I'm not sure whether polytarp is a wonder material, but it's a really cheap and simple way of making durable sails for small boats at a price which enables lots of experimentation. (And it comes in a few colours!) Our original sails were Blue, made from the cheapest quality we could find. We managed to get two sails from a $20.00 Tarpaulin sold to cover loads on semi trailers.
They've stood the test of time, although after two years, they are starting to get a little ragged looking. The new white ones are of a heavier material supplied by Duck Flat, and are a much better sail, albeit at a few times the price. Duckworks and Duckflat both stock the material, and will supply finished sails or kits if you don't wish to make your own.
If you do, or are just mildly curious about the process, read on, it's not a difficult job, and if you build from the plans you will have a sail with a surprisingly high performance capability.
THE SAIL LOFT
Firstly, you'll need somewhere with enough space to lay out the sail flat in one piece. Fortunately, with a bit of moving of furniture, our living room is just about perfect! A real sail loft would use pins to hold the fabric to the floor, but I didn't even dare suggest it, so we used masking tape.
Spread out the sail, and set out the three corners of the sail. Mark them.
For marking out, you won't need anything terrible sophisticated. Grab the fairing batten you had for lofting the hull curves, a stringline or two, some heavy weights, a tape, and a roofer's square. If you don't have a roofer's square, you can use the corner of a cardboard carton, or a book or chopping board, or anything that will give you a reasonably accurate right angle.
Stretch a stringline between any two corners to give a straight line, then measure the offsets as shown on the drawings. Repeat this process for the other two sides.
Once you have the offsets marked, hold the batten against all marks till it sits in a nice fair curve.
You may need someone to help you here, and a few heavy weights to hold it in place while you draw a nice line. Make sufficient allowance for your seam, I've found a one metre steel rule is about the right width, and cut using and ordinary pair of household shears.
READY TO STICK
Here is one of our older sails overlaid to highlight the seam and strengthening process. Patches in high load areas are stuck in place with double sided tape, and tape is run the full perimeter of the sail, to stick the seams together.
First though, we'll go round the whole perimeter and fold on the line we've marked earlier, we'll make a kink so we get a nice crisp edge.
ALL THE BITS TAPED
There are many people who have relied on tape as their only means of adhesion with sails. Many of the exotic film sail materials available today can't be sewn, and the super adhesives are perfect for use in high spec racing craft.
We just don't trust poly that much.
We know some use simply carpet tape, or even duct tape and get perfectly acceptable results, but we'd rather sail that repair sails.
In our testing, the laminate in the polytarp has always failed long before the tape joint itself, so we like to oversew the joint to be sure.
Once all the bits are taped in place and the sail looks like a sail, it's time to sew!
SEWING THE SAILS
It took a bit of persuasion to convince the Quilter in the family that no harm would come to her precious machine. No harm did, but Polytarp is quite abrasive, so be careful that it doesn't wear any of the machine surface as it travels over it.
Even the multi layer pieces are easy for a normal domestic sewing machine, although if you have access to a heavier machine, it would be good to be able to use a heavier thread.
We use a triple zigzag stitch everywhere. I bought a large spool of black synthetic thread for $1.00 at a discount store.
It's nowhere near the strength of a commercial yarn, but more than adequate for what we need.
By holding the sail up to the light, we can just make out the multiple layers of reinforcing. (It may be easier to click on the photo for a larger view)
The head of the sail ready for stitching, another view showing luff reinforcement patches taped on. These will be stitched around their perimeter.
GRATUITOUS SAILMAKING PICTURE
Yours truly trimming away, while the Two Foot Skiff and Eureka Canoe look on from his study!
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