Here’s one opinion…
From NC Kayak website:
http://www.novuscomposites.com/faq.htm
Yes, we offer a carbon/Kevlar blend at the upgrade price of $599.00. However, we don’t recommend that you choose this option. We believe carbon and Kevlar are not the best materials for kayak construction. Carbon is generally recommended because it is very stiff, and stiffness translates into speed. Yet, carbon is brittle and does not handle impacts very well. Kevlar can take impacts, but it does not have a long life-expectancy. The sun’s ultraviolet rays weaken Kevlar. Also, Kevlar does not make a molecular bond with other materials, and with its unique properties, it will begin to separate from the rest of the kayak over time. Because of this, a kayak made from Kevlar will begin to absorb water, and will gain weight drastically. A carbon/Kevlar blend does compensate slightly for their respective weaknesses, but does not solve them. Our LT fiberglass kayaks are within a pound of our carbon/Kevlar kayaks. You get more bang for your buck with a considerably longer lifespan.
marketing
I don’t think a kevlar kayak will gain weight drastically unless it’s cracked and sitting in water all the time. I have seen water stains in a kevlar kayak at cracks in the hull but I don’t think it adds noticable weight. The amount of water in a 4" diameter stain can’t be very much.
Methinks that the weight gain story is marketing to focus on whatever is the proprietary layup of a manufacturer.
Focusing on the fabric leaves too many other variables out of the picture.
True to an extent
Kevlar doesn’t like to stick to things in the matrix as well as other materials. As such, it is “prone” to interlaminar shearing which is a gradual breakdown within the lay-up / matrix. Good epoxy or vinylester resin lay-ups minimize this, but it’s still an issue. Surf kayaks that take lots of pounding if made with Kevlar can become softer after a couple of years. Carbon / glass surf boats last longer and retain stiffness longer in my experience. Kevlar is hydroscopic and will absorb some moisture, but I believe this is insignificant really. Most kevlar boats are actually also glass or Carbon as the latter adds stiffness. I think it’s a decent material when used wisely. The inner layer of the matrix would be a better application. Where weight is primary and the other variables secondary, Kevlar is a good call. It’s just a material with pro’s and con’s, so the trick is to apply materials where their strengths are maximized.
Thanks Salty for saying that …
Yep, how many times do we have to hear that misinformation … ahhhhhh.
And another …
This is an overview of the materials as they apply to kayaks without really going into specifics of fabric weights and weaves. Each of these needing another page each. The gentle reader should glean all needed info from this to figure some things out.
Fiberglass is stiff, strong and relatively inexpensive when compared to other exotics.
Carbon is super stiff, stronger than equal areal weight glass. It does cost a lot more.
Kevlar is amazingly strong and tough. It costs more too but the real expense is working with it. Cutting and trimming is difficult at best.
Some interesting numbers for 5.7 oz cloths.... all have similar 18x18 type weaves.
Breaking strength: 5.7 oz. E glass 225-250 lbs.
5.7 oz. Carbon (6k?) 300 lbs.
5.0 oz Kevlar 650 ! lbs.
One would think the Kevlar is the only way to go. It is and it isn't.
There are many ways to lay up a boat. It would be refreshing to hear manufacturers reasons behind why they choose to do one thing or another rather than just offer something as the end all.
Are they building with Kevlar to save weight or to have a stronger boat? (Or to make more $$$?)
Which is stronger? Glass or Kevlar?
Before my head explodes with all I have to say and do not have time to write....I will say this.
A glass boat layed up thoughtfully will take more minor bumps and grinds and will also absorb a greater amount of energy than kevlar BEFORE it STARTS to fail.If a equally layed up kevlar boat were built it would not take as much abuse before it would start to soften up .......BUTTTTT. A kevlar boat WOULD endure catastrophic force far better.
If a giant were to pick up a glass boat and wack it across a log it would probably break 1/2 - 3/4 of the way through on the first hit and fly to pieces on the second.
A kevlar boat would make a dull thump on the first hit and show some damage in the form of delamination of plys but would be mostly intact. The second hit would probably cause failure of the resin and the boat would lose it's shape at point of impact but it would still most likely stay together. It would take several more hits by an increasingly frustrated being before the boat would come apart.
This is what kevlar can do.....now picture what would happen if a jetski plowed into you to offshore or you bailed on a big set and your "lifeboat" pounded on the rocks for a set or two before getting spat out.Kevlar can provide security a non balistically layed up glass boat could not.
A quick synapsis of my personal construction opinions. Please note I do not follow the same line of thinking many of the Majors do.
I can build a super light all glass boat but I do not recommend this. The thinner glass layup is not quite as tough as the light Kevlar layup and due to the extra labor involved I would also charge the same price to build one.
If boats are going to be bounced off of rocks on a regular basis in any conditions other than blue water go for the standard glass construction. Unbelieveably tough and resistant to bump and grind damage. Still light and does well enduring the day to day stuff for a long time. Save some $$$ too.
If boat will see occasional rocks only and will not be abused with IN heavy surf / rescues with boat wallowing full of water etc. AND a light weight,stiff, super strong, safe build is the goal , go for the Lightweight Kevlar layup........ I just call it Kevlar layup.
Blue water, real potential for life threatening conditions , boat may hit a submerged rebar at speed it, MUST stay together after shark , jetski or cargo ship attack........ Go for a kevlar layup built up around the weight of a similar glass boat then add a bit. Please let me know what you are thinking / picturing.
So much to say here...... Until I really write down each scenario I am trying to describe briefly here all this might sound confusing.
Especially if you go by what other manufacturers are doing. I do not have a generic Kevlar layup. Each one is custom built based on it's intended use. Most of the added cost of a kevlar boat over a standard glass layup is labor.....Carbon does more even though it is easier to work with...... but the thread was glass vs. kevlar.
Two boats by the same builder
Kevlar will be lighter, faster and more expensive.
Fiberglass will be heavier slower and cost less.
I like speed and since I am over the hill I also like lightness, so I’ll opt for the lighter kevlar one.
cheers,
JackL
Faster?
Considering that speed is a function of drag, which is identical between Kevlar and fiberglass models of the same boat, how can the former possibly be any faster than the latter?
If you’re referring to acceleration, a 5 pound difference in boat weight is ~2% or less of the total boat+paddler+gear weight, so it’s not going to make much difference there, either.
acceleration
There is a slight acceleration with each stroke I take to make up for losses during the recovery ( “glide” )portion of my stroke. Given the distances that I paddle, I’ll take that extra 2% you say 5 lbs difference in boat weight gives me.
curious
for an all glass construction wouldn’t unidirectional glass layed transversely in the mid-section be a good idea? It’s interesting to see manufacturers go through different layups. Regular heavy woven roving was standard for a glass boat. Now everything has a layer of core material with lighter glass on the inside.
Necky is doing interesting stuff reinventing the wheel but the flat bottom sections in the Chatham where there isn’t core material make for noticiable “ringing” when plunging on waves.
Have owned boats made of all
materials discussed, and I have not seen any special tendency for Kevlar to delaminate with time in my whitewater boats, which obviously take a lot of hammering. The bond of epoxy resin with Kevlar is just as “molecular” as the resin bond with properly pre-coated glass, or Nylon, or polyester/CAP. Now, if you use vinylester resin, you can get an unusually tenacious bond to CAP because the resin temporarily eats into the surface of the fibers. But vinylester bonds about the same to S-glass as to Kevlar. Millbrook is using S-glass outside, Kevlar inside with vinylester resin, and gets excellent results. Kaz could use CAP for better bonding, but he races his boats, and he apparently finds they last fine with Kevlar.
Good thread here
full of logical information. Onnopaddle, I agree with your post but would only add that the values would be for tension. Kevlar, as noted is crazy strong in tension, but very weak in compression. To g2d’s point about good bonding, I believe it’s possible to minimize inter laminar breakdown very effectively. I recall chatting with an Aerospace guy about wing to body fairings on some jets that they made of Kevlar initially to save weight. These did experience breakdown and water absorbtion, but were not structurally critical.
It’s going to be interesting to see how the new carbon epoxy airliners hold up through years of compression / de-compression. I don’t believe there’s any Kevlar in these layups, but not sure on that. Of interest is the fact that more Titanium has o be used as aluminum interacts badly with Carbon / Graphite.
Lee, absolutely. I do that in all my
boats to get some ‘hoop’ strength … also think about the seat ‘hard spots’ coming back the other way while you are sitting on it … This helps support the kevlar’s sort of weak compression from the inside out + helps boat hold its shape here too. Uni on the aft deck too.
I always like the image of a person sitting on a flower, with its uni petals radiating out from under the seat.
Yep Salty, don’t want to send the wrong
wrong message about kevlar. From my experience, I feel kevlar IS weaker in compression from a real world standpoint than what the actual charted numbers would tell you. But marry it up with S-glass and the two support each other in a wonderfully symbiotic relationship. IMO, if using carbon, go all the way with it. Otherwise a properly scheduled kevlar / S- glass layup is my close second favorite from a pound fo pound perspective Never had any problems with delamination either but using epoxy… i did call Dupont years ago about using polyester with kevlar too to get the scoop form the tech guys over there. A good description of using ‘esters’ with kevlar can be found on the Sission kayak website. Yep, kevlar can fuzz on the inside @ wear points and sort of trap water, but it still drys back out … so easy to prevent this though and just another thing that suprises me why it does not get done by the big guys.
that’s what I thought
For the year I had the necky Chatham 18 it was neat to see the application of knit fabrics and what appeared to be unidirectional glass (lengthwise though) but there were a few anomalies on layup that didn't make sense like the ends where impacts would occur didn't look any thicker than the adjacent panel. The gel coat chipped off a section of the bow and with a flashlight I could get a decent gauge on the shape of the inside.
When I saw a Chatham 17 which had a slightly larger flat section the rigid soft chine met a fairly flexible flat section which made the whole kayak rattle on pounding waves. It looked like the kind of place that transverse unidirectional cloth or core material would have made a difference. It's funny how some kinds of flexibility in the hull bottom isn't bothersome (old Necky Swallow, QCC400) but in the higher tech Necky Chatham 17 it rang like a drum enough to make the deck vibrate visually. Which is something the wider Chatham 16 didn't do. Funny what a difference placement of core materials makes.
I know racers that
raise their rudders to save on drag.
I know another one who has shortened his to save on drag.
If I can lose a pound or two before a race I’ll gladly take the 2 percent or what ever you figure it will be.
Put me in a kevlar QCC-700 against me in a fiberglass QCC-700 and me in the kevlar one will beat me in the fiberglass one.
Just my take!
cheers,
JackL
Too light
I’ve seen more than one kayak made from kevlar where the deck was made too light. The decks cracked during rescue practices in the surf or ocean chop when many boats were in very close proximity. I think they try to make them too light because floks want light boats and they have to justify the extra cost of a kevlar boat.
If you aren;t racing then you don’t need a light boat. All you need is a barbell and about 60 pounds of weights. In less than a month or 15 separate 20 minute workouts you will be able to lift a heavier boat with ease. Studies done by Nautalus showed that even floks in their 80’s could build muscle as fast as youngsters. So get the weights and start out easy and keep at it.
On the other hand, if you are racing and you have plenty of money then get the lightest boat you can and do whatever you can to make it lighter. After all it only needs to last through this weeks race. Train in your heavier boat. 
Frank… Getting it up was never a
problem, but as I get older, KEEPING it up is more difficult.
Even when I was 30, and lifted weights seriously before a 12 night Quetico trip, I found lofting and portaging our 85 pound fiberglass canoe difficult. I had a good padded portage yoke, but the pressure of that boat would make me miserable on longer portages. Lifting weights does nothing for that.
Now I have a 48 pound Bluewater Chippewa. Getting it up and keeping it up is no problem.
Never had to keep it up for so long
Since I’ve never been on a trip to Quetico, I’ve never had to keep it up that long. I guess I just finish earlier than most…
We are still talking about portaging right. What I mean is the portages here are short. 
The actual benefit is considerably less
For one thing, the marginally improved acceleration on each stroke is partially offset by the marginally increased inertia of a heavier boat.
More importantly, since drag - not weight - is the major factor curtailing speed and acceleration for a given amount of horsepower, a 2% decrease in weight does not translate into a 2% increase in speed. I have no idea how to calculate the exact effect, but I'd be surprised if it was significantly more than 0.2%.
The bottom line is that saving five pounds makes no significant difference on the water for a touring kayaker. I vary the amount of gear I carry when paddling by at least that much and I can honestly say that I have never noticed a difference in the speed of the boat.
While Kevlar kayaks can have other benefits, higher performance is not one of them.
Weight…
It’s funny how weight is perceived in different fields of kayaking.
Last week I helped my training mate collect a 2nd hand Nelo Vanquish ICF kayak in marathon(8 kg) layup. The seller adviced us that by exchanging the rudder cable, it might be able to shave off 100g…
While 100g might sound laughable, anyone used to a 12kg sprint ICF kayak can immediately feel the difference when placed in an 8kg version of the boat. Much faster to accelerate. It might make the difference between drafting or being left behind.
Still when touring in a sea kayak, I doubt I’d feel the difference between a 24kg boat + gear and a 21kg boat + gear.
/Peter