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Dravis
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If you already have a vacuum pump (capable of full vacuum) then the extra cost of going to infusion would probably be offset by the savings in resin  (You will get a much better resin to fibre ratio, probably even with the Soric) Of course the Soric is a bit more expensive than straight foam core. You could use cheap floor cork .. I've done some tests on that .. It will give you a lighter panel than the Soric, and much cheaper - You may even be able to use it with hand layup- It has very low resin uptake, definitely lower than Soric.
"Sapere Aude"... Dare to KNOW! The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind... 103% of all people do not understand statistics... Do not adjust our mind, theres a fault in reality :-)
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Junior
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Infusion would obviously be my first choice if money was no object, but this will be a budget build which is why I am aiming for wet-lay and vacuum bag.
I was intending to use foam as it will not add as much weight as soric due to it not absorbing extra resin.
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Dravis
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I would do this as an infusion, with a 2 or 3 mm Soric core and the biaxial glass Stack: Carbon/kevlar - Glass - Soric - Glass - Carbon/kevlar
I did a set of motorbike fairing panels like this, except with 300 gsm biaxial Carbon instead of the biaxial glass, and they came out way stiffer and stronger than needed, and too heavy as well-
I ended up doing without the core -- and with only one layer of Biaxial Carbon- -
"Sapere Aude"... Dare to KNOW!
The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...
103% of all people do not understand statistics...
Do not adjust our mind, theres a fault in reality :-)
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Junior
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Ok....yet more samples arrived so I have done some laminating.. I did one square with 1x650g Carbon, 3x 180g Black twaron Carbon/Kevlar. This was not as stiff as I'd hoped with some visible torsional flex. Next one was 1x180g Black twaron Carbon/Kevlar, 2x650g Carbon, 1x180g Black twaron Carbon/Kevlar. This was better and would probably be a minimum i'd like in stiffness. The last one which surprised me was 1x228g Carbon Kevlar, 2x600g Biaxial Fibreglass, 1x228g Carbon Kevlar. This was just as stiff (if not stiffer) than the one before but gives a much overall lower build cost.  My only thought that comes to mind this time is could I separate the two layers of biaxial glass with a foam core to achieve a stiffer panel, or do they need to be laminated on top of each other to achieve a stiffer result? If I could separate them and achieve a stiffer panel, this could be the combination I am looking for! Any advise on sandwich cores would be brilliant!
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Junior
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Yeah i came across murky waters the other day but their website has been down for maintenance. Won't be taking shape for a while as i will need to fun it first, just in the planning stages for now.
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FLD
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Indeed it is. I had a brief look at their site. I made a hardtop roof for my car which was the 2x200 foam 2x200 layup which is why I suggest trying it. It was a large panel which had a bit of flex but with its inner it was more rigid. I think this will be on the limit for a boat but only you can judge that. I'd be worried about a big wave folding it. Murky water might be a good site to browse too to see how they lay up their squirt boats. These are usually GRP though  Keep us posted, I'm loving your project. I keep thinking about making a composite sub7 as my plastic one is a bit heavy.
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Junior
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Thank you. Yes, very familiar with Mega Kayaks (they are the boats I struggle to paddle which is why I want to build a composite version of mine). They give a very brief description of the build materials for each spec, but they don't however go into detail on how much they use so it's hard to determine what is needed.
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FLD
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Have a try with 2x200g-3mmfoam-2x200g. This will give a stiff panel but when you mould an entire hull it will be a bit floppy. Only when you bond on the deck will you see the stiffness back. IMO this will be a bit weak for a kayak but small panel will give you a start. You are right that the gelcoat will take the scratches. You'll just need to redo it from time to time if you're aggressive with your beaching. If it's just surf with the odd beach landing you'll get away with a thinner layup but big surf will strain the boat somewhat too. Have a look at mega surf kayaks for some ideas.
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Junior
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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?
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Warren (Staff)
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Not being a kayak designer I would not be able to give you accurate advice as to what is generally used in the industry for that kind of boat.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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