i've put a terrible beating on my kayak this year, and while it is quite solid, i want a more rigid bilge, especially for those launches off the top, and heavy drops into the trough.
i reckon that adding a layer of carbon fabric into the belly (remove seat) is the best way to achieve this at the least weight.
my boat is glass and cheap polyester resin. i've done a number of repairs and modifications on the boat but never worked with carbon fabric or different resins. anyone out there familiar with the ins and outs, resin compatibility issues or other things i really need to consider before going forward? anyone, anyone, bueller, Onno...
I recommend carbon fabric and epoxy
Carbon fabric doesn’t “absorb” resin. I coat the hull with epoxy resin , lay the fabric, then coat the fabric also. Use a plastic squeegee to work the resin in and also to remove any excess.
epoxy resin may be the way to go with carbon cloth but you may have trouble with it adhereing to polyester resin. Contact West Systems and ask. good luck
Epoxy should bond to other resins, it’s the other way around that you have problems.
I have used carbon tape, not woven but like strands bunched up, to stiffen a very thin wooden catamaran and it worked well.
An alternative approach…
…is to lay in some 1/4" structural foam and glass over it. That will provide a bigger increase in stiffness than a layer of carbon fiber.
Carbon fiber is used like fiberglass
The only difference I found with carbon fiber is that it can be hard to see if it has been wetted with epoxy. Fiberglass turns from white to clear when it’s wetted out with epoxy but carbon fiber is black and you have to be careful that you are wetting out all of cloth. Removing the excess epoxy with a squeegee is important for getting a solid bond and to reduce the weight. Epoxy adds no strength.
There are two ways to stiffen a hull. Stiffer compression layers, usually substituting expensive carbon for inexpensive glass works. Per weight of fabric, carbon is twice as stiff as E glass. Increasing beam thickness by using foam or some other core material will work too.
Installing a partial foam core is going to be a difficult job. After acquiring the foam, shaping it and feathering the edges, you'll need micro- spheres to make a bedding paste, glass, 2 layers of carbon/glass/arimide for the cover, peel ply, nylon film, yellow sticky tape and a vacuum pump to hold the thing in place while the resin sets.
It's easier to wet out a patch. A partial section of core mat covered with glass would probably do the same job as a double layer of 6oz carbon at lower cost. I'd use Vinyl Ester resin because it will wet out either patch more easily. Peel plying the edges of the patch will eliminate the need to sand them.
Listen to BNystrom!!
He’s absolutely right on. Adding some core will greatly increase stiffness and glass is all you need. Don’t get hung up on this or that resin. Plain old Polyester, glass cloth , and some core material will do a great job.
i’ll see if the local industrial plastics has some Soric core mat. i like the idea, but am a little intimidated by it. also, i want a thin addition, so as not to change seat height/foot depth. looks like i need to go and see the materials first hand.
you ever tried to get polyester resin to adhere to epoxy resin??? I’ll bet not!
To keep it thin, use 2-3 layers of carbon; successively larger prismatic shapes, rectangles with pointed ends aligned on the keel line. The size variation softens the edge to reduce the stress riser effect and to have a more finished edge. [Peel ply will flatten the edge of one layer nicely; three would be asking a lot.]
Be sure to sand the entire area where patch[s] and peel ply will contact the existing hull, then clean w/ acetone, to improve bonding.
He said his boat was Polyester
resin, and I’m suggesting he stick with that. I was not clear.