fiberglass vs. kevlar kayak

This is my first composite boat after many years of plastic. I have been reading with interest a few posts about flex in kevlar hulls. One of the reasons I bought a kevlar hull was light weight and I thought it would be stronger than fiberglass. Also, plastic has some flex to it and produces a slower hull is that what I am to expect from kevlar? What other than weight are the benefits?

Kevlar vs galss

– Last Updated: Apr-25-05 10:55 PM EST –

It depends whether the superior tensile strength is used to lighten, make the boat stronger at the same weight of a bit of both (usually the case).

So a kevlar boat will be lighter and more likely to be duct-tapable in the event of massive damage. Or more impact resistant and duct- tapeable.

Most Kevlar boats are both.
Kevlar layer inside - S-glass (under gelcoat)outside.



Lots of combinations and levels of quality.



How they perform really depends more on manufacturer. You shouldn’t pick by the material name alone.

I have both
I have both and had no flex problems with the kevlar. But I would not spend the extra money next time unless wieght is the main concern. I’d get the glass and use the money for some gear or a paddling trip.

my boat

– Last Updated: Apr-25-05 7:01 PM EST –

is made by QCC so the quality should be very good. I was mainly wondering about the flex issue and if this was the same as flex in a plastic boat. Also, would it lead to damage of the gel coat. I had no idea composites could flex.

Some info. from Tideline kayak site


Which is stronger? Glass or Kevlar?



Before my head explodes with all I have to say and do not have time to write…I will say this.



A glass boat layed up thoughtfully will take more minor bumps and grinds and will also absorb a greater amount of energy than kevlar BEFORE it STARTS to fail.If a equally layed up kevlar boat were built it would not take as much abuse before it would start to soften up …BUTTTTT. A kevlar boat WOULD endure catastrophic force far better.



If a giant were to pick up a glass boat and wack it across a log it would probably break 1/2 - 3/4 of the way through on the first hit and fly to pieces on the second.



A kevlar boat would make a dull thump on the first hit and show some damage in the form of delamination of plys but would be mostly intact. The second hit would probably cause failure of the resin and the boat would lose it’s shape at point of impact but it would still most likely stay together. It would take several more hits by an increasingly frustrated being before the boat would come apart.



This is what kevlar can do…now picture what would happen if a jetski plowed into you to offshore or you bailed on a big set and your “lifeboat” pounded on the rocks for a set or two before getting spat out.Kevlar can provide security a non balistically layed up glass boat could not.



A quick synapsis of my personal construction opinions. Please note I do not follow the same line of thinking many of the Majors do.



I can build a super light all glass boat but I do not recommend this. The thinner glass layup is not quite as tough as the light Kevlar layup and due to the extra labor involved I would also charge the same price to build one.



If boats are going to be bounced off of rocks on a regular basis in any conditions other than blue water go for the standard glass construction. Unbelieveably tough and resistant to bump and grind damage. Still light and does well enduring the day to day stuff for a long time. Save some $$$ too.



If boat will see occasional rocks only and will not be abused with IN heavy surf / rescues with boat wallowing full of water etc. AND a light weight,stiff, super strong, safe build is the goal , go for the Lightweight Kevlar layup… I just call it Kevlar layup.



Blue water, real potential for life threatening conditions , boat may hit a submerged rebar at speed it, MUST stay together after shark , jetski or cargo ship attack… Go for a kevlar layup built up around the weight of a similar glass boat then add a bit. Please let me know what you are thinking / picturing.


Be carefull.
I have a kevlar 400xl which has some small gel coat cracks around one of the tie down areas.

I went from a plastic kayak to the qcc not knowing exactly what to expect. It appears i caused the gel coat cracks by tightening the straps too tight. Yes there is considerable flex in this lightweight hull. It’s part of the tradeoff for a lighter weight hull. Just be carefull how tight you tighten those straps.

Enjoy the boat!

Talk to Phil at QCC
Pretty sure he’ll (still) explain that their Kevlar layup is their toughest all around option (and all carbon the stiffest - but also weakest).



Stiffness DOES NOT = Strength.



Get a skinnier 600 or 700 and the flex isn’t as big an issue as on wider decks/hulls. Rounder surfaces are more rigid - flatter have more flex.



Over cranking rack straps is unnecessary and always a bad idea. People used to manhandling heavy plastic would crush my all glass surf ski (which is far more fragile than my Kevlar QCC).



My 700 has not been dropped far or rammed into many rocks - but has been put down hard, had my 200# on the rear deck and coaming doing cowboy rescues, had a heavy glass Brit boat teeter tottering across the foredeck doing T-rescues, put up with me siting in it and flopping about on land testing outfitting options, and been car topped at up to 85 mph - all with no gel coat cracks or any other structural issues.



These are not weak kayaks - not by a long shot. Their warranty and customer service pretty much says it all.

Hey, thanks for the mention…
Please note that above statments are based on my boats having over 50 separate plys placed strategically throughout hull and deck.



Some boats are built with no more than 7.

Tell Phil to ditch the gelcoat.
It detracts from the QCC image.

advertising
it’s not the same. Unfortunately plastic is bad mouthed because it’s flexible and composite is somehow better because it’s rigid. When it’s simply a description and not true in all circumstances. For marketing reasons it’s easy to make a description with positive modifiers which constructs a chain of logic that appears to mean something significant,when it’s not.

Your image maybe…
… but contrary to popular belief - QCC does not make racing kayaks - and the gelcoat serves a purpose.



Still waiting for a Q900 - Something above EFT…

Why
Why ditch the GelCoat?



Wether it is glass or kevlar something has to provide a waterproof and astetics layer. There are some boat manufacturers that use some of the high tech polymer paints, re Hatteras. But as far as I know these newer coatings have as many downsides as the gelcoats.



Mark

not having flex

– Last Updated: Apr-26-05 9:15 AM EST –

is why I decided to buy a composite boat. Everyone would tell me, there is a HUGE difference between the way a plastic boat paddles and a composite one. Mainly it had to do with stiffness in the hull. When I think of flex I think about my royalex canoe and my old plastic touring kayak. Reading a few posts lately referring to flex in their kevlar hulls kind of makes me disappointed in my choice.

I did know when ordering the boat that kevlar was stronger than fiberglass and lighter so I thought that was the way to go. Will the flex make the boat which is already a boat that is not designed for speed slower?

Thanks everyone for replying to my post I learn so much from reading this forum. A newbie to composites.

You want stiffness and speed?
Then buy an all carbon race boat and be careful with it.



You have a good boat - and no reason to be “disappointed” until you actually have a problem with it!



Less reading, more paddling!

I am not sure which kevlar boat you
purchased, but I have a 18 foot kevlar yak, and a 17’-3" plastic yak.

I cannot notice any flexing in my kevlar yak.



As far as speed goes, I think most paddlers buy composite because they are lighter than plastic, and therefor are faster and more maneuverable.

I don’t think many folks take into consideration the flexibility of a kayak before purchasing it, and if you do end up with a little flexing, so what, I wouldn’t worry about it.

Enjoy the boat!



Cheers,

JackL


None of my composite WW boats has

– Last Updated: Apr-26-05 9:03 PM EST –

gelcoat, but I had gelcoat on two canoes we used in WW. One, an early Mad River, showed star cracks and hydrolysis in the gelcoat. And it quickly wore off in keel areas, so that I had to put on thin glass/epoxy layers-- which wore much better than gelcoat. The other gelcoat canoe, a '73 Moore Voyageur, had unusually good gelcoat, no problems.

So, what is the advantage of gelcoat, I ask again? It doesn't wear well, it adds much weight, and it doesn't look better. My Millbrook, Dagger, and Noah decked boats have excellent coloring at no weight cost. The Dagger and Millbrook have S-glass in the outer layer, and wear like iron.

Gelcoat is like Kevlar felt skid pads.... a stupid idea, clearly inferior to alternatives, which stays around due to vague customer expectations. It is so hilarious to see someone order a Carbon/Kevlar boat with gelcoat. Might as well skip the gelcoat and order a glass boat.

Gelcoat is not for waterproofing anything. Even when polymers such as Nylon or Kevlar are used as the outer layer (bad idea), they do not absorb water to any significant degree when the surface of the boat is scratched.

The only area where gelcoat may have an advantage is UV protection. But I have a 22 year old no gel coat c-1 made with vinylester which never chalked in the sun.

Not talking a WW boat here
Keep it in context. I completely agree that Gelcoat in WW would be stupid!

All my glass boats flex
when they slide over boulders or logs in a shallow stream. I thought that was a desireable quality. The over all hull is stiff & rigid and doesn’t oil can, but the impact location flexes during the impact. Is there a problem with this?