Appendices -- Useful Supplemental Information


The amount spars bend under the influence of the sails attached to them determines, in part, the design of the sail. Use these guidelines to get accurate spar-bend data for masts, gaffs, yards, and booms.

1) Support gaffs, and lug, gunter, or lateen yards, at the ends. For unstayed masts, support the spar at the tip and where it passes through the partners. (Booms are a special case. If the sail is loose-footed, i.e. attached only at the tack and clew, no bend data is needed. If the foot of the sail is laced, sleeved, or otherwise attached along the boom, bend data may be required, depending on how the main sheet is rigged.)

Mark the upper side of gaffs, yards, and masts. When the sail is laced on, that edge should again face up/forward. If there is a prebend before adding the weight (a curved spar) the curve should be down for the test, so it will become part of the measured offsets. If the spar is rectangular, be sure the long section is vertical.

Hang from the midpoint (masts & gaffs) or halyard attachment point (lug, gunter, and lateen yards) a weight equal (in pounds) to:

1/2 the sail area for masts bearing Bermudan, gaff, or sprit sails.
1/2 sail area for lateen yards and booms.
1/3 sail area for gaffs and lug or gunter yards.

Water @ 8.3 lbs/gal makes a convenient weight.

A 50 sq ft Bermudan sail on an unstayed mast, for example, requires a weight of 25 lbs (3 gallons of water). A 50 sq ft lugs’l yard would be tested with a weight of about 16.5 lbs (2 gallons of water).

2) Measure, against a string line, the offsets at three equidistant points on the spar. Call these the 1/4 (nearest the butt), 2/4, and 3/4 points. Try to measure to 1/8” accuracy.

The resultant numbers will be interpreted according to the sailmaker’s previous experience with a similar rig, and will dictate certain aspects of the sail design. Basically, the shape of the edge of sail attached to a bendy spar will be designed with additional fullness that will be absorbed as the spar bends in increasing wind -- flattening the sail just when it needs to be flatter.

Masts bearing lugs’ls do not need to be measured. Ditto for sprit booms and sprits’l sprits.

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