Carbon Reinforced Hardtops - Need Input

[BoatHaus]

Looking for some experienced input on using carbon fiber in a hard top layup. I am building several custom hard tops from a female mold. I want to keep the part as light as possibe but not drive the cost thru the roof. I would prefer to not use any coring nor do I want to bag them and was thinking on a 6' x 8' top, skinning with 1.5 oz mat, cover with 1808, 6-8" carbon uni-directional tape around the perimeter & criss-cross 4 pieces in a star pattern, another layer of 1808 and finish with veil. Does this sound like it would be rigid and strong enough to last and be a quality part?

[mark775]

I don't know. I don't know 1808. I would like to offer a little input, tho, if you don't mind. Stiff maybe but one also needs to look at using it and how it looks. If it is razor thin, accidently brushing against it might abraid or cut you. Also thin objects tend to look too lightweight. If it has enough support, it will work. What kind of matt are you using that is compatible with epoxy? Have you considered Coremat?

[BoatHaus]

1808 is a triax e-glass that is 18 oz weave with .8 oz mat on one side. I plan on using polyester resin and I think coremat would soak up too much resin...

[mark775]

Well, you need to use epoxy if using carbon fiber. If you are trying for a carbon fiber look on the under side, or whatever, SB112 would work and the carbon would add stiffness and you could still gelcoat the top, if desired. If the thing has some shape, it will be much stiffer. Is it going on an aluminum frame 10 - 14" inside the perimeter? If so, a turned down edge would add visual weight and huge stiffness. With no core, one could bolt any ol' place. A male mold with the first laminate carbon fiber would be a high-tech look and help justify a higher price for your product and keep the epoxy out of the sun.

[Typhoon]

If you want stiff and light with no core, how about moulding channels/ribs into teh part and a nice wide lip around teh edges?
Or an inner and outer shell bonded together?

Regards, Andrew.

[lymanwhite]

I've built carbon hardtops, but used epoxy carbon laminates over 5/8 in core ( balsa end grain), and bagged it. I don't think you will have structural stability for any weight, like walking on the hard top or falling on it.
We chose the core because we were planning to use the hardtop as a place to walk.

[gonzo]

Carbon fiber and mat together is a waste of money. Mat is a material used for bulking up and is heavy. Also, it has a binder that prevents it from adhering to epoxy, which you have to use with carbon fiber. To make a light flat panel a core is the only way to go. If you want a solid panel, e-glass and polyester is the cheapest and most sensible way to build it.

[BoatHaus]

Thanks for the input guys, I think I will just have to build them mor "user specific"