Great article, William. Can I quote it and provide a link to it from
my website? Most of the people using alternative sail materials are
using polytarp, but a few of my readers have asked about Tyvek. I
have just a little bit about it in my article on alternative sail
materials at http://www.messing-about.com/weekender/sails.html and I'd
like to include your experience, as the information I have is spotty
(and needs to be updated!)


On 27 Jun 2004 14:01:47 GMT, (William R.
Watt) wrote:

following up on a previous post where I was asking for info on Tyvek sails...
I just finished making a tyvek sprit sail on a sewing machine.
The description below is also at www.ncf.ca/~ag384/TyvekSail.htm.
I hope to add photos when the film in the camera is done and developed.

-----------------------------------------------------------

This tells how I made a 30 square foot sprit sail out of tyvek
(tm Dow Chemical) house wrap. The tyvek came from a construction
site. I assumed house wrap came 10 feet wide so I asked for 10
feet to get a 10x10 piece. This tyvek was only 4.5 feet wide. I
didn't say anything when the guy brought me a narrow 12 ft strip
of tyvek. He wouldn't take any money for it. At home I tried to
figure out how a sail could be cut from the narrow shape but gave
up. The tyvek was rolled up and put in the back of a closet.

The home made light nylon sprit sail on the Dogskiff was
getting baggy after four years of use and losing its ability to
point, so I took another look at the tyvek. I've come to prefer a
sprit sail with a mast sleeve after making one for the one-sheet
Loonie. The sprit is tied to the sail, not the mast, so the sail
can rotate freely around the mast. Ideally a rotating mast is
wanted for a sprit sail but masts don't always rotate well.
Hanging the sprit on the sail frees the sail from the mast so the
mast doesn't have to rotate. By taking two 18 inch slices off the
top of the tyvek and folding them over to make a mast sleeve I
was able to draw a sail 5.5 ft wide and 9 ft tall. For the shape
of the sail I used the information I collected from various
written sources and put on my website, and got a sail of the
recommended proportions.

Before making the sail I cut an 8.5 ft, 1.75x1.75 inch mast
out of a used 12 foot spruce 2x4. The corners were roughly sawn
off with the blade set at 45 degrees to make an 8-sided mast and
then a 40 pound weight was suspended at the midpoint of the luff
to measure the mast bend. (The weight is supposed to be 50 pounds
but I had a 40 lb concrete block handy.) That's when the mast
broke. My plan to cut around some nail holes in the wood had not
worked out. I went to the public library, consulted Fred
Bingham's book, made an 8-sided spar gauge according to his
illustration, and cut a shorter mast out of an 8 foot spruce 2x4
which had no nail holes in it, avoiding the larger knots. The
mast has a 2 inch bend, the same as the 7.5 ft mast for the
existing sail which was also cut from a spruce 2x4. Recently I
read a different opinion that the weight for measuring the mast
bend should be half the sail area. I assume that's in pounds and
square feet. For a sprit I decided to use the one off the nylon
sail, a sectional spar made out of three discarded tubular broom
handles, by replacing the middle section with a shorter one cut
to suit the new sail. By interchanging the middle section the
sprit serves both sails.

All of the descriptions of tyvek sails I found on the Internet
used double-sided outdoor carpet tape to join the seams. I wanted
to try sewing the sail on a sewing machine instead. From the
condition of the mould on the delaminating carrying case I'd say
my second hand portable sat in a damp unheated garage for a few
decades. I had to hold my nose and discard the case when I bought
the machine for $5 at a rummage sale. It was cleaned and oiled it
and put aside for a couple of years until I decided to make this
tyvek sail. In lubricating the sewing machine again I got
sidetracked dismantling the machinery to see how it worked. It
has stitch length adjustment, tension adjustments, zigzag
adjustments and decorative stitch cams all cleverly built into a
small space. Eventually I put the sewing machine back together
again and started sewing the sail.

Cutting the tyvek was easy. The scissors did not have to be
opened and closed, just pushed along the pencil line, cutting
like a knife. Sewing the tyvek was a lot easier than sewing
cloth. (I had previously sewn the nylon sprit sail on a sewing
machine.) I read somewhere that a zigzag stitch should be used on
sails to allow for seam stretch so I set up the machine for a
zigzag stitch and tested it on some of the cutoff scraps. Sewing
hems in the edges was a cinch. Tyvek is like stiff paper. To make
a hem just fold the tyvek over and crease it down and it stays.
Then run the hem trough the machine. Tyvek is slippery and
doesn't get pulled through under the needle by the jaws on the
sewing machine very well so I helped feed it through by hand.
Being stiff and slick the tyvek went through fast and clean. Very
easy to sew. The only problem was I set the jaw (foot) tension
tight to try and pull the slick tyvek through the machine and the
jaws scored the underside of the tyvek. I don't know if that
weakened the fabric very much. Another time I would not set the
foot tension so tight, checking for scoring on the test material
before starting to sew the sail. The machine was able to sew
triple thick reinforcement patches at the corners of the sail.
When sewing through four thicknesses of material at the ends of
some seams I turned the wheel by hand. Because of my lack of
sewing ability the seams are pretty ugly. I didn't want to take
the time to double stitch until I tried the sail to see if I
liked it. I found it helpful to push two tables together to
support more of the sail when sewing with the machine.

The things I don't like about tyvek are the advertising
printed on one side; the way the surface wore away when I tried
to erase pencil lines (decided to leave the pencil lines on the
sail); and the noise. Tyvek is very stiff. It makes a loud noise
when it moves, not what you want for bird watching and wildlife
study. I call it "thunder paper". According to reports on the
Internet the noise subsides as the tyvek gets broken in. One
other disagreeable thing about tyvek is the force needed to push
a needle or pin through by hand. Hand sewing is more difficult
than with fabric.

Here are a some details about this particular sail.

1. The curves were measured back from the edges of the sail.
That may be obvious to most people but I had to think for a while
about how to do it. The sail was cut straight as large as
possible from the piece I had, and the camber measured in from
the edge, then a batten was bent around three bricks (two
endpoints and point of maximum camber) to draw the curve.

2. The luff has two cambers, the normal one 1/3 up from the
foot, and the one for the mast bend 1/2 way up. The two curves
were drawn independently along the edge. A pair of dividers was
used to add the curves together at several points along the luff,
and the combined curve drawn freehand by joining the points.

3. The luff curve was drawn on the sail and the mast sleeve
was sewn on along the curve. That may also be obvious to most
people but it took me a while to figure out how to avoid cutting
a curved mast sleeve.

4. A triple-thick pocket was hand sewn into the top of the
mast sleeve at the front to receive the top of the mast.

5. The sprit hangs off a permanent loop of line which slips
around the mast and runs up the inside of the sleeve to the top
at the mast pocket. The loop around the mast keeps the sprit
close to the mast. The loop protrudes through an opening in the
front of the mast sleeve. Because the mast sleeve on this sail
was made from two pieces I arranged the opening where the two
pieces are sewn together, making it easy to hem the opening.

6. Someone wrote on the Internet that grommets do not hold up
well in tyvek. One eighth braided nylon line was hand stitched
along the edges of the corner reinforcements leaving a loop at
the corners for tying on the sprit and mainsheet. The line was
crossed over itself at the corner so the strain is directed along
the line.

- END -

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