer displacement.

`````````````````````````````````````````````

In respect to your present focus:

I am a bit concerned about HOW: all the beams shown,
are inter - connected.
It's all very well to resolve stresses within the beam itself.
( That look good, on a two - dimentional computer screen )
However, I always get nervous when I see a multitude
of right angle corners - with a minimum of tri - angulation.

The forces on a vessel are 3 dimentional - and come from
ALL directions.

So another " RULE of BEAM " to remember:

When a beam DEFLECTS as little as 2 to 3 degrees from a
vertical, downward force it loses as much as 90% of it's
ability to resist, said force.

Given the above and from what is visible:
If it was my boat I'd be inclined to releave the stresses
on your center beam - with some triangular elements.

Cheers !

[ActionPotential]

To bilbobaggins:

Re: Beam Design.

One reason a Tri, generaly, will have a stiffer forestay is
because a beams resistance to bending goes up by
the sq.

i.e. 2 two x fours, side by side will be twice as strong as
a single two x four.
However, a SINGLE two x six will ALSO be twice as
strong as a single two x four.

- And, most important for multi - hull designers,
a single two x six is - obviously - going to be
significantly LIGHTER, than 2 two x fours.

So it follows:
With most cruising tris - the center hull ( as a beam ) will have
more resistance to bending, than a cruising cat can sustain
( of the same displacement ), as the center hull will - most likely
- be significantly deeper - than one of the cat's single hulls.
Especialy, if you includ the cabin stucture, as part of said beam.

Therefore:
The force that can be applied to a typical tri's forestay,
backstay AND mast - without making a ' banana ' out of the
vessel is, almost always, going to be greater than can be
applied to a cat of similer displacement.

Therefore Decision 35 will have less resistance to bending than a 'true' tri with a deeper centre hull and the cat above with it's not very deep at all centre longitudinal beam will have much less resistance to bending again.
The whole argument relates to stiffness to allow forestay loading.
I suggest that this is no longer relevant to the cat vs tri question as forestay stiffness is no longer very important with the modern emphasis on mainsails or wings. A tri will be faster (overall, range of conditions and courses) than a tri of the same length, not because it can load it's forestay more.

[bilbobaggins]

To Cormoran....

Thanks to you, and others, for input.
I'm very interested in this approach, and am considering how/whether I can adapt it for my own use, on a 13.5 metre hull-set.

Quote : "Given the above and from what is visible: If it was my boat I'd be inclined to releave the stresses on your center beam - with some triangular elements."

I attach another shot showing the centreline beam is triangular in section, and has a convex topside curve. I don't know at present what is internal to that beam e.g. does it have an internal long vertical web; does it have mini-bulkheads? I certainly agree that the sea provides lots of unanticipated loads/forces and would want to come up with an arrangement that 'triangulated' wherever needed.

So how would you suggest a re-structure of the centreline beam and its fastenings, the better to address these loads? How would I calculate what I need to have there, to carry the loads reliably?

Would a pair of similar longitudinal beams, arranged in a 'V', better cope with torsional loads?

[brian eiland]

Therefore Decision 35 will have less resistance to bending than a 'true' tri with a deeper centre hull and the cat above with it's not very deep at all centre longitudinal beam will have much less resistance to bending again.
The whole argument relates to stiffness to allow forestay loading.
I suggest that this is no longer relevant to the cat vs tri question as forestay stiffness is no longer very important with the modern emphasis on mainsails or wings. A tri will be faster (overall, range of conditions and courses) than a tri of the same length, not because it can load it's forestay more.

Longitudinal Discussion
I would like to point out that I have been looking at this longitudinal stiffening problem for a significant number of years, particularly since my mast-aft rig designs needs tight forestays. Here's some excerpts from several postings I made quite far back:

1)"...BUT, what you may not have noticed was my alternative to the CB's in each hull. Look at the attached drawing, (or the very bottom profile drwg that denotes 'asymmetrical CB's, nacelle mounted'. First, imagine a flat plate, on edge, mounted down the centerline on the underside of the bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel, a somewhat weaker characteristic in a catamaran structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber (kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the rigidity could be even greater (sort of akin to a bottom truss structure, or a flange of an 'I' beam). Now on either side of this flat plate I propose to mount a centerboard, not a single, symmetrical one, but rather two asymmetrical ones; sort of like a single board split in half. The flat sides of these asymmetric boards would fit up against the flat plate nacelle......"
http://www.boatdesign.net/forums/showthread.php?t=2225 (http://www.boatdesign.net/forums/showthread.php?t=2225)

2)"....I am 'pressing' the CB loads onto the 'flat-plate nacelle board', that in turn can be stabilized athwartships via two diagonal support 'wires' (maybe spectra or PBO) that carry the bending load imparted to the flat plate to an athwartship frame member (sub-bulkhead). Thus, very little exposed structure to create drag (flat plate aligned with water flow and two wires attached to bottom edge). Further I would recommend VERY large diameter CB bearing(s) to spread the CB bending loads to the flat-plate nacelle."
http://www.boatdesign.net/forums/showpost.php?p=37041&postcount=41 (http://www.boatdesign.net/forums/showpost.php?p=37041&postcount=41)

3)"There is a requirement for a transverse bulkhead in the boat structure at this CB location to which diagonal 'wires' can be attached to offset the big side-loads of the CB's"
http://www.boatdesign.net/forums/showpost.php?p=36348&postcount=36 (http://www.boatdesign.net/forums/showpost.php?p=36348&postcount=36)

4)"...The front of this nacelle/plate could be configured to act as a wave splitter to actually attack, up front, the formation of those peaky waves under the tramp areas that eventually slap at our bridge deck underside. We kind of slice those waves down a bit. A lightweight fairing might also be added to this 'flat plate nacelle' so it appears outwardly much more esthetically pleasing, as well as more curvature to shed those peaky waves."
http://www.boatdesign.net/forums/showpost.php?p=35993&postcount=30 (http://www.boatdesign.net/forums/showpost.php?p=35993&postcount=30)

I believe you can begin to understand my position with reference to this longitudinal discussion. In fact my 'faired' center nacelle would appear very similar in idea to that 'mini center hull' of Decision 35 and Alinghi

Headsail/Headstay Discussion
I would simply redirect you attention to the discussion of the development of this most advanced race boat Alinghi and the attached PDF document,
http://www.boatdesign.net/forums/showpost.php?p=98787&postcount=39 (http://www.boatdesign.net/forums/showpost.php?p=98787&postcount=39)
quotes..."We chose a rig with one extra foresail, a smaller mainsail, and progressively overlapping foresails", and this "the platform was heavily influenced by the overlapping headsails..."
So I discount your observation, "that forestay stiffness is no longer important..."

[bilbo]

Quote2)"....I am 'pressing' the CB loads onto the 'flat-plate nacelle board', that in turn can be stabilized athwartships via two diagonal support 'wires' (maybe spectra or PBO) that carry the bending load imparted to the flat plate to an athwartship frame member (sub-bulkhead). Thus, very little exposed structure to create drag (flat plate aligned with water flow and two wires attached to bottom edge). Further I would recommend VERY large diameter CB bearing(s) to spread the CB bending loads to the flat-plate nacelle."

That's all very well.

However, in real-world sailing one frequently encounters at speed a heavy semi-submerged object - such as a shipping container, a whale, or a tree trunk. Experience shows that a catamaran's structure frequently comes off worst - 'Queen Anne's Battery Marina', 'Jet Services', and many others. Where there is a structure depending down into the water, such as a 'dolphin striker' or indeed a 'flat plate nacelle with wires attached', then catastrophic structural failure frequently results.

This is not an outcome that the hapless owner and crew - faced with walking home from halfway across Biscay or somewhere west of the Azores - would thank you, the designer.

IMHO, it is essential that yacht structures be designed and built to survive predictable hazards; hence crash bulkheads, positive flotation, rigging 'fuses', and surface piercing structures.

[brian eiland]

That's all very well. However, in real-world sailing one frequently encounters at speed a heavy semi-submerged object - such as a shipping container, a whale, or a tree trunk.
I rather doubt it is as 'frequent' as you imply, but granted it only takes one time to be memorable.




Where there is a structure depending down into the water, such as a 'dolphin striker' or indeed a 'flat plate nacelle with wires attached', then catastrophic structural failure frequently results.
Let me correct one misconception if there is one. I did not mean to imply that this 'flat plate nacelle' extended down into the water, but rather just skims the surface in flat water. Granted this is still venerable to being crashed, but it might not result in the lost of the rig, as it is intended to take the really excessive extra loads of the rig rather than the primary standing ones.




Experience shows that a catamaran's structure frequently comes off worst - 'Queen Anne's Battery Marina', 'Jet Services', and many others.
Most vessels are not going to like coming into a speedy contact with a partially submerged container, but that goes for all portions of the vessel. I would site the RACE catamaran "Team Adventure" on its attempt at a transatlatic record hitting some submerged object up off the Nova Scotia Banks. She lost a portion of her bow (usually the front portion of the vessel is the first to contact a foating object), which damaged her bow crossbeam attachment, which affected her forestay thus mast integrity...almost lost her rig. But this lost of the rig would not endanger her crew's lives. The flooding of the hull might have.
Hitting the vessel's 'boards' at speed might well result in very quick flooding




This is not an outcome that the hapless owner and crew - faced with walking home from halfway across Biscay or somewhere west of the Azores - would thank you, the designer. IMHO, it is essential that yacht structures be designed and built to survive predictable hazards; hence crash bulkheads, positive flotation, rigging 'fuses', and surface piercing structures
There were a number of reasonings I looked at when considering this 'central board' location. Of course I saw the potential to incorporated the 'boards' onto the truss framing I was considering for the vessel's structure itself. But also I have always favored 'kick-up centerboards' over daggerboards on cruising vessels particularly. Should you hit an object in the ocean or in shallow areas, the CB-board and the hull are not as suseptable to damage as with a dagger arrangement. But there remains a 'hole' in the hull's intregrity to accomodate either. What if we could eliminate this 'big gash' in the hull? Seems to me we've lessened the building cost and the increased the water tight integrity of the hulls at the same time.

[brian eiland]

I was always lead to believe that the tri configuration permitted a stiffer rig and a much stiffer forestay - leading to an efficient headsail, and hence more speed.

Readers might care to view the attached photos of 'DaddyLongLegs' - a one-off ( rotating ) foiler presently sailing at the UK Sailing Academy, Weymouth, Dorset - the site of the next Sailing Olympics. It will be seen that a centreline beam is used to mount the mast, distributing the compression loads between the two carbon crossbeams. This would appear to have some merit.
Reference Posting #63 (http://boatdesign.net/forums/showpost.php?p=109469&postcount=63) above. I don't believe that this mounting of the mast on this aft position of the center beam has anything to do with distributing loads. Rather I believe it is to move the sailplan to a more aft position (mast-aft, dare I say it) and lessen the tendency of that mainsail to drive the bows under on a power reach downwind.

I'm personally interested in this configuration, and whether I can 'borrow' the carbon beam-end 'lugs and pins' arrangement, and make it so for the alu crossbeams I already have.
I 'm not excited about their beam attachment, as I would guess it will allow to much 'flex' under heavy loading. And done in alum it would be lucky to last one season before all of the pin holes elongated.

[ActionPotential]

AP:
“The whole argument relates to stiffness to allow forestay loading.
I suggest that this is no longer relevant to the cat vs tri question as forestay stiffness is no longer very important with the modern emphasis on mainsails or wings. A tri will be faster (over a range of conditions and courses) than a cat of the same length, not because it can load it's forestay more.”
Brian:
“Headsail/Headstay Discussion
I would simply redirect you attention to the discussion of the development of this most advanced race boat Alinghi and the attached PDF document,
http://www.boatdesign.net/forums/showpost.php?p=98787&postcount=39
quotes..."We chose a rig with one extra foresail, a smaller mainsail, and progressively overlapping foresails", and this "the platform was heavily influenced by the overlapping headsails..."
So I discount your observation, "that forestay stiffness is no longer important..."”
AP:
I suggest that Alinghi is a modern anomaly and the future lies with unstayed rigs where of course there is no forestay. An intermediate phase is the stayed rig with no headsail, with a wing mainsail, again no need for a tight forestay.
I believe a tri will be faster (over a range of conditions and courses) than a cat of the same length and I don't believe the fact that the tri can achieve a straighter forestay is a significant factor in this.

[creightonious]

In all this talking of the advantages of great beam in multihulls, let's not forget the dirty little secret of tris (which configuration I favor): Once the windward ama is clear of the water, we are dealing with the tri's half-beam, not the overall beam.
This accounts for the increased heel and the increased susceptability to wave-induced capsize.
It also introduces a fairly powerful set of reasons to take a very serious look at Rob Denny's Harry Proa concept.

[Doug Lord]

I'm not sure I agree with that: the square or over square tri puts the CG furthest from the center of buoyancy(when mainhull is just clear) of any multihull and that's good for enormous power. Combine that with the banana boards in the ama's and a rudder t-foil and you have enormous power and the means to use it all with the least wetted surface and greatest pitch resistance. When all that power can't be used in light air you still have more power and less wetted surface than a cat. At least so far....
Rob Denney's innovations in proa's are extraordinary-I sure do agree with that.

[rob denney]

G'day,

Thanks for the compliments.

Tris are wider for structural reasons, but also because when it is time to tack, they only have half the width in the water. A square cat struggles to tack, particularly in waves. Proas don't tack so can be much wider than cats, possibly even than tris. There limit is diagonal stability, which could be augmented by foils (bit tricky as they have to work in both directions) or, my preference, a longer lee hull. Because there is nothing attached to the ends of the hull, this is neither expensive, nor draggy.

I am currently building a proa for the 2008 solo Transpac (SF-Hawaii) which has the same sail area and weight as a 7m/26' Firebird cat. However, the proa is 7.3m/27' wide and 15m/50' long. Should be an interesting test of the above theory.

regards,

Rob

[Doug Lord]

Rob, would the windward hull of a racing harryproa still be the"heavy" hull as it is in the crusing version? And would it be designed to fly-just kissing the water-for minimum wetted surface and maximum power?
I've gone oversquare on rc model foiler tri's with no negative effects on tacking with the lateral resistance disposed equally at the ama's-no main daggerboard. From that -and what you said(good point!)- I don't see any limitation on beam(except structural at some point) on your boats or tris -as long as diagonal stability/pitch stability are controlled.

[rob denney]

G'day,

Rob, would the windward hull of a racing harryproa still be the"heavy" hull as it is in the crusing version? And would it be designed to fly-just kissing the water-for minimum wetted surface and maximum power?

Still the heavy one. On the solo boat, the windward hull which has me, all the safety gear, food and water etc in it, weighs 330 kgs, the lee hull 176 so it is considerably heavier percentasge wise.


[QUOTE=Doug Lord;112385] I've gone oversquare on rc model foiler tri's with no negative effects on tacking with the lateral resistance disposed equally at the ama's-no main daggerboard. From that -and what you said(good point!)- I don't see any limitation on beam(except structural at some point) on your boats or tris -as long as diagonal stability/pitch stability are controlled.

Tris are more limited than harryproas in max width as their beams see a lot more load from the rig. They have more diagonal stability though due to hull shapes and crew aft. A proa with a canting beam solves this. We have a 10.5m/35' canting beam proa under way at the moment, will be interesting to see how it goes.

regards,

Rob

[ActionPotential]

G'day,

[QUOTE=Doug Lord;112385]Rob, would the windward hull of a racing harryproa still be the"heavy" hull as it is in the crusing version? And would it be designed to fly-just kissing the water-for minimum wetted surface and maximum power?

Still the heavy one. On the solo boat, the windward hull which has me, all the safety gear, food and water etc in it, weighs 330 kgs, the lee hull 176 so it is considerably heavier percentasge wise.




Tris are more limited than harryproas in max width as their beams see a lot more load from the rig. They have more diagonal stability though due to hull shapes and crew aft. A proa with a canting beam solves this. We have a 10.5m/35' canting beam proa under way at the moment, will be interesting to see how it goes.

regards,

Rob

Sounds great! Can you steer from the lee hull (to get the windward hull flying sooner) or do you have to stay in the windward hull?

[ActionPotential]

G'day,


Tris are more limited than harryproas in max width as their beams see a lot more load from the rig.

Doesn't the load from the rig ease the load on the beams?
Like the windward hull being lifted by the sidestay rather than by the beams.

[rob denney]

G'day,



Sounds great! Can you steer from the lee hull (to get the windward hull flying sooner) or do you have to stay in the windward hull?

Steering is from the windward hull, but will be done with a wind vane on a long arm (minimal electrical equipment to save money, weight and complexity of generators,). Nothing to stop a keen crew shifting gear (liferaft, anchor etc) and self to leeward in light air to lift the hull. Windward hull is sitting in my garage at the moment, weighs 27 kgs, has bunk and shelf to be fitted, so should be pretty easy to fly if unloaded.

[QUOTE=ActionPotent][QUOTE=rob denney;112447]ial;112452
Doesn't the load from the rig ease the load on the beams?
Like the windward hull being lifted by the sidestay rather than by the beams.

My early boats had shrouds for this very reason. Took them off as the shock loads in waves get pretty high, they are always in the way, are draggy, and prevent the rig rotating 360 degrees. They also require major beefing up under the mast to take the compression loads. The beams do not get much lighter as they must be strong enough to capsize the boat in either direction (even though a windward capsize is theoretically impossible) and nor does the rig as it needs to be self supporting from the leeward side, particularly in a capsize.

I daresay a temporary shroud to stop the top of the mast laying off would be possible, but we are working on including this in the mast construction.

regards,

Rob

[Vega]

Hey guys, take a look:cool: (photos from "The Route du Rhum" 2006):

[ActionPotential]

Great photo's! No cats there. These are built to a rule and they can't build a competitive cat to that rule (they tried and failed). For the same money they can build a longer faster cat. Maybe they should alter the rule to allow 60' tris or 80' cats? When they built 60' cats tothe rule they were not competitive but were significantly cheaper.

[brian eiland]

(Attached is an article from seahorse written by Sebastien Schmidt on the Alinghi Catamaran that I got most of my information from.)
Dear RMG,
I forgot to thank you for posting this article. I missed seeing it as I do not get this publication anymore (got rather pricey here in the US, & I already get tooooo many publications).

For reference I reposted under this very applicable subject thread, "Sail Loading on the Rig, Rig Loading on the Vessel". and specifically here:
http://boatdesign.net/forums/showpost.php?p=114487&postcount=59 (http://boatdesign.net/forums/showpost.php?p=114487&postcount=59)

If you have any more such material please contribute it. And you might be interested to contribute to this other subject thread. Thanks

[brian eiland]

After reading through the many posts I was surprised to see that nobody has brought up the Lake Leman multihulls used in the Bol d'Or regatta and other various lake events in Switzerland. Following the 2003 Bol d'Or, the Lake Class box rule, which limits overall length to 19.6 meters, waterline length to 12.5 meters, and height to 24.5 meters, was scrapped due to escalating costs and was replaced with the Decision 35 class, which was based off of the Alinghi Catamaran that dominated the scene from its launch in 2000 through 2003.

Throughout the 1990s, trimarans won a majority of the lake regattas in Switzerland. Prior to the commission of the Alinghi Catamaran, Ernesto Bertarelli was sailing a yellow Gino Morrelli designed trimaran also named Alinghi. In 1999 Ernesto Bertarelli asked Sebastien Schmidt & Jo Richards, Gino Morrelli, and Van Peteghem & Lauriot Prevost to propose a new multihull design under the Lake Class box rule. The commission ended up going to Schmidt and Richards.

What I found so interesting was Schmidt and Richard’s design process. They first started out by designing the most optimal sailplan that best suited the tricky winds of Lake Leman often ranging 360 degrees from 0-30 knots, without taking into consideration the rig, beams, or hulls. Computer tests were then run using the already designed sailplan on optimum tri and cat platforms. They found that in light air, the difference in wetted surface area favors the tri only if sailing on the central hull, which is not possible. The tri goes through an increase in wetted surface area until flying on one hull. To fly two hulls, the tri will be heeling at the very minimum of10 degrees. The wetted surface area of a cat only decreases with heel. The cat has a weight advantage of 400kg in this case, 1200kg compared to 1600kg. The cat only needs 3.5 degrees of heel to fly on one hull. What about righting moment? Obviously a tri is going to have much more righting moment than a cat. This was solved with 320 liters of water ballast and six crewmembers on racks. This extra weight is movable unlike on a tri.

On this 1.2 ton boat, 23.7 tons of mast compression was calculated, similar to that of AC boats. An innovative carbon truss/tie rod structure was used to solve the compression and torsional deformation problems prone to cats. Two carbon trusses spaced 4 meters apart on the rear beam meet at the mast base and continue forward as a single truss to form the bowsprit. The structure looks like an upside down Y. A complex system of PBO rigging was used to support the trusses attached by tie rods.

This catamaran was untouchable. None of the trimarans under the same rule came close to beating the Alinghi Catamaran. I think that this is a perfect example of how a catamaran platform is more optimal than a trimaran platform. It would be interesting to see this concept applied to larger racing catamarans. (Attached is an article from seahorse written by Sebastien Schmidt on the Alinghi Catamaran that I got most of my information from.)

...two recent postings related to this Alinghi cat. Wonder what we will see from Alinghi for the America's Cup??
Another 'Structured' Cat
http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-6.html#post277098

Boat with NO HULL
http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-7.html#post277099

[ThomD]

Whille we are waiting, we have the Gougeon racing cat/tri supposed to make it on the water this summer according to the lattest issue of Epoxyworks. Always interesting to hear what blend of features Jan comes up with. I thought it might be G32 ish, with amas for greater stability in blasting mode, but I now don't think so.

[oscarvan]

Greetings....new around here and I see there's lots of reading to do, which is good as I have many hours to kill holed up in hotels on various continents. (Airline pilot).

To me the Cat/Tri is the same discussion as the snow board/ski discussion. It's a different motion. I grew up on two boards, and never was able to change my mindset to a single board.

I also grew up a mono huller. When I realized that carrying all that lead around (8300 pounds on my last boat) was pure insanity I saw the multihull light. So I went tri, because to me it's a mono hull. Minus the lead, just two floats for stability....LOTS of stability....:D A cat is, again to me, a snow board.