Making a Polytarp Sail
by David "Shorty" Routh

Making the sail

This is another easy set of techniques that I have found for making polytarp sails. Please note that it isn't the "best", but rather just another set of methods for making tarp sails. There are many, many different techniques that you can employ when making the sails, you need to decide for yourself which ones you employ. And since the sails are so easy to make, have fun and experiment around with different ideas.

For this sail, I wanted to do the technique where the original edge of the polytarp is used, and then make a "mother dart" to create the shape of the sail. Jim Michalak has some great essays on making sails in this method, he also has accurate calculations on exactly how big the darts should be.

click to enlargeI started off by moving all of the furniture out of my livingroom so I could have some clear workspace. Notice the white tarp, this sail was being made for a fiberglass sailboat that I wanted to resell, so I bought a higher grade of white tarp from Dave Gray at It is much stronger than the blue stuff you can get at the local store, also it looks more normal like a dacron sail.

click to enlargeKnowing the dimensions of my sail, I found where I wanted the center of the draft to be and marked it.

Folding a dart over from the tack area, the dart ends at the point I previously marked. I am not a very good seamstress, but have noticed that the secret to sewing seems to be marking your work accurately, and pinning it in place. A trick I picked up from Bill Tosh at is to use clear packing tape to hold the seams. You can easily sew right thru the packing tape, and pull the tape off later. Some people use duct tape and then sew thru it, but I have heard the duct tape will grab the needle, so you have to grease it up with vaseline often, and be careful.

click to enlargeWith the dart held in place, I can mark the rest of the sail. I just drew straight lines from the head and tack, back to the clew. Many people will make a small inside curve on the leech of the sail, this is called "hollowing out the leech". It will prevent the leech from fluttering in the wind. I just made a straight line, it won't flutter (atleast won't flutter that much).

click to enlargeTo sew the dart, you have to do something with all the extra material on the the sewing machine side of the sail. I roll it up on the top side, so I can feed it thru and sew one side of the dart. Then pull it out, and feed thru again and sew the other side of the dart.

A mistake I made when I first started sewing was to bunch the material up instead. What happened is that a loose flap of material went right under the sewing foot attaching it to the dart. Had to cut the threads loose, and re-sew it again.

For the foot and leech, I need to fold the edges over twice and then tape them into place. Doing it free hand is rather difficult to create a straight edge. One technique is shown here, you stretch the material between two solid places, then fold and tape. click to enlarge
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Looking at it from this angle, I have created a little bit of curvature to the edge, but it was simple and fast. Taping down the seam with more packing tape, then run the edge thru the sewing machine.

Repeat for the leech.

Since the original edge of the polytarp has grommets in it, and I used that edge for the luff, with the head ending at a grommet, the only thing left to do on the sail is make the clew.
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I took a scrap piece of tarp that had a grommet in it, and folded it, then sewed onto the clew of the sail. Not only does it make a grommet for me to attach the sprit to, but it forms a reinforcement patch to strengthen that corner of the sail.

Mounting the sail

There are many types of snotters, this is one very simple type. It is just a snap clip that is laced to the mast, and the lacings are held in place by a small cable clamp. You could also keep the lacings there by running one thru a grommet on the sail.
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click to enlargeThe end of the sprit boom has the snotter line permanently attached to it, this line is pulled back thru the snap clip and then goes down. The tension you put on this line controls the tension on the sail, and how flat the sail will be when sailing. If you loosen the line, the sail will have a more fuller shape, if you tighten it, the sail goes flatter.

Down to a cleat on the mast. This sail rig is free standing, and can completely rotate in the mast socket. If the mast doesn't rotate, then the snotter will get tighter or looser depending on where the line is cleated.
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click to enlargeThe clew and aft end of the boom are simple, just 2 lines are taken thru the boom. One is the outhaul from the sail, and the other is the main sheet. Both are just tied thru the boom. You really can combine these, the only reason I had them seperate is because I swapped main sheets around.

Notice that there is no hardware on the boom, so during storage there are no metal fittings to rust and damage the sail. Also nothing to scratch your body as you set and take down the boom.

Dousing the sail is very easy and quick. Just release the snotter line and point the loose end of the boom towards the head of the sail.
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click to enlarge Start wrapping it up, and tuck the main sheet in there.
Keep rolling .... click to enlarge
click to enlarge With a bungee, the sail is completely stowed away.
The last problem to solve is where do you store such a long mast? This is my favorite solution so far, haning from the garage ceiling.
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click to enlargeWith the far end of the mast supported by a ceiling hook, the other end is supported by mounting a line to the ceiling as close to the open garage door as you can. Then just lift up the hook on the line, put around the mast and presto the mast is put away.

Before I heard about this technique, I used to use a pair of ceiling hooks, but the only way I could get it up there was to close the garage door. I found myself opening the garage door to get the boat out, then closing it to get the mast down, open to go load it on the car.... Was rather funny, every trip to the lake involved so many garage door opening cycles. :)

And to prove that the mutton isn't just for home made sailboats, here are a few links to commercial boats that use the mutton: