Lightest layup for a female deck/coachroof mould

[Roly]

I am replacing my deck on a 34' sailboat.
Does anyone have suggestions?
I figure, poly gelcoat to within 200mm of sheer (gap for bonding to hull) and then lay up with epoxy/glass-foam or balsa-epoxy/glass. Maybe carbon or kevlar beams in stategic places?
Prerequisite is light.

Any books or links for reference would be much appreciated.

[Herman]

www.marinecomposites.com could get you started.

200 mm seems to be quite generous, I presume.

I have no idea of the deck to hull detail on your existing hull, so giving options is somewhat difficult.

Gelcoat can be used, however in my experience only a good ISO-NPG gelcoat is suitable for a boat. After that you need a bonding layer (ty-coat) or a layer of 225 grs CSM with polyester, sand after cure, to get a good bond between the gelcoat and the epoxy laminate.

The stiffest option would be carbon laminate with balsa sandwich, or with honeycomb sandwich. However, I have no idea of the scope of your project, so the carbon option could very well be over the top.

Please also keep in mind that ultra-lightweight construction means thin skins, and thus little protection against point loads. (falling spi poles, etc).

Aramide as a means of getting a stiffer laminate is of little use. Impact strength is good however.
Carbon for stiffening certain areas is possible, but keep in mind that, when adding carbon fiber to a glass laminate, only the carbon will bear the loads. Using it in certain small areas (corners of hatches for instance) is possible, but do the utmost to blend the stiff carbon in the relatively flexible glass laminate, or you will end up with cracking at the borders of the carbon laminate.

So far for now.

[Roly]

Thanks Herman, for the words of wisdom. Easy to get carried away with this
rebuild and just waste money.But we are shedding a bit of weight and lowering the c.of g. of the keel fractionally, so hopefully the results will be positive for such an old design. Having to rebuild the coachroof and deck in parts seems somewhat a waste of effort considering we have access to a female mold, and be able to replace the lot. I will pm you our project photo site.
If you think we are nuts you are not alone!