Kevlar or Kevlar/fiberglass?

I read some negative things above kevlar in this forum. Is kevlar/fiberglass composite any better?

I’m known as a kevlar basher here!
But really am not. Kevlar 49 is what’s used in kayaks. It is very strong in tension and is abrashion resistant. It is also light and secondary to its tensile strength great for impact resistance. Secondary to it’s weak compressive strength it tends to be less stiff than glass or carbon. Good builders get around that by complimenting the material with glass, carbon, or coring. Now the part that pisses kevlar nazis off. It is a material (aramid fiber) that is prone to interlaminar break down over time with constant flexing as the material resists bonding with resin. Every composite person I speak with, along with kevlar suppliers has aknowledged this. Now…

Having said that there are some really well built kevlar kayaks out there, so that has to be taken in perspective, just as the hydroscopic comments. While the material is definitely hydroscopic, in reality this has very minimal effect on kayaks, as they are out of the water more than in the water and dry out. Matrixes are thin relative to a yacht hull! Again, also testimony to good manufacturing.

My experience having owned many kevlar boats, glass boats, and carbon, glass boats, is that the lighter kevlar hulls in sea kayaks do get flexy with years, but do also take abuse. The notion that a big hit will not tear the kevlar has not been my experience. I’ve split the lay-ups clear through, but others have had their boats stay in tact better than would be the case without the kevlar. So there’s merit there for sure.

Past kevlar surf kayaks have become soft after two to three years. My friend who builds them no longer uses kevlar as a result, rather carbon/glass. The latter have held their stiffness far longer. Now, again, that’s pretty extreme abuse. I’m just reporting our experiences here and fully expect a negative reaction. Kevlar / Carbon co-weaves held up better, and I think boats like Gala produces are awesome. Combo co-weave, coring, epoxy…

So, it is a material that has great values. When complimented with other materials and good construction methodologies it can make for a great kayak.

I would want glass or carbon in my kevlar kayak without any doubt. When it comes to materials there can be a lot of emotion around simple facts. Facts can be blown out of proportion.

Now for impact…I can beat on my carbon / glass / soric hull with a hammer. I would suggest that carbon fibre actually is the material that gets mis-represented as less durable than it actually is.

I sincerely hope this message does not cause conflict…it’s not meant to. Others will have different takes and experiences. Research the materials thoroughly, talk to many, and experience things for yourself. I say by all means get kevlar for its weight and impact qualities, but enhance it’s dtiffness with glass, carbon, or coring. Good day.

Kevlar - Carbon woven together
Do you think builders who use a cloth that has both kevlar and carbon in its’ weave address satisfactorily some of the issues you have well addressed with a boat that is primarily Kevlar?

That would be my preference
Now, again, I’m NOT saying a pure multi layered kevlar kayak is bad. But yes, I prefer the co-weaves. The Gala boats I’ve seen are awesome.

most kevlar kayaks
have some glass in them somewhere. Don’t get hung up on it. What boats are you looking at?

Laminate engineering
Glass and carbon are stiff in compression. Carbon twice as stiff so 5 oz carbon w/ 5 oz resin equals 10 oz glass with 10 oz resin. Ratio 1:4.

Carbon is $ 50/yd, glas is $ 10/yd, so all things are the same, one gets whyat one pays for there. The more you spend the less, weight, you get.

Kevlar is weak in compression and strong in tension. All Kev hulls oil can, or flex, and loose speed thereby.

Better laminates have glass/carbon on the outside and kev on the inside. The compression layswer eliminates hull flex. When an ob ject is hit, the compression layer comes under tension, the kev, rounding a larger curve, comes under tension and keeps the stiffer outer from fracture.

Laminates featuring this engineered structure include Bell’s Black/Gold, Hemlock Canoe, Swift Canoe and Placid boatworks.

with the notion of kevlar on the inside. Engineering wise that makes sense.

I have never seen a boatbuilder claim
that Kevlar is inferior to glass or carbon in its bonding to resins.

One reason it may >appear< that Kevlar has delaminated in a hull that has taken a bashing is that the Kevlar layer is the one that has held together. On my Millbrook boat, the S-glass shows compression cracks, and then (if not repaired) will gradually disintegrate into flakes, while the Kevlar layers underneath adhere to one another just fine. But that’s what a good hull designer wants to happen with a boat using these cloths. If the boat was made entirely from S-glass, then the cracking would often extend inward to the inside of the boat, and it would leak.

Did I hand you that Allison site where the builder explains why all-carbon ocean boats crack up catastrophically?

dont forget about the process
hand lay up

vaccume bagging

Vaccume infusion

are not all created equal…

a high level manufacturing process will produce less voids (in the mold), and overall better structural inetegrity. So with that being equal then you can have a discussing about materials.

Own all types
Infused carbon / glass boat is the stiffest and toughest by far. I know boat builders who would say kevlar doesn’t like to adhere as well, as well as a kevlar salesman. That doesn’t mean it can’t.

You and I will never likely agree on this and that is OK. I in fact discussed this today with a world record holding shaper of sailboards and shaper of over 10,000 surfboards, and a few kayaks mentioned here. Helped Barton with first foam cored wings. He agreed totally with what I have said here. Aerospace and yacht composite engineers that I know likewise agree. But you don’t have regard for them. I do. They showed me what I didn’t know. I fully believe they know more about kevlar than you or I. They process hundreds of thousands of lbs. of the stuff. Have for years. They don’t get emotional about a material.

You will never hear me bash any of the fine builders who utilize kevlar. Clearly excellent boats are made of the stuff. You are hearing me share my knowledge and experience personally as well as via relationships with experts in composite technology. The guy that lives three blocks from me was a compsite engineer with NASA.

Carbon can indeed fail catastrophically. Some masts are too light and fail. The pursuit of ultra light weight comes at a cost. Interestingly Lance’s bike frame had no kevlar in it and did pretty well. We don’t see solid kevlar paddles very often do we? Why is that?

Why are the skins of our future aircraft that must take years of pressure changes carbon epoxy?

Kevlar is used in avialtion all the time, where its properties add value. Ducting, engine shrouding etc. Not in the air skin. When I asked my neighbor why, he said interlaminar breakdown was an issue. But what the hell does he know?? Guy’s an idiot clearly.

Consider this on Kevlar’s supposed
adhesion problems. You know that glass fabrics require special coatings, matched to the resins, to have top notch adhesion. Carbon does not require such coatings. Kevlar is not coated, though it is “scrubbed.”

Kevlar 49, with its advantages and disadvantages, has been around for decades. You say it is deficient in adherence to resins, compared to glass and carbon. By implication, you are saying that boatbuilders and aerospace people have been using it for decades and >no one< has developed a coating that corrects Kevlar’s supposedly deficient bonding. Doesn’t seem likely when you think about it, does it?

Seems more likely that any >apparent< deficiency of Kevlar in resin bonding is actually caused by Kevlar’s incredible stretchiness and tear-resistance, and that by the time Kevlar imposes a final limit on laminate distortion, the resin matrix has failed, leaving the Kevlar layer to pull free.

I have been sceptical of mixed fabrics (Kevlar/carbon, S-glass/carbon), but perhaps the “success” of Kevlar/carbon is that the parallel carbon fibers do a better job than Kevlar of preventing the resin matrix from being distorted to the point of failure. When the laminate of mixed cloth fails, it is likely to do so by splitting or cracking rather than delaminating the way pure Kevlar would do.

You do what makes you happy.
That’s OK with me. I agree with some of your points about the material being tough and resisting tearing. Just had coffeee with my neighbor as I walked my kid and we chatted at length about kevlar. He laughs. This guy worked with the military on composite fighter skins. He said there used to be individual strands of Kevlar every few inches in the graphite for fabric orientation purposes. Those were taken out and replaced with dyed glass because of absorption! (Don’t get confused here and assume I’m saying kevlar kayaks get heavier) Direct quote from him “You will not see a piece of kevlar in the air skin of any military air craft”. You will see it used in material applications etc. Straps, ties, ducts etc. BTW, this guy also built a record holding 30’ composite sailboat, and has consulted with several kayak manufacturers. He loves kevlar in many applications. He dislikes it in a structural matrix. I asked him if he would post here and he laughed saying “What’s the point?” Those guys won’t get it… He’s right once again.

Friend who builds the surf kayaks consulted with my friend. He wanted to solve the softening issue with high use. He, like me,thinks very differently now. His boats are way tougher and stiffer now.

In the end we’re all learning, and neither you nor I have all the answers. For me, the smart composite guys opened my eyes and what they said proved hugely true on the water. Good day.

The boat
Thank you all for your expert opinions. The boat I am considering to add to my tandem fleet is Lincoln’s Two Lites. The boat layup from outside in: gelcoat, kevlar, glass, kevlar, foam core, kevlar. Epoxy is vacuume bagged into all layers. This option is $500 less than the all kevlar layup but a few lbs heavier. If this is stronger than the all kevlar boat, I can live with the weight.

I’d do as you are thinking
and go with the glass and core which will add stiffness. That will make a good all round tough combo. Enjoy the kayak.

2nd that
Thoses combinations will be great as long as they “layed” up effectivley, good luck