Kevlar / carbon-- Worth it?

D

Dave Archer

New member
I completed by duck boat and have quite a bit of Knytex X-Mat (bi-axial fabric). I have a ten-foot river pram that is old and very heavy. I plan on using it as a male-mold. I have lost a lot of range of motion and strength in both shoulders. I really need to keep the weight down on this river pram in order to load it in the back of my truck on occasion. It will have a top deck and lots of enclosed foam. I loved the material Lou recommended. If I stay with the X-Mat, I would probably only need two layers of X-Mat and two layers of mat, maybe less. My question is this. Would I really gain from using Kevlar as one layer? I can't really afford it for this last boat project (sniffle...). But I am keenly aware at 68 that constant pain in both shoulders and a loss of strength is only going to get worse. If you have had experience laying up a small fiberglass boat using these exotic and very expensive materials, I would really like to hear from you. What would the layers be? X-Mat first followed by Kevlar and then topped with a layer of mat? This pram would be used on the Bitterroot River in Montana. The river is an easy to navigate river in the summer, but boats take a banging on the shallow riffles.

Dave Archer
 
The river is an easy to navigate river in the summer, but boats take a banging on the shallow riffles.

Dave Archer

I have been told that kevlar is less abrasion resistant than glass cloth. Don't know if it's true.
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The river is an easy to navigate river in the summer, but boats take a banging on the shallow riffles.

Dave Archer

I have been told that kevlar is less abrasion resistant than glass cloth. Don't know if it's true.
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Not true, abraision resistance is an important use. The reason that I think people say that is because ultralight kevlar canoes are often damaged. They are light and very thin (and can be made so because kevlar si very strong per weight). Because of the thin-ness they are a bit fragile. Our big 17' kevlar is only i layer of 5 ounce cloth in places and 2 in others, if you made a canoe with unsupported 5 ounce glass, it would fail before you even got it out of the mold, so kevlar is often "weak" because it is put on in a thin layer. A glass boat to have the same strength can be twice as heavy and require many layers of cloth.
 
I didn't say Kevlar was weak--I said it was not resistant to abrasion. My canoe racing friends love Kevlar boats for their light weight and high strength, and if you whack a rock hard in the rapids with a Kevlar boat, it resists breaking (impact resistance) far better than fiberglass would. This very high impact resistance is also what makes it ideal for bulletproof vests.

But my firiends say their Kevlar boats do not stand up well to repeated scraping over rocks, gravel or sand. Many of them go so far as to "wet foot"--they won't beach the canoe before unloading it. I know folks who make their own canoes, and while they may use kevlar for strength and light weight, they usually put a surface layer of something else (often S-glass) at the stem and stern, where abrasion is going to be an issue.

There is some more information from a canoe perspective here: http://www.outdoorplaces.com/Features/Paddle/pickcanoe/newcanoe2.htm
 
I'm not sure how it is used in canoes but on my current sneak boat build I have a layer of kevlar on the outside of the hull with a layer of 6oz glass over it. I accidentally sanded through the glass at one point and a high-speed wheel with 80 grit only fuzzed the kevlar a bit, and didn't burn through it. I thought the whole advantage of using kevlar in boats was abrasion resistance?
 
I didn't say Kevlar was weak--I said it was not resistant to abrasion. My canoe racing friends love Kevlar boats for their light weight and high strength, and if you whack a rock hard in the rapids with a Kevlar boat, it resists breaking (impact resistance) far better than fiberglass would. This very high impact resistance is also what makes it ideal for bulletproof vests.

But my firiends say their Kevlar boats do not stand up well to repeated scraping over rocks, gravel or sand. Many of them go so far as to "wet foot"--they won't beach the canoe before unloading it. I know folks who make their own canoes, and while they may use kevlar for strength and light weight, they usually put a surface layer of something else (often S-glass) at the stem and stern, where abrasion is going to be an issue.

There is some more information from a canoe perspective here: http://www.outdoorplaces.com/Features/Paddle/pickcanoe/newcanoe2.htm
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Sand some kevlar if you want to experiance its abraision resistance compared to glass. The kevlar boats don't stand up to rocks and people wet foot their boats (I do too) because they are thin. Thick kevlar boat are not made, because it wouldn't make sense. If a kevlar hull was equal in thickness to a typical glass boat, it woudl weigh about the same as the glass and you woudl never wear through it.
 
I'm not sure how it is used in canoes but on my current sneak boat build I have a layer of kevlar on the outside of the hull with a layer of 6oz glass over it. I accidentally sanded through the glass at one point and a high-speed wheel with 80 grit only fuzzed the kevlar a bit, and didn't burn through it. I thought the whole advantage of using kevlar in boats was abrasion resistance?
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Yes it is. My experiance is the same as yours with sanding.
 
Dave:

I went back and reread your original question. It sounds like what you are interested in is getting a structurally sound boat that is as light as possible. I don't know the dimensions of your boat, but at 10 feet, you ought to be able to come up with something very light.

While you could play around with various combinations of glass/carbon/Kevlar/other fabric to reduce weight, I think you can probably do far more to restrict weight on the design side. In particular, having a top deck and enclosed foam is likely going to add a lot of weight.

I suspect you can realize bigger weight reductions by thinking critically about design and reducing absolutely any surface or structure you don't need than you can by playing with materials. For example, instead of a top deck, could you use a fabric cover or spray shield? Instead of a large amount of enclosed foam, can you incorporate a hull material that will be bouyant without added floatation. (Some composite canoes and kayaks incorporate thin sheets of foam into the laminate to add both stiffness and floatation. Can you save the weight of a gelcoat layer?

Most importantly, I think if you want to save weight, you want to stay away from fiberglass matt. Matt will soak up a lot of resin, and that will add weight a lot faster than you can take it away by changing what fabric you laminate with the matt.

The lightest canoes I see save weight by using strong and light fabrics, but they also eliminate any excess materials, minimize the number and extent of decks and other surfaces, and use vaccuum-bagging techniques to minimize the amount of resin needed to saturate the fabric.

All of that is going to be hard to do in a backyard build, but not impossible. (Though vaccuum bagging may be). At the end of day, I bet the difference between using carbon fiber or Kevlar instead of the material you have on hand is minimal compared to other ways you can save weight. And the bigger difference will be how much resin the cloth sucks up--not what the weight of the fabric is.
 
you might try calling the people at bell canoe works or wenonah and speak with them about your questions. they build fantastic kevlar and carbon canoes that can withstand the rigors of wilderness tripping in the canadian shield(granite and other hard things like that). i have several of the wenonah kevlar boats and they take an impact. the ability to take an impact also depends on the core(rigid/stiff or flex core) between the layers of kevlar. the rigid core is more efficient and loses less energy on stroke but not as impact resistance on head on hits. however, you are probably looking for a more flexible core in your layup for impact resistance. of my two boats, one has a gelcoat and the other just has a thin "skin" coat layer. the skin coat boat bottom(keel ends) are much more susceptible to abrasion. when this happens, the thin top layer rubs away and the kevlar gets fuzzy. i just touch up with epoxy and old 35mm film negative and good as new. you might think about a thin gelcoat and possibly a keel protector. my 16 1/2 ft kevlar canoe in skin coat weighs 39lbs. the 18 foot canoe in gelcoat weighs aprox. 55lbs and through repeated beachings and impact, the kevlar has never been exposed.

i would say that going from fiberglass to kevlar is worth the extra cost in weight savings. going from kevlar to carbon is shaving off just a few pounds for much more money. for example my 16 1/2 boat in carbon would weight around 30-31lbs but cost much more than the kevlar.
 
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Dave
With all your boat building experience, I'm sure you have heard of this technique , but Ill throw it out anyway. Many if not most wood driftboat builders mix graphite powder in their final epoxy coat which goes on the bottom of their boats. I have done this myself as it looks really cool, but I remain skeptical concerning its actual resistance to abrasion. Recently, an employee of mine who worked in some sort of charter boat business in Hawaii for many years claimed they used graphite on the bottom of all their fiberglass bottomed boats which were regularly beached on sandy shores. He did the annual maintenance on 4-5 such boats and was sold on the idea compared to straight epoxy.

For what it's worth.
Troy
 
Kevlar is worth it if you are putting your self into abrasive conditions...I would suggest before building to look a the Y-series canoes from Holy Cow company out of Canada. If you are doing a lot of portaging the weight advantage helps...Have trekked through the Quetico many of times in a the Sportsman series 16' without any problems.

Regards,
Kristan
 
I want to thank all of you who took the time to answer my question. Some of you wrote especially detailed responses and have challenged me to rethink. It is true that I have built lots of boats, but many of them have been tanks. It is essential that I build this little 10.5 pram as light as possible because I now have serious limitations on what I can lift and manhandle. I have never owned a canoe, and I was honestly shocked at the size and weight of some of the canoes that were mentioned. Oops! I wanted to thank by name but I forgot to jot down the names. It think it was Richardson who challenged me to rethink the design, especially the top decking and use of enclosed foam cells. Also having the names of commercial boat makers using kevlar really helps. I can see now that I was heading down the wrong path with my concept of layering and how kevlar is used. I have used graphite added to the last coat. It works great for slipping off rocks here in Montana. Again. thanks to all of you who responded. I had a set back when my 20+-year old Johnson 15 died. I replaced it with a Honda 15 four-stroke so my boat building fund is depleted for now.
Dave
 
Hi Guys - Build a line of prams and drift boats in Oregon under www.watershedboats.com (cheap plug - ha ha ) Ok - look at a triple weave product called Nytex - I use it in the chines and possible high wear or abuse areas - no getting away from starting layer of mat on your mold or inside chines - then for structual strength roving comes into play, as roving binds everything together and gives you strength through out your boat. for your first lay up you have to use matt but this nytex is awesome - strengh -but not only that - one layer does the job of 2 layers mat and one layer of roving - check it out. Now - (damn I should be paid for this info.) Check out Thermo-lite - Made in Portland. It's a fiber-reinforced urethand board made in 1/4, 1/2, 5/8 etc. Super lite and unreal as far as strength. You are going to see super light boats made out of this stuff - unreal - All for now
 
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