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Should you care...
First the Material:
Most of the "plastic" kayaks you see today are made of rotomolded
polyethylene, a tough, flexible and relatively soft plastic. In this
process the resin pellets are pulverized into powder and the
appropriate amount is poured into an aluminum two part mold that is
then closed and basically 'tumbled' in an oven. This causes the
powder to melt and coat the inside surface of the mold. The
'tumbling' and heating methods vary widely. Within some minutes, a
rubbery hot kayak emerges from the mold and is supported while it
cools and shrinks.
The thermoforming process requires an intermediate step that can
involve quite a variety of different materials. Before a boat can be
formed, the resin pellets first must be extruded into a flat sheet
of appropriate size and thickness. This is where the technology
takes a major departure from the rotomolding process, which is
limited to a much more narrow selection of material types.
When such a sheet is created, the process allows two or three layers
of differing but compatible materials to be formed into a single
fused layer of even thickness. Typically, the sheet that will be
used to make outdoor "weatherable" products will consist of at least
two layers of different plastic material. The first or outer layer
is frequently a modified acrylic. Acrylics have long been known to
have outstanding UV resistance and are often used in glazing, car
finishes, paints and even waxes. This layer will provide the sun
protection, gloss, and exterior color of the product. Sometimes
there is a second similar layer that exists for a special graphic
effect, such as metallic or pearlesence. Next comes the "muscle"
layer. The substrate will be much thicker and is often some form of
high impact ABS. It can be the same color but is not necessarily so.
Here I would like to dispel a myth. I often hear remarks of the sort
"Those kayaks are all made of the same stuff". Except for the fact
that yes, they are all made of plastic, nothing could be farther
from the truth. Each resin manufacturer has unique patented
formulas. They often manufacture varying grades of the same material
that have different properties. The sheet can vary in the
manufacturing process in many ways such as the ratio of thickness of
differing layers, the amount of recycled content and so on. All
these variables affect price and performance. Needless to say, the
old adage still holds true for the most part: "you get what you pay
for".
Now the process:
Unlike fiberglass or rotomolded kayaks, thermoformed kayaks are
typically formed over a mold rather than inside of one. With a
female mold, the mold determines the surface quality, but with
thermoforming the surface quality is already in the sheet and our
job is not to mess it up. There is another reason for male molding.
The sheet will stretch some as it forms. A male mold will see the
greatest material thickness on the bottom of the hull where the most
wear occurs. During the molding process itself, a sheet is clamped
into a frame that holds it like a piece of glass in a window frame.
The frame moves into an oven that heats the sheet to a high
temperature, commonly between 350 and 400 degrees. At that
temperature the sheet becomes quite rubbery and will stretch with
ease. At this point the frame moves out of the oven to a position
over a mold. The mold moves into the sheet until the edge seals
against the hot plastic. At this time a vacuum is applied to the
mold. This quite literally sucks the material down around it and
into any fine detail on the mold itself. Once cooled in this
position, the material now has a new shape and a kayak part is born.
Remaining steps to an actual boat are trimming, rigging, assembly
and detailing.
What are the essential differences? Thermoforming provides a product
similar to the quality of fiberglass in appearance and performance,
but at a lower cost. A wide variety of high performance materials
are available that are expensive, but labor requirements are much
lower than that of fiberglass composite kayaks. Thermoforming
technology itself is not new, it has been around as long as plastics
themselves. However the biggest changes are in equipment, process
sophistication and the plastics themselves. Plastics used in
thermoforming kayak are strong and they are easily repairable. Outer
surfaces are harder than other plastics and even gel coat. This
provides better abrasion resistance, no fuzz up, better UV
resistance and more weight reduction. Other changes that have
brought thermoform technology to the surface again are advancements
in adhesives. Modern structural adhesives now regularly available
have made possible the assembly of a variety of plastic parts with
high structural integrity. Unfortunately, they still do not work
well on polyethylene, but they do work well with the more expensive
plastics used in thermoformed kayaks.
What is the downside? Fiberglass will probably have the edge for a
while in overall longevity as will polyethylene in the extreme high
impact world of whitewater. Nevertheless, modern thermoform
materials offer great value and performance for the dollar spent on
recreational and performance sea kayaks and with reasonable care
will provide many many years of pleasurable use.
The future is bright too. Since Eddyline introduced its first
thermoformed kayaks in 1996, at least five other companies have
introduced one or more models, and the list is growing rapidly. We
will continue to see significant advances in material and forming
technology. We will also see more development of hybrid technology
combining plastics and composites. Ultimately, these advances will
continue to lower manufacturing costs and improve performance. Last
but not least, all trimmed and unused material is 100% recyclable.
Nothing need go into the land fill.
Tom Derrer
Eddyline Kayaks |
