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Originally Posted by Dirk Diggler
Lol, is that right?? I'd say it's far easier to work with than fibreglass, and it works perfectly well with polyester resin, although most manufacturers use vinylester.
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You got there before me...
Digressing a bit, in the days when I made kayaks, Kevlar was often used. It has good tensile strength and little stretch. When a material bends it has to stretch on the outside of the bend so if it resists stretch it also resists bending, ie. it is more rigid. So, for lightweight kayaks they could be rigid and handle well. I guess it'll be similar for a performance boat hull. The downside of this for lamination is that once it's trapped inside a rigid medium (resin) it doesn't dissipate energy too well so it is fairly easy to puncture or cut, 'easy' being relative of course. The other disadvantage is that it's a slippery material and adhesion to its surface is poor so where bending does occur, it's more likely that internal delamination may also occur. It's a super material but it does have to be used intelligently. It's not sufficient to simply presume a hull will necessarily be superior because Kevlar is used in its construction.
In the kayak world, if the hull was to take a prolonged battering such as constantly being used in rocky rivers, my preferred choice was to use one piece of Kevlar in the high load area (under yer bum) to keep the boat's shape, and back that with full length Diolen which is a strong but flexible polyester cloth. It wasn't uncommon to have a well used boat with all over resin crazing and Kevlar delamination at impact sites but it all stayed together and was still usable.
In the rib world I've used Diolen with good results where there is a high stress area which needs a bit of flexibility to absorb the load, I'm thinking specifically where a transom joins into a deck area or cleats/u-bolts fasten through a hull or deck. It's common to see stress cracking here and often the thinking to deal with this is to make the area thicker and more rigid. Maybe not good thinking. Adding 5% flexible resin to the mix and use a forgiving reinforcement might be a better solution - I don't mean wobbly board, of course!
Anyway, 200 grand for an open rib does seem excessive but if there has been substantial RnD I guess those costs need to be recouped.