Although I agree that we shouldn’t do something against our best judgment simply because consumers want it, I think the issue of using kevlar falls into a gray area of personal preference… The fact of the matter is kevlar is very resistant to abrasion and impact. A few months back, I had a Griffin Expedition (kevlar exterior skin) fall off my roof rack because the plastic base of the forward j-cradle was cracked. The whole j-cradle slipped off my bars and the boat landed with bow against pavement and the stern still locked in the rear j-cradle. I was on a busy road driving around 30-40 mph and couldn’t pull over immediately, so the boat was dragged bow down for at least two blocks with the forward motion pushing the boat hard against the rear cradle. Despite the trauma, the boat emerged with very very little damage. Although the gelcoat was worn off in the 1" area that made the most contact with the pavement, the kevlar was largely undamaged and the core material, carbon inside skin, and end pour were completely unscathed. Had the outside skin been glass, carbon fiber, innegra or anything else, it wouldn’t have survived as well.
There’s no doubt that some other materials offer excellent properties that I (and Salty and others) may deem sufficient, but some customers believe that the added measure of durability offered by kevlar is worth the other trade offs (added weight, harder repairs, added cost, etc.) I think our job as the manufacturer is to help educate the customer about the limitations of kevlar and make sure the material is really best for them. If the customer (armed with all the necessary information regarding cost/benefits of the material) still feels that the added margin of durability offered by Kevlar is worth it, we as a company won’t try to beat them over the head and convince them otherwise.
Anyway, just my two cents, now time to head out paddling before it gets dark.
I’m liking the idea of a Griffin LT as a downriver racer! Has anyone used it in this application? Currently I’m paddling a 17.5 foot kevlar Ruahine Swallow in Class I - III rivers, but sometimes it’s nice to have a “shorter” boat.
For all the kevlar bashing going on, it still seems to be the material of choice for wildwater and downriver racing kayaks.
I don’t like fabrics that wear the way
Kevlar does. It fuzzes and shreds. I’ve had to resurface a kayak that used Kevlar as an outside cloth.
I assume you’re aware that laminate tests documented in the old Boatbuilders Manual showed that Kevlar did not work as well as one might expect as an “outside” cloth. It has mediocre compression strength. Kevlar works best for inside layers, where its excellent strength in tension and ability to stop catastrophic tear propagation come into play. The tests in Boatbuilders Manual showed that SSKK was the best 4 layer laminate, where S= S-glass for the outside layers and K is Kevlar. I don’t know how that can be compared to your rather complex layup. And you’re dealing with gelcoat, which is no longer seen in composite whitewater canoes and kayaks. My SS/KK canoes wear smooth and wear slowly.
I have, in fact, not seen this study but it sounds extremely interesting. Any chance you might have a link to the article or know where I can find a copy (haven’t done my google searching due diligence, so ignore this if it’s rather easy to find). Anyway, you’re totally right about kevlar being nearly useless in compression. Many many tests have shown that glass/core/glass is stronger than glass/core/kevlar if kevlar is on the compression side of the laminate. In normal use, the outer skin of a kayak laminate is in tension (which is one of the reasons we put the kevlar on the outside). In the case of an impact that’s significant enough to deflect the laminate inwards, the outer skin goes from being loaded in tension to loading in compression. This is admittedly not ideal for kevlar, but our expedition laminate really doesn’t deflect much no matter how hard you hit it. The kevlar is there primarily for the abrasion resistance. Like you said, wear on kevlar can cause some unsightly fuzzing. Although it can be repaired by someone skilled in epoxy and glass repairs, it’s not the easiest thing in the world. The S-glass skin coat we put on the outside most layer helps limit the fuzzing, but enough abrasive contact will eventually wear through this s-glass outer layer. Although we could use an all S-glass outer skin instead of kevlar + s-glass (I think much like the one in the study you mention?), getting a thick enough outer layer to effectively protect the core from damage would mean a significantly heavier laminate. All of this just goes to show that the choice between laminates is a pretty personal choice that depends fully on what one’s highest priorities are. And for this reason, we’re all about custom-tailored construction and won’t claim that a single solution will fit everyone’s needs. But anyway, please do send that study along if you have a copy!
Due diligence done and I’ve realized that you’re referring to a book… Is this the book by Charles Waldridge? Just wanted to double check before I order it off amazon. I did find an online link to the Waldridge book’s table of contents and it looks pretty damn comprehensive. Even if it’s not the one you’re talking about, I might just have to add it to our bookshelf.
It is the Wallbridge book.
There’s a Chicago firm that claims to have the last ('87) edition, but I don’t have the link on this laptop.
I’m having trouble communicating with my router. Will have comments on compression and tension later.
it’s a great book
lots of practical knowledge in it. My $.02 is that the idea kevlar is good for abrasion is a hangover from kevlar felt skid plates on canoes where a THICK layer of epoxy/felt is a big part of the abrasion resistance. I’m surprised at all the kevlar kayaks where the wear spots in the heel area have worn half way through the kevlar layers in the cockpit to the core. I just don’t think there’s that much abrasion resistance to a layer of 5oz cloth. My old Mariner Express with it’s heavy roving had much less wear on the heel spots than the cored kevlar kayaks I’ve patched up.
Weighing the choices I’d rather replace all the gel coat with another layer of s-glass then use paint for UV/cosmetics protection.
The boats look cool!
Material stuff is, as I’ve said, another discussion. I’m sure the Walrus kayaks are great and Kevlar can be used wisely in kayaks. My history with composites involves a significant amount of interface with Aerospace composite folk and their ideas about Kevlar are different from the common kayak community beliefs. Their observations have matched my experience over the years with various materials.
In engineering there’s a slogan: No bad materials, only bad applications.
Again, as I’ve stated MANY times, while I would not employ Kevlar 49 in a kayak hull matrix, I think good hulls can be built with the material if it’s applied wisely.
Nice looking kayaks and good work and best of luck!
Looking at the photos on their website I noticed that there seems to be very little freeboard at the cockpit area. I have no thoughts or opinion, but if so it might be a wet ride in choppy water? Lower windage?
Compression and tension strength…
I think the rationale offered to us has been over-simplified. For the outer layer of a composite boat, just considering the issue of proper stiffness, carbon cloth is excellent, and S-glass is pretty good. Kevlar is quite good as an inside cloth, although some of the stress of a loaded canoe sitting in the water will put inside cloth in compression. (Think about it.)
When a canoe or kayak strikes something hard, compression strength is needed at the point of contact, but nearby, the laminate will be put in tension. Probably if hulls were always spherical or tubular, the analysis of the effect of blows on the laminate would be simpler.
But take a chiny canoe or kayak going over a ledge. An example would be a composite version of a Dagger Ocoee, or my own Millbrook. The ledge slams the center of the stern, putting the outer cloth layer in compression at the point of impact. But these boats seldom break there. They break out at the sides, along the chines, because the stern getting pushed up bends the chines. S-glass cracks may appear along the chines, and (surprise!) cracks in the Kevlar may appear inside, because it does not stand up to the compression caused by sudden closing of the chine angle.
Both for building and for repairing, it is necessary to consider what the effect of blows will be, in terms of compression and tension. I now sometimes use Kevlar for outside chine repairs, and if the inside of the chine breaks, I may reinforce it with carbon or glass.
More Info ???
Till I get close enough to a place that has one to demo, does anybody have info to what the characteristics of their Jaeger in lumpy waters will be like compared to other big sellers like the Explorer or Cetus or Etain or Tempest etc. as this seems to be that slice of the market share it will be competing in. How maneuverable, quick to plane and surf, tracking, speed etc. should one expect from this hull? Optimum paddlers weight?