Cedar Compared to Other Materials
Though wooden kayak building is too labour intensive to compete in pricing with the fiberglass* and some high end composite** counterparts, wood is still one of the best structural materials for small boats. Wood and epoxy are used to build some of the best multi-hulled sailboats, sprint kayaks and rowing shells.
Wood is up to ten times stiffer than fibreglass and nearly six times stiffer than a kevlar/epoxy composite. It is strong in tension (pulling); strong in compression (pushing); strong in torsion (twisting); strong in shear (tearing) across the grain; and is less affected by severe fatigue cycles than more stiff and brittle materials like carbon or GRP*.
Cedar/epoxy kayaks are lighter than comparable fiberglass craft, so they accelerate quicker, carry more gear and supplies, and are easier to "spin" on wave tops and in surfing conditions. Lighter boats are better on shore too; they are easier to carry or lift on or off a vehicle.
Cedar/epoxy kayaks are tough. The wood (aside from being beautiful) provides a very stiff core material that is less likely than a foam core to seperate from the sandwich core. Wood is also much lighter for its given stiffness than a hull constructed from solid fiberglass. These kayaks are are puncture and abrasion resistant and tolerate normal use like dragging over gravel or sand beds better than fiberglass or plastic because scratches are the same color and texture as the surface. Repairs are easy to do and can be completely hidden. Even serious damage, should it occur, can be effectively repaired so as to completely restore the original strength, performance and beauty.
* Fiberglass kayaks use glass-reinforced-plastic (GRP.)
** High end composite kayaks use materials like carbon fiber and kevlar.
Strength and Stiffness
The mechanical properties of the sandwich core are the main source of strength but there is an additional bonus that comes with
wood strip kayaks. The cedar strips forming the kayak are inherently stiff and strong themselves, making the shell stronger.
No other lightweight core material I know of has the same self supporting qualities. I notice this unmistakably, as soon as
the kayak is completely stripped and still on the strongback mold. The 1/4" shell of white cedar stays rigid even in the spans
between the stations of the form. There is no flex when you sand or plane. One enormous advantage of a rounded wood strip kayak is
its compound shape. Try to flex an egg shell of an unbroken egg. It is enormously stiff because of its compound shape,
not the thickness of the shell. The examples of this principle of nature are everywhere around us and the same applies
exactly to the smooth round surfaces of wood strip kayaks. A flat plate such as a plywood panel will always be less stiff
than a compound shell made of the same material and thickness. Because of this structural advantage, you will be very
surprised how solid the whole kayak feels when out in rough water.
As an example of strength, Ted Moores of Bear Mountain Equipment builds a 30 foot C15 sprint-racing canoe. It has a crew of 15 paddlers weighing about 2,350 lbs. He builds these out of exactly the same materials I use to build kayaks: 1/4 inch cedar strips with a single layer of 6 oz fiberglass cloth
Light weight is the forte of all core structures used in boatbuilding and wood strip kayaks are no exception. They belong to a class called monocoque shells. (From French- mono: single and coque: shell) Monocoque shells are structures where the walls support themselves including all other loads and stresses. They don't need any internal reinforcement such as ribs, stiffeners etc. This eliminates a lot of superfluous weight. This is where wood strip sea kayaks really shine. The composite core has sufficient reserve stiffness and strength that even long and larger kayaks can stay light. This means that everything you do with the kayak is simplified: loading and unloading, paddling, steering and covering longer distances with less effort.
Wood-strip kayaks are designed to please the kayaker, not the material from which it's built. Compound, concave or convex sections and almost any radius of curvature are possible to achieve with wood strips. Wood strip kayaks hold their shape through any conditions and the strip method imposes no restriction on hydrodynamic efficiency. A smooth low friction hull means that you will get where you want to go faster with much less effort. This is the ultimate hallmark of strip building.
No matter what kayak type you have, there is always some compromise to deal with. Plastic kayaks weigh a ton and are slow, composite kayaks are expensive and are heavier than 'strippers', fabric kayaks rip and need very high maintenance, plywood kayaks do not have the aesthetics of strip kayaks and most do not have the optimal hull forms at that. Wood strip kayaks do have a weakness and that is that they are sensitive to impact. Thus you should not anticipate using your wooden kayak in white water. I have done this and ended up with only a few scratches but I did not have any direct impact with rocks only passing scrapes. Regardless I do not recommend it.
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