Trimaran basic questions

Discussion in 'Multihulls' started by Kudzu, Oct 30, 2012.

  1. Kudzu
    Joined: Jan 2008
    Posts: 50
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SE US

    Kudzu Junior Member

    I am playing with a design for a lightweight recreational tri. What I have in mind is something around 18' long day sailor and have a few basic questions. My background is designing skin on frame kayaks and small boats, not sail boats.

    I started out wanting to alter one of my designs by adding outrigger so it could be sailed. The more I looked into this, the more I realized that it was just to much of a comprise for me. And way too wet a ride for my tastes. So I started from scratch and have a good start but I am am starting to questioning some things.

    My goal is a fast boat that is fun to use in higher winds. I am not interested in racing and not looking to squeeze every bit of speed possible out of it either. I designed it with a multi-chine hull to make it more round and keep the wetted surface low. Now I question the advantage over say a shallow Vee hull which is obviously simpler to build. Would a flatter bottom has some advantage in sail powered boat? It would see that a flatter hull would want to plane in the right conditions where a rounded hull wouldn't. But the bottom line is I really don't know if I my thinking is sound or not. So it's better to ask.

    I have a couple of other questions but one step at a time.
     
  2. jamez
    Joined: Feb 2007
    Posts: 523
    Likes: 41, Points: 28, Legacy Rep: 231
    Location: Auckland, New Zealand

    jamez Senior Member

    There have been many successful tri's built with flat bottom 'dory' main hulls. As an example Richard Woods Strike 18 has one and seems to perform well. If you're not concerned with ultimate performance I'd simplify as much as possible for an easier build.
    http://www.sailingcatamarans.com/Strike 18.htm
     
  3. warwick
    Joined: Jan 2012
    Posts: 423
    Likes: 7, Points: 18, Legacy Rep: 63
    Location: papakura south auckland new zealand

    warwick Senior Member

    Kudzu,

    The thread basic multihull knowledge may be of help for you as it is following a similar line. in providing answers to design aspects.

    Richard woods has a flat bottom trimaran.
    I think there may have been a thread on the W 17 by Mike Waters which also is flat bottomed. The thread is W 17 trimaran what do you think?
     
    Last edited: Oct 30, 2012
  4. cyclone
    Joined: Jun 2012
    Posts: 15
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Trenton, Maine

    cyclone Junior Member

    Also check the John Marples' Seaclipper 16.
    JT
     
  5. upchurchmr
    Joined: Feb 2011
    Posts: 3,203
    Likes: 206, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    The problem with a SOF sailboat is that the higher speeds will make a bigger load on your flexible skin. When you have a ply skin it will naturally not distort as much.

    I suggest a round bottom with narrow regular spacing of the frame will better support the skin and sail faster since you wont have distortion.

    No proof, but I have been thinking about the same boat. For myself, my questions are centered around the ability to take the twisting of the hull from the mast step, cross arms, board (center, dagger, lee) and the rudder.
    I also am concerned when sailing on a reach, much of the sail load will bury the nose of the boat, causing the hull to bend up.

    I just recently measured a Yost SeaTour 15 for bending due to weight in the cockpit. The boat was supported on sawhorses at the #1 and #5 frame. 50# was put in the cockpit about where the seat (mine) would rest. Without skin the hull bent 1/2 inch at the center. With skin the hull bent 1/2-1/16 at the center.
    The frame contributed the majority of the stiffness, engineering principles suggest the bend would have been about the same as without the skin without ever assembling the frame. I.E., the stiffness was the same as the bundle of stringers loosely collected together.
    Catamarans are under a tremendous load with the bow supporting the entire weight, the mast punching down, and the sailors weight countering the entire load.

    My conclusion is that you need more bending strength and stiffness than a typical kayak construction and the skin only helps minimally.
    You need more torsion which I don't see how to get easily since there is no wood in that direction.

    I am really interested in how you make all this work.

    I didn't start out to be negative - I really want to do this my self.

    Marc
     
  6. Kudzu
    Joined: Jan 2008
    Posts: 50
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SE US

    Kudzu Junior Member

    Warwick, I can't find that thread. You can't use a singe letter 'W' in a search and without it, it just pulls up to much. Designers name didn't find anything either. Got a link?


    upchurchmr I have the same concerns and have been thinking on this for a while. To get the performance/speed I want I have about decided that plywood makes more sense. I can beef up the frame and add a lot of extra support but I am still concerned about twisting the frame. One way around that might be attaching the outrigger and mast together so that some of the forces are taken by the outrigger instead of all on the frame.

    One thought was doing what Plat did on his Geodesic boats and using the Kevlar(?) roving on the frame. Never tried it but I think that would add a lot of stiffness. But then you probably don't have a smooth hull shape at speed. I suspect you have a faceted hull then and that would be a speed killer.

    I haven't give up on the idea but I do think that plywood is a better choice. So at this point I am just playing with ideas and seeing what I can come up with
     
  7. ImaginaryNumber
    Joined: May 2009
    Posts: 435
    Likes: 59, Points: 28, Legacy Rep: 399
    Location: USA

    ImaginaryNumber Imaginary Member

    W17 trimaran...What do ya think??
     
  8. Richard Woods
    Joined: Jun 2006
    Posts: 2,208
    Likes: 166, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

  9. Kudzu
    Joined: Jan 2008
    Posts: 50
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SE US

    Kudzu Junior Member

    LOL! I thought the thread was 'w 17 trimaran'. If I had searched for the whole thing I would have found it. :rolleyes:

    Richard, Dave Gentry and I are acquainted, we hang out in some of the same forums. Here is my web site. www.kudzucraft.com.
     
  10. warwick
    Joined: Jan 2012
    Posts: 423
    Likes: 7, Points: 18, Legacy Rep: 63
    Location: papakura south auckland new zealand

    warwick Senior Member

    Kudzu, at least you where able to find it, May be I should have mentioned that it was the thread title.

    you may be able to find out more about the W 17, on Michael Waters web site http://www.smalltridesign.com/ I think Michael might be on the members list as well, having responded to the thread.
     
  11. Richard Woods
    Joined: Jun 2006
    Posts: 2,208
    Likes: 166, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    I suggested Dave as he recently built a SOF sailing canoe so has tried a fast, big rig boat, not just kayaks. We were both presenters at the recent Sail OK event where he demonstrated SOF construction and was out sailing a little outrigger canoe he had just finished

    Richard Woods
     
  12. HASYB
    Joined: Jun 2011
    Posts: 310
    Likes: 16, Points: 18, Legacy Rep: 143
    Location: The Netherlands

    HASYB Senior Member

  13. warwick
    Joined: Jan 2012
    Posts: 423
    Likes: 7, Points: 18, Legacy Rep: 63
    Location: papakura south auckland new zealand

    warwick Senior Member

    Thanks Hasyb for your post.

    It is an interesting way to get a larger radius on a flat bottom.

    I wonder if there would be any strength benefits in using a ply, foam, fiberglass construction.
     
  14. Kudzu
    Joined: Jan 2008
    Posts: 50
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: SE US

    Kudzu Junior Member

    I have seen his web site and I like some of his ideas. I like the basic concept of his boats too.
     

  15. SpiritWolf15x
    Joined: Apr 2010
    Posts: 194
    Likes: 1, Points: 18, Legacy Rep: 15
    Location: Vancouver, Canada

    SpiritWolf15x Senior Member

    What is the difference in performance between flat and rounded bottoms?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.