New Mainsail Measuring Method Explanation

This page is a discussion of the change to the measurement of the Bullseye Mainsail.

The Bullseye Class has always measured the mainsail in the traditional method of measuring the Luff, Foot, Leech and the Girth from Mid-Luff to Mid-Leech. Several factors have suggested that a change to this methodology was necessary. One is the fact that the bolt rope on the Foot and Luff can stretch and shrink causing the inability to get repeatable measurements on any given sail. Another is the advent of the tackless mainsail. With a tackless mainsail it is impossible to use the traditional method of measurement because there is no tack point or apex to use for the Luff and Foot measurement. This necessitated a change to the method of measurement to keep traditional cut sails and tackless sails equal in size.

If you look at the drawing below, you will see that in the traditional method the Girth is a line from the Mid-Leech to Mid-Luff which forms the hypotenuse of a triangle. The Mid-Leech to Nearest Luff method creates a line which is perpendicular to the Luff. This line is shorter than the hypotenuse. If the original Girth Length of 6'3" and the Mid-Leech to Nearest Luff method was used to design the sail, the roach of the mainsail could be increased, thus producing a larger mainsail.

To make all sails, both traditional and tackless, come out the same in size the Bullseye mainsail Girth measurement has been changed to 6'1". This change has a side benefit in that the measurement of mainsails will be much easier. Sail makers will now be able to create sails in many configurations and still provide a mainsail which will measure into specification.

Twelve mainsails which were recently delivered using the old Girth dimension limit of 6'3" and the Mid-Leech to Nearest Luff method have been measured at a maximum of 6'2". This puts these sails very close to all sails which must comply with the new specifications.

Although tackless mainsails cut with the larger girth are slightly larger, approximately 2 square feet (if the maximum 6'3" is used) added to the roach of the sail, it is felt that this does not provide a significant increase in sail size and performance as to make traditional sails, cut using the same girth measurements and old measurement method, less competitive. It should be noted that the performance of any boat is controlled by, the skill of the skipper and crew, the tune of the standing rigging, the preparation of the hull, the age, cut and design of the sails, the amount and placement of extra gear on board and the condition of the air tanks under the main deck.