I’m in the process of buying a kayak for touring and have noticed that there are some made out of Kevlar. Anyone know what advantages/disadvantages a Kevlar kayak would have over a more standard Polyethylene Composite? I’m aware price is one major difference.
Also, I saw in an add that the Kevlar kayak was lightweight. I was under the impression that Kevlar was quite heavy. Aren’t Kevlar bullet proof vests extrememely heavy?
My favorite general all-purpose answer: It depends
Specifically, it depends on what you are planning to do w/ the kayak. Are you planning on dragging across and bouncing off ricks? Poly is a good choice. Gonna do sea kayaking? Fibreglass or kevlar will be better and lighter. Kevlar adds weight to a glass kayak, but the material isn’t as heavy as poly. Cost is also a factor. From lower to higher, it generally runs poly -> glass -> Kevlar.
Just a WAG here, but I’m pretty sure the reason Kevlar vests are heavy is because of steel(?) plates sewn into the garment. I would also guess that a lot more Kevlar is woven into a square inch of bulletproof vest than you would find in your average kayak.
As far as Kevlar vs. Polyethylene for your kayaks, you should ask yourself: how well-armed are the fish you’ll be disturbing? 
D
I think that Kevlar buys you a bit more strength and less weight than fiberglass. Both will be stiffer and lighter than a plastic boat, which means that if you’re an advanced paddler, you’ll notice some difference in handling and response. (Paddlers tend to get snobbish about materials.) The composite boats usually have a gel coat which makes them prettier. I seem to recall that you also get somewhat better hull shapes with the laid-up materials.
On the other hand, Kevlar is labor intensive (and the material is also more expensive) so you end up paying a LOT more for a boat.
As paperbackwriter noted, most people spend a lot of time dragging their touring kayaks up beaches, which is hell on gel coats, but is only a minor cosmetic problem for the polyethylene boats.
Kevlar kayaks are usually made of Kevlar strands embedded in epoxy, which is similar to fiberglass but a lot stronger. I would only get the Kevlar if you are really serious about touring and plan on going long distances, because they are about three times more expensive in my experience. Plastic kayaks will scratch on the surface (from sand, rocks, etc.), but it’s only cosmetic. They will last you a long time. Fiberglass is a sort of a compromise between the two, but remember they are the most brittle.
Kevlar vests are heavy because they have dozens of layers of kevlar all packed in there. The interceptor armor the Army uses doesn’t have metal plates, but it can have ceramic plates added on for extra protection.
The advantage of a fiberglass, carbon fiber or Kevlar boat over a plastic boat would be weight and stiffness. If the boat flexes as you paddle, the less energy from your paddling goes into going forward. A plastic boat will flex a relatively large amount compared to a fiber boat. It’s not a huge factor in a pleasure paddle one afternoon, but if you’re doing a long, multi day paddle it can be noticeable.
That said, if I were to get another kayak tomorrow, it would probably be a plastic boat (I currently have a Perception Eclipse). They’re cheaper and I don’t have to worry about it getting banged up moving it around. If I were doing something like paddling the 20 mile ocean crossing from Long Beach to Catalina Island, then I’d probably look into a kevlar boat. As it stands I’m lucky to get on the water twice in one year.
Here’s a page on building kayaks that goes into way more detail than I ever could on the different materials used:
http://www.oneoceankayaks.com/Abrasion.htm
Actually, that whole site is pretty cool… hmmm… bulding your own boat… What’s one more hobby? I’ve already got about twenty. 
Pound for pound, kevlar is lighter than plastic, so for identical designs, kevlar will permit a lighter boat, and a lighter boat is a more responsive and faster boat.
Plastic boats tend to oil-can at a younger age than kevlar boats, meaning their bottoms go wakka-wakka-wakka rather than remaining rigid. Oil-canning slows the boat.
Plastic tends to scratch and stay scratched, whereas kevlar scratches can be filled with gel-coat or epoxy. Scratches slow the boat down.
You pay for what you get. If you are seriously into paddling, kevlar can be worth the bucks, but if you are only an occasional paddler, or a new to paddling and do not yet know what design of boat up to which you will be trading, then plastic makes for an easier price entry into the sport.
Hull design is usually more important than weight, so find the boat that works best for you and then decide whether to go plastic or kevlar.
Cheers,
Richard Culpeper
CCA sprint instructor
OWWA wild water instructor
Past director W.C.A., Canoe Ontario, O.R.C.A
Any opinions on inflatable kayaks, for poking around the harbour?
Inflatable kayaks by seyvlor(sp?) and Stearns are light duty and might last a summer or two of poking around the harbor. They are not much fun to paddle.
Whether a 20ft fiberglass screamer or 10ft plastic recreational boat, you still want a reasonably rigid hull and hopefully some kind of keel to keep yourself going straight. An inflatable boat offers neither.
A reasonably-priced recreational/entry level plastic boat is a much better option, IMHO.
First, let me establish my credentials here. I was a production manager for Current Designs in the late 80’s and early 90’s and I have built about 2000 kayaks mostly fiberglass reinforced polyester/vinylester vacuum bagged composites. About 5% of these kayaks were made with various kevlar layup designs with some including carbon and/or spectra. It wasn’t until I left that Current Designs began production of the cheaper rotomolded thermoplastic kayaks.
Although it was fun designing with the various “high tech” materials getting the same fiberglass kayak weighing 50 lbs down to 27 lbs in the case of the carbon/spectra composite, I would never buy a kevlar kayak. Any damage is much more expensive to fix .
Quite often, to be called a kevlar kayak, all the manufacturer needs to use is one ply of 5 oz. per square yard kevlar (roughly equivalent to one ply of 9 oz fiberglass cloth) while still applying another 33 oz per square yard of fiberglass to the hull composite. In other words there are many variations and the design objective for kevlar can range from satisfying egos for cheap to serious weight reduction while maintaining strength and stiffness
In my opinion if you plan to use your kayak a lot and plan to do some serious touring stick with a vacuum bagged fiberglass composite. Its a proven commodity.