Paddlewisers, The local rock garden guru here in Southern California compiled some interesting info about composite vs. plastic kayaks that may be of interest. It's not scientific but is interesting. The link is: http://www.brown-web.net/kayak/discussion/plastic-composite/plastic-rules.htm Duane Strosaker *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Duane, since you are recycling this old troll of yours from a few years back I'll recycle some of what I wrote back then and add a couple of new bits. I will admit there can be vast differences in the toughness of various fiberglass kayak models due to materials used, construction techniques, and even hull shapes and sizes. Most paddlers are seeking a craft they can lift up to their car rack by themselves and will pay the extra for fiberglass or even Kevlar (TM) or carbon fiber in the laminate to save weight (at the cost of about $100 per pound saved). Yes many fiberglass kayak owners baby their kayaks but not necessarily because they have to. When you have nice things you tend to treat them better. I however revert to the "ram it full speed up the beach to keep my feet dry approach" once I have gotten a couple of scratches in the gelcoat of a new kayak. If the rocks are especially jagged and sharp edged or if there is enough barnacles that I can't miss most of them I will try to avoid landings on those spots and look for a better landing spot nearby if the waves are too big to step out in shallow water. Of course if I had a rotomolded plastic kayak I'd do the same thing to try to minimize the fins and curly-Q's that fuzz up the plastic and disrupt the smooth flow of water around the hull by sticking up into it. If I put a scratch in fiberglass it scrapes away some material rather than plowing it up into the boundary layer where roughness can really add a drag penalty to a hull. I know of kayak companies that ship their fiberglass kayaks packed into a large shipping container like cordwood and report no problems (it would worry me though that a hard raised spot on one kayak--like the peak of a coaming rim--might make a little dent in a new "green" fiberglass deck of the one it may be pressed hard against). My understanding is that the first shipment of plastic sea kayaks sent across the country were packed in a rail car this way. Apparently, there should have been a sign on it warning the customer that "contents may settle in transport this container was full when it left the factory". I heard from those who unpacked them that some of the kayaks on the bottom were only 4 inches deep. This brings up another major problem with plastic. It is plastic (that is, it changes shape). Here is a quote from Eddyline's Tom Derrer being interviewed in Paddlesports Business (Spring 1999): "I've designed polyethylene kayaks for roto-molding for other people in the past." he says. "I'd always design a good beautiful shape that would end up nothing like my original design after the molding largely because of the unstable nature of polyethylene. It's always changing shape." Not only are rotomolded kayaks likely to be different than the designer intended but once they come out of the mold they aren't even the same as other kayaks made out of the exact same mold. I learned this because of my timing turn and spin speeds in a lot of kayaks. Sometimes I would test a kayak model I had previously tested to see what effect different water temperatures or densities might have on my results and also to test my consistency over time. One day I paddled a plastic kayak that I had timed years earlier. The results were astounding. It turned twice as fast as before. Before it tracked okay but now it was downright squirrelly. I knew I had improved my turning technique a little in the interim but not nearly that much. I called the designer to see if the design had been changed. He said no but my divergent results didn't surprise him at all "They are all different" he said. He then went on to explain how they come out of the mold all warm, rubbery and soft and someone tries to wrestle them into a reasonable shape before they cool and take a set. I have since done retests on other plastic kayaks and while the differences were definitely a lot more than retests of fiberglass kayaks of the same model none was as dramatic as the one reported above. This means that if you are going to buy a plastic kayak it would make sense to try the one you are actually going to buy and then be very careful not to distort the shape too much after that. Careful storage in a cool dark place with regular rotation of position is recommended for plastic but far less necessary with glass. I tried unsuccessfully to find the newsletter article I read a several years back about the roof rack with four kayaks on it that slid off the roof of a car. Given the reputed toughness of plastic the occupants we surprised that even though it was one of the middle kayaks on the rack it was the plastic kayak that shattered and the fiberglass kayaks suffered either only minor easy to repair damage or some scuffs. If I recall correctly the plastic kayak was way beyond repair and offered in the newsletter to anyone who might want it for use as a planter. Some of my customers had a similar experience. One guy looking for a new boat was looking to find a new plastic kayak to replace the Chinook he had had for years. Seems he dropped the old Chinook and it shattered into many pieces. I guess better to find out it had gotten brittle that way than by landing hard after jumping a steep wave in the surf. Rotomolded plastic has a very limited time during which it stays flexible and therefore not brittle. Some plastic kayaks come pre-dented from the factory. Under the seat is a favorite place for them to dish inwards. Too tight shock cord bungies can create major distortions in their decks and most will dent just under there own weight (but a lot more on a hot day). Oil canning, and dents and distortions sure can be ugly and have some negative effect on the speed and handling of a boat but they are mild problems compared with some of the other disadvantages of polyethylene plastic as a building material for sea kayaks. Contrary to the pipe dreams of some folding and skin boats folks energy is lost to flexing and this is especially noticeable when the force is applied off center as it is when paddling a kayak. There is a reason Olympic racing kayaks are made as stiff as possible. Every time I test paddle a rotomolded kayak I get the feeling with the first few strokes that somebody has tied a bucket to the boat and that is what is hurting my acceleration. I then realize that I'm paddling a heavy and soft plastic kayak and that explains the slow dead feeling I get when paddling it. In fact if you made glass kayaks the same weight as you have to make rotomolded kayaks to have them just barely keep their approximate shape you would probably find out that a well build fiberglass glass kayak was tougher than a roto-molded plastic one as well (even when they are both new). Of course by the time they are both ten to twenty years old the plastic one has stiffened up a lot more as it has lost plasticizer to the environment. It gets stiffer and stiffer and more and more brittle in the process. Eventually it can be easily broken or might just dry out and crack on its own. Because it has no fiber structure to hold it together any crack will probably be catastrophic. When this grim fact becomes widely known, as more and more of the earlier plastic kayak fleet ages to this point, the resale value of used plastic kayaks will likely plummet. Fiberglass kayaks are often sold used for more (in inflated dollars) than the original buyer paid for the boat. In other word the value of the fiberglass kayak degraded slower than the value of a dollar. Storing a plastic kayak in the sun, (or ozone, or around some breakdown products of natural gas) can greatly increase the rate of plasticizer loss. Some plastic kayaks stored outside in the Baja sun only last a couple of years. A fiberglass kayak can be repaired to look like new and simple repairs are easy to do. Those plastic kayaks that can be repaired usually look like an ugly mess afterward. Repairing an old cracked (from plasticizer migration) plastic kayak is hopeless, it will just soon crack somewhere else. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. 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At 11:21 PM 2/25/03 -0800, Matt Broze wrote: >I however revert to the "ram it full speed up >the beach to keep my feet dry approach" once I have gotten a couple of >scratches in the gelcoat of a new kayak. If the rocks are especially jagged >and sharp edged or if there is enough barnacles that I can't miss most of >them I will try to avoid landings on those spots and look for a better >landing spot nearby if the waves are too big to step out in shallow water. I was getting a little ashamed of the look of the bottom of my kayak, which is currently hanging in the garage for lack of liquid water. A bottom like that isn't something you want to show in public . . . thanks, Matt, glad to know I'm not alone on this one. Coming from you, it makes me feel better. -- Wes --------------------------------------------------------------------------- Wes Boyd's Kayak Place NEW URL! -- http://www.kayakplace.com Kayaks for Big Guys (And Gals) | Trip Reports | Places To Go | Boats & Gear --------------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt's lecture about the plasticity of plastic reminded me of a friend's old Sea Runner, which had a permanent cylindrical dent in the deck caused by keeping his water bottle under the bungees there. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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