There has been interesting discussion recently about durability, especially as it pertains to the NDK Romany. While I think the Romany 16 is a fine boat, I feel that it is much heavier than a 16 foot kayak needs to be. This seems true of most of the British boats. NDK and Valley Canoe do not seem to use the vacuum bagging tehniques that are common practice in North America. Also,the decks of the Brit boats seem to be laid up with a heavy fiberglas matte which must take a lot of resin to wet out. This certainly does make for a stiff deck but the added weight factor must be significant. I wonder if rigidity equates with strength in a boat as small as a sea kayak that travels at such minimal speeds? Are British boats stronger or are they just resin-heavy? My own priorities are skewed with a bias toward light weight. My Arctic Hawk weighs 46 pounds [floatation bags, no bulkheads or hatches] and, in four years of actively paddling this boat, I've not experienced any hull or deck failures. I do not surf the Hawk because the design is not suitable for that kind of use and I would not use a fiberglass boat in those kinds of hydrokinetics. That is a great place for plastic. I've also noticed that after a lengthy paddle, all kayaks seem to gain weight. On a favorite 16 mile trip, for instance, my Hawk seem to gain about 10 or 12 pounds which makes carrying it back to the car something of a chore. This is another reason I prefer a light boat. Has anyone out there experienced hull failure in a fiberglass or composite boat that could be attributed to an overly light layup? What boat and under what conditions did it fail? John *************************************************************************** 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/ ***************************************************************************
John Myers wrote: > NDK and Valley Canoe do not seem to > use the vacuum bagging techniques that are common practice in North America. This I can't understand. Are vacuum bagging techniques significantly more expensive? The advantages, to me, outweigh any disadvantages I know of. > Also,the decks of the Brit boats seem to be laid up with a heavy fiberglas > matte which must take a lot of resin to wet out. This certainly does make > for a stiff deck but the added weight factor must be significant. I wonder > if rigidity equates with strength in a boat as small as a sea kayak that > travels at such minimal speeds? I learned about boat design from a naval architect friend who taught me to sail back in the '70s. He left me with the impression that glass mat construction is for the cheapest boats and "real designers" use woven glass cloth. I just double checked Walbridge's Boatbuilder's Manual and he says that mat's good for bathtubs but not recommended for boats. One advantage of mat is that the resulting material is closer to isotropic - that is, the material properties are the same in all directions. Woven cloth is stiff and strong in two directions (along the length of the threads) but less so at angles to the thread. I've heard of folks laying multiple layers of woven glass cloth at angles to each other to reduce this problem, but my guess is that is not significant in kayaks. John, Matt or others may have more insight. > Are British boats stronger or are they just resin-heavy? If anyone wants to volunteer their boats, I can supervise the testing. I've broken more than a few big steel beams in university research. Fiberglass and kevlar should be easy! > Has anyone out there experienced hull failure > in a fiberglass or composite boat that could be attributed to an overly > light layup? What boat and under what conditions did it fail? It's not easy to compare realistically the strengths of kayaks that have failed under different conditions. Anecdotal evidence tells us less than an instrumented kayak. Also, there are other details besides the shell construction. The bulkheads, coamings, hatches and other details contribute to the overall strength and stiffness, so you'd have to compare different versions of the same boat. Make a Romany Explorer using the best vacuum bagging techniques and good woven cloth then compare it to a Brit built battleship version. That'd tell us. Mike PS - Anyone care to corner Nigel Dennis or other British designer/builders at a symposium and put the question to them? *************************************************************************** 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/ ***************************************************************************
John writes: "I do not surf the Hawk because the design is not suitable for that kind of use and I ould not use a fiberglass boat in those kinds of hydrokinetics." This makes me wonder whether a kayak which you are not confident to surf is really seaworthy. Surf and breaking waves might come unexpectedly. "Are British boats stronger or are they just resin-heavy? " A good question, which could be considered along with wondering whether light boats are of adequate strength. I haven't noticed any objective measurements of boat strength claimed by manufacturers. How would strength be measured? Chain the boat from both ends and drive a truck over? I wonder if any non-destructive testing could be devised. Otherwise, all the boat buyer has to go on is anecdotal evidence from paddlers, for instance via this list, or self serving claims by manufacturers. Does anyone know of objective strength measurement for kayaks? > *************************************************************************** > 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/ > *************************************************************************** *************************************************************************** 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/ ***************************************************************************
Peter Treby wrote: > I haven't noticed any objective measurements of boat strength > claimed by manufacturers. How would strength be measured? Chain the boat from > both ends and drive a truck over? I wonder if any non-destructive testing could > be devised. Otherwise, all the boat buyer has to go on is anecdotal evidence > from paddlers, for instance via this list, or self serving claims by > manufacturers. Does anyone know of objective strength measurement for kayaks? We could devise quite a few objective strength measurement, but getting folks to agree on which to use and how relevant they are is another story. I'd like to know what parameters are used by designers. For large ships, first order calculations can be done by assuming the ship is suspended by the ends on its bow and stern waves. Things then get complicated real fast. In general, non-destructive tests will indicate the structural integrity, but not the limiting strength. (I was an non-destructive testing technician when a university student.) Stiffness can be measured non-destructively. I would be interested in a few test results for comparisons - but these are destructive: 1 - Flexure of the overall craft loaded at its centre and supported at the ends (sagging failure), 2 - Flexure of the overall craft loaded at its ends and supported at the middle (hogging failure). These would indicate the strength of the kayak as it is supported by waves at its ends or by one wave crest at the middle. Basically we'd be testing both the deck and hull for behavior under both tension and compression. Relevant loading patterns are up for discussion. Should a day boat be subject to the same loading as a long distance touring boat (ie. load in the middle [paddler] vs load distributed [paddler + gear])? How do we support the ends - small area or large? Support the middle? 3 - Puncture of the hull from the bottom and from the side. 4 - Puncture of the deck from the top. The hull has to deal with rocks, floating objects etc. The deck has to deal with the paddler, rescue techniques, deck mounted gear (eg. towing rigs) etc. Should the puncture test be static (press slowly to failure) or dynamic (whack it with specified energy levels to failure)? What should the area of contact be and how rigid should the impactor be? What shape should it be? There are standardized testing techniques in other areas of engineering, so this has been done. The debate is about how to standardize. The problem for the consumer is how to compare the results for the purposes for which they intend to use the kayak. If folks are keen, this could probably generate as much debate as feathering or rudders. 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/ ***************************************************************************
Michael Daly wrote: > John Myers wrote: > > Has anyone out there experienced hull failure > > in a fiberglass or composite boat that could be attributed to an overly > > light layup? What boat and under what conditions did it fail? > > It's not easy to compare realistically the strengths of kayaks that have > failed under different conditions. Anecdotal evidence tells us less than > an instrumented kayak. Also, there are other details besides the shell > construction. The bulkheads, coamings, hatches and other details > contribute to the overall strength and stiffness, so you'd have to compare > different versions of the same boat. Make a Romany Explorer using the > best vacuum bagging techniques and good woven cloth then compare it > to a Brit built battleship version. That'd tell us. I think Mike's point about the low validity of anecdotes is a good one. Even so, it is useful to know which boats have broken under "normal use," and what steps manufacturers have taken (might take?) to prevent breakage. In that vein, I offer the following anecdotal evidence for Eddyline's Wind Dancer: Old layup (pre-1990): oil-canned in big surf (before I bought it) ahead of the cockpit. Serious cracks in the hull/deck seam, and lesser ones in the deck. Hull was unaffected, AFAICT. I fixed these problems, at the cost of a few pounds of resin and glass. My assessment: I believe this layup was never intended to survive 6-7 foot surf in the impact zone, and was too light in the deck region. I'd call this a case of misuse of the boat. Newer layup (vintage 1993; seems about the same weight as the earlier boat): stress cracks in gel coat on the rear deck, from self-rescue-induced oil-canning. My assessment: layup is too light, and flexes unacceptably. No kayak should yield that much when I slide my fat bod onto the rear deck! (This boat also had a 4-inch diameter tree limb fall on the very top of the deck, about 2.5 feet in from the bow, and only shows gel-coat cracks. Asessment: plenty tough for tree-limb attacks.) Also has a couple gel-coat cracks aft where some yardape over-tightened polypro line to keep the yak on a rack on a Zodiac. Assessment: I blame the yardape for this one. If I buy another Eddyline boat, I will check the layup of *the deck* for too much flexure, and suffer the extra weight needed to stiffen the boat. My field use is not abuse. -- Dave Kruger Astoria, OR *************************************************************************** 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/ ***************************************************************************
I totally agree that anecdotal evidence is just that. Tests could probably be (have been????) done with sample pieces of fabrics. Much more uniform than busting up different boats and cheaper too. Tests for breaking point, puncture resistance etc. could probably be easily done. The problem is all the different things to be tested. Hand-laid and vacuum bagged; glass; multi layers in various directional layups, kevlar, carbon and combinations thereof. Carbon-kevlar (woven together in same cloth); glass over wood and then add finishes from clear-coat (popular on expensive fabrics to show them off) to various thicknesses of gel-coat not to mention different types of epoxy or other resins used. The thing to do would be duplicate pieces of layup for various manufactures (or get them to provide them if they dare). Break and punch holes in them, then publish the results. Seems Sea-kayaker or some other publication could have a ball with it not to mention follow ups as various other layups are offered. And once the first test is done, costs for all subsequent tests would be very low. Or else some manufacturer who had confidence in their product would have them done and then be able to add a great selling-point when presenting their boats. I intend to order a boat this spring and such info would rate VERY high on things I would be considering. There would be arguments about test methods and standards but the first one to actually perform the tests and publish them would pretty much set the standards. I think it would be a great winter project for someone with more academic experience than me. Bob ----- Original Message ----- From: Peter Treby <ptreby_at_ozemail.com.au> To: <jmyers_at_longbranch.k12.nj.us>; Paddlewise <paddlewise_at_lists.intelenet.net> Sent: Tuesday, January 05, 1999 1:47 PM I haven't noticed any objective measurements of boat strength > claimed by manufacturers. How would strength be measured? Chain the boat from > both ends and drive a truck over? I wonder if any non-destructive testing could > be devised. Otherwise, all the boat buyer has to go on is anecdotal evidence > from paddlers, for instance via this list, or self serving claims by > manufacturers. Does anyone know of objective strength measurement for kayaks? *************************************************************************** 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/ ***************************************************************************
Snip** Peter Treby wrote: "Are British boats stronger or are they just resin-heavy? " I just read in Derek Hutchinsons book "Expedition Kayaking" on page35 under the category that he calls maneuvers a launch method called a "Side Drop". I am not confident that my North American made kevlar boat would survive such a launch. Maybe it can only be done in Bristih boat? Has anyone ever tried such a launch? Hal Wilton, NH Power your boat with carbohydrates, not hydrocarbons. http://www.jlc.net/~hlevin *************************************************************************** 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/ ***************************************************************************
Bob wrote; > I totally agree that anecdotal evidence is just that. > > Tests could probably be (have been????) done with sample pieces of fabrics. > Much more uniform than busting up different boats and cheaper too. > (Large Snip) An extensive body of test data exists for a wide range of laminates (done by fabric and resin manufacturers and others) but, while it provides some comparative measure of the various strengths it doesn't answer the basic questions, "How strong is strong enough" and "what are the relative importance of weight, impact resistance, stiffness .etc. etc". I love the numbers but they don't tell me the difference between "just right", "under built", and "overbuilt" not to mention the difficulty in understanding them. Try comparing such disparate materials as Royalex, FRP, Polycarbonate and Polyethylene and the numbers don't make a lot of sense without expected loads. A tough problem where publication could cause more confusion than good. Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** 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/ ***************************************************************************
Hal Levine had written: > I just read in Derek Hutchinsons book "Expedition Kayaking" on page35 under the > category that he calls maneuvers a launch method called a "Side Drop". I am not > confident that my North American made kevlar boat would survive such a launch. > Maybe it can only be done in Bristih boat? > Has anyone ever tried such a launch? I've used a P & H Sirius in "side drops" off a pier 4-5 ft above the water a couple of times strictly for showing off and it worked well for the stated purpose. The Sirius which has a pronounced v hull is excellent for this sort of tomfoolery as the boat can be positioned with its keel slightly over the edge of the pier resting on the pierside slab of hull before you (carefully) enter the boat. The apparent strength of the hull inspires such horseplay that I would never have considered in a typical American made boat. Larry Koenig Baton Rouge, LA *************************************************************************** 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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