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PolySail International
MAKING A HIGH PERFORMING
WHITE POLYTARP SAIL
By Dave Gray, Principal
Partner
All Rights Reserved
White polytarp sails or PolySails are inexpensive polyethylene
sails that are simple to construct and nearly indistinguishable from
traditional sails in looks and performance. While often dismissed by large
sailmaking firms and independent sailmakers as “plastic” sails that have no
place on a fine wooden boats, those who have used the tough laminate PolySail material to construct their own
sails have rarely been disappointed in the results. New research using an
Instron machine to test initial fabric strength shows that a 1” x 14” strip of
5.5 oz. white polytarp material fails at 95 lbs./sq. in. That figure was twice
the breaking strength as rip stop Nylon, 150% stronger than Dupont Sorona, 72%
as strong as Dacron, and 94% as strong as one of the North Sails’ laminates
that was tested.
Using one of our White
PolySail Kits and the following simple, ten-step construction process, even a
novice can create a small, taped PolySail
within a few hours. Make your sail in the morning and be on the water by
afternoon–often for under $100. Allow additional time for constructing and
rigging multiple sails, large complex sails, and sewn sails.
To
make a PolySail, you will need your sail plan dimensions and the following
materials, space, and attitude:
·
A
PolySail Kit (available from Dave Gray at PolySail International (317)
915-1454).
· A large, clean, dry, and open work space inside or out, e.g., lawns (but not with wet or freshly mowed grass), garages (but not with oily or dirty floors), clean driveways, large decks, gym floors, etc.
· A long, fairly stiff steel measuring tape to create nicely curved (fair) lines and stakes or large pole barn nails for stretching out the material on a lawn. On other surfaces use heavy weights for holding down the material.
· Finally, you simply need a strong determination to finish up and get out on the water quickly.
Sailmakers
mainly use two methods to create the curvature (camber or belly) needed for a
sail to work. Professional sailmaking lofts create part of this curvature by
cutting and shaping panels of cloth or synthetic material and then sewing these
panels together. This part of the process is generally labor intensive and very
expensive.
The second method involves cutting the edges in a curve. The more curve, the more belly in that edge of the sail. When the curve is straightened by a mast or the tension of a rope, shape is forced into the sail. This edgecut method probably preceded the “shaped panel” approach by centuries. We use this simple edgecut method along with carefully placed V-Darts on large sheets of white polytarp material to construct PolySails that are difficult to distinguish from loft-made sails in appearance or performance.
Like
many small boat builders, once you get "hooked" on PolySails, you
will probably build a number of experimental sails improving your technique and
the appearance of your finished product each time. But enough theory for now,
let's get started!
(Note: This is
a simplified version of our 8-page kit directions for constructing
high-performance PolySails.)
STEP 1, STAKE OUT THE MATERIAL: Unfold the polytarp material and stake or weight the
corners and edges.
STEP 2, LAY OUT THE SAIL
PLAN: Mark out the rough dimensions of the sail on
the polytarp material with the kit’s dry-erase marker. (You can remove these
marks later.) Use the measuring tape to make a line of dots or dashes between
each corner. These lines becomes the baselines. Sight along the tape to make
certain the baseline is straight and make a mark at each foot of measured
length. Do the same for each side.
STEP 3, MARKING THE EDGE
CURVES: Most
sails have some edge “rounding” in the foot and luff to help create belly or
fullness while the leech is often straight or “hollow”. After you have marked
the baselines, use your tape measure to create a fair curve to the outside of
the luff and foot baselines as shown in the illustrations below. These
“rounding lines are about 2 ½” from the baselines at apex of the curve. Next,
run double-faced tape along the new lines in the luff and foot and along the
outside of baseline in the leech.
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Notes on the
illustrations: The illustrations show 3"-4" cutoffs at the head and tack. The cutoffs allow you to insert a headboard at the head of the sail and a V-Dart at the tack of the sail. These cutoffs can be eliminated if you are planning to use only edge rounding to shape your sail. I recommend at least a 3” x 18” V-Dart in any four-sided sail of 70 feet to 100 sq. ft. (The dart is 1 ½” at the base once it is closed.) The dart should be increased for larger sail areas. |
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STEP 4:
CUTTING OUT THE SAIL SHAPE: Starting from the tack, work your way up the luff,
cutting out the sail shape with a utility knife or sharp shears.
PRECAUTIONS:
Fold and tape up any
V-Darts before cutting out your final sail shape. Note that finished
V-Darts will affect edge shape and dimensions. - Use the outside edges of
the double-faced tape as a guide for cutting!
STEP 5, TAPING
IN THE ROPE: Once
the sail shape has been cut out, you can fold up the excess material and remove
it. Make certain that you have a clean place to work, then stretch out and
weight or stake the sail at the corners. Remove the protective covering from
the top of the double-faced tape and lay rope along the inner edge of the carpet tape all the way around the edges of your
sail. The rope should be just to the inside of your exposed double-faced
tape. At the tack, the loose ends of the
rope can be spliced or knotted with a fisherman’s knot.
STEP 6,
FOLDING THE EDGES OVER: After laying out the rope, fold the polytarp material with the
double-faced tape on it back over the rope and smooth the taped edges down.
Because this step gives you the final shape of your sail, make certain that all
curves are fair and the sail shape is what you expected before you firmly tape
down the overlap.
STEPS 7 & 8, TAPING THE EDGES AND CORNERS: After the rope is covered and the overlaps are folded down, you must decide whether you want to sew the perimeter of the sail or apply vinyl tape to the corners and edges. If you have no intention of sewing the edges, you should reinforce the corners and edges with vinyl tape–or reinforce just the corners alone. The tape alone will normally last a season or two without sewn reinforcement, but all adhesives will eventually loosen from the slippery polytarp surface. As a guideline, we reinforce the corners of our finished sails with tape as shown in the diagram below, then stitch around all the overlapped edges and reinforce the corners with more stitching. Tape experts suggest using a rubber mallet to “set” the tape. Finish the corners by adding diagonal strips of tape to each corner for appearance and reinforcement as in the diagram above.
Sewn
Bermuda-type sail showing grommets in the luff and foot
STEP 9, ADDING GROMMETS: In order to attach the sail to a mast or boom, place
grommets into the tape at intervals along each side of the sail that is to be
attached. These grommets have other functions, as well. They help hold the tape
and internal sail rope firmly in place, and provide a means of varying the
"belly" of the sail. Grommets should be spaced no more than 18"
apart on a PolySail to avoid overstressing the material. Separate instructions
for setting the grommets in the sail are included with the grommet kit that is
a part of the regular PolySail Kit.
STEP 10: ATTACHING THE SAIL TO THE MAST AND BOOM: Once the grommets are
installed, you can attach the sail to the mast or spars in a number of ways.
Our kits contain plastic cable ties rated at 75 lbs.each that can have you out
on the water quickly. If attached loosely, these plastic ties will slide up and
down the mast with a pull on your halyard. Later, you can replace these
temporary ties with wood mast hoops, rope mast hoops, or the illustrated lacing
technique to attach the sail to the mast. Attach the sail to the boom or other
spar with the same spiral lacing technique or by individual lengths of rope
attached with a clove hitch at the grommet and a square knot under the boom.
(See the knot-tying guide enclosed with your poly rope.)
Here is a picture of a finished jib-headed, sprit boom PolySail on my test boat Essence. (Some designers also call this sail a Leg O’ Mutton sail.) Only edge rounding and a single V-Dart were used to create shape in this sail, but note the nice curvature and lack of twist in this simple sail.
Happy PolySailing!
Dave Gray
Fishers, IN 46038-1366
Phone: 317 915-1454
Fax: 317 915-1578
Email: polysail@aol.com
Instructions revised 4/7/2007