Graphite vs Kevlar UltraLight

Think about how many high end canoe
makers use Kevlar as the inside layer, where after vacuum bagging or infusion, the sides of many Kevlar fibers are right there at the surface of the layup. If Kevlar in a resin matrix actually absorbed water, don’t you imagine those manufacturers would paint the insides of their boats?

Maybe they know something about what Kevlar does, and doesn’t, do.

I guess a policeman or soldier caught wearing Kevlar armor in a tropical rainstorm would be really screwed, no?

What about the sailing industry? Kevlar sails? Rain-soaked, would they turn a sailboat over?

Aren’t suburban myths wonderful One or two in every garage.

Graphite vs Kev-Lite

– Last Updated: Feb-06-13 9:13 AM EST –

Unless you really want the look of carbon I would go with Kev-Lite. The boats are built almost exactly the same way. The difference is that in the graphite boat the outer Kevlar fabric layer is replaced with a lighter layer of carbon cloth. This accounts for the slight weight savings. That and the black trim are the biggest differences. Here is a link to the Prism spec page:

If anything the graphite boat is slightly less tough than the Kevlar boat, as Jackl's experience has shown. This is because the carbon fabric doesn't have any tensile strength to it and it is a little bit thinner than the Kevlar cloth so there is less material to abrade in use.

Thing with these boats is that all of their structure and stiffness comes from the PVC foam core. It doesn't really matter what materials are used as far as how the boat paddles because there is an absolute minimum of cloth in the boat. If it were a standard layup composed of layers of cloth the order and type of fabric would have an impact on strength or stiffness. But since it is a rigid foam core layup this doesn't really matter as much.

Here is how Wenonah describes the layups:

The graphite boats aren't really stiffer in this layup. Maybe theoretically, but not practically. You'll never know the difference.

Bottom line?

Buy the Kev-Lite boat unless you really like the look of the carbon. If you like the look of the graphite and don't mind the extra cost, go for it.

Composites and Water Absorbtion
On water absorption:

Composite boats do absorb water, but it is the resin, not the cloth that does the absorbing. This is a particular problem with polyester resin in thicker laminates–much less of a problem with the vinyl-ester resin that Wenonah uses in it’s ultralight Kevlar boats.

In the sailboat industry people are aware of the problem of osmosis blisters in fiberglass hulls. These are formed when water is absorbed into the fiberglass laminate and undergoes a chemical reaction with polyester resin.

Here is a link to osmosis blister information:

This is not a problem with any canoe, since the boats are stored out of the water and have a chance to dry between use. But composite canoes and kayaks can theoretically absorb water.

Usually it is composite kayaks that will show a slight increase in weight with a little bit of water absorption. The enclosed hull of the kayak allows water to be trapped and absorbed in a high-humidity environment. And almost all kayaks are made with polyester resin. Storing kayaks with hatches removed allows air to circulate inside the boats and keeps water absorption to a minimum.

But–the effect is pretty minimal overall one way or the other. Certainly not something that people have to worry about.

For all practical purposes it’s probably safe to say that Kevlar boats don’t absorb water and gain weight over time.

Osmosis is a documented fact as opposed to a belief; air inclusions in Poly Ester resin allowing water in by osmosis over time.

That said, most builders now use VE resin, minimizing water transfer. Better builders also infuse, which completely eliminates air voids or wet bag which, when everything goes right, should also eliminate voids.

Lastly, Kevlar/Twaron is minimally hydrophylic, and, even when skin coated, as per the exterior on some, mostly race, boats and on the interior of just about every bagged canoe, is completely resin filled.

We’ve all seen skin coated boats in their second decade with resin flexed out of the fiber. Time for a new boat. Designs and construction have probably improved anyway!

Sorry, but
Sorry, I’m having a bad day concerning belief verse data based systems.

Common Kevlar, taffeta or crows foot weave, weighs 5oz per square yard. Carbon commonly available weighs between 5.7 and 6.3 oz per sq. yd.

Infused, we would assume ~45% resin content and more for the wet bagging system WeNoNah uses, so lets double fabric weight to arrive at approximate and comparable weights for the Minnesota firm’s laminations. Carbon is 5.7X2= 11.4oz/sq yd, Kevlar is 5X2= 10oz/sq yard. A Prism blanket layer will have about 5 sq yards of fabric, so the Kevlar outer skin weighs ~4lbs, the Carbon outer 4lbs 12oz. Yet the carbon boat is lighter. How can that be?

That is because while Kevlar is has great tensile strength it has poor compression resistance. It takes more Kevlar layers to build aqequate thichness to stiffen a hull. Carbon has marginal tensile strength but great compressive strength. Combining the two positive characteristics allows fewer and/or smaller partial inner pieces or layers to construct the boat. So, the half carbon boat weighs less because adequate stiffness is achieved by combining fabrics.

We can design a lamination schedule to any weight or strength we desire, but we cannot max strength and minimize weight at the same time. It is useful to remember that laminate thickness increases stiffness, just like increasing web on an I beam. Cores do this; the lightest being honeycomb, with foams, balsa and various poly mats following in ascending-weight order.


– Last Updated: Feb-05-13 9:35 PM EST –

Without a doubt.

My comments about the difference between the two layups were based on what the Wenonah boys told me back in the day. I talked to those guys a fair bit back when I worked at Rutabaga, and had a friend who built boats for them and worked in the repair shop. That's how they described the layup to me at the time. But they may have glossed over some technical aspects of the construction when they were explaining it to me. Which would explain my confusion on particulars.

Maybe they leave out two layers of Kevlar cloth and replace it with a single layer of carbon. Certainly plausible. I haven't seen the cutting schedule, so I don't know.

One way or the other, as you said, they are putting less material in the boat--either by using a lighter weight carbon cloth or by replacing multiple layers of Kevlar and selective reinforcement with a single outer carbon skin.

So the carbon boats are less durable, as you suggested and Jack observed.

My point, which maybe I didn't make very eloquently, is that it is pretty hard for people to tell the difference between these two particular layups on the the water because the stiffness in the Wenonah ultralight hulls comes primarily from the PVC core.

Given the thickness of the core, and the minimal amount of cloth used in the boats, the materials used outside the core don't have as much impact on the overall stiffness or paddling "feel" of the boat as they might otherwise.

Its hard to perceive much difference between the two hulls on the water. I certainly haven't when I have paddled them. So the decision of which to buy has to come down to other factors, like weight, cosmetics, cost and durability.

Which is why I was thinking it makes sense to go for the Kevlar. Unless you really want the graphite look. Or you really want to save those two pounds.


– Last Updated: Feb-06-13 6:37 PM EST –

Don't think I claimed the Carbon/Kevlar hull is less durable; you're putting your beliefs on my keyboard, and old, anecdotal, beliefs at that!

The combi, dual material layup may be more durable than the all Kevlar layup, maybe not, but it no doubt performs better in the context it was designed for; citizen racing.

Certainly Wenonah is not replacing two Kevlar layers with one carbon. Yes, Wenonah could special order atypical fabric weights, but chances are they do not. We'd need the lamination schedules, which are probably closely guarded, to guess at differential durability and fairly exhaustive testing to determine if any guess, even one based on real information, was correct.

OP should get what he likes, I do not consider either laminate a particularly rugged tripping choice.

Fair Enough
Apologies, I think I misunderstood your earlier post. Certainly not trying to put words into your keyboard.

Let me see if I follow correctly.

As I understand it you are saying that we can’t really tell if the carbon or Kevlar version of the ultralight Wenonah layup in the Prism is more or less durable unless we know exactly what goes in it.

And we shouldn’t assume that one is more or less durable than the other because one has carbon and the other has more Kevlar.

Have I got it straight?

Considering the potential difficulties of finding out the exact laminating schedule for the boat, do you think there is a reasonable way for a person to choose between these two layups if he is set on buying a Prism?

What would be your advice to Duckhunter in response to his initial question?

Anectodal UL experience
I do a lot of Canadian Shield tripping and one of the facets of UL boats is the foam core added for stiffness.

I managed to wreck a UL boat as it folded around a rock in Temagami. There was some foam core damage…rather difficult to fix.

My understanding is that foam is added to stiffen the bottom. Since that miserable experience in which I owed my life to a roll of duct tape to get the 100 km to nearest town, I have gone with CF/Kevlar boats without a foam core. The CF adds enough stiffness to make the core unnecessary.

Just wrapped up another two weeks of paddling with such a boat in Florida which has surprise surprise, limestone laden rapids and oyster bars… each of which will literally slice a skin covered boat.

I am pretty hard on boats. Never again any UL all kev layup for me.

BPD, I think you’ll find that there are
no longer any makers of quality canoes or kayaks who are still using plain ol’ polyester. I think vinylester is getting to be near universal. There are just a few builders using epoxy, which is even more resistant to hydrolysis, but more expensive and apparently not amenable to the new infusion process.

My experience
When I had my Savage River-carbon/kevlar with an extra layer of kevlar with intrigal gunnels, It once fell off the top of my pack frame onto solid rock bounced and fell another 10’ onto another round rock-no damage. I also once collided with a rock head on in fact current-a little chip.Also ran a lot of beaver dams loaded. I was very pleasantly surprised both times!