Trimaran centerboard advice wanted

Discussion in 'Hydrodynamics and Aerodynamics' started by massandspace, May 7, 2021.

  1. massandspace
    Joined: Sep 2017
    Posts: 39
    Likes: 0, Points: 6
    Location: Salt Chuck

    massandspace Junior Member

    Doing a full renovation of a recently purchased 1985 Eagle Tramp folding trailerable trimaran.

    Issue: Pivoting centerboard jammed in the case. Used some force and it came out. Looked like someone sloppily coated it with heavy epoxy. Sanded it way down through the thick epoxy and also a lot of original fairing compound. Main objective was to decrease the maximum thickness (chord?) enough so that even when I add a layer of 6 ounce cloth and a couple final fill coats of epoxy is it will NOT bind in the case.

    After sanding out I checked the board with a straightedge, and was surprised to find that the bottom 1/3 of the board (as when lowered straight down) was quite a bit thinner (in chord) than the top half.

    Question: Is that normal? The TAPER in the chord as it goes down? I can at this point add corecell and/or thickened epoxy to the bottom 1/3 then longboard to bring the board back to a uniform chord thickness from top to bottom.

    Advice accepted....
     
  2. messabout
    Joined: Jan 2006
    Posts: 3,156
    Likes: 321, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Chord is the distance from leading edge to trailing edge. Thickness is degree of camber as a function of chord. Thickness is often stated as a percentage of thickness compared to chord. If your board has a diminishing thickness toward the tip, that too may be a function of chord differences down the length of the board. Think of a Spitfire wing for example.
     
  3. SolGato
    Joined: May 2019
    Posts: 114
    Likes: 57, Points: 28
    Location: Kauai

    SolGato Senior Member

    I don’t know if the Eagle followed the original Tramp design with respect to the centerboard, but at one time the info and drawings were posted to the Tramp Owners users Group which was on Yahoo and is now an IO Group.

    I do believe the centerboard is somewhat tapered if I remember correctly.

    It would be wise to do a search on the owners group and read up on the common repairs needed to make the centerboard swing freely and modification made to keep the trunk from leaking which is quite common, especially since you already have it removed for repairs.

    TrampEagle groups.io Group https://groups.io/g/TrampEagle
     
  4. massandspace
    Joined: Sep 2017
    Posts: 39
    Likes: 0, Points: 6
    Location: Salt Chuck

    massandspace Junior Member

    Hello

    I used the word chord improperly. I will try again.

    The THICKNESS is my question. The thickness decreases at the bottom of the board....is that normal?

    Also, the CHORD decreases as well. Maybe 2-3 inches less chord at the bottom.

    So, to get the best results from it.....should the thickness be tapered, or the same? If tapered, that means the foil section will be different at different points of the board.....and that does not see optimal?

    Also, I was planning on making some type of an a section sanding board that I can run down the board to get a proper profile back into it. Is that the best strategy? Again, I had to sand off some of the board as it was jamming in the case.....so just trying to get a slightly less wide, but properly faired, board back in place.

    David
     

  5. Steve Clark
    Joined: Jul 2004
    Posts: 205
    Likes: 15, Points: 18, Legacy Rep: 163
    Location: Narragansett Bay RI

    Steve Clark Charged Particle

    Maintaining a constant chamber chord ratio is typical, but not always done.
    SHC
     
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