Hi all!

I’ve recently discovered the world of composites and have been fascinated with the whole subject and intrigued with what can be produced.

I am a very keen kayaker and have a burning desire to build a composite version of my current plastic surf boat, a Fluid Element which weighs around 15kgs and measures 202cm x 64cm (widest part).

I have tried paddling some other boats which are produced in carbon/kevlar, but due to their design I just haven’t got on with them aswell as my current boat. 

My boat was produced in carbon/kevlar in a limited amount (around 30), but these are very rare to come by and as you can imagine, fetch a large amount of money as they retailed at £1395 new. I am therefore planning a long-term project to build myself a composite version but have come across the usual problems that most people encounter such as which combination of materials to use.

I will be on a tight budget with not much room for error, so I need to keep costs down by using cheaper materials/resins if possible. I plan to take a mould of my current boat in either two or three parts, then create the boat using wet-lay and vacuum bagging.

My initial thoughts are one of the following four lay-ups with Polyester/Vinylester resin with a target weight under 9kgs:

(From Outside the boat to Inside the boat)

Outer layer of 300g Black Diolen 2/2 twill

1x 300g plain Diolen 2/2 twill

3mm foam core

1x 300g plain Diolen 2/2 twill

1x 300g Black Diolen 2/2 twill

or (if the Diolen only lay-up is not stiff enough)…

Outer layer of 300g Black Diolen 2/2 twill

1x 300g S-Glass 2/2 twill

3mm foam core

1x 300g S-Glass 2/2 twill

1x 300g Black Diolen 2/2 twill

or (if the lay-up needs to be stronger still)…

Outer layer of 300g Kevlar 2/2 twill

1x 300g Carbon 2/2 Twill

3mm foam core

1x 300g Carbon 2/2 twill

Or (if my budget will stretch to it)…

2 x 228g Carbon/Kevlar Aramid

3mm Foam Core

2x 228g Carbon/Kevlar Aramid

My question is, firstly will the lay-ups be strong enough for white water use in the sea (waves) with the odd scrape and knock from pebbly beaches? It will no doubt take more of a beating than a longer sea kayak as it’s more of a play boat style kayak. And secondly, which lay-up will be stronger? I could possible use a mixture of the lay-ups with a stronger/more expensive one making up the base of the kayak, and a cheaper one making up the top half of the kayak?

I have chosen to put either the Diolen or Kevlar on the outside layer to give better abrasion resistance and to protect the Carbon/S-Glass, however I have found some conflicting information online that suggests the Kevlar/Diolen should be on the inner layer?? Being that Kevlar/Diolen can take more damage before splitting, I would have thought if it were on the inner layer, the carbon would crack on the outside before the Kevlar/Diolen, whereas on the outside it would keep the cracked carbon beneath the layer of Kevlar/Diolen protecting the boat from splitting?

Pages where I have gathered inspiration has come from:

Kevlar Playboat:

http://shanesliquidlogic.blogspot.co.uk/2011/12/composite-playboat-prototype-1.html

Carbon Zet Playboat:

https://www.youtube.com/watch?v=IA9vkauvxGY

Carbon Vadja Playboat:

http://vajdafreestyle.com/en/Kayaks/Beast/Beast-series/

Lots more questions to follow no doubt, but any help/suggestions would be fantastic!

Cheers,

Junior.

Ok, I ordered some samples to get an idea of stiffness. I layed up one square with 200g Diolen, 3x300g E-Glass, 200g Diolen, and another square with 180g Black Twaron, 3x650g Carbon.

The Diolen and Fibreglass didn't feel very stiff at all, it flexed quite a bit and after a few bends I could hear the fibreglass cracking. The carbon square on the other hand was very impressive, a lot stiffer than I expected but after calculating the overall weight, it would make the kayak not far off the current plastic weight. I think I will try another test with less carbon, possibly 180g Black Twaron, 2x 650g Carbon. These are obviously tests without a foam core, so once that has been added it will give a much stiffer/stronger lay up than expected.

Questions that come to mind are...
1.How may layers of Carbon/Kevlar should be used to give enough abrasison resistance? Is one external layer enough on top of Carbon, or should there be multiple layers?
2. I find it hard to get my head round how the Kevlar is actually abraisive resistant compared to other materials, as it would be the gelcoat/resin that takes the scratches?
Surely its the outer coating that makes the difference rather than the material beneath it?