Molded dagger board manufacturing technique

Discussion in 'Boatbuilding' started by arekisir, May 27, 2014.

  1. arekisir
    Joined: Jul 2010
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    Location: Australia

    arekisir Junior Member

    Looking at ways to build a dagger board.

    Rather than hand shape a core / glass / fair I was considering the following:

    Make split mold for expanding epoxy to use as core.

    Layup reinforcements dry around this core molded expanded epoxy core.
    Insert into a final shape split mold and infuse resin in.

    Has this type of technique been used?

  2. keith66
    Joined: Sep 2007
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    Location: Essex UK

    keith66 Senior Member

    Why bother? Look at how a Laser sailing dinghys dagger board is made. Its obviously made in a split mould but is basically a foamed or microballooned polyester core with steel reinforcing wires inset into it to give it the required strength, no glass on the outside at all.
  3. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    Ive built daggerboards and rudder blades in a simple sheet metal mold, a method i learned from the late Malcolm Tenant and used on many of his designs. Basically you have a sheetmetal shop fold a piece of steel or aluminum about 1/16" thick the length you want with a fold in the middle to form the leading edge and open at a 45 degree angle, none of the local shops can fold to the nose radius i want so i run an appropriate fillet, there are 2 more 90 degree folds at the trailing edge where you attatch wood strips to clamp to, so what you have is a female mold in which you layup your laminate then bend in and clamp the trailing edge. As i recall Malcolm laid up a lot of uni at the thickest point and then filled it with a syntactic foam made of epoxy filled with polystyrene beads and pushes it into a jig to set the maximum thickness. I prefer to close the mold around a shear web and leave it empty if the chord id not too long. You end up with a molded gelcoated part with no fairing. I will be doing a pair of rudder blades sometime this summer for a Gemini cat this way, about $60 for the mold.


  4. SukiSolo
    Joined: Dec 2012
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    Location: Hampshire UK

    SukiSolo Senior Member

    Actually the Laser foils in the UK were made from a foaming polyurethane around a steel mesh. I t so happened I ran into the company who made them a few years back. They may have changed the process and or materials since but circa mid 90s' that was the case.

    As far as I can work out the moulds for making foils could be pretty much any material. For a 2 off, I'd be tempted to make a glass one, off a pattern, but if you have access to sheet rollers, steel and aluminium might be OK as you suggest. Even coated ply or MFC would work OK with just a local shaped part for the nose (leading edge parabola) joined on. If you have a lot of expanding going on with the foaming core do not underestimate the clamping required to maintain shape.
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