The recent thread(s) regarding boat durability, etc, have once again proven that there are no ultimate conclusions to the boat construction methodology debate. I would like to shoot some more "anecdotal" ammunition at the elusive target, if you all aren't worn out yet: 1. The quality of the finished boat, both as it relates to visual appeal and more importantly strength issues, has much more to do with the individual (or builder-team). A "good" fiberglass worker can get fiberglass to "wet-out" at just the right amount of saturation, but he/she/they must be _good_ at what they do, really good. 2. A ill-experienced vacuum bagger can be responsible for some awful work. Some kayak manufactures pay their people just above minimum wage, and you just don't get good people for that kind of money. So too for hand-laid. 3. I find gelcoat does not bond as well to vacuumed bagged kayaks _if the gelcoat is put on thick_. The British hand-built kayaks are capable of retaining the thicker layers, allowing for more abrasion wear potential. However, some Euopeans take it to extremes. 4. The higher resin content of non-vacuumed fiberglass does wear a bit better once the gelcoat is breached, though at that point, incipient problems should be dealt with. 5. I have witnesses catastrophic failure of a vacuumed bagged hull - not a good thing. Never seen this with a Brit heavy - just extra chiropractor visits :-) 6. All the guides/instructors that I know in Souther BC, who work with or for stores/manufactures and always custom order their boats (at reduced costs) usually ask for extra-heavier lay-ups. What does that tell you about their faith in the standard lay-up vacuumed bagged kayak? 7. There is a famous picture of a standard duty, vacuumed bagged kayak exiting west coast surf that appears in national advertising. I know the guy who was involved with some of these shoots. The kayak flexed and the back deck/coaming broke - and the add reads "quality". For my money, you can't beat a stiff, strong kayak, including the deck. 8. There are ways to stiffen up a kayak with high tech solutions that reduce weight. Unfortunately, the British kayak manufacturing industry is a "cottage" based one, and so far, has stayed mostly with tried and true (to them). P&H are the most progressive, though Valley Canoe remain high for overall consistency. 9. All the above guides/instructors I know, also usually order the extra outside seams, especially over the extruded plastic seam. Even then, I have seen outside seam failure concurrent with inside seam failure. This can be a bit catastrophic in the middle of a gale during a long crossing. For my money, an extra outside seam of two layars done with _epoxy resin_ is the only way to go. There is some debate in this area of seams, currently, as evidenced with one of the Australian clubs who deal more exclusively with rough water issues. 10. Kayaks are relatively small vessels, but don't underestimate the stresses faced. A fully loaded kayak undergoes incredible flexing motion. Next time your kayak is fully loaded, have two people pick the kayak up by the ends. As it is slowly lifted by said hardy individuals, look closely at the alignment between stern and bow. Whoa, there's a ton of flexing going on. Now, think about adding your weight in too, throw in some ruff, choppy seas, and then tell me stiff isn't important. (Baidarkas, folders, and plastic not withstanding). PS For your information, I saved the recent boat durability thread for discussion with SK mag (no names retained, concepts only to be related outside of this list). The word count on the file is over 6,000. Only on Paddlewise! Make sure, if you are able, to paddle as much or more than you post!! BC'in Ya Doug Lloyd (who may pontificate, but needs to get out more, too) *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Doug Lloyd wrote: > 5. I have witnesses catastrophic failure of a vacuumed bagged hull - not a > good thing. Never seen this with a Brit heavy - just extra chiropractor > visits :-) > Is there a typical failure mode or are they all different? Or are you talking about one failure? > 6. All the guides/instructors that I know in Southern BC, who work with or > for stores/manufactures and always custom order their boats (at reduced > costs) usually ask for extra-heavier lay-ups. What does that tell you about > their faith in the standard lay-up vacuumed bagged kayak? But how much time do they spend in their boats compared to the weekend warriors? That factors into the decision. I've also found that guides don't want to baby their boats and will do seal landings in conditions that I'd exit offshore and walk. Construction workers don't buy the same tools that weekend woodworkers do either, so I think your observations are valid in the appropriate context. > 9. All the above guides/instructors I know, also usually order the extra > outside seams, especially over the extruded plastic seam. Even then, I have > seen outside seam failure concurrent with inside seam failure. This can be > a bit catastrophic in the middle of a gale during a long crossing. For my > money, an extra outside seam of two layars done with _epoxy resin_ is the > only way to go. But reinforcing may result in local stress concentration that increases the likelyhood of failure. The key is a balanced design; adding reinforcement to an existing design may not be a good idea. I'm a former engineer who specialized in stress analysis techniques and I can't see a reason why inside-only seams can't work; they don't need to be any stronger than the hull and deck they join. > 10. Kayaks are relatively small vessels, but don't underestimate the > stresses faced. A fully loaded kayak undergoes incredible flexing motion. > Next time your kayak is fully loaded, have two people pick the kayak up by > the ends. As it is slowly lifted by said hardy individuals, look closely at > the alignment between stern and bow. Whoa, there's a ton of flexing going > on. Now, think about adding your weight in too, throw in some ruff, choppy > seas, and then tell me stiff isn't important. (Baidarkas, folders, and > plastic not withstanding). My xc skating skis are almost two meters long, weight barely more than a kilogram (the pair) and can handle my body weight repeatedly pounding on them for many seasons without failing. Fiberglass, cap construction (sorta like a kayak hull) with honeycomb core. Their ability to deal with stress comes in large part from their flexibility. It's important to distinguish two different kinds of stiffness in a kayak. Your example is one of overall bending of the kayak, supported at the ends. In this case, the skin of the kayak is not flexing, but is in either tension or compression. (If held up from the ends, tension on the bottom and compression on top.) If the skin is subjected to a local load, like hitting a rock, the skin itself flexes and near the point of impact will be in compression in the gel coat and tension on the inside. Away from the impact, the flex will reverse to tension in the gel coat and compression inside. The thickness of the skin will have a strong influence on the stiffness where flexure of the skin is concerned, but will be less significant where tension/compression of the skin is involved (since the fibers carry the load). Hence, the reputedly thicker Brit boats should show their stuff in oil canning but should show less advantage over a vacuum-bagged kayak on overall bending. When I look at the difference in weight between fiberglass and Kevlar canoes (around 30 lb), I would only buy Kevlar (say 55 lb canoe). In a kayak, the difference is only about 5-9 lbs - my kayak, when new, was 55 lb in fiberglass (49 in Kevlar). If I'm going to go to Kevlar in a kayak, I'd want it for strength, not weight savings. So - my approach to the "idea" constructed kayak: Kevlar built up to the same weight as (flimsier?) fiberglass. Vacuum bagged construction to maximize fiber to resin ratio. Epoxy rather than vinylester resin. Not _too_ heavy gel coat layer - after all, I'm fixing it every couple of years anyway, why carry excess around all the time? (Is there not the potential for a _better_ material to coat than gel coat?) To increase stiffness, I wonder if a thin core material should be considered. Not foam or balsa or any of the thicker materials. I'm thinking more of a light fiber layer(s) between the Kevlar. Walbridge's Boatbuilder's Manual discusses this in the context of home-built WW boats in the days before plastic. Nylon, for example, increases the toughness (ability to survive impact) without adding much weight (4.2 oz vs 5 oz in kevlar). Hmmm. Builders, please comment! Mike *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Doug Lloyd wrote: ... > 5. I have witnessed catastrophic failure of a vacuumed bagged hull - not a > good thing. Are you referring to that Necky that started to break up prior to your rescue? The reason that I ask is that Necky boats are NOT vacuum bagged, and so if this is the incident to which you are referring it does not serve to illustrate your point. (Necky boats are lightweight, but without the advantages of vacuum bagging.) If you are referring to some other boat, please give us the details. Dan Hagen *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced outside PaddleWise without author's permission Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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