I will be purchasing my first canoe in about one month (have been kayaking for 10 years)and would like to know what the advantages and disadvantages of kevlar vs royalex in terms of maintainance and durability and fragility.
A little added info…
Kevlar is extremely strong. That is why they use it for Bullet Proof Vests. It is extremely difficult to cut, and about impossible to tear.
A kevlar boat will have the ability to flex, without breaking the reinforcing fibers of the Kevlar. But, the Gelcoat will crack, if the kevlar flexes too much. The “good” is if you hit a rock, the hull will “give”, rather than break apart or puncture, but the gelcoat could crack or break off of the kevlar fibers. Another “good” is the boat will probably get you back home, because the integrity of the hull will still be there. It may leak like the devil, but it won’t break the hull apart.
The benefit of Kevlar over Fiberglass cloth is toughness, and a lighter weight layup. A fiberglass lay-up can crack open if you would hit a rock. Fiberglass is as it states, a cloth made of glass fibers. It can be stiff, but a little brittle. Kevlar is extremely tough, but not as stiff (in itself) as fiberglass cloth. A lot of boats use a two layer layup. The less expensive use 2 layers of fiberglass cloth in the layup, and more expensive use an outside layer of fiberglass, and an inside layer of kevlar in the layup. This later layup is a decent compromise of stiffness & toughness.
My Impex “Assateague” uses a cloth that has Kevlar fibers running in one direction, and Carbon fibers running the other direction. This is a good compromise where the Kevlar gives it toughness, and the Carbon fibers give it stiffness. It is interesting to see the gold fibers running one direction, and the black ones going the other direction, all in the same cloth. It is very stiff, and strong, and lighter than a fiberglass layup.
Royalex is a fairly tough plastic, but it is not reinforced at all. If you hit something hard enough, it will flex, bend, crack, or break apart in an extreme situation. It is cheaper, as it is not reinforced with any fibers. It is good for boats that may get a little knock or so, but would not normally get beaten up.
I understand Royalex can easily be glued, with a patch on the inside of a crack, but you will see it. Fiberglass, or Kevlar can be re-gelcoated, and unless the boat was torn up, you may never see the repair if done by someone competent to fix it right.
I hope this info is of some help.
Kevlar…
Kevlar is a fine material, but like any has it’s limits. It is very strong in tension, very weak in compression. Most Kevlar kayaks have glass or carbon in them to stiffen the laminate. I did some informal testing recently of a Carbon Polyester co.weave - Glass -Kevlar laminate, and when flexed the Kevlar did tear completely. Actually the Co-weave was tougher to tear. The point is that once in a cured matrix the Kevlar can tear. I’ve broked ends completely off a kevlar boat. It also doesn’t like to bond as well and “can” result in interlaminar shearing and breakdown, resulting in a mushier layup over time. I am not saying don’t go there. I’d have it on the inner layer of a boat for sure for it’s toughness and weight savings. Clearly race boats benefit from the weight savings. But it’s the combination of differing materials that make a boat tough. Carbon glass surf boats hold up better than Kevlar glass in my experience. They stay stiffer longer, and that’s what we all want eh!!
From My Experience
– Last Updated: Feb-13-06 4:10 AM EST –
If you are going to paddling lots of rocky rivers like I do in New England then a royalex boat is probably your best bet. It will get scratched and scarred but it's unlikely to to suffer damage that requires repair. Royalex won't crack unless it's compromised by long exposure to sunlight (UV rays) chemicals, or repeated stress (sometimes caused by outfitting). If it does crack or puncture though repairs are difficult and often only good for short term.
If you are going to stick to deep water then kevelar boats in general are lighter and can be formed into finer more efficient shapes. Composites (glass, kevlar, carbon) will crack and suffer gelcoat damage (especialy if you drop them in the parking lot, DOH!) but are easier to repair. Done right repairs can be as strong and permanent as the original hull.
I agree with what was said.
When I bought my tripping canoe an 18 ft Champlain, I really thought about buying a kevlar or Royalex. I opted for the kevlar because it made the canoe so much lighter. I do own two other canoes which are Royalex. I was really concerned about the durabilty of the kevlar boat which isn’t an ultalite; however, after after beating it for a couple of years while tripping it hardly has any major scratches. I got hung up in a rapids when it was fully loaded last Fall and thought I going to have major repairs. Not so. The damage was trival and easily repaired with a little epoxy and sandpaper. A Royalex sure can take a pounding though and slides over rock with no problem. If a lot of rock gardens aren’t in your future get the kevlar, you’re back will thank you for it.
NOT the same stuff.
Kevlar 29 is a balistic material NOT used for composite construction.
Kevlar 49 is the stuff used on boats etc, NOt used for vests.
Please remember this next time as it drives builders crazy to hear that over and over in mass media and generic marketing drivel.
Kevlar IS a super strong and tough material. Failure of part begins with the fact that a less strong resin ( ‘ester’ type) might have been used in the matrix and cannot hold on as the fiber gets cycled. Another thing is even though Hexcel states ‘esters’ are o.k to use with Kevlar, practical experience shows that the fiber does not willingly accept the resin nor does the resin bond or ‘co-mingle’ with cloth to well and as a result, less than optimum strength is acheived for the fiber’s potential strength. Epoxy lets Kevlar shine.
Said it before … S-Glass and Kevlar are an almost perfect marrage of fibers for boat building. Both almost equal in #s with one supporting the other in different yet complimentary fashion.
Agree about epoxy
I agree totally that an epoxy resin will bond better with Kevlar. I’d go with S-glass, Carbon, coring, and Kevlar on the inner layer. The Carbon Polyester weave I’ve seen recently was pretty tough stuff. Yeah, I suspect a bullet will easily travel through a dozen Kevlar kayaks side by side 
I’m a technical ingoramus, and…
…appreciate (if not fully understanding) all these explanations of Kevlar/Royalex/FG. I paddled Royalex for years, but switched last year to a “Kev/graph?” layup in my Wenonah Vagabond, strictly for weight. I went from a 37 m/l lb boat to 23 m/l, and I couldn’t be happier. Far easier to load, carry, launch & retrieve for my aging body. It has a harder, brittler feel, but of course is not brittle. It’s not as soft and warm as Royalex (these are all nontech descriptions), but is right for me. I feel it moves faster/easier because of lightness and sharper prow, but speed isn’t that big a deal for me.
Kevlar in my boat not bullet proof??!!
well dammit then, i’m through with it, i want the best and i thought that kevlar was the best because it stops bullets…
it’s unfortunate that materials like aramid fibres and Gore Tex are so effectively marketed that they develop such a misinformed general publicity about them. not that this is the case with the orignal question- just a commentary on how these and other materials are misunderstood.
having worked in the outdoor industry a long time, i call any composite boats just that- composite boats, and try to speak to them in terms of each boats specific layup in the hopes of mitigating confusion about what the main fibre is and what it does… and it’s one of the great things about pnet that the people who work with the stuff and know best like to share their insight with us.
Update…
…just ordered a W kayak, the catamaran-hull jobbie.
Shows how irrational a paddler can be-the bloody thing will weigh about 60 pounds in polyethylene, but I want it primarily for the grandboys, who live on Puget Sound, which occasionally gets rough & has lots of boat wakes in their area. It’s so stable you can surf with it.