Subject: Re: [baidarka] Gunnels
From: Peter Chopelas (pac@premier1.net)
Date: Tue Oct 16 2001 - 22:45:31 EDT
Jeffrey,
I think there is probably more concern for this than is warranted, and a lot
more folk lore than actual science behind the idea. The gunnels are held in
place pretty good by the deck beams, frames and skin, I do not think they can
move much to allow warpage. Water saturated wood can be reshaped under
stress, but it will not move much from your "as-built" position once
assembled. Especially if you sealed and finished the wood during assembly, it
will not gain or lose much moisture.
You do need two gunnels that are the same stiffness, that is so it will flex
the same amount under the same load, or it could make your kayak squirly I
think in rough conditions (it would cause the keel line to flex to one side as
the frame flexes, steering the kayak as it goes over humps and through
troughs).
It is simplest to match the stiffness if they are cut from the same piece, but
even that is no assurance of similar behavior under load. The grain may be
more dense on one side of the plank then the other, there could be a defect or
sap pocket hidden from sight on one side, etc.
If you can match the stiffness of two totally different pieces they should
behave the same in the kayak. It is easy to check in a lumber yard. Support
each end of two pieces side by side and put a heavy brick on each one, if they
deflect the same, they will behave the same in the kayak. You can do this by
pushing down with your hands and feel the stiffness. this is a good idea even
if you cut them from the same piece. Ideally you would want to test the
deflection with the pieces this on edge, but I think testing them this way on
the flat will work just fine, you are only comparing flexural properties of
the wood, and if it is matched on one axis, it will match on the other
presuming the grain runs the same way in the plank.
BTW, Doug fir is a good strong wood with a fair amount of rot resistance and
will work fine in a skin kayak, but it is stiffer than most traditional kayak
frame material and about 25 percent heavier. Consider using the lightest
woods which Northern white or red cedar [the lightest of all], and some types
of spruce with balsam fir and Eastern white pine not far behind, Redwood is
not bad either, but a bit stiff too. the cedars, and Redwood also have the
highest rot resistance, but if you store the kayak dry in a shed or garage, it
will not make much difference. Shop by price if you like or by what is
available.
If you select from a pile at the lumber yard, find the lightest, most strait
and open grain pieces, test for similar stiffness, and do not worry about it
too much. Anything and everything has been used for a kayak frame, from
bamboo to aluminum to hardwoods (too heavy!).
kayak frames have been
Peter
----- Original Message -----
From: Jeffrey Hatton
Sent: Saturday, October 13, 2001 2:15 PM
Subject: [baidarka] Gunnels
I am moving toward starting my first skin kayak. Do most people split their
gunnels from one piece of wood or utilize two separate pieces of wood? In
my
area, clear 1X Douglas (tongue and grove flooring). fir is relatively easy
to
come by. Clear 2X material is significantly harder. Does anybody have any
experience with the boat becoming warped due to the gunnels not being cut
from
the same piece of wood?
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