Durability of Kevlar

Hello all,

I'm contemplating my 1st purchase of a Kevlar canoe and wanted to tap the cumulative experience on this list before I throw down the cash. To make it interesting, instead of just asking for advice I'll ask for some stories ... but please, no fish stories ;-] What is the ugliest beating your Kevlar boat has withstood and do you think you were just lucky? And for the abuse it couldn't take, how difficult/costly was the repair? Since there are lots of different composites using kevlar these days, please describe your layup.

Thanks in advance, Trey Downey

PS: I'm not looking for a boat to beat the hell out of. I simply want to hear about the durability of Kevlar boats from people who use them a lot instead of from people who sell a lot of them.

If you want a wide array of stories, try contacting an outfitter for the boundary waters such as those in Ely, Minnesota. They use a lot of Kevlar canoes and, if I remember correctly, an outfitter I used said they last only about three seasons with the beatings they get up

Judging from UV degraded boats we've rebuilt I'd have to think that clear-coated kevlar boats (those orange/yellow beauties) fare the worst if stored in direct sunlight.

As far as I know, all wooden boats have a fiberglass layup which is susceptible to UV. They are typically coated with polyurethane with UV absorbers to form a sacrificial protective coat. The polyurethane is supposed to be sanded as reapplied every so often (depending on use) to maintain protection for the underlying epoxy. (Epoxy gets white and chalky after long exposure to UV, but I think the fiberglass could probably take it)

Jake

I've made a couple of canoes from kevlar. It's not easy to work with. They say use (buy) kevlar for the strength, and not for the light weight. If you want to compare durability against a rolalex type of boat, the composite is not as strong, but way lighter. Since kevlar is superior to most other fabrics for tension, it is best used on the inside layers and perhaps s-glass on the outter. Many boats have kevlar on the outside where compressiuon forces are in play. As far as a story... a two or threelayer hull is still rather fragil but when you start adding layers like Stolquist did for his kayaks, they are right up there with poly boats at 2/3 the weight. A friend went to No Calif for a boating holiday, and the ended up rolling their Blazer with the boats on top, No real damage, they still went boating. The Truck needed some

Kevlar fuzzes badly when you sand it. I think there is a considerable difference between layups for canoe, kayak, and between various vendors.

Many production canoes, especially clear-coat are just kevlar, reinforced with more kevlar. I seem to be doing a fair amount of repair work on my race boats due to low water levels this year. Even a zipper tear can be dried out, roughed up and covered with 4 oz glass and resin. Make sure to talk to the vendor about what kind of resin they recommend. While you *can* use epoxy on a vinylester boat, it may not bond quite as well in the long run. To fix minor wounds, Lightly sand,use a mix of resin and carb-o-sil or microballoons to fill any deep gouges, apply an oval of 4 oz cloth, saturate the cloth, and top it off with saran wrap stretched tightly and taped over the area. With practice you can get by with only a little 400 grit sanding over the repaired area. Buff it out with rubbing compound and you may not even know it was hurt.

BTW, if you zipper the hull, make sure you reinforce the inside too.

Engineering is all about simplification

I probably wouldn't have bothered to look at the shell stresses, but would have considered the longitudinal strength of the hull girder (but does the canoe hog or sag?)! Looking at the shell the way you have does kind of suggest that you need kevlar on the inside as well as on the outside (from the girder approach).

Something that seems to be missing though is a component for stiffness - carbon is good for this which is why carbon and kevlar are used together frequently. Another good way of stiffening the hull is by using sandwich construction.

As for the original question, sorry I have no stories because I've never had a kevlar canoe (have a carbon/kevlar C1 but haven't used it)! I have heard reports from the liffey descent though, that kevlar race boats that break on the weirs tend to remain together, it's just that the resin breaks away at the stress points so you get a kind of articulated boat that sinks rapidly This is due to the difficulty in getting the resin to permeate the stuff properly in the first place (someone quoted that it is difficult to work with) - if the resin and kevlar become one as they are supposed to you wouldn't get this!

As for the abrasion resistance of kevlar, I'm sure I was taught that aramid is poor for that, it certainly blunts knives and clogs abrasives but I think it gets considerably weakened by that - it seems an expensive material to use in such a way!

I'd stay away from pointy stuff in any composite boat!

Both. However, Kevlar shows its value on impact loads (hitting something) rather than overall flex.

Before you jump for carbon fiber, look at the stiffness of Kevlar on its own. The difference between them is more in how they handle tension vs compression.

Carbon and Kevlar are often used in a single weave - the yellow and black checkerboard pattern - even though it is more efficient to use separate layers of carbon and Kevlar. This info told to me by John Winters.

Don't compare ultralight racing boats with a practical Kevlar canoe.

Most of the folks commenting on Kevlar canoes don't seem to use them. Hell, they are the most practical canoes for flatwater. Lighter than either plastic (Royalex & such) or fiberglass and plenty tough except in the flimsiest layups.

As far as life expectancy in rental fleets, consider that they are usually sold off long before they degrade significantly. Why keep a valuable asset in storage over winter when you can sell it while it still has value? If you own the thing, and you treat it like a rental, you deserve its short life. Folks I know that own their own Kevlar canoe have them for ages thru regular use.

Kevlar kayaks are another story. They don't get significantly lighter in Kevlar compared to fiberglass (advantage of monocoque construction) and cost a lot more. But if you want a tough kayak, get Kevlar with the same weight as fiberglass and no gel coat (outer layer of glass for abrasion).

Thanks to you all for a good discussion. But please, can someone clear up a little confusion? Kevlar is polyaramid resin. I thought Kevlar canoes (I have one) are made of Kevlar and fiberglass. Is that not true? Also, is there a quick and easy way to fill scratches?

Kevlar isn't used as a resin in boats - it's a fibre. Woven into a fabric, it is used as a structural component in the boat. Often it is mixed with layers of glass. All of this will be saturated with another resin, usually a vinylester.

If you have gelcoat covering the canoe, just get gelcoat and catalyst from a marine shop. There are two types, with or without wax in it. The wax is used to prevent oxygen from inhibiting curing at the surface. If you get the waxless stuff, cover the surface of the gelcoat with plastic wrap (kitchen stuff like Saran Wrap works fine) to keep the air off it til it cures.