Kevlar questions

scraping - good to know
You can also file it.

True, some terrible boats have been made
out of Kevlar, and then beaten to a sodden mess on the river. And careful use of glass can result in a very durable boat.

Varnish isn’t very abrasion resistant
Epoxy simply holds up better, especially if you mix in some fumed silica (Cabosil).

I’ve used both
I have sometimes applied varnish over the epoxy, partly for UV protection (although I doubt my hull interiors would see enough UV to degrade the epoxy) but also just to be certain that the cured epoxy won’t blush with water exposure, even if the maker says it won’t.

It just seemed to me better to use epoxy if the aramid fibers seemed to be getting exposed.

But I have used varnish only on a couple of Bell hull interiors to get rid of the annoying Bell blush that they were prone to, and that seemed to work fine.

There are some excellent varnishes,
and they sure go on a lot easier. The interior of a canoe is often less exposed to scraping wear than the exterior.

I used to drive one

“Stump” for short.

After seeing how Wenonah’s
tuff weave holds up and Nova Craft’s experimental basalt/Innegra coweave holds up it makes me wonder why one would build kayaks out of kevlar anyway.

In the SSKK layup used by Millbrook, it
is quite durable. Kevlar needs to be mostly an inside cloth.

Partial Data

– Last Updated: Feb-18-15 8:57 PM EST –

Partial Data is always a problem, particularly when leavened with personal bias. Here's my incomplete take on Kevlar, Innegra, Glass, including Basalt, and Carbon, also with incomplete data

E glass, Basalt and S glass are silica variants, 2.5 times as heavy as water, with tensile strengths, ie breaking in tension, of 500ksi for E, 600 for Basalt and 650 for S. Modulus of stiffness is, 10msi, 11, 12 respectively, again about a 10% difference. Costs vary, E is $6/lb, Basalt and S ~ $20/lb. Basalt has an attractive brownish color.

Tuff Weave is polyester/Diolon with a specific gravity of 1.4 that of water. Elongation to break is 14 %, about three times glasses ~5% with a tensile strength 180 ksi, about a third of the glasses, but it's modulus is 11 msi, same as basalts. So it flexes quite easily but will take more impact than glass and costs about $10/lb, a little more than E glass.

Seems like it'd best be used inside hulls, but the elongation is past what our resins can match; it's a less expensive substitute for Kevlar. It's weight, about half glass's yields a 25% savings in similar panel thickness, as resin weighs the same for everything.

Kevlar [49] is also about 1.4 times the weight of water but has tensile strength of 580 ksi, elongation to break of 2.8%, ~ half glass' and stiffness of 19 msi, twice that of glass and Poly. So it's stronger in tension and stiffness at about half the weight of glass. With resin added, that leaves panel weight of ~ 75% of similar volume glass panels and about the same as Poly except it's much stronger, but there are problems. Kevlar costs ~ $25/ lbs, it doesn't bond with resin, it's captured in it, and it's hydrophyllic, absorbing 7% of it's weigh in water where freezing/thawing, etc. etc. Silica and Poly absorb less than 1% water by weight.

Enter Innegra, a High Density PolyPropolene/polyolefin with Sp Gr. of .84, significantly lighter than water. It has physicals below glass or poly with those numbers improving because it is so light we can use more of it. It's elongation to break is 10%, a problem with resin physical characteristic, and while it absorbs no water, 0.0%, it does not bond with resin any better than Kevlar. 100% Innegra Layers need a veil mat to improve adhesion and Innegra floats on resin so must be vacuum bagged, preferably dry bagged for debulking. Innegra costs about $20/lb and needs to be mixed with other fibers. Glass, Basalt and Carbon are the available choices.

Carbon has a Sp G of 1.8, tensile strength of ~600 to 800 kst, modulus of 33-40 msi, elongation to break of 1.5-1.8%, zero water absorption and cost $50/lb or more. It is the good stuff!

It can be blended or co-mingled in individual threads in roughly a 50/50 mixture. or co woven, with Innegra in one axis, Basalt or Carbon in the other. Quad weave, Innegra and in every other thread in both directions is the most complex offering. The blending solves bonding issues, and the Innegra "fail safes" it's fabric mate. All the mingling and multiple weaves cost more money than straight Innegra.

And that's where my data runs out. Early testing suggested co-mingled thread was higher in impact resistance but recent anecdotal information prefers the more expensive quad weave product. We can suspect bi weaves fail as Kev/Carbon bi-weaves do, zippering in one direction. Innegra/Carbon blends are lighter and stronger than Basalt/Innegra but they cost significantly more. As the research studies haven't arrived yet, I'm guessing too.

So it remains to be seen if Innegra will replace or compete with Kevlar as the intermediate priced laminate. Kev has had a good long run and M-5 is coming, in the words of Ian Tyson, "Someday Soon". We'll see about that too.

Thankyou, in what circumstances is water
absorption a practical problem for a laminate containing Kevlar?

Straying off topic…
…but, I have built several canoes using Innegra S over the past few years. In my experience I have found secondary bonding is not good. The Innegra needs to be buried in the lay-up, not as the final layer of cloth. And yes, it behaves like Spectra.

Not much in the Lit, just anecdotal data from folks working in the industry. we note motor and sail craft are not often made with the stuff where carbon is common. ??

OK, but how would the tendency
to absorb water affect a canoe owner? If the resin gets worn off the inside of a Kevlar boat, does the tendency to absorb water cause the Kevlar to try to expand and pop out of the matrix?

I recall an arcane study where aramid plus epoxy was baked in hot water, and they found that, up to a point, the matrix became a little stronger, without delaminating. Maybe they cheated.

Who knows?
WHo knows? I’ve a suggestion from a very top Oxeon lamination guy that Kev eventually delaminates and ends as loose strands in the resin??

Kevlar has has a great run as a top, then, after carbon arrived, a semi top lamination fabric for Kayaks and Canoes. It’s good stuff. Quad woven Innegra may be better, especially if the carbon/Innegra price drops a little.

It seems to me
It should be critically important for the fabric in a lamination to absorb the resin in order to become something other than a mere spacer. I realize that in wood based builds, the plywood, or wood strips probably absorb very little of the resin used in the layup, but then the wood is not a limp fabric either.

I don’t think C glass has been mentioned and I’ve been wondering why. I read somewhere that it is supposed to be about 50% stronger than E glass.

On the other hand, I have seen a remarkable demonstration of the strength and resilience of E glass where vinyl ester resin is employed. At some point, strong is strong enough; it doesn’t have to be bullet proof.

If bouncing off rocks is your thing, I thought that polyethylene had answered that call–at least as concerns cost effectiveness.


– Last Updated: Feb-19-15 9:22 AM EST –

Well, it seems to me that some of the people engaged in this discussion are talking more about canoes than kayaks. When it comes to standard open-topped canoes (not the little WW ones that are just about shaped like kayaks), is there any material that's WORSE than polyethylene? Okay, there probably is, but it's the worst of all choices actually being used these days, in terms of retaining the boat's designed shape (that and the fact that it takes two people to carry a poly canoe).

You mean “S” glass, and Charlie’s
figure shows that S glass is nowhere near twice as strong as E glass. But in my experience, S glass is definitely stronger, and is also the hardest cloth one can use for the outer layer of a boat. (Don’t know about basalt.)

If you look…
at the Sweet Composites website, you’ll find mention of a “T” type fiberglass. I have used this in the past and did not find much difference as compared to S2 type glass.

Nose cones

– Last Updated: Feb-20-15 10:14 AM EST –

T glass seems to be a thermal varient of C glass, a more chemically inert version of Eglass. Google/Wikipedia has enough data for most of us. Higher strength S glass was developed as an ablative layer for missile nose cones re-entering the atmosphere. It has been replaced by High Modulus Carbon, the lowest tensile strength but highest modulus carbon variant. Maybe we should be using this HM carbon on the outside of WW Canoes, except it costs ~$75+/lb, or maybe Boron at $250/lb.? Naw. WW paddlers want inexpensive bottoms because they need to replace them a little more often than the flatwater crew does theirs.