Carbon/Kevlar Blend compared to fi/glass

Anyone have any special insights comparing the strength and durability of these two materials?

Some lightweight carbon/Kevlar layups
would be less durable than some fiberglass layups. A carbon/Kevlar boat might be nice and stiff and also very light, but might not be able to withstand the big hits expected in whitewater. You have to decide what use the manufacturer intended when the layup was designed.

I have owned several fiberglass boats, and have hammered them in whitewater. They stood up quite well. But they weren’t very light. My only boat having carbon is a slalom c-1 with S-glass outside and carbon inside. Very stiff, fairly light, but while it has never broken, I know that it is too rigid to take a big hit. It would hold up better with some Kevlar for the inner layers.

I don’t know of any canoe builders who are offering carbon outside/Kevlar inside boats that are too flimsy for the intended use. However, so far as I know , NO ONE offers a carbon outside/Kevlar inside canoe for whitewater. The most experienced whitewater builder, Millbrook, routinely uses S-glass outside/Kevlar inside. I have two Millbrooks, and they handle hard hits pretty well, though not as well as Royalex.

Carbon is stiffer and lighter than S-glass, but when used as an outside layer, carbon abrades easily. S-glass does not. S-glass is a bit tougher and less brittle than carbon, but glass is much heavier than carbon cloth, and heavier than Kevlar. Decisions, decisions.

I guess I would always take Kevlar over carbon or glass, since it really combines the best of both. High strength with light weight. Depends on the situation.

Whitewater aside I would go:

Carbon for racing. Its stiffer than glass or Kevlar, but a lot lighter than either.

Kevlar for long distance tripping. It is light enough to be pleasant yet tough enough to withstand daily abuse.

Glass for everyday general use. It’s cheaper and relatively light and tough.

Personally I think fiberglass is an almost obsolete hull material, since it does not offer enough for the price to sway me over a Kevlar boat. Usually Kevlar can be had for around 1000 more, and when you break that down over the 20 years of its life you are not looking at a very significant cost. I think poly might be a better choice as far as cost VS strength. Glass is probably more easily repaired than poly or Kevlar though.

Kevlar can be a little tricky for repair because if you sand it it turns into a wild mess of fuzz. I don’t know about carbon. If you are looking for a general use composite boat, my recommendation is Kevlar.

Yeah, cap… you can make a boat
entirely out of carbon, Kevlar, or glass. But realistically, an all carbon boat is kinda brittle, no matter how stiff, and the exterior abrades easily. There are all Kevlar boats on the market, but the mediocre compression strength of Kevlar makes it a mediocre fabric for the outer layers of the boat. And, Kevlar fuzzes badly when worn. As for glass, my E-glass boats were pretty stiff and pretty durable.

The best way to lay up a composite boat is to use a high compression strength cloth for the outside layers, meaning glass or carbon, and a fabric with maximum ability to resist propagation of splitting or tearing on the inside, meaning Kevlar.

Back in the 80s, Charlie Wallbridge published the Boatbuilders Manual, which included tests of various 4 layer cloth combinations. (I believe they used epoxy resin for the layups.) The tests were related to whitewater durability. The best combo was SS/KK, meaning 2 layers of S glass outside and 2 layers of Kevlar inside. SKSK was close. No other single cloth (they tested carbon) did as well, nor did any other combination.

So, you can buy a single cloth boat, but you shouldn’t. Not if you want a stiff boat that isn’t brittle.

Are you talking about…
separate layers of carbon and kevlar or the combination weave? I had the combination weave and it was very stiff and light.

Hmmm much has happened
since the 80’s in composite technology. Dupont spent millions on selling Kevlar 49 to the outdoor industry…very successfully. I would not, and will not have it in any surf or touring boat I own, and I have a lot of experience with the material. Poor compressive strength, poor long term stability in a flexing matrix, hydroscopic, more difficult to repair, inter-laminar breakdown over time…bla…bla. Yacht folk know this by now, which is why we rarely see it anymore. Ever wonder why we don’t see Kevlar in bike frames, sailing masts, most paddles, etc… The misconceptions around composite materials are huge with kayakers and I for one am too burned out to challenge it.

Kevlar 49 is perhaps the most over-rated material, whilst good old glass is the most under-rated. I could explain why but I’m tired.

Buy what you like and go paddle it…

I guess I assumed it was understood
that Kevlar, etc boats were made using glass as well.

I guess I assumed it was understood
that Kevlar, etc boats were made using glass as well.

BI-Weave Woes

– Last Updated: Dec-14-09 9:20 AM EST –

Bi Weave fabric is cool to look at. It is also pricier than all carbon fabric, despite that Kevlar is ~60% of carbons price per unit weight.

The downside of bi-weave is that it combines high tensile strength material with high compression strength materials in one layer of a composite. If that layer is stressed, the Kev tends to stretch, which over stresses the carbon. If a stress point, say a rock, aligns across the carbon the carbon can "zipper" open as the Kev elongates.

Better laminate engineering would have stiff Carbon or S glass as outer layers and high tensile strength Kevlar used as inner layers. The stiff outer resists deformation, the tensile layers reinforce the notch sensitive compression layers.

Note the s in layers. Bell Black/Gold hulls have three full blankets and multiple shaped and placed partial layers. The Average Placid boat has 38 separate pieces of fabric. Colden's first FlashFire had 43 pieces of fabric in the mold. Other manufacturers practices are similar. Also of note, Bells "Tweed" inner is 3/4 yellow Kevlar 49 and 25% black Kevlar 29. It looks cool and hides partial lines. 49 is the structural Kev/Twaron normally resinated; 29 is the treated variant used unresinated in ballistic apps such as bullet prove vests.

All that said, we're trying to replace Kevlar for the reasons listed above; hydroscopic, frays, hard to cut, etc. Spectra or Dynema hasn't worked out because it requires a surface treatment to accept resination and that treatment has a short, 1-3 month shelf life. Using first in-first out inventory management places aging Spectra in composites, which then tend to delaminate. The alternative is even higher costs as the stuff is sent back to the mill for re-treatment or pitched.

Another tensile layer[s] option is Vectran. We've seen it combined with glass, which makes no more sense than combining Kevlar and Carbon. It is wildly pricey, pretty much unavailable and must be cut with a hot knife, but may replace Kev as inner laminae in paddlecraft if/when pricing and availability improve. Vectran is currently used by NASA for balloons, tethers, etc. A minimum buy in weights/weaves/widths appropriate for paddlecraft includes a $10,000 loom set up fee, so vectran requires a huge commitment.

Replacing Kevlar with Vectran will reduce hull weight and increase production costs. We figure 2.5 lbs saved in a 12 foot solo hull. A 2.5# reduction from a C/K skittle that weighs 14# is a whopping 20% weight savings on the hull. Trim and outfitting remain the same, so finished hull savings is 10%; still pretty heroic. The hot knife to cut it is a $1500 item, and a heat resistant cutting table is required. Vectran does come in attractive colors, and would carry that NASA cachet, if there still is one.

Both products are woven by the same plant, so the pros and cons discussion points can be assumed to be valid.

More to the initial point, bi-weave looks cool and hides partial layers but doesn't justify its cost or make engineering sense. I particularly like the look of Kirton ICF hulls alternating Twaron and carbon in both warp and woof.

No one is mentioning the ease of repairing plain old glass and gelcoat. It may be heavy, compared to the the composite boat out there, but once it’s in the water does it really matter? I crash my boat into rocks, sea cliffs, other boats, etc. At the end of the day it’s about ease of repair and availability of mat’l. Perhaps the cost of repairing that fancy composite boat prevents the paddler from really beating up on it.

Paddle it like you stole it!

My surf boat of Vectrane / glass
is holding up well after a few years. Better than Kevlar Carbon versions of the past. However, Stoddard Aerospace, who built my boat, says lab testing of the Vectrane panels yielded mixed results and didn’t live up to the spec sheets?? They were a bit disappointed.

Eddyline also messed with it a bit with their Modulus construction and had issues. But those were related to different material expansion rates.

While agreeing that gel coats make sense in UV deterioration, damage control and easy of repair, the differences in repairing glass, Carbon and Kev are minor. Carbon resinates and sands as easily as glass.

Kev/Twaron frays when cut and peel ply is needed to get patch edges to lay down, which is a requirement because they cannot be sanded smooth. That said, peel ply is available in small lots from Jamestown and Sweet, and peel plying patches is easier and safer than sanding glass or carbon, so, in essence, all three repair the same.

Just have to say again, Salty, that
none of my Kevlar/whatever boats have had the problems you cite, in spite of hard pounding, and I don’t know of any others in the whitewater community who report such problems. This is not to discount the lessons learned in composite sailboats and composite boats. But that inside Kevlar layers have worked well, better than available alternatives, in whitewater boats is just a fact.

Plastic food film works as well as
peel ply for small patches. Especially if you don’t ask for perfection, which doesn’t last long in whitewater.

Besides, Kevlar is mainly an INSIDE patching cloth. Outside patches are going to be glass or carbon, and it’s outside where one wants perfect smoothness anyway.

Your experience is valid, and
you have heard me repeatedly state that good boats can be made with Kevlar. I believe that, especially when combined with glass.

My experience has been with surf and touring kayaks where a lot of flexing occurs, and slamming on drops etc. The material has not held up for me, as well as other choices, especially long term.

Like I always say, buy what you like and believe in and go use it. For me that’s not Kevlar 49.

The difference in the kind of blows that
are destructive might be the key. A typical killer blow in whitewater is similar to having a low-speed car crash. The hull is forced way in from the side or bottom, and the inside Kevlar layers are put in tension. I can see where surf incidents, such as pitoning or certain kinds of slams, might put inside Kevlar in compression, where it is no better than E-glass, maybe less so. Almost all of the damage done to my boats is little compression cracks in the outside S-glass, with the Kevlar inside usually showing no disruption.

I can see that there might be problems making longer craft with Kevlar inside, unless other means are used to control compression along the long axis of the boat.

Tastes Great! Less Filling! NM

I think the niche for 'glass over poly is for the individual who cares not about weight, but wants a bargain canoe that is aesthetically pleasing and well designed. I would much prefer a 'glass canoe for soloing around a cottage than a plastic one (comparing, say, an Esquif Champlain to an OT discovery - and yes, their is a price difference, so I would also rather have a 'glass nc prospector than a poly one if flatwater was the use).

Glass can be repaired easily, too.

special insights
thick and heavy laminates are stronger and more rigid than thin ones.

Red and white is faster than black or blue.

The fancier laminates reflect a consumer base willing to spend more for marginal reduction in weight.

If I had a finite budget to build a kayak I’d want a painted all s-glass kayak over a carbon/kevlar kayak with or without gel coat.

Btw has anyone heard of HiPer-tex fiberglass? It looks to be a better material for the money than carbon or e-glass.

I wish I hadn’t lost that book