Resin in itself
does not add strength. Infusion allows for less excess resin in the matrix which equates to a lighter lay-up that is less brittle and just as strong or stronger. I think non-composite folks confuse thick gel-coat, and heavy lay-ups with strength. I believe the kayak industry is just now catching up with modern composite technology, and that’s great for consumers. The best resin to material ratios are achieved through pre-preg / autoclave technology, but that’s costly. Infusion is a realistic, excellent way to go. I would guess that the infused Valley boats will be just as strong, if not stronger than their traditional lay-ups. I’d definitely go that route.
Resin, etc.
“I think non-composite folks confuse thick gel-coat, and heavy lay-ups with strength. I believe the kayak industry is just now catching up with modern composite technology,…”
It would be nice if there were a non-technical, but accurate source of information for paddlers that explained all this stuff. My impression is people have thought thick gelcoats and heavy layups made a kayak tough in terms of overall durability. Frankly, not sure how that relates to “strength”. I suspect there is more to that story as in many mistaken impressions and no doubt just what makes for a tough kayak is a function of what represents tough enough for a given use as well as what compromises one wants to make.
Don’t get to hung up on constructions!
Even though I obviously believe in the changes we are making please don’t get to hung up on the whole construction issue. “Old School” thicker gel-coat heavy glass lay up constructions are very tough, hard wearing and more than suitable for the purpose they were intended. No they are not “sexy” in technical sense, yes if tested to destruction (for a given weight) they will fail first and yes they take more effort to lift on your car at the end of a days paddling but that doesn’t make them a bad kayak because they are still over engineered.
Due to the industry I’m in I have been lucky enough to have access to the very best toys in paddle sport. I used to race slalom to a very high level and set out to build the lightest boat I could, I made a sub 14lbs race boat, foam sandwich fully outfitted. To the best of my knowledge it was the lightest fully outfitted boat racing in the UK at the time. Truth was I never enjoyed paddling it to the same degree as my previous boat (same design, same mould, approx 4 lbs heavier). It felt so flighty it took the best part of a month to get used to it, even then it never seemed to feel as smooth and most of all despite the sandwich construction making it incredibly ridged I didn’t have confidence in it durability (although it never failed in two years of racing with it).
What I’m trying to say is - Remember to choose a kayak you enjoy paddling, in a construction you are confident in and happy with the weight of. Yes our new constructions are a big step forward and yes I’m happy to be part of that change but equally the products that Valley made in the past and the other British manufactures are making are still very sea worthy craft, more than suitable for there intended purpose.
What are stress risers?
as mentioned in a post above. I have a 2003 glass Avocet and Aquanaut…Not sure I’ve heard the term…thanks
stress riser
Imagine a flexible thin fiberglass hull with no bulkheads, you turn it over and press up and down on the hull and the hull flexes up and down.
Now put in a couple rigid bulkheads then push up and down in the middle. The hull will flex in between the bulkheads but not beyond. The pressure that results in movement stops at the bulkheads and increases the stress in the hull material where the movement stops.
THEORETICALLY the hull can fail more readily right before the bulkhead IF the stress is great enough. THEORETICALLY if you put in flexible bulkheads the hull is less likely to develop cracking failures at the bulkheads.
Most likely any stress that results in slight cracking due to a stress riser will develop somewhere else anyway because of the wide range of stresses beyond level X in an unintended event.
For example I had the foredeck of my Express develop cracks inbetween the recessed cleats when a double kayak was dumped on it. The cracks theoretically developed there and not elsewhere because the shape of that area confined the flexing to a small area.
Likewise on the aft deck near the edge of the deck a long 14" crack developed because the 3" interior seam tape wasn’t layed carefully to ensure that the inside edge of the deck was supported with the tape. The tape ended in the middle of the sharp curve whereas on the other side the tape carried up another 1/2" onto the deck. During a paddlefloat rescue one side flexed right to the edge of the stiff tape in the middle of the curve and the other side made a better transition from a thin/flexible deck to a rigid curved sheer edge.
It can also be evident where it’s really not a structural issue but the boundary between a rigid part and a flexible hull with gelcoat unable to accomodate the difference. The skeg box of my Chatham 18 is like that, there’s a heinous spray of cracks radiating out from the edge of the skeg box on the bottom of the hull. The hull is perfectly strong but there’s not a transitioning element for the thin hull connecting to the rigid/keel/skeg box and the gel coat is cracked.
thanks for the reply…
stress riser - in real life
I’ve never seen a stress riser in a Valley boat. However, the Romany I borrowered this past summer did have such a ridge in the foredeck above the bulkhead. I had heard of such but this was the first time I actually saw one.
BTW: the Romany I borrowed was officially a blem boat.
materials driven marketing
it took me the longest time ($$) to learn that replacing economical glass with expensive materials didn’t really represent “better”. And that a theortically stronger material didn’t necessarily result in a more durable kayak. In the case of my Chatham18 even a more sophisticated construction method with a very high glass/resin ratio doesn’t necessarily result in a light kayak. Seems that once the kayak is X by Y by Z it’s going to weigh what it weighs for a given level of durability and cost. And that reducing weight of materials, even if it’s being replaced with theoretically stronger materials often brings an unforseen weakness somewhere.
s&g kayak
I talked to a fellow who heavily used his Coho, dragging the loaded kayak over things. It developed cracks right in front of the aft bulkhead where it would be pulled/levered over objects. The same would happen to a $3500 kevlar kayak loaded with 75#'s of stuff and levered over a log.
On the s&g kayaks I’ve made I would glass the interior with 60" wide pieces of glass overlapping at the bulkheads with a 3" overlap of glass that the 4mm bulkhead sat in the middle of.
Chasing stress
Good thread here… You bring up good points Lee. My buddy and I have been messing about with surf boats for some time, and we’ve chased stress around the boat! Strengthen one area and stress is transfered…beef that up and you’re heavier. Finding the balance for a given weight is tough. Competitive boats obviously go for weight savings. The other end of the spectrum would be my old Nordkapp, and Romany. Heavy, gel-coat cracks and crumbles, bubbles, etc.,(cosmetic stuff) but tough boats that lasted through a lot of abuse…to Peter’s point. (Those kayaks are still alive) In the end it comes down to what’s economically practical for the builder to produce, and the customer to purchase. And I know Lee that there have been many improvements to the Necky composites in the last few months, partly due I’m sure to customer feedback.
Valley scalloped bulkheads
> The hull will flex in between the bulkheads but not beyond.
The pressure that results in movement stops at the bulkheads
and increases the stress in the hull material where the movement stops.
Isn’t that why Valley (at least used to) use “scalloped” bulkheads, with a cupped shape – they flex a little?
–David.
stuff just is
there’s a lot of stuff to play with,just watch the Magic Chef show.
I know what you mean about chasing weak links around. At some point you have to say “ok,the rewards are diminishing on this one,instead of seven different pieces of cloth and layups how about we just put a layer of this stuff down”.
I look in my old mariner that has what I assume is 24oz roving and the Chatham that has a whole bunch of interesting knit,woven and core materials,it all works,but the 12yr old gel coat on the Express sure doesn’t have the cracks and chips that 12mo Chatham does.
Valley scalloped bulkheads
Yes, to avoid such stress is why Valley uses curved bulkheads. However, custom placed forward bulkheads are not curved and I’ve not seen any stress risers there either.