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member (7)member
09/24/2019 10:30AM
I need technical advice from people having experience working with Kevlar. I plan to make a kevlar canoe myself. The plan is for an 18' canoe with 3 or 4 layers with vacuum epoxy infusion. But I recently got over pretty inexpensive kevlar sheets 3 ft x 5 yd pieces which means it will be made from many pieces.

From your experience, how much may it affect hull strength? Is it worth it to consider making it from pieces or better not to take a risk and go with one piece per layer?

Thank you for your time.
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senior member (64)senior membersenior member
09/24/2019 12:41PM
Contact Marshall & Heather Monthei. They built a kevlar canoe so they have actual experience. Heather is a contributing writer for the Boundary Waters Journal. Heather is on Facebook. Nice folks. Good luck.
distinguished member(747)distinguished memberdistinguished memberdistinguished memberdistinguished member
09/24/2019 01:20PM
Partials will be fine for the internal layers as long as there is sufficient overlap between pieces (8-10 inches perhaps) But I would want to have a full blanket for the most outer fabric layer: both for strength and aesthetics. Infusion would work fine in a female mold: infusing partials over a male mold would leave an irregular surface on the outside of the boat. Partials should not affect the infusion too much, though if the overlap areas are all on top of each other it may be slower to infuse in that particular place.

I infused a boat Earlier this year.

Strength for regular Kevlar canoe use should be fine. I have seen partial layers delaminate at the seams when rocks/rapids come knocking on the hull, though. Remember, Birchbark canoes of old were made of partials stitched and pitched together and they worked well enough to develop the entire fur trade industry.
member (7)member
09/24/2019 02:18PM
Thanks for the info, but I'm kind of old style guy. Probably the last on the planet without a Facebook account. :) Maybe you have their email, by any chance?

Thanks a lot!
member (7)member
09/24/2019 02:24PM
Hi muddyfeet, I read your thread on canoetripping. Amazing work, really inspiring. I plan just for one canoe, at least for now, so I thought about male mold.
With fiberglass as outer layer, next 2 layers of 5oz kevlar, next foam core and kevlar over core.
It will be my first serious project, so I'm not really run for perfection, just to have decent view.

How it all sounds for you, if I do it from pieces, doable?
member (7)member
09/24/2019 02:40PM
Actually, after reading your post once again I think I will follow your advice. First kevlar layer from full sheet and next inner layers will be from pieces.
member (7)member
09/24/2019 03:18PM
How this plan looks for you: On male mold put full sheet of kevlar and on kevlar put fiberglass - it will be first two outer layers. Infuse it, let it cure and take out from mold. Put inside of first two layers partial sheets, foam core, cover it with kevlar and infuse it second time.
Can two infusions make overall weaker hull?

One more question: I see people usually doing thwart and gunwale from carbon fiber. Why not kevlar?
distinguished member(2184)distinguished memberdistinguished memberdistinguished memberdistinguished member
09/24/2019 04:39PM
ak44: "

One more question: I see people usually doing thwart and gunwale from carbon fiber. Why not kevlar? "

Kevlar only surface bonds with the resin (the main reason that a kevlar hull is lighter than fiberglass is due to the reduced need for resin rather than the weight of the cloth), the fibers don't "wet through"- any abrasion that goes through the resin results in the exposure of frayed fiber.
member (7)member
09/24/2019 05:46PM
Ok, I see it makes sense, thank you.

Any thought about my other ideas?
distinguished member(747)distinguished memberdistinguished memberdistinguished memberdistinguished member
09/24/2019 06:49PM
Yes, the two-infusion technique would work on a male mold, But:
-you will use twice the infusion consumables (peelply/mesh/tubing/vac bag).
-you will need to finish the outside of the canoe to a gloss by ‘filling the weave’ with epoxy and then sanding/polishing to a gloss.

Given the complexity of infusion, you might want to reconsider if it is the right technique for your build. I can recommend the James Moran book on building a Kevlar boat over a male mold- I’ve seen some very functional boats built with that technique.
member (7)member
09/25/2019 09:18AM
Just ordered the book.
From your thread on canoe you used 5lb foam for core. I have access to 4lb and 6lb. Will 4lb work or better to go with 6lb?
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