kevlar canoe build

1. most homebuilt kevlar canoes are built on a male mold, not a female one
2. i was talking more about dragging over rocks/etc... the kevlar will be fuzzy when scratched, fiberglass will not

 

Perhaps a study of basic structures is in order. When a shell bends the material near the center provides little or no contribution to the stiffness and strength other than keeping the material near the surfaces separated and from shearing. Kevlar is an expensive material to use for that purpose. It should save some weight though being lighter than glass. But there will be little to no benefit in terms of strength or stiffness from using Kevlar in the middle unless the Kevlar is thicker than the glass it replaces.

I've also seen claims that Kevlar shouldn't be used on the outside because it is weak in compression. That sounds reasonable.

 

In that case it is not sensible to use kevlar. An all glass canoe will be cheaper and easier to build. It may end up being stronger too, because kevlar is hard to wet and lay properly. They make all kinds of cores that are better .

 

Unless the goal is have a Kevlar canoe, ie one with some Kevlar in the laminate.

For some reason cores don't seem to be used in kayaks and canoes, other than the thin foam layer in Royalex. Perhaps the skin on a Kevlar or carbon fiber canoe is so thin that a two less than half thickness layers on either side of a core would have insufficient impact strength for localized loads. Don't really know though.

CORRECTION - Wenonah uses foam cores in some of their lightweight canoes. Other builders may do likewise. http://www.wenonah.com/craftsmanship/composites.php

 

I have built canoes for sale. We always use female molds. Kevlar, combined with vacuum bagging or infusion can give you a lighter, tight laminate. Otherwise the kevlar is just for show and plain glass is just fine.

 

Zachjowi et al.

Kevlar is used because of its light weight. We-no-naah canoes use thin foam core material to form a diamond shaped bottom and ribs. I believe is it just one layer on each side to encapsulate the foam. I think the sides of the canoe above the diamond shape are a single layer of kevlar.

I have built about 25 or so canoes and haven't ever had a problem with wet out and lay.

The glass is probably mainly there to be able to sand. If you try to sand Kevlar you will most likely ruin the boat. It will just fuzz up and get nasty.

Hope this helps.

Allan

 

If you have to lay fiberglass outside and inside of a canoe just to sand it, that is an awful method. Laminate in Kevlar and use a fairing compound.

 

Here is an example of an unpainted glass, Kevlar, foam composite canoe. This combination gives you an ultra-light, strong hull with a great finish.

http://www.wenonah.com/stock/gallery_photos/WC-MNII_picture2.jpg

 

That canoe appears to be their "Ultra-light construction" with "a structural-foam core and ribs are laminated into the hull and sides". Not quite the Kevlar with glass on either side described earlier in this thread. Here's a link to Wenonah's description of the construction of their canoes:
http://www.wenonah.com/craftsmanship/composites.php