Round tubing beam material "akas" for trimarans?

Discussion in 'Multihulls' started by sailor182, Jun 9, 2013.

  1. sailor182
    Joined: May 2013
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    sailor182 Junior Member

    Hello I was curious about beam materials specifically round tubing materials. What materials are standard on coastal cruising trimarans whats the pros and cons of them? 25'-30' LOA is the size I'm thinking of.
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Once you have determined the loads on the beams, it is dictated by cost, availability of materials and fabrication as much as anything else, as well as the obvious material properties. It is not a clear cut of material properties of XX over YY, even though it may appear to be, but rarely so.
  3. Corley
    Joined: Oct 2009
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    Corley epoxy coated

    Round tubing in the form of aluminium tubing augmented by a waterstay is still a reasonably popular choice for homebuilt trimaran beams.

    look at Kurt Hughes website for examples in his economy cruisers section. He actually notes on his cylinder mold construction video that the idea came from Lock Crowther's application of the method on the Buccaneer series of trimarans.
  4. aussiebushman
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    aussiebushman Innovator

    Probably just a personal preference, but in practical terms, mating and joining cylindrical cuts is a lot more difficult than rectangular sections.

  5. gonzo
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    gonzo Senior Member

    That is true. Rectangular or square sections are much easier to work with. However, they are not isometric, so the stiffness and strength is not equal in all directions. It is not a huge drawback, specially in a smaller boat.

  6. Richard Woods
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    Richard Woods Woods Designs

    One of the big problems with a trimaran beam is that the mainhull end has to be deep as that is where the biggest loading is. But it is also the part which slams into waves. So any way to reduce the wave impact is a good thing. The simplest is either a truss beam, or by using a waterstay.

    Research by the Wolfson Unit has shown that a trimaran beam needs to be about 1:0.3 strength in the vertical and horizontal directions. Vertical takes bending and horizontal takes drag loads. So a round tube is not ideal, a rectangle or oval is better.

    If you are glassing or epoxying a beam to a hull then a round tube is usually easier as there are no corners, but you have to stop the beam twisting, which of course is easy with an oval.

    The aluminium welded or bolted together truss beams were never reliable, I like the Kelsall method of making a truss in UDWR (as on Triple Fantasy for example)

    Richard Woods of Woods Designs
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