Hull flex...good, bad, indifferent?

Upper end
I said up to. Some boats probably more, some less. I’d say the matrix in the infused Necky’s that I’ve paddled has been silly strong. In absolute abuse the boats have held up. Early models, like mine had the gel-coat issues, but I could care less about that. I think they could lighten the boats even more and equal industry standards for strength. I at 205 lbs. don’t need a kayak I can stand on! The materials are very tough.

I’ve seen non-gel coat boats that were far lighter and just as strong. Sure, UV is an issue, but use the right materials and that’s a long process. I don’t like gel-coat. But I’m a function guy.

here here
Well, Jed, you certainly hit the proverbial nail on the head!

Regrettably, my experience shows that to express a strong opinion on this board that deviates from the norm (i.e. we’re all cool, our boats are cool, and everyone who doesn’t agree with us is ignorant) is pretty much a waste of time and energy, unless you’re willing to fight the evil forces of coolness.

There is great truth to the phrase posted here earlier this month:

  • Arguing on the internet is like runng in the Special Olympics.
  • Even if you win, you’re still retarded.

YES Gelcoat adds pounds of weight
Salty, … soric looks cool too and I love the double function.

Divinycell is not the best thing out there for foam core… still lets extra resin in ( surface ) and breaks down over time… and thats all I’m sayin’ … LOL

What I really wish for is colored glass.

Not Texalium either.

Yeah, what I hear
Have a surf boat with Divinycell core and it’s stiff as can be, but I do have dents on the hull from rocky shore landings. Overall very happy. Composites, and the surrounding technology fascinate me.


You’re really reaching, Jed…

– Last Updated: Feb-27-06 6:19 PM EST –

...and with all due respect, you're wrong on virtually every count.

You can put stiff bulkheads in flexible boats and flexible bulkheads in stiff boats. All it takes is one look at a well used "British heavy" to see all the spider cracking around the rigid bulkheads to see that your assertion is simply untrue. You can get stress cracks in any hull with rigid bulkheads and you will if you use the boat hard enough.

The same is true of your leakage assertion. I've seen just as much leakage with rigid bulkheads as with flexible ones. It's all in how well they're installed.

The only truly flexible bulkheads are those made of Minicel foam, but they're almost exclusively used in plastic boats. It's harder to seal them long-term in plastic boats, but that's because it's difficult to bond anything to polyethylene. It has little or nothing to do with the flexibility of the bulkhead material. I have installed Minicel bulkheads in fiberglass boats with ZERO leakage and it's easy to do.

Flexible hulls do not "fail catestophically" as you imply. They spread impact stresses over a larger area, so they are less likely to be damaged by an impact than a rigid hull. When the do fail, the most common initial failure mode is that the resin matrix fails and the hull gets "soft in the impact area". Structrual integrity is most often maintained and leakage is usually minimal. Given enough stress, they will ultimately fail, but it happens gradually.

In contrast, rigid hulls DO fail catestrophically, which is what a hole or crack is. If they cannot flex enough to absorb an impact, they laminate dissipates the stress by crushing or fracturing. You've seen rigid hulls nearly broken in half and with sheer seams blown wide open. That would be less likely to happen with a more resilient hull built with better materials (such as 'glass cloth instead of chopped strand mat).

A good analogy is bending a "green" stick vs. a dried one. The former will flex more and when it fails, it gets mushy at the failure point, but most of the fibers remain intact. The latter is more ridgid, but when it fails, it snaps in half or nearly so, with most or all of the fibers breaking.

As for repairing flexible layups, I can tell you from firsthand experience that it's no more difficult that repairing rigid layups and if it's done properly there is NO change in flex. I'll bet that you can't find spot that's more rigid than the original layup in any repair I've done.

While I can't vouch for Pat's construction, you know as well as I do that you could not do what he did to ANY rigid Brit' boat and expect it to survive more than one or two blows with the face of a hammer and I seriously doubt that they'd survive ANY blows with the claw. For that matter, they wouldn't survive being flexed flat, either. Dismissing Pat's video as mere "showmanship" is a cheap shot and knowing you to be a man of good character, I'd say that such a comment is beneath you.

We should all paddle what we're most comfortable in, but there's no valid defense for any company using antiquated, 1960's materials and methods in 21st century kayaks. I'd much rather have the new layups that VSK is using in my Pintail and Anas Acuta than the older ones I have.

Don’t know Jed, but
He seems an awesome guy from reading his posts throughout the past few years. I think he, like a lot of people, is simply not informed about composite technology, and like I some years ago, is simply repeating bad information given to him. I’m FAR from an expert on this stuff, but gosh I’ve had my eyes opened in the past four years. I agree with bnystrom and onnopaddle heavily on this thread. And that’s with a lot of years owning Brit boats. I look forward to Valleys new stuff!