I have used the heat shrink Dacron to make a 14 pound canoe of Platt
Monfort's design - for that purpose it works great. It's really strong - for
a 14 pound canoe.
However, I don't think it's going to work out so great for an 80 pound Old
Town. The heaviest Dacron I can find is 1.9 ounces/sq.yard - way lighter
than the 6 ounces per yard glass you would probably use for a canoe or the
13-14 oz/yard that #10 canvas duck weighs. (Many people, myself included,
use 2 layers of the 6 oz glass on a canoe bottom). Of course I'm comparing
apples to oranges to grapes - these are 3 different fabrics with different
properties and they are used with different coatings which may be as
important as the fabric itself, but my point is: the Dacron is in a
different weight class than the glass and canvas fabrics typically used for
traditional canoe construction.
I believe the main function of the fabric covering on a wood canvas canoe is
to make the hull water proof and provide abrasion resistance and increase
impact resistance. The way I waterproofed the 1.9oz Dacron was by simply
varnishing it - doesn't add much weight, but it doesn't add much abrasion
resistance, either, at least not to the degree that 2 layers of 6 oz glass
in epoxy will, and not to the degree that #10 duck canvas properly filled
with a good hard filler will. There are other coatings used on the Dacron
and you could add 2 or 3 layers, but I think you would have to agree, in the
context of the Old Town, using the Dacron would be experimental.
Has anybody actually tried this?
I'm curious to learn what you mean by:
covering with glass fibre and resin adds weight faster than strength
There are many kinds of 'strength' - impact resistance, tensile strength,
puncture resistance, etc.
I prepared test panels and dropped a 46 ounce window weight on them from
various heights. The damage I saw from a 4 inch drop on a panel with epoxy,
no glass, was about the same as from 16 inch drop on a panel with the same
amount of epoxy, but 1 layer of 6 oz/yd glass. Judging the damage was
somewhat subjective - I measured the diameter of the craters and looked for
hairline cracks.
I know from weighing a 14 ft canoe before and after glassing the interior
that one layer of 6 oz in epoxy added 3 pounds to a canoe which weighed 48
lbs, completely finished. So it would appear that a 6.7 percent increase in
weight added a 300 percent increase in impact resistance. This assumes the
impact force has a linear relationship to the height of the drop - I don't
know enough physics be sure this assumption is valid, but I'm guessing if
it's not linear then it's MORE than linear, so my assumption is probably
conservative.
--
Gary Wright
you can see the 48 pound canoe at:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=3617885338
___________________________________________
In article ,
(William R. Watt) wrote:
covering with glass fibre and resin adds weight faster than strength.
one method of recovering canvas is to use heat shrink dacron. Platt
Monfort has an inexpensive booklet of instructions at www.gaboats.com.
you'd have to replace any bad wood for strenght but you don't have to
stretch the dacron or fill it like you do the canvas. I don't know about
making up your own ribs as they are usually half round to save weight.
(You could try the oak trim at your local home improvement store if its
not full of finger joints.)
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