Sprit Sail

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SPRIT SAIL

Sprit sails were the favorite sails for working boats under 40’ until the late 1800’s, according to Howard Chapelle. With only a free standing mast and a sprit spar, this four-sided rig required little attention and hardware to function effectively, leaving the captain and crew free to attend to other tasks. Although it has fallen out of favor with many sailors today, the sprit sail has much to recommend it if cut, rigged, and set properly. First, it does not require a very tall mast to support a large sail area. Second, the sail is low and compact with its center of effort (CE) well below the CE for triangular sails; consequently, there is less heel for the sprit-rigged boat. Third, the head of the sail has no eddy-creating spar to spoil the air over the top of the sail like most other traditional sails. Finally, the sprit sail can be reefed fairly easily by loosening the sprit, hauling in the peak to a grommet near the mast, and repositioning the sprit to a grommet in the leech.

A sprit sail requires a sturdy mast that has only a little taper in the top one-fourth. The sprit doesn’t need to be so heavy, but needs to be more substantial where it intersects with the mast. It’s not a bad idea to wrap the sprit with some tape at the point of contact to extend the lives of your running rigging. The head of the sprit can be either inserted in a pocket at the peak or inserted in a loop of line. By cutting a notch in the head of the sprit, either option can be used. To work well, the head of the sail and thus the peak must be heavily tensioned. Consequently, the peak pocket must be very strong, and the halyard and snotter must be heavy, non-stretch line. Many small boat sailors simply dispense with a halyard altogether and simply unstep the mast leaving the sail attached. That way a much stronger tie off can be used at the throat. If the captain chooses to sail the sprit rig lloose-footed, the sheet must split the angle at the clew to work correctly. Otherwise, a boom or full length batten should be used at the foot.

Sprit sails function best on very small boats such as dinghies, prams, canoes, and kayaks since the sail is easy to step and remove. With the sprit removed and the peak folded down to the mast, the sail can be rolled on the mast for storage. In most cases, the spars can easily fit lengthwise within most small boats. Optimist prams, for example, use a small sprit sail as the class standard. A sprit would also be a good choice for a PDRacer. Below is a visual guide to making a sprit PolySail.

Note: Depending on the size of the sail and the weight of the material, I sometimes do not include a dart in the throat. When I do include one, it is generally less than 3/8” (closed) at the base of the dart and less than 6” long. Sufficient rounding in the luff and head will usually compensate for the need for a throat dart.

Note: More recently I have taken to overlapping the ends of the line at one of the less stressed corners and then sewing the overlapped line together with both straight and zigzag stitches. If I think that the leech will hook because of the cut of the sail or the number of wrinkles in the material that will be gathered up in sewing the leech, I will often just run the ends about 3’ into the leech and just sew the lines in securely. Either method avoids the unsightly loose ends that must be tied off.


Peak pocket made from multiple layers of polytarp material	Peak pocket made from polytarp edge material	Peak pocket made from tape and multiple layers of material

Below is a diagram of a 47 sq. ft. sprit for a pram or dinghy.

Below are some pictures of various sprit sails I’ve constructed ranging from about 33 sq. ft (D4) to about 80 sq. ft. (custom). There are also some photos of various corner treatments used.