load change going from straight dagger boards to curved?

Discussion in 'Boat Design' started by themanshed, Apr 21, 2010.

  1. themanshed
    Joined: Sep 2009
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    Location: Palm Beach County

    themanshed Senior Member

    I've been thinking of putting curved dagger boards on the boat I'm building 20' trimaran. The plans call for 3 foot long boards 12 inches wide 1 inch thick in a foil shape. I thought about 5' long curved boards same foil, thickness, and width. My plan was to make the 1/2 board out of foam then curve the foam in a jig glue the other side to it and then made a mold from it. Any comment, suggestions, or ideas.

    What load differences need to be considered. The connecting tubes for the ama's are going to be composite of Carbon and Kevlar. The plans call for a mast section 5.5 by 3.25 4 mm thick aluminum stock. I'm making an elliptical shape 4" in the center 1.5" in the ends 6" between the centers of the end circles, so the width is 7.25" I had some engineering done on the beam it will be stronger then what is called for in the plans. The lay-up will be 90 / 45 alternating layers of 200 gram uni carbon with at least one layer of Kevlar - 4-5 mm total thickness. The lay-up will be in a mold 1/2 at a time (top/bottom) and vacuum bagged using West System Epoxy.


    Picture of Jig under construction for the mold - beam length approximately 17 feet

    Attached Files:

  2. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    One thing you should do is to make sure that your design for the trunk of the curved board allows the board to be pivoted so that when full down the board tip can be moved fore and aft. That would allow you to adjust the vertical lift the board provides. If you don't have this facillity AND carefully design the board there could be times where the it develops enough lift to lift the whole boat most certainly resulting in a nasty crash . That actually happened on a few ORMA 60's that had no ability to adjust the angle of incidence of the lifting portion of the board-or had it wrong for the conditions.
    My opinion is to get the designers input to make sure that the boat will take it structurally and to help you with the board/trunk system-so the board works efficiently in all conditions. Don't guess at it.
    You are doing a first class job on the boat!
  3. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Make sure your beams are up to it. You don't want this to happen to you!

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