small trimarans

Discussion in 'Multihulls' started by casavecchia, Jan 6, 2005.

  1. casavecchia
    Joined: Jan 2004
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    casavecchia Senior Member

    Hi all,
    I keep wondering why there is so little interest in small trimarans around 4/4.5 meters long.
    They are inexpensive , easy to build, light and cartoppable, sail fast and are reassuringly stable.
    Besides , being not so phisical, are well suited to older and /or handicapped sailors.
    So why are not more widespread?
  2. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Kurt Hughes has offered some nice designs, but I think the real advantage of a trimaran over a catamaran is its ability to carry greater headstay tension. At this size, jibs on cats are quite small relative to the mainsails, so there's not much need for the third hull.

    I think an open center hull would be nice, though. It'd make a nice fishing boat for some areas (developing countries, etc.)

    One could convert an International Canoe to a trimaran. Come to think of it, the WindRider Rave and the Hobie TriFoiler are basically trimarans.

  3. casavecchia
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    casavecchia Senior Member

    With the obvious exception of the Rave and the Trifoiler,
    the small trimarans I see on the web are too low on the water and this is so much in contrast with the spydery look of the big racing trimarans. The small ones dont trasmit the impression of agility and nimbleness that their bigger brothers suggest. May be that's the reason for their scarce appeal. Anyway they are a good platform for testing hydrofoils. They are easily and cheaply built in plywood, sharpie style, and lend themselves perfectly to workboat use.
  4. terhohalme
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    terhohalme BEng Boat Technology

    Why not Junk Proa?

    Junk Proa has less to build than trimaran and have all the goodies.

    Attached Files:

  5. grob
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  6. Doug Lord

    Doug Lord Guest

    I've always loved small tris. (and other multi's as well.) I built a 14 and 20 footer with planing main hulls years ago.
    I haven't seen any small tris 20' and under- that take full advantage of the potential of the tri. The big 60 footers are square and yet the smaller tris all seem to be much less than that.
    A small tri can develop massive righting moment but the capacity needs to be generated by flying the main hull and I've never seen a small tri designed by anyone doing that (but I'd like to!)
    If you consider the realities of pitchpoling that is still no excuse for not using the max righting moment because the use of foils can eliminate pitchpoloing. You don't need a full flying foil set up either to take advantage of all that power.
    As was said before a full flying foiler takes good advantage of the trimaran concept but I'm not sure they are the ultimate in speed for small tri's. I think there is a lot of potential with planing hulls on ama's and other combination's of foils and planing hulls.
  7. Skippy
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    Skippy Senior Member

    Frank Bethwaite's HSP is a small tri, but he doesn't use the lee ama. He hikes out off the windward ama and flies both of them, planing the main hull a lot of the time.

    Derek Kelsall discusses the cat/tri issue for large racers here:
  8. Doug Lord

    Doug Lord Guest

    small tri's

    My 14 was similar to the HSP in that it was designed to have the amas(buoyancy pods) out of the water at top speed.
    Lots of potential and HUGE RM availble in small tri's that fly the main hull as opposed to the HSP concept and are at least as wide as they are long...
  9. henrikb
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    henrikb Senior Member

    I am currently designing a 6.5m tri together with a friend. The main hull is almost completed (beams, floats, rig not final design on picture) and we will start cutting frames any day.
    Beam is 5.8m, displ is 650kg fully loaded. Sailarea 33m2 upwind.
    The floats will have a volume of aprox. 3*displ, so it will be possible to fly the main hull!

    Attached Files:

  10. Doug Lord

    Doug Lord Guest

    small tri

    Looks great and sounds very interesting; good luck!
  11. Skippy
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    Skippy Senior Member

    You have to be careful about separating the flotation and the ballast too far. If you do, you'll have more problems with pitching than with roll. That's one reason a cat's L/B is about 2. All the flotation is at a distance of 1/2 the beam from the boat's CoM on the centerline around a rolling axis, but the average distance of the flotation from the CoM amidships around a pitching axis is less than 1/4 the lwl.

    And the moment exerted on the sail by the wind is not directly athwartship even when close-hauled, so as you can see on the aussie racing skiffs, you eventually have to move the ballast aft of the transom! That's why Malcolm McIntyre's 1930s catamaran could be distorted into a parallelegram, lee hull forward.

    (slightly modified for accuracy)
  12. Doug Lord

    Doug Lord Guest

    mini max tri

    I think the utilization of foils such as on the Rave is suited well to a square or over square tri platform since the foils are developing the RM for the boat-and the anti pitching moment.
    But with the trailblazing work of the Moth foilers using just two foils that just do the lifting -and pitch control-I've thought about the potential of a small foldable(for trailering) tri say 18'LOA by 18' or so wide. This concept would use the crew for ballast(2) and smallish planing hulls for the ama's and would be designed to fly the main hull.
    Small hydrofoils would be used on the rudder for pitch control in conjunction with a small altitude controlled main foil that would lift up as well as down.
    So the boat would only have two foils both relatively lightly loaded. The question is can a planing ama on a boat like this be less drag than a fully submerged foil that lifts and develops righting moment? I haven't attempted to answer this question yet but I will at some point.... Any thoughts?
  13. Skippy
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    Skippy Senior Member

    A foil trimaran is very different from nonfoiled. The foils act kind of like a catamaran, moving the flotation away from the centerline. Whereas the Windrider is for people who just want to sit in the cockpit. My biggest question has always been, wouldn't the planing ama be uncomfortable when you're hiked out on the windward one and it slams down on the water in a sudden lull?
  14. Doug Lord

    Doug Lord Guest


    At static the two amas would not touch the water at the same time so in a sudden lull the first thing that would happen is that the main hull would tend to come back down but because of the foil on the daggerboard it wouldn't precepitously drop. Now, in a wind drop from 20+ to zero the windward "ama" might come down first but I doubt that it would be uncomfortable as much as heart poundingly exciting. And I doubt that that is any realistic concern.
    This boat ,if built and designed well-and lightly- could potentially compete successfully with small cats. It amazes me that -as best I can tell -a maxed out mini tri hasn't been done yet;at least that I've seen. It would surely be more expensive than a cat but I'd bet it would be faster in light and heavy air. And if the planing amas work top speed could be much faster at least in relatively flat water...
    Last edited by a moderator: Jan 6, 2005

  15. mattotoole
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    mattotoole Senior Member

    I'm becoming intrigued by small tris, for a lot of reasons.

    I lived in Australia when I was a teenager in the late 70s. I remember the original Farrier 18' Trailertris well. They were the best daysailors going, certainly more exciting then the Rhodes 19s, etc., we had in the States. They were no harder or more athletic to sail either. Small tris allow a less athletic person to avoid scrambling all over the place, while experiencing very high performance. Of course they're lighter and easier to trailer than any monohull with a keel.

    I think Farrier is really onto something. People want to go fast, but they don't want to work hard (or swim, as with small cats). We're also running out of marina space. The solution is drysailed boats, at least in the under 30' range. So 20-30' tris may have a big future.

    I've always been intrigued by boats like the Tremolino, which used widely available components (Hobiecats) cobbled together into something simple, low-cost, easy to handle, and very fast. The sharpie-style concept mentioned above is interesting too.

    I saw an interesting boat a couple of years ago in Garden Bay, BC. It was a very small, one person tri, with short amas, of rotomolded plastic construction, and about 13' long. It had a simple cat rig, and IIRC it might have been boomless. I couldn't figure it out at first -- why someone would build a boat like that. But then I saw it sailing -- faster than anything else its size. And on a windless day, I really saw the advantage -- it could be paddled like a kayak, at a pretty good clip. Just wrap the sail around the mast, and paddle away. It was probably cartoppable too. Does anyone know anything about this boat? I've seen a couple of sea kayaks fitted with amas and a mast/sail too. Even with a tiny sail, they really moved along.

    My dream boat right now is a 24-33' Farrier. I'm curious to see what the promised 22' model will be like, especially if it's more affordable.
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