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Comparison of S-Glass, E-Glass, Kevlar and Carbon for Canoe Hulls

Glenn MacGrady

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How do S-glass, E-glass, Kevlar (aramid), and carbon composite fabrics compare in compression strength, tensile strength, stiffness, and weight—and where in a canoe hull should you put each fabric?

I've posted the following information, graphs and video buried in the middle of two build threads here, but thought the topic deserved its own thread for future searchers and researchers.

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Just considering strength, which is not the only factor in hull building and patching, you want a material with high compressive strength as the outside layer of a canoe hull, and a material with high tensile strength on the inside.

The green bars in this first chart show that S-glass followed closely by carbon have the highest relative compressive strength/weight, so that is why those two materials are frequently used as the outside layers of a canoe hull. Carbon is lighter and stiffer than S-glass, as can be seen from the red bars in the third chart below, so it is often chosen as the exterior layer to lighten and stiffen the canoe overall, but at a much higher dollar cost than glass. Kevlar is very low in compressive strength, so it is rarely put on the outside of the hull. The exception is the rare all-Kevlar hull, which might be made simply to prioritize total canoe weight as much as possible because Kevlar is lighter than glass or carbon.

compressive-strength-to-weight-jpg.131843


For the inside hull layer where you want tensile strength, this second chart shows the relative ultimate tensile strengths. S-glass is the strongest here, too, followed in a close almost-tie between Kevlar and E-glass.

ultimate-tensile-strength-jpg.131844


So, to build the strongest canoe, the first two charts above would suggest S-glass on both outside and inside of the hull. And, indeed, such canoes are made. But they are heavy because fiberglass is much heavier than carbon, which is slightly heavier than Kevlar.

The blue bars on this third chart take fabric weight into account and show the relative tensile strength/weight of the fabrics. Kevlar is very commonly used as the inside layer of a composite canoe hull because its tensile strength is high and its weight is the lowest, resulting in the best tensile strength to weight ratio by a significant margin.

relative-tensile-strength-to-weight-jpg.131845


Kevlar would also be a very good choice for an inside patch on a hull because of its tensile strength and low weight. However, there are other considerations besides tensile strength and fabric weight for an inside patch. On a wood strip canoe, for example, one likely would want the internal patch to be as invisible and transparent as possible so that the wood will show through. Only glass is transparent, and no one would likely want a yellow Kevlar patch on wood.

In addition, Kevlar is harder to cut, easily frays, is hard to sand, and is generally reputed to be harder to work with than fiberglass. That's why even on a canoe with a Kevlar interior an inside repair may be made with fiberglass instead of Kevlar, unless the repairer is quite experienced working with Kevlar. Even then, transparent fiberglass may be preferable for aesthetic reasons if the the new Kevlar patch can't be closely color matched to the older, sun-darkened Kevlar hull interior. This aesthetic factor for a patch may not apply to a banged-up, dedicated whitewater canoe with a Kevlar interior.

The three charts above were taken as screen shots from the following video, which compares the different composite fabrics in even greater technical detail:

 
Like the charts Glenn. Up until last year I had never dealt with kevlar. After working with it for a little it is not to bad. Just make sure you have a good pair of scissors and pay attention to the wet out.

Very interesting about S glass. Sounds like the best all around go to material. Wish we could get it in wider rolls.

Here is another video of someone comparing Carbon, Kevlar, Innegra and Diolen. I thought it was interesting also.
 
Very interesting post, Glenn.

When I was looking around for a new solo sport canoe this winter, after narrowing it down to two models with similar hull designs, I learned about their hull layups. I wanted something that was light and relatively durable, but didn't need a true whitewater layup. I wanted to be able to paddle Class 1 and occasional Class 2 rapids without worrying too much about glancing off a rock or scraping bottom in the shallows.

The layups that surfaced to the top were laminations of carbon outer combined with Kevlar/aramid inner using a vinylester resin. (There was a third builder that has a similar layup option but didn't have the canoe design I was after.) The big difference between the two builders was one of them offered a reinforcement outer build up of S-glass for increased durability. I think that's probably the best combination (the third builder uses it) but I ended up ordering from the builder that didn't offer the S-glass option. I'll mainly be paddling flat water and quick water rivers so the extra durability isn't critical. Still, it would have been nice to have that extra reinforcement for peace of mind.
 
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I liked the way "Kyle Engineers" approaches this presentation, the speaker obviously knew what he was talking about and the info is easily understood. Watched it last year and would also suggest a second video he does talking about making composites using different materials, can be found here


Helped me understand a bit about placement of various layers when going beyond a simple 2 layer composite

Brian
 
The caution of using carbon and e-glass in a composite layup is interesting but I'm still convinced that the carbon/Kevlar plus s-glass combination is a darn good one. He did mention the warning was mostly for amateurs and I'm pretty sure builders like Dave Curtis, Ted Bell, John Diller, and others know what they're doing. 😉

His presentation had a few unexplained caveats and assumptions (at least for this layman) and used a bit of hyperbole but he did have a point regarding elasticity and breaking strength.

I found the descriptions/videos of the composite layups available from Hemlock Canoe Works, Northstar Canoes, and Savage River to be educational and helpful in understanding the benefits and disadvantages of each layup. Savage River in particular has a helpful interactive chart for composite material strength and stiffness with the ability to add reinforcement options to see how they would improve those parameters.
 
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The caution of using carbon and e-glass in a composite layup is interesting but I'm still convinced that the carbon/Kevlar plus s-glass combination is a darn good one. He did mention the warning was mostly for amateurs and I'm pretty sure builders like Dave Curtis, Ted Bell, John Diller, and others know what they're doing. His presentation had a few unexplained caveats and assumptions (at least for this layman) and used a bit of hyperbole but he did have a point regarding elasticity and breaking strength. It may be that a carbon/s-glass layup could potentially have problems.

I found the descriptions of the composite layups available from Hemlock Canoe Works, Northstar Canoes, and Savage River to be educational and helpful in understanding the benefits and disadvantages of each layup. Savage River in particular has a helpful interactive chart for composite material strength and stiffness with the ability to add reinforcement options to see how they would improve those parameters.
In the video he specifically talks about wrapping carbon on glass .... so 3 glass topped by a carbon = BAD .. .. however ..... 3 carbon topped with glass = good

I think the point he is making, is to understand how each layer will play with the others ... it isn't just mixing layers, it's mixing them in the right order to get the characteristics you want. You can bet the professional builders have done just that and there is a lot of engineering that goes into those layups.
 
I have to confess that I didn't watch the entire video. I stopped near the end. It is useful information but I was more interested in learning about s-glass.
 
I have to confess that I didn't watch the entire video. I stopped near the end. It is useful information but I was more interested in learning about s-glass.

The confession side of this, is that I ran across these videos and several others, last year, I am planning my next build for spring. To make it work I needed to use some higher performance materials and S glass was the pick.

.... and Jim if you are reading this, I have secured 20 yards of 4 oz x 60" S glass, for the next build and the plan is to also go stemless.


Brian
 
I was wondering about the glass wrapping on strippers. If there was a good reason to use s-glass vs e-glass.
It really comes down to your build goals ... we don't all want the same thing. In my case, I portage the canoe, sometimes a fair ways and I am conscience that as I get older, weight matters .... a lot. So if we put weight as an important factor in a build, the following points give an idea of why you may want to use S glass instead of E glass.

S glass is more expensive and about 40% stronger than the equivalent weight E glass. So to replace the standard 6 oz E glass used for most strippers, with a roughly equivalent strength S glass would require a 4 oz cloth. Obviously, you could swap 6 for 6 and take an increase in strength, so there is a choice, save the weight or take the strength .... in my case, I have chosen to spend the performance on saving weight.

The 6 oz cloth is roughly 8 mil thick and 4 oz is roughly 6 mil, meaning that the 4 oz cloth will weigh about 25% less than the E glass, once wet out. The 6 oz glass sheath on a 15' boat will weigh in the neighborhood of 12 pounds. Substituting 4 oz S glass in a build should save about 12 x .25 = ~3 pounds on a typical build, while providing a similar strength as the 6 oz E glass.

The abrasion resistance is just a bonus to using the S glass.

To answer your question honestly, there is no good reason to substitute S glass for E glass on a regular strip boat build, the E glass is plenty strong, is less expensive and only moderately heavier. However, if you start pushing away from "regular" and want to save weight, (as in this example) while maintaining strength, then better materials make sense as a way to achieve the goal.

Brian
 
Brian, seems reasonable. Saving weight usually comes at a cost. For many of my recreational hobbies it's well worth it.
 
Awesome Brian !
I'm confident your build threads will far surpass mine ! Looking forward to you experience!
I've been tied up at the shop lately. I did get outwhales cut for my Stripper. Maybe pick up some Bell aluminum gunnels for the Kevlar. I will see how things go this Spring.
 
Thanks for the Post Glenn !

Some great charts to enlighten us !

Jim
 
It really comes down to your build goals ... we don't all want the same thing. In my case, I portage the canoe, sometimes a fair ways and I am conscience that as I get older, weight matters .... a lot. So if we put weight as an important factor in a build, the following points give an idea of why you may want to use S glass instead of E glass.

S glass is more expensive and about 40% stronger than the equivalent weight E glass. So to replace the standard 6 oz E glass used for most strippers, with a roughly equivalent strength S glass would require a 4 oz cloth. Obviously, you could swap 6 for 6 and take an increase in strength, so there is a choice, save the weight or take the strength .... in my case, I have chosen to spend the performance on saving weight.

The 6 oz cloth is roughly 8 mil thick and 4 oz is roughly 6 mil, meaning that the 4 oz cloth will weigh about 25% less than the E glass, once wet out. The 6 oz glass sheath on a 15' boat will weigh in the neighborhood of 12 pounds. Substituting 4 oz S glass in a build should save about 12 x .25 = ~3 pounds on a typical build, while providing a similar strength as the 6 oz E glass.

The abrasion resistance is just a bonus to using the S glass.

To answer your question honestly, there is no good reason to substitute S glass for E glass on a regular strip boat build, the E glass is plenty strong, is less expensive and only moderately heavier. However, if you start pushing away from "regular" and want to save weight, (as in this example) while maintaining strength, then better materials make sense as a way to achieve the goal.

Brian
Brian - Awesome information.

When using smaller material width wise. How much overlap do you need to keep the strength? Generally I can only find S-glass in 30" width. Do you mind sharing where you found the 60"?
 
Brian - Awesome information.

When using smaller material width wise. How much overlap do you need to keep the strength? Generally I can only find S-glass in 30" width. Do you mind sharing where you found the 60"?

Sweet Composites ...... 6522-60" 4 oz S Glass they were very good to deal with

As far as overlap in width for strength, I have never done that, so no clue .... personally, I would avoid that id at all possible, it seems a lot of work when you can just buy the right stuff for the job.


Brian
 
Great thread. I feel much better informed about fabric selection. Brian. I'm in the "same boat" as you. Getting older, and realizing I portage more than I thought when I started my first build. I was weight conscious, but not miserly with weight. Portaging a 58 lb. canoe plus pack in BWCA made me realize 216 rods is longer than it used to be, and 90 lbs is heavier than it used to be. Next build I'm going to put more emphasis on minimizing weight.

Jim: Thanks for steering me here.
 
Sweet Composites is Davey Hearn, a legend in slalom racing.. bought my kevlar and dynel and peelply from them, good supplier.

I have a kevlar boat, SS from Empty Canoes in MT. The builder recommended kevlar patches for interior, s-glass on exterior.
The recent slalom races at Wausau WI were hard on me and my boat, have a good deal of patching to do now..
Pic is my boat but not me, my friend Jeff borrowed it for one of his runs..

jeff little drop.jpg
 
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