Fiberglass and divinycel advice - How to make my dagger boards?

[zstine]

for what it's worth, here is the cross section of an Americas cup foil. very high loads. But you can see it was made in 2 halves, female molds. seam in leading and trailing edge. the highest loads are at the thickest part about 30% back from leading edge on the skin (tension), low load (shear) is in the center-line, which coincidentally is at the leading and trailing edges. This is why they put the seam there...

[Chotu]

Originally Posted by zstine

why not use what's left of the old boards to make a female mold? The outer shape is not only important for the in-water performance, but also needs to match the trunk.

And the width of the final product. Good lord is that trunk matching important.

It’s so important that when you build a boat, you actually build the boards first, keep them labeled port and starboard, then you build the trunk around the board to get a perfect fit.

Definitely pay attention to this detail.

[zstine]

Originally Posted by Chotu

.

Hi Chotu, I don't know the dimensions of your boards or boat, but the laminate schedule for your light 50ft wouldn't be crazy to start with for his Privilege 435. Maybe you could share them with him? The stress on the board comes down to boat's righting moment and board length/width. should be fairly easy to tell the difference in stress on your boards compared to his and make appropriate changes in lamination schedule.

[captnknopf]

Originally Posted by zstine

why not use what's left of the old boards to make a female mold? The outer shape is not only important for the in-water performance, but also needs to match the trunk.

I agree. I made a half mold for my dagger boards and rudder on a 39 foot tri . Add a layer of light biax or thin mat first, then biax or triax then either uni in the long direction or enough graphite. a little bit does no good, it will just snap. make foam to fit (at least 4.5 pound per cubic foot for clegecel or divinicel) and mush it in on top of the glass. grind flat and make four of these. The most strength is needed where it exits the case so there may be two different layups for the four pieces. Make a rebate in the mold for the glass that will wrap around the front and back. once cured, vacuum bag two together with maybe a layer of 1.5 oz mat and thickened slow epoxy. Leave one half in the mold when doing this.