Small trimarans under 20'

Discussion in 'Multihulls' started by Doug Lord, Jun 24, 2012.

  1. Skyak
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    Skyak Senior Member

    Beam limit would determine the winner. If the beam is limited to length, the tri will be favored, because the cat's weight increases too much when it tries to get to full beam. If the beam is limited to 60% of length I am not sure the tri can get an advantage other than tacking.

    Cost limited? I don't know what to say. Skill limited? As I said, fast tris are much easier to sail at high speed than cats.
  2. Jetboy
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    Jetboy Senior Member

    I'm asking pure beam limit with no length limit. Makes roughly as much logical sense as a length limit, although less popular for racing classes.

    In reality for 99% of sailors, the question is $ limits. What's the fastest boat you can build with $20k or $200k, or $2M? Then you make a class that kinda fits and people with similar budgets race eachother.
  3. Gary Baigent
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    Gary Baigent Senior Member

    Formula 40 didn't reduce the main beam of F40 tris - well, they did - but originally the radical thinking Gougeons built Adrenalin with a greater beam than 40 feet, 42 or thereabouts if I remember correctly ... so initially the team was forced by early rule changes to reduce beam to square l/b. I think this is where the misconception of "unfair" French hierarchy regarding Adrenalin's history began. I mean 40 by 40 feet is hardly a beam reduction.
    What killed F40 wasn't the forced beam reduction - the Biscuit Cantreaus and Full Pelt and other F40 tris (all were square or near square, Full Pelt had racks) was supposedly the greater expense of the tris and the fact that they just slaughtered the cats ... which decimated the fleet numbers because it was near useless to race the expensive, more powerful, more radical tris with catamarans.
  4. TedWarren
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    TedWarren Junior Member

    Square is good. My W27 is 27 ft wide, and my W23 is nearly square at 21 ft.
    The relationship is simple, wider generates more horsepower. It also gives you a
    resource that can be used in multiple ways. I got caught off of Boston in a
    thunderstorm, 50+ kts of wind at the airport in my W27, a very light tri at 1200
    lbs. We reefed down and were very comfortable doing 6 kts to windward.

    My UltraLight 20 is 75% square. As the boat gets lighter and the crew
    becomes a higher percentage of total weight, the specific righting moment
    increases. Any easy way to see this is that the CG moves to windward. With
    two up on the UL20 the crew is ~66% of the weight. That simplifies the design.
    At square you need pretty hefty beams. A good rule of thumb is that the beam
    height at the main hull needs to be 5% of the BOA. The ORMA 60s had 3ft. of
    height for a span of 60 ft. You need to consider aerodynamics at that height.
    My W27 beams are tapered ellipses in section.
  5. Doug Lord
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    Doug Lord Flight Ready

  6. Corley
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    Corley epoxy coated

  7. oldsailor7
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    oldsailor7 Senior Member

    If you want to build your own small Tri and want it simple and fast----you can't go past the Piver "Frolic".
    Plans are still available from the Maritime museum, Newport News. :cool: 16ft X 8ft with self tacking jib.
    Road towing legal without folding. :)
  8. Tom.151
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    Tom.151 Senior Member

    A rare bird

    Another little known small trimaran - the Dobler designed Triad 19'er - might interest more than a few if it were better know.

    Joe Dobler (now deceased) designed the hull shapes specifically for planing and it seems he did a fair job.

    He also designed a 30 footer to the same principals and it showed much promise when built in plywood. A f'glass production prototype was purported to be too heavy.

  9. upchurchmr
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    upchurchmr Senior Member

    At 700# it seems to be heavy in plywood.
    Have you seen any performance reports?
    Besides the Designers of course.
  10. Tom.151
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    Tom.151 Senior Member

    I just looked at the plans... my guess is that the pile of wood might weigh in at 350 pounds (my guess).
    The boat seems designed to be very strong for a 19' boat (subjective opinion), with a 1/2" ply bottom, 1/4" elsewhere.
    But then again, Dobler was probably expecting speeds in the 20kn range.
    My guess is that the 700# would be a ready to sail weight.
    With 2x175# crew that would give a Bruce No. at 1.746
    I could live with that ;)
  11. upchurchmr
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    upchurchmr Senior Member

    I seriously doubt the "weight" is the full up displacement (boat plus crew and gear, as designed).

    Check out the Cross 18. I actually have a set of plans ( but no boat) and it is made of 1/4 and 1/8 inch plywood at 400#. I am pretty sure this one is empty since 2x175# crew would leave 50# for the boat.

    I have always wanted to see a comparative sail test but could never find one.

    So another foot with twice the thickness of ply, the boat probably is 700# empty.

    Personally I like the Cross better, same as when I saw the competing plans 30 years ago.

    FYI, the original Tornado Catamaran was made from 4mm marine ply (.160") and at 20' it weighed about 320#
  12. Tom.151
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    Tom.151 Senior Member

    (1) Actually I didn't say that 700 was the "displacement", neither did Dobler.
    (2) I was simply offering another design for consideration
    (3) Troll elsewhere
  13. upchurchmr
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    upchurchmr Senior Member

    I'll troll anywhere I want.

    But I don't understand why asking a pertinent question is trolling.

    Understanding the facts are generally the beginning of deciding to build something.
    But if this is just throwing out designs for no other purpose, I can deal with that.

    Sorry you took it wrong, I thought you might have some genuine interest.

    Just re-read your post. My mistake- you did not say or imply displacement.
  14. rcnesneg
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    rcnesneg Senior Member

    Hey all, First time posting, don't mean to wake a dead thread, but this is very interesting! Been lurking around for a while. I got into sailing this last fall when I decided I wanted to harness the wind. I built a 16' sailing trimaran, and then learned how to sail with it this spring. I figure you guys will find it very interesting, and I'm curious to see what Doug Lord has to say about it, seeing as he seems to be very knowledgeable about this sort of thing.

    Here's a video to wet your interest:

    It weighs about 100 pounds assembled, and cartops on a Honda Civic. It takes me about 30 minutes to get it fully assembled and rigged to go. I just replaced the mast with something much stronger. The next problem I am working on is the small size of the Amas and their tendency to submarine and flood, because there are zippers on the top to get bolts in.

    Here is a picture of the original configuration:


    Ideas are welcome and I would like to reinforce things to the point that I can fly two hulls, but I need much larger amas for that, and there is a lot of flex in the boat between the front and rear crossbeams.

    Also, I noticed people talking about a lack of high-performance small trimarans. Not sure if it has been mentioned, but the Ultralight 20' by Warrencraft seems to fit that market more, although it doesn't use lifting foils and whatnot.

  15. upchurchmr
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    upchurchmr Senior Member

    That looks like a very nice build.
    We haven't seen SOF in a trimaran although there has been a thread by Jeff Horton (kudzu) about his desire to make one.
    What kind of flex are you getting between the crossarms? Does it bend up and down or twist?
    Is that a PVC mast? If so you might want to keep the small amas (floats). I thought I saw the mast bending when the boat hit the waves. PVC has very little stiffness - once a mast bends out of straight, it can quickly fail under sailling loads.
    Did you homemake the sails? They set nice with no major wrinkles that I saw, but seem to need more belly or curvature - which develops power.

    Do you have a centerboard or leeboards?

    There are more things to talk about, but many would require some kind of a redesign, and it would be much better for you to tell us what you have done, than to get uninformed opinions.

    The guys on the forum can get a little harsh with their comments. (Including me).
    Develop a thick skin quickly. There will be value in most comments.

    I've thought about doing the same thing and couldn't decide how to fix the typical problems with a SOF sailboat. Congratulations for getting it sailing nicely.

    It would be interesting to know more about your construction.
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