Catamaran vs Trimaran

[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.

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

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,

[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.

Originally Posted by Doug Lord

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]

[quote=rob denney;112447]G'day,

Originally Posted by 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?

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]

Originally Posted by rob denney

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]

Originally Posted by ActionPotent

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 (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]

Originally Posted by RMG

(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

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]

Originally Posted by 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.)

...two recent postings related to this Alinghi cat. Wonder what we will see from Alinghi for the America's Cup??
Another 'Structured' Cat
Sail Loading on Rig, Rig Loading on Vessel

Boat with NO HULL
Sail Loading on Rig, Rig Loading on Vessel

[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.... A cat is, again to me, a snow board.