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.

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...ngPhotos_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

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, 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.

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?

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.