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Reduction of weight in the manufacture of a kayak with the use of the sandwich material Easy Cell 75 Closed Cell Foam PVC, 3 mm thickness.

 

We have previously used Soric 3mm in a construction of a kayak with one layer of carbon fiber and one layer of Kevlar, then sorric as sandwich and finally a layer of carbon fiber, all produced in a single resin vacuum process.  A strong construction, but a little too heavy.

 

To reduce the weight we have now used Easy Cell 75 Closed Cell PVC Foam, 3mm thickness as sandwich.

In the design we have, with the vacuum resin infusion process, performed the outer carbon and Kevlar layers, and after the final curing, glued with resin, a layer of 3m EasyCell75. After this glue has hardened, we have again, with the vacuum resin infusion process, performed the innermost carbon layer on top of the foam.

 

Unfortunately,the weight is almost the same, and it is apparently a weight gain that occurred during the infusion process in the foam, and the last carbon fiber layer. We know from the past that the carbon layer itself occupies only 50% resin by weight.

 

Why do we have this weight gain?

Wich methode should we use to reduce weight?

Is the infusion process and the foam not suitable?

Hello from me,

I would suggest two approaches:

first: You could try to use prepreg as the inner layer. If you got the oven for this, of couse. Do it all in one shot in prepreg would be an more efficient solution, but kevlar prepreg isn't easy to come by.

second: There is a different kind of soric, called "soric lrc". Lrc means low resin consumption. As you might guess this is sort of a light weight type of soric. The difference is about 700kg/m^3 to 450kg/m^3. This doesn't quite get you to your target, but combined with a lighter kevlar layer, and strict resin measurement you should be able to get there. maybe try to keep the resin pod about a metre below your mould. This prevents most of the resin overflow. I reached around 1930 g/m^2 with the following layup: 200g/m^2 carbon; soric lrc 3mm; 200g/m^2 carbon. Even with 80g/m^2 kevlar this would be a little above your target. But if you swith the inner layer to 160g/m^2 you sould be able to do it.

regards

Hi oekmont, thanks for your reply

Unfortunally we dont have a oven in that size 5.5 meter, it could be worth to make one. We have no experience with prepeg so it must wait untill next project.

Part of your second suggestion seems to be able to solve our weight problem, but i´m not quite sure. Our first test hull with this layup ended up on 6.5 kg.

Gelcoat 800g + 1 layer 200g carbon + 1 layer 200g kevlar + 2mm soric + 1 layer 200g carbon + 0.7 sqm kevlar all infused in one shot... very easy methode, but the total weight was 6.5 kg. I guess that something vent wrong in the infusion process, perhaps we could save 1 kg there, and another 500g if we use 80g kevlar instead of 200g, then it still be to heavy 5 kg. But with soric light 1.5 mm instead of 2 mm i guess we could cut of 500 g more, and 2 k clear coat instead of gelcoat now we are almost there.  

There is a lot of factors to think and test through

Best regards Keld