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  carbon vs. kevlar
  Posted by: old_user on Apr-23-08 1:13 PM (EST)
   Category: unassigned 

which holds its shape better at high speeds, 6-plus mph? people say stiffer is better, and i just wonder if paying the extra money for carbon is worth it. i paddle marathon canoes, so any percentage of a mph is a plus.

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Messages in this Topic

 

  Sounds like a Charlie Wilson question.
  Posted by: string on Apr-23-08 1:46 PM (EST)
I thought the advantage of carbon was weight savings.
 
 
  Carbon
  Posted by: salty on Apr-23-08 1:49 PM (EST)
-- Last Updated: Apr-24-08 7:47 AM EST --

Kevlar is NOT stiff, and weak in compression, yet strong in tension. Discussing materials on this site will only lead to more confusion. Opinions based on years of marketing influence tend to rule, and Kevlar is a "holy" material with kayakers it seems.

Kevlar is used in race hulls for it's weight advantage, but you also see heavy use of core materials to take care of the stiffness issue. Epic's elite lay-ups with Nomex core are a perfect example. Kevlar, un-re-enforced makes for a soft boat.

As much as it is misunderstood so is Carbon. Carbon technology has exploded and carbon is stiffer, and very strong. Bike frames, exotic car body parts, fishing rods, aircraft skins, race yacht hulls, etc. You don't see as much Kevlar in these applications if at all. There are reasons for that not worth confusing folk about.

Now, before the Kevlar lovers call me out as slamming their beloved material....IT CAN MAKE FOR A GREAT KAYAK AND HAS VALUE IN THE RIGHT APPLICATION. There are many great uses of Kevlar in paddle sports. Again, where light weight and impact resistance are important it's a good choice, when the laminate is well engineered.

I prefer carbon glass laminates that are cored as well. These are likewise extremely tough regarding impact, and very stiff.

 
 
  I can't
  Posted by: OldBill on Apr-23-08 3:04 PM (EST)
Give you a technical answer but when you go to a big marathon race all the top boats are black.
 
 
  carbonite plus kevlar
  Posted by: pagayeur on Apr-23-08 4:30 PM (EST)
CEW can explain this much better than I but here goes: kevlar has many strengths but lacks tensile strength. In other words it is a bit brittle and could crack. Carbonite is light and has good tensile strength so the combination of kevlar and carbonite makes for a stronger lightweight hull. Plus, black and gold is a good color combination.
 
 
  "Lacks Tensile Strength"?
  Posted by: guideboatguy on Apr-23-08 5:09 PM (EST)
-- Last Updated: Apr-23-08 5:49 PM EST --

Did you intend to say that Kevlar lacks tensile strength? I wondered that because usually the one thing people already know about Kevlar is that the tensile strength is very high. The thing is, tensile strength alone can't create a stiff hull. To create a material with high flexural strength, it takes plenty of tensile strength AND compressive strength. I suspect that very stiff hulls made entirely from Kevlar (such as a Kruger Sea Wind which has something like 17 layers of the stuff) gets a lot of it's compressive strength from the huge amount of resin that goes into such a hull, but I'll leave confirmation of that to the experts. In normal boat-building, Kevlar-only portions of the hull (no glass layers or foam cores) are very flexible.

 
 
  just so
  Posted by: pagayeur on Apr-23-08 10:42 PM (EST)
I always got those two things flip flopped. I'm no chemist, I just remember when Bell started the Black and Gold series, CEW told me at a canoe symposium that one lacked tensile strength and the two together made a good combination. That was good enough for me. I really enjoy paddling the B G series. Bought my wife one too.
 
 
  I sort of suspected as much.
  Posted by: guideboatguy on Apr-23-08 11:02 PM (EST)
That's why I started off my reply to you with a question asking if that's what you really meant to say. I guess I didn't "explain" anything you didn't already know :)

Regarding the Black Gold layup, I've sometimes had second thoughts about my decision to get the Kevlight instead of the Black Gold when I bought my Bell. Based on comments like yours, with some being quite detailed, it sounds like it must be a really good hull material. Of course, when I made that decision, it was an unusual situation where I was quite literally pressed for time. With both boats being discounted 15 percent, and with several thousand other people being at the boat show, if I'd have hesitated for another 10 or 20 minutes, I'd have found myself waiting at least two additional months for delivery instead of taking a boat home with me that same day.
 
 
  There might not be a straight answer
  Posted by: guideboatguy on Apr-23-08 5:17 PM (EST)
When I bought my Merlin II, I had the choice of buying one with a carbon hull (I can't recall what Bell calls this material) or Kevlar (which in this case Bell calls "Kevlight"). I pushed and poked the hulls of both boats, and the carbon boat was a lot stiffer on the sidewalls, but I'm not sure there was much difference in stiffness on the bottoms, where the foam core is used to stiffen the hull. Maybe the carbon boat was stiffer on the bottom as well, but if it was, I wonder if it would make enough of a difference to counteract the rather significant weight advantage of the all-Kevlar boat. There's certainly more than one issue to think about here, if marathon racing is the boat's purpose. Fortunately, I'm not a racer and didn't get too stressed-out about the decision. I ended up buying the cheaper boat!
 
 
  my experience with matrix carbon/kevlar
  Posted by: damiano on Apr-23-08 9:00 PM (EST)
I recently purchased two sea kayaks (I'm sorry if it's not exactly releavant to the craft in question but the material seems to be) in Kevlar/Carbon weave matrix.
Sure looks good but there is major problem that nobody so far has addressed.
Most Kevlar hulls are constructed with epoxy resin (apparently better penetration into the fabric) and so are my kayaks.
The hulls use a matt for coring (not sure what exact brand.. Nomex?) and a second Kevlar skin on the inside.
I believe the hulls are very strong against penetration (landing on sharp rocks) but there is a real problem with stiffness.
All seems to be good in the water but the hulls are a real problem once on land.
What?
Since there was mention of Florida I assume that summer temps are rather high there, same as where I live.
Well, my two kayaks deform severely if left in the sun. I can not car top the kayaks with the belly down/deck up on standard cradles (Thule or Yakima).
I have tried to manufacture a perfectly shaped cradle out of closed cell foam for transport but the hulls still deform. These days I transport them with the hull up resting on the stronger deck area.
The hull is so soft that if left on the beach in the sun and not on a perfeclty smooth surface it will dimple.
Now, I know I am ruffling a few feathers out there.
If you don't believe me I can send you some pictures I have taken.
The dimples will disappear usually in a day or so, once placed in a cooler environment, and most times no damage is visible however in a few instances there were a few hairline cracks left on the very light skin layer just under the clear coat.
Structurally the hulls are hopefully sound but deformation is an issue. Only time will tell if other problems will arise from such "soft" hulls.
I would not mind more insight on the matter from an expert.

Gnarlydog
 
 
  deformation
  Posted by: old_user on Apr-23-08 9:15 PM (EST)
Unusual issue to have with an epoxy based composite. If they were very recently built they may not have reached a final cure, otherwise they are getting really hot due to the black of the carbon, hot enough to approach a temperature transistion point for the resin where it gets soft.

It will be interesting to see if things improve in a month or two in the heat. - John
 
 
  wondered this
  Posted by: paddletothesea on Apr-24-08 12:21 AM (EST)
I've often wondered if it makes any difference. When you look at the "time results" for say...the Ausable Marathon or the Le Classique....the "times" are about the same over the last 15-20 years however the boats have gone from kevlar to 99% Carbon... So what Im saying...in the 80s, kevlar canoes were paddling the Ausable(120miler) in the 14-15 hour range for the top 15 teams. Today...the top 15 teams are still coming in at 14-15 hour but are all paddling Carbon boats... So whats the draw there?? Seams like if you work on the engine and train more it will make up for it. I think S. Corbin could have won any of hi recent Ausables in a Kevlar canoe instead of his Carbon.
Any thoughts on this???
N
 
 
  Intresting Topic
  Posted by: CEWilson on Apr-24-08 8:38 AM (EST)
-- Last Updated: Apr-24-08 8:49 AM EST --

I think we can assume the marketplace is efficient, but remember we're chatting about the race boat market, not recreational hulls. Race equipment is generally disposable, recreational gear is expected to last a couple decades.

Almost all race boats have skin coated exteriors, a very light glass and resin layer against the water, that is reinforced to control flex with a foam core. So why include carbon?

As Eric Nyre has pointed out, carbon has high compression resistance, it is stiff, like fiberglass, but it is several times more resistant per unit, so boats can be made lighter. Parts are resistant to deflection but tend to snap when deformed.

Tensile strength, resistance against being pulled apart, is another useful engineering tool. Parts tend to deflect, not break. While Arimids like Kevlar/Twaron are the most used tensile strength material for canoes, Spectra is often used in race boats and Vectrane is being explored. I am pretty excited about Vectrane for recreational hulls because it is much more abrasion resistance than Kevlar.

Race boat builders often combine both compression and tension resistant materials to reduce hull flex and potential breakage where thin sidewalls but into stiff cored bottoms and ribs. The hulls last longer.

Spectra gets the nod in race boats because it provides lighter weight tensile strength. Unfortunately, it needs be laminated under vacuum, and reduces repairability, so it's seldom seen in recreational boats.

Solid cored recreational boats, like Hemlocks and Placid's have similar but different engineering constraints than foam cored products.

Resin systems also influence engineering decisions . Epoxy is used for strippers because it penetrates wood and is easy enough on the nose it can be used in an attached garage.

Most race boats use epoxy resins. They work well in skin coats and are a little lighter and stronger.

I recently chatted with a rep who sells epoxy resins. He suggested we stay with our Vinyl Ester because it costs less, infuses better, is 95% as strong, is more resistant to UV degradation, and doesn't require oven curing. It is better suited to recreational products that need to last a couple decades.

That kayak deformation may be a cure issue. Different epoxies have different cure requirements; sometimes higher than in the sun in Florida can provide.

Is a carbon/Spectra/foam cored race boat "better" than a Kevlar/foam cored one? Crozier, Grasse River, Savage and WeNoNah customers certainly think so. These companies are all building the best product they can in a very competitive market with its unique constraints.

 
 
  Good Post
  Posted by: salty on Apr-24-08 5:22 PM (EST)
and I would totally agree with the comments about Vinylester being a great resin overall.

A local Aeropspace composite company did some testing with Vectran and it did not test nearly as well as it's spec sheet would indicate. That was three years back, so who knows what's been learned. My Carbon Vectran surf boat is OK so far.
 
 
  Vectrane
  Posted by: CEWilson on Apr-24-08 7:26 PM (EST)
-- Last Updated: Apr-24-08 8:34 PM EST --

We'd be using it as a replacement for Kevlar in a Carbon/Kevlar lamination.

Only woven fabric we've found to date is a bi weave with carbon, which is kinda contra- indicated as per Eric Nyre above.

What were the issues w/ Vectrane

 
 
  dam quriky resins
  Posted by: old_user on Apr-24-08 8:36 PM (EST)
epoxy- great cept for that UV degredation
vinylester- terribly short shelf life, so questionable to buy over the counter
polyester- well, it's cheap, guess that counts for something...
 
 
  shelf life
  Posted by: CEWilson on Apr-24-08 8:57 PM (EST)
Our biphenol based Vinyl Ester has a 6 month shelf life. As we use a 55 gal drum every 6 weeks, degredation is hardly an issue. And, it certainly is not an issue once catalyzed and gelled. A larger issue w/ VE is the smell. No one with a house mate will ever live to finish a stripper in an attached garage.
 
 
  Vectran
  Posted by: salty on Apr-24-08 9:16 PM (EST)
-- Last Updated: Apr-24-08 9:27 PM EST --

Not sure what the specific issues were, but email me off line and I can put you in touch with the President of the company that built my surf boat with the co-weave, and did the testing. They are a major producer of parts for Boeing and are experts with composite construction. They in fact make their own composite aircraft. I recall Bruce being less enthusiastic about the material after sample testing, but can't recall so best you chat directly. I sure learned a lot from these folk!

Eddyline also had some issues with their Modulus process using Vectran, but that was more an issue of incompatible material expansion rates etc. I believe.

PLEASE experiment with the Carbon Polyester co-weave. Unbelievably tough and I could not tear the stuff. My next boat will have that! I think Patrick at ONNO has messed about with it, but don't know what he thinks?

 
 
  kevlar
  Posted by: old_user on Apr-25-08 12:16 AM (EST)
I have a kevlar kayak and added another layer of fiberglass and epoxy to the hull under the seat and feet area. It added some stifness as well. So, you can repair kevlar real easy and make it stiffer in critical areas if you want. Not sure about carbon.
 
 
  could it be that the bond
  Posted by: Dirk_Barends on Apr-25-08 2:41 AM (EST)
between the resin and the polyester fibers is better than with Kevlar fibers?


 
 
  Basic Information
  Posted by: CEWilson on Apr-25-08 8:42 AM (EST)
Sweet Composites has a very informative web site that provides basic info on resins, fabrics, coatings and capabilities.

John Sweet recently sold the business Davey and Jennifer Hearn, but the good service continues.

For example, Fiberglass must be coated to have an affinity for resin. Carbon does not need coating.
 
 
  How about S-glass and cedar???
  Posted by: old_user on Apr-25-08 11:44 AM (EST)
One more material to consider...

I've got an old J200 that's build from cedar strips and S-glass. It weighs about 26 pounds, and it's probably as rigid as a factory boat made from carbon or kevlar.

Nor is it a boat I'd consider "disposable." (Not that any racing canoe is.) No, it's not for whitewater, or a shallow, scratchy river in August. But for usual racing conditions...

You may be able to get a cedar strip racing marathon racer built for a price that's competitive with the factory canoes. Just one more option...

Al
 

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