Subject: Re: [baidarka] Kayak Covering
From: thomas-simpson (thomas-simpson@shaw.ca)
Date: Tue May 18 2004 - 15:48:15 EDT
The very thin urethane coating doesn't sound good . The weight of the
fabric may be 12 oz but it is the tightness and type of weave that is
important.
George Dyson has gone to the trouble of finding a variety of uncoated
nylon and polyester fabrics which work for kayak skins and offers them
to the public at reasonable prices.
Another alternative is to use what TomYost uses , an 18oz PVC coated
material which by all reports works very well.
http://yostwerks.com/SkinMenu.html
Dyson, Baidarka & Company
435 West Holly St., Bellingham WA 98225
telephone: 360-734-9226 -- fax: 360-671-9736
Kayak Skin Materials, September 2002
Over the past 22 years, we have sold 38,189 feet of kayak skin
material--now covering some two thousand boats. This sheet makes no
attempt to ex-plain how (or why) to cover kayaks with these mate-rials;
it is just to help you select which of the avail-able materials you may
want to use. Before discuss-ing specific fabrics, there are three
general ques-tions--closely related and without definite answers--to be
discussed first:
1) Nylon vs. Polyester. About 3/4 of the material used so far has been
nylon (polyamide); but use of polyester (Dacron) has been growing in the
past few years. There are two reasons for this: a) we are selling more
material to builders of traditional wood-skeleton kayaks, and
dimensionally-stable polyester is less likely to distort
lightly-constructed wooden frame-works by shrinking up too tight, and b)
more builders are using one-part or water-based polyurethane coat-ings,
whose lesser elasticity and adhesion is better matched to polyester than
to nylon. (The coating should be more elastic than the fabric to which
it is expected to adhere). If you use an elastomeric, solvent-based
coating like Hypalon (chlorosulfonated polyethylene), Neoprene, or one
of the elastic but very expensive 2-part polyurethanes, however, nylon
will produce a tougher, more damage-resistant skin. Nylon's greater
elasticity makes it easier to cover complex curves, but the looser-weave
polyester fabrics drape pretty well too--especially in twill. Bottom
line: polyester is better for the perfectionist; nylon is better for
those who paddle loaded kayaks into rocks. Most kayak builders fall
somewhere in between.
2) Shrinkage. An essential characteristic of all the fabrics we sell is
that they will shrink. The question is how much! Shrinkage usually
ranges somewhere between 1% and 5%. Getting the tension right re-quires
careful tuning--see what happens if you loosen or tighten a guitar
string by a quarter of an inch. Nylon's behavior is especially
complicated be-cause it tends to loosen (even when coated) by ab-sorbing
ambient moisture and then tightens as it dries out. So you are aiming
for middle ground: the skin (before coating) should fit snugly, but not
drum-tight. As one builder describes it, "If you drop a quarter on it,
it shouldn't bounce." From the point of view of the boat's structure and
performance, it is better for the skin to be too loose than too tight,
but from the point of view of the builder, too loose (suggesting sloppy
workmanship) is worse. You shrink nylon by apply-ing moist heat (wetting
it and going over it with an iron so that you are steaming it without
drying it out). The moisture relaxes the skin while the heat shrinks it,
so that when it dries out it will be taut--hopefully not too tight. If
you attempt to shrink nylon with dry heat--either with an iron or a heat
gun--the combined drying and heat will tighten it up so much that the
fibers are permanently stretched, and when it returns to room
temperature and absorbs ambient moisture, it will be looser than when
you started out. Polyester, however, which does not absorb moisture, can
be shrunk with a dry iron (safer than a heat gun) and the resulting
tension remains stable: "what-you-see-is-what-you-get." Some people view
nylon's idiosyn-crasies in response to moisture as a disadvantage; some
people view it as an acceptable part of a craft whose relationship to
water should be that of a living thing.
3) Coatings. No coating (so far) is ideal. In general, more poisonous
solvent-based coatings perform bet-ter--especially in sticking to
nylon--but water-based coatings can be toxic too. The main reason to
favor polyurethane over Hypalon is that it is more widely available (as
floor coatings, concrete coatings, etc.) and results in a translucent
skin. In general--and there are numerous successful exceptions--if you
want to use a translucent polyurethane coating that is a good reason to
choose a polyester skin. If you choose to use Hypalon--best, in our
opinion, for long-term du-rability, both because of UV resistance and
because the surface can be easily replenished over the years--that is a
good reason to favor nylon skin. As for which coating to use on the
lighter fabrics: Hypalon is definitely more robust. But if you use
translucent urethane, the kayak is slightly lighter, looks a lot
lighter, and tends to get treated much more carefully, and so may last
as long or longer in the end.
Now the specific fabrics (weights in ounces per square yard, and prices
in US Dollars per lineal foot):
8N67: 8-ounce Nylon, Oxford weave, 67-inch width. One of our most
popular fabrics, easy to work with and very low cost. The supply is
reliable and it is usually in stock. The low cost is because it is
"sec-ond" quality which means there may be very occa-sional minor
cosmetic flaws. If we find a serious flaw in rolling out your order we
stop and go on to the next acceptable length. The weave (Oxford is your
stan-dard over-and-under symmetrical weave) is just about right--loose
enough to drape acceptably and tight enough to hold a seam. Shrinkage is
moderate, and well suited to lightly-framed wooden boats. $2.00
9PE66: 9-ounce Polyester, twill weave, 66-inch width. This is our
lightest polyester--and still more than twice the weight of the
3.7-ounce Dacron com-monly used for covering aircraft. Since the fabric
has not been shrunk at all at the mill, the weave is very loose and it
can be difficult to work with (in general, the heavier fabrics are
easier to work with than the lighter ones). And since it shrinks
considerably, seams have to be sewn (or stapled) carefully to avoid
pulling the weave apart. A few people are very happy with this
material--especially Harvey Golden, who has used it in covering his
growing series of replicas of the kayaks he has been surveying at
museums around the world. The twill weave (same as denim) holds coatings
well, and because of the light weight, even with minimal coating the
surface remains quite smooth. $2.00
12NB65: 12-ounce Nylon, 2x2 basket weave, 65-inch width. This is classic
"ballistic nylon"--now popularized in sporting goods and luggage, if no
longer used in bulletproof vests. Basket weave (sym-metrical
over-and-under, but with two bundles of fi-bers at a time) makes for a
less-smooth but pleasantly textured surface. Weave is a bit loose, and
shrinkage is moderate. Cost is low. We do not have a reliable supply,
but presently have lots in stock. $3.50
12N75: 12-ounce Nylon, twill weave, 75-inch width. Our most popular
fabric, middle-of-the-road all around and reliably supplied. Very
user-friendly weave, moderate shrinkage, drapes well, holds seams. Twill
weave is tough and good at holding coatings, resulting diagonally-ridged
surface looks good on deck where less coating conceals the weave. Well
suited to wood-framed baidarkas that will be actively used.
Near-identical sibling to the slightly heavier 15N72. $5.00
13PE79: 13-ounce Polyester, Oxford weave, 79-inch width. This was the
first polyester fabric we distributed, and it has developed a small but
loyal following over the years, led by custom kayak-builder Bill Low.
This material has been almost fully pre-shrunk, so the weave is
exceptionally tight--making it somewhat stiff and difficult to use.
Because of the dense structure, it takes very little coating to
saturate, but there is very little porosity to encourage the coat-ing to
mechanically adhere. Due to UPS length re-strictions, it is much more
economical to ship small quantities of fabric folded than rolled, but if
you re-ceive this material folded, unfold it and roll it up smoothly as
quickly as possible, since like permanent press polyester trousers, it
tends to hold a crease. $6.00
14N88: 14-ounce Nylon, Oxford weave, 88-inch width. This material will
probably be discontinued when the current supply runs out. It's a tough,
dense cloth that has been used (predominantly in 65-inch width) on many
kayaks over the years, but we have not found enough demand to purchase
it regularly in large quantities and have been focusing our attention on
products from other mills. The main reason to use this material (over
the 12 or 15-ounce twills) is if you have a need for the extra width. $7.50
15N72: 15-ounce Nylon, twill weave, 72-inch width. We have been
supplying this material to builders since 1982, and it has proved its
worth on many hundreds of boats--ranging from short retrieval kayaks and
surf boats to 25-foot aluminum-framed triples whose builders want to
keep the boat light enough to be easily lifted on top of a car. It is
slightly heavier, but otherwise identical, to 12N75. Almost always in
stock. $6.00
16PE82: 16-ounce Polyester, 2x2 basket weave, 82-inch width. We acquired
a large run of this material about a year ago, and it has been receiving
good re-views so far. Weave is a bit loose, but it will still hold a
seam and of the three polyester fabrics available it is the easiest to
use. Shrinkage is moderate and easily controlled. The price is
excellent, especially given the extra width. $5.00
26N68: 26-ounce Nylon, double weave, 68-inch width. An amazing fabric,
which we discovered in 1980 and which has withstood decades of severe
abuse on many large, heavy boats. It is the heaviest material we sell,
but it is also one of the easiest to use. The thick, interlocking
structure makes it behave more like real sea-mammal skin than any-thing
else we have seen. Coatings penetrate and bond well, and because of the
layered structure the surface can suffer serious abrasion and the skin
will still not leak. Unfortunately its manufacture has been
discon-tinued, but we bought up the last production run of this material
and should have it on hand for many years. Also unfortunately, it is
available only in 68-inch width, so wider doubles and triples require a
small patch on deck where the two sides of the fabric don't quite meet.
Otherwise perfect for covering large, hard-working baidarkas--and
umiaks, too. $10.00
George Dyson 9/14/02
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