Cats & Tris

[chas]

Ellen has a tri. Other ocean going speed merchants use cats. Obviously both are faster than monohulls, but what are the relative pros and cons of each for ocean racing and record attempts? Would a tri be better to windward than a similar sized cat? Can a cat carry more sail in heavier weather? I would be very interested to have an insight into the process of choosing which design to use (not that i intend to upgrade from my 30 year old Moody ....yet...).

 

[Talbot]

tris are better to windward.
cats are better off the wind and tend to sacrifice some perfomance for better accomodation

 

[boatmike]

Don't quite agree. Trimarans are inherently faster downwind because their hydrodynamic resistance is lower. The Tri is usually thought of as a three hulled boat. This is not strictly true. The outer hulls are called "sponsons" and normally only one of them will be in, or more correctly "on" the water at a time. Theoretically, dead downwind in a flat sea neither sponson will be in the water and the main hull which is typically pencil thin has very low resistance. Of course this rarely happens in practice, but the load, and therefore the wetted area of each sponson is minimal downwind therefore the boat is faster than a cat. To windward the tri will point better in flat seas but in high seas like Ellen has just experienced they can be dangerous to windward as the hydrodynamic resistance is off centre to the centre of pressure of the sails. In other words a big wave hitting a sponson will tend to lift and turn the boat around. There is also a structural consideration in that a tri can have both sponsons in a wave with the hull unsupported in a crest one minute and vice versa the next. This puts fantastic loads on the structure. You are of course quite correct that the cat has better accomodation, and tends not to be quite as good to windward, but also is less likely to be "broken" in high seas. Ultimately a cat under bare poles in really bad conditions will survive with a drogue or sea anchor where the tri wont. Also, while no multihull likes to carry weight the cat has more ability to take a load than the tri as its inherent and reserve bouyancy is higher. That's why you see lots of cruising cats but few cruising tris. It's also why brave little Ellen has chosen the ultimate speed machine for her record knowing that there is a risk that taking everything to the wire will mean she could possibly lose her life in the attempt. What a fantastic achievement and I am sure we all look forward to seeing her back home safely!

 

[Salty]

Big cats are also easier and cheaper to build than big tris, and since a lot of these record breakers do have budget considerations, this is presumably a factor.

Otherwise, its a compromise depending on the likely route and weather to be encountered: assuming equal sizes, trimarans are supposedly faster to windward and better in light airs. Cats will be faster reaching, unless light weather. Both are similar running. Tris can be chucked about much more and tack more easily. On balance tris win the day for this kind of round-the-world stuff, and I think most serious new build projects are now tri- rather than cat designs.

 

[Goodge]

Now that the Oryx Quest is under way we'll see whether cats are betther than Tri's or vice versa.

Apparently Geronimo the big tri is very well prepared but she's up against some big cats so the out come will be interesting.


Wouldn't want to put my money either way at the moment... lets wait and see....

 

[boatmike]

Re: Cats & Tris

Yes it will be interesting. I think Salty is correct in that it will depend on the sea conditions met en-route. Don't quite agree regarding "cats are faster reaching" but I suppose if you re-word it that cats can carry more sail on a reach in high seas tan a tri can there is some justification for the statement.
In simple terms, shitty weather will favour the cats, good weather, the tris. Chas original question was regarding Ellens record attempt though and in favourable conditions the tri will always be faster. Thats why Ellen was well ahead of the previous record until the storm hit and will, God willing, still cross the line in front safely.

 

[Salty]

I'll put my money on Geronimo. A look at original build dates gives you an idea of how current multihull thinking seems to developing:

Daedalus (cat): originally built 1984!!
Doha (cat): launched 2000, after beng built for the Race (rules were cats only, if I remember correctly)
Cheyenne (cat): Built 1998
Geronimo (tri): Built 2002.

 

[Goodge]

I see it as a two horse race between Geronimo and Cheyenne.

I think Geronimo is favourite but Cheyenne is well proven although I believe she lost some of her crew to Geronimo as they declared their entry first and Cheyenne
weren't sure at the time.

Either way its gonna be a fast race.

 

[Sybarite]

I understood that the main objection to a tri was the risk of the sponson (with its lesser buoyancy) digging in and pitchpoling the boat in extreme conditions.

John

 

[P57]

Re: Cats & Tris

Not quite sure that is ultimately borne out - wasn't Orange II, Peyron's new boat which is currently going for the Jules Verne record rather than the Oryx, built after Geronimo? And Cheyenne, not Geronimo, holds the current outright record round the world.....

 

[Salty]

Re: Cats & Tris

er, fair enough. What do they say about words written in haste? I'd still put a few quid on Geronimo for the Oryx race if I could find a bookie interested in sailing!

 

[Jacket]

Nope, the Race allowed anything - cats, tris and mono's.

The reason that everyone went for cats was that apparently the engineering was felt to be easier. I never quite understood that - a tri has the mast stepped on the main hull, where the loads can be taken, whereas a cat has it ballanced in mid air on a cross beam.

 

[boatmike]

Re: Cats & Tris

I agree. In my imperfect way that's what I tried to say in my original post. Imagine boat on close reach with leeward sponson in water. Big wave comes along, windward sponson gets lifted. leeward sponson gets buried and boat rotates around leeward sponson. Main hull gets bow buried and you have a pitchpole....

 

[Talbot]

Re: Cats & Tris

I bow to your far greater knowledge and understanding, I was merely trying to generalise. IMHO both cats and tris are a bit susceptible to a pitchpole when being pushed very hard downwind in a bigish sea, and both are far beter than a single hull!

 

[chas]

Thanks for that - exactly what i was after.

 

[chas]

Thanks to all. It would seem that tris are better to windward, cats on a reach and much of a muchness downwind. Cats have better accommodation but tris are easier to handle. They are also cheaper to build than tris. I suppose as Ellen chose a tri, one has to assume that they are currently on top.

Well done Ellen - brilliant, gutsy job!