e-glass vs. aramid/kevlar vs. carbon

I'm looking into producing some fiberglass canoes for retail sales. Want to keep it small scale at first and will probably just go with e-glass and polyester resin.

After, I'd like to look into more performance, light weight hulls.

For a canoe/kayak that sees fast rivers and rocks, is it appropriate to have carbon fiber in the hull? I know an all-carbon fiber hull would not be a good idea without some sort of fiberglass layer over it.

I received a sample from a vendor of a stitched multi-layer fabic. It's a 3.7 ounce carbon at 90 degrees (for hoop strength) layered with 4.5 once kevlar, 45 and -45, with 3.84 ounce e-glass on one side at 90.

So it's

e-glass 90 degrees
aramid 45 degress
carbon 90 degrees
aramid -45 degrees.

The carbon is not constant. It's in a zebra pattern alternated with e-glass.

The rep says it would be the best but I'm not sure if he's just trying to push that product or what. For a paddled boat that is meant for use and some abuse, does carbon even belong in it?

The Kruger Canoes boast of multi-layers of Kevlar/aramid. I have one on loan and it's layers woven kevlar, covered by poly fabic and s-glass. Would axial be that much better? Would they benefit from carbon?

I've heard one fiberglass shop say that for equal strength, using aramid/kevlar does not yield enough significant weight savings. Not sure I'd agree but what does everyone else think?

 

sounds like an interesting fabric

I'd like to see some figures on it

 

Jem,
An issue to consider is that in a fiber-composite you have two different materials. If you deform a composite enough to make the matrix resin fail, it doesn't really matter what the fibers are made of. In the case of carbon, the fibers will fail too, and turn into nasty shards, in the case of aramid, the fibers will tend to stay together, but, regardless, the composite has still failed.

Yokebutt.

 

Who makes that fabric? It sounds very interesting.

Aramid is a fantastic material overall but its expensive and hard to come by these days just by itself. For the most part it is easiest to find materials that are hybrids, like the one that you found.
That material recommendation sounds good but one thing I'd consider if I were you is adding a little extra reinforcement in the areas that are at the most risk. I guess for your canoes that would be the bottom, underwater portion if the rower happened to ground it on the rock in a river. If can come by some pure aramid fabrics it probably wouldn't hurt to add a light layer on the outside below the waterline.

 

I think you can make your canoe or kayak lighter and stronger with the composite materials, but beware of the problems with water egress. Kevlar loves to wick up water. Not sure about Carbon. We used some Kevlar eons ago in some large industrial Neoprene/Hypalon fabric tubes for Zodiac RIBs and found to our surprise a couple of gallons of water in the tubes after only a week or so sitting at the dock. I cannot remember the name of the company, but there was a kayak maker around Seattle that was solving the problem, so he claims, by vac-forming a light and tough poly shell into his female mold, that he then vacuum bags his Kevlar composite fabric inside of. If I remember the advertising, the outside shell is tougher and better than gelcoat while similar in weight.

RWL

 

Carbon's advantage is that it is very stiff for its weight, and very strong. But it is also brittle and, as Yoke says, makes nasty shards when it fails. Kevlar is stronger than glass for its weight, but generally doesn't give as stiff a laminate as carbon. For a canoe this could be a good thing...
Everyone has their own pet favourites, and every manufacturer naturally claims superiority. What I would do is to make samples a foot or two long of your different proposed laminates, and bend and twist them till they fail. This will give you at least a bit of an idea how your proposed laminates compare to each other.

 

Another important factor to consider is density, glass is about 2.5, (density of water is 1.0) carbon around 1.7, aramids about 1.4 and spectra about 0.9.

Yokebutt.

 

If this is a whitewater boat, I'd suggest kevlar, or spectra or dyneema cloth as yokebutt suggests. All of these fabrics are much harder to obtain, and to work with as they float in the resin. Any of those cloths in a high elongation resin will probably rebound from abuse nicely. I'd steer clear of carbon fiber if this boat will ever see sharp corners. Unless you have some sort of strength or stiffness problem, the carbon is only going to reduce the damage tollerance of the laminate.

 

Kevlar soaks up water and is useless in compression. The molecule structure of the fibre buckels under compression which leads to debonding of the fibres from the resin.

What you want is a tough laminate. First get a tough resin with high extension before tension failure. Epoxies are best and polyesters are usually the worst. Then look at the fibres and also use the ones with most elongation before failure. E glass is usually quite good and is also good against abrasion. I would think about a foam core. This makes the hull much stiffer without adding much weight. Besides that it acts like a bumper. You can break the outer skin and the inner skin stays intact and can ensure that the boat is not going towards the bottom. Look into CoreCell or PVC foams that are not cross linked for tough cores.

 

JEM What would the canoes be disigned for? Are you talking whitewater or merely a design to used in moving water? Is this a small whitewater canoe or a larger tripping style?

Generally I would stay away from carbon, if these are general purpose canoes. I know people like the stuff, but if it's not being built for competition; then the customer would have to have dig a bit deeper than most whitewater canoe customers choose to.

As for Kevlar on the outside of a whitewater hull, Forget it! It's really low in compressive strength (as mentioned), and as it abrades it will pile up (make little balls). It is really good on the inside of the hull (laminate stack) due to it's high modulus of elasticity and high tensile strength. Kevlar is nice, as it will also : 1) will hold the laminate together long enough to get downriver and home 2) help make patching easier, as the two side stay reasonably lined up usually (2facts-of-canoe-life, whitewater at least).

Good Luck

 

I just want to echo the person who suggested Core Cell as a good coring material for your application. That stuff is simply outstanding and I would recommend that over the PVC foam cores (such as Divinycell). Since it isn't an organic material like balsa it won't rot if water gets into the laminate. Core Cell's A-Foam is thermoformable (if that matters to you) and is a little more ductile than cross-linked PVC foam core.

 

Thanks for the replies. Project is in development for my own design and future customers. No whitewater. Just the occassional fast moving water and hard bump against a rock or log.

 

Buoyancy is always necessary. Aramid sounds nice for a little extra strength. Take a look at other body-armor materials, perhaps that may help.