Although there are more than two types of manufacturing processes for producing kayaks, really only two are worth talking about – composites and rolomolded polyethylene. Composite fiberglass, Kevlar and carbon fiber kayaks are considered to be the pinnacle of kayaks to aspire to have. After all they look nice and cost at least twice as much as their rotomolded high density polyethylene counterparts. The rotomolded yaks look like some kid’s toy in comparison to the composite kayaks. I want to want a composite kayak, but yet when I think about it logically, I just can’t. The rotomolded is where it’s at, and I am actually amazed that so many composite kayaks get sold. I guess I should back up a bit to explain what rotomold and composite is.
Rotomold is the process by which there is a large mold cavity which is filled with some pellets of plastic – in this case high density polyethylene, a low cost tough plastic. The mold is heated up until the pellets melt and cooled slowly while the mold is rotated – hence the name rotomold, huh? As the mold cools, the plastic solidifies more or less on the outside of the mold in a consistent manner, the end result in this case being a kayak. Rotomolding is good for when you can’t access the inside of a part to put another mold in for the injection mold process, which is the case for the shape of a kayak.
kayak rotomold
Composite on the other hand is a fabric – either fiberglass, Kevlar or carbon fiber, impregnated with a resin which hardens. The fabric is mixed with the epoxy resin, then hand-laid into molds forming the outside surface. A bag is placed over the mold under vacuum, making sure the resin is throughout the fabric and also is pressed firmly against the mold. The part against the mold is the outer surface of the kayak and is very smooth, the inside surface is rougher. Nowadays gel coat is applied to the mold before laying in the fiber so the color becomes part of the outer surface. The parts are taken out of the mold, and the edges are trimmed. In the case of a kayak, the top and bottom have to be formed separately, since the mold needs to be accessible. The two halves are glued together after hardening with a strip of molding. The end result of a composite is a very stiff material and is lighter than rotomolding, since the material is very thin and controlled by hand laying.
hand laying the composite cloth in the mold
There’s really only two functional reasons why one would want a composite kayak over a rotomolded – stiffness or weight. Composite construction is extremely stiff, though is not necessary for the function of a kayak. By nature of it’s shape and geometry a kayak itself is very stiff compared to a canoe because the top is closed and not open. Not only that, stiffness counts when there are high loads involved, that’s not the case in a kayak. The weight concern is a little more practical, although not much. A composite kayak is maybe 7 lbs lighter than a rotomolded one when you’re talking about a 50lb kayak, or about 10%-15% which is decent but not a huge advantage. There is one other advantage, although not functional is aesthetics. Composite kayaks look shiny and great which I think sways many people.
Rotomolded material on the other hand looks like kid’s toys probably because many kids toys themselves are rotomolded. They’re plastic in all kinds of crazy bright colors- orange, red, yellow. One disadvantage is the color will fade or discolor (i.e. red turn to pink) with constant exposure to UV light, although nowadays UV inhibitors in the plastic minimizes that effect. Where HDPE shines it it’s toughness. I throw my kayak around like a midget at a carnival and play plinko with it off the rocks on a regular basis and it keeps on ticking. Most of the adventures and the geography of the area I paddle in, tend to have vary sharp rocks everywhere (i.e. Canadian shield) or are shallow rivers with shallow rocky bottoms (i.e. Grand River). I also drag my kayak around on the grass and through stump covered and rocky portages. With a rotomolded kayak, despite the scratches the hull gets, it’s not a problem. If my kayak was a composite kayak, it would be shattered, full of holes and have patches all over it by now, not to mention I am sure a few trips would have been ruined due to a leaky kayak. Not only that, it costs half as much as a composite kayak, as composites are very labour intensive. All that makes a rotomold kayak the obvious choice.
The bottom of my kayak showing it's battle scars
Like I mentioned earlier... I want to like composite kayaks because they look real nice (esp. carbon fiber), but I just can’t in the end – the rotomold’s functionality is just so much better than a composite kayak. When I see someone driving down the road with a composite kayak I wonder what these people actually do with their kayaks, because I’m sure they aren’t having as much fun as I am with mine. I admit that I do refer to people with composite kayaks as posers. Perhaps if you kayak in places with sandy beaches, not many rocks around, and deep water everywhere that’s fine, but if you really want some adventures the rotomold is the only way to go.
how much does the mold weight ??
ReplyDeleteGood read, thanks:)
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