It's easy to build, easy to control, easy to put up and take down. It tolerated gusts well and can be tuned for really light winds also.
I use an aluminum sign as a leeboard and steer with a paddle.
If you don't have a canoe yet, try these complete plans for an outrigger sailing canoe.
action photos by Star
Step 1: The Sail
It's heavier material than such tarps are usually made these days.
Polytarp is a fabric woven from strips of polypropylene that's then heat-laminated to a sheet of polyethylene.
Each side and corner of the sail has a traditional name.
The sides are called Foot = bottom, Head = top, Luff = front, Leech= trailing edge.
The corners are called. Peak , Throat , Clew, and Tack.
The Leech and Foot are the original edges of the tarp. That saves some sewing.
The other edges are cut, folded over and sewed.
Sometimes I'll put a "bolt rope" cord inside for extra strength.
I used a regular home sewing machine with the thickest needles I could find for it.
Here are the dimensions of the sail:
throat to leech distance: 55"
This sail is made for a mast that rakes backward at a 15 degree angle.
If your mast is vertical you you should use the other sail drawing, or your clew will be too high. The leeboard stays in the same place but the mast partner is moved a few inches back.
I reduced that version of the sail to 5 sq. meters, which wise Canadians have decreed is the perfect size for a canoe sail.
Step 2: Leeboard
When I tack and turn the canoe so the wind is on the same side as the leeboard it swings up.
I pick up the leeboard and toss it into the water on the other side of the canoe.
The leeboard should be just in front of the center thwart to balance this sail well.
Then it's very easy to steer with the paddle.
When things are right the canoe will turn into the wind when you pull the paddle out of the water.
You'll have an easy time steering and water pressure will hold the paddle against the leeward side of the canoe. This set of conditions is called moderate "weather helm".
Step 3: Sprit
Hence the sail's name, "Sprit Sail".
My sprit is a cypress pole from a Florida swamp.
I cut it from a standing dead cypress sapling to use as a push pole.
You don't need a push pole if you're sailing and vice versa, so it's nice to use it for both jobs.
This pole is very light wood but it's springy. It's about 2" thick at the thick end and just over 1/2" thick at the tip. Mine is about 10 feet long.
At the thick end I attached a fin Seminole style to steer the boat at the end of the push stroke, and to paddle in spots of deeper water.
Step 4: Mast, Mast Partner, and Mast Step
It's about 12 feet long, 1.5" thick at the top , 2.25" thick where it passes through the mast thwart.
The mast thwart, also called the "partner" is a board with a hole in the middle that holds the mast up.
I added this board across the canoe near the bow of the boat. It's attached with epoxy, screws, and lashings.
I wanted to make sure it would stay put.
The base of the mast tapers down to 1.5" thick. It sits in the "mast step", a block of wood I epoxied to the floor of the canoe just ahead of the mast thwart. The mast step has a socket carved in it that's just big enough to accept the base of the mast.
Step 5: Simplest Sail
If you're in a hurry a rectangular 5'x7' army poncho will work well as a spritsail on a canoe.
The extra stick at the bottom isn't necessary.
It's called the "boom" because of the noise it makes when it hits your passenger in the head.
This sail is tuned for very light wind. When you tighten the "snotter" to raise the sprit as seen here, that puts belly into the front part of the sail. Good for light winds. In heavy winds you can remove the sprit entirely. The peak of the sail flops over and doesn't draw.
That's called "scandalizing" the sail. It looks bad but it works fine. It reduces the sail area by almost half and the area that's left is very low and easy to manage.
Notice the sticks the canoe is sitting on. If you make a little stick railroad like this you can drag your canoe over rocks without harm.
Here's a cute old book with a discussion of other types of sails for canoes.