Technical Articles
How Star Sails are Made
By Mark Reynolds
Apr 16, 2003, 14:43

Design and Materials
The overall dimensions of the main and jib are pretty well defined by the class rules. You normally go to the maximum dimensions, but there are a few dimensions that are short of maximum. The most extreme being the jib luff which is 24 cm short in order to get the whole foot down on the deck to create an “end plate effect”. There are a few other areas where some decisions need to be made regarding measurements and since cloth stretches and shrinks that must be taken into account. Deciding on the materials to be used, the orientation of the material and the shape to be put into the sail is, of course, very important. All three of these factors are also very related. Different materials have varying stretch characteristics, and the orientation of the cloth can be very important as well. A well designed sail will react to the changes in loads in a positive way rather than a negative way. Instead of just stretching and getting fuller the sail can be designed to not stretch as much or even stretch in a way that the sail gets flatter when under stress. The cross sectional shape in a sail is the result of curves put into seams and the curve put up the luff of the sail. The amount and shape of the curves as well as the balancing of the seam and luff curves is a combination of computer design and trial and error. It is then confirmed by thousands of hours of 2 boat testing and on the race course. Today’s sails feature more stable fabrics, very stable radial corners and rocked panel midsections. These improvements which began in the late 70’s have resulted in sails that are powerful in light wind but flatter and straighter leeched in strong wind.

Cutting
The cutting process really consists of drawing and cutting. Almost all of the curves that make up the shape in the sail are made by matching the straight edge of one side of the cloth to the curved line that is drawn on the other side of the panel. When the two are put together this gives the shape to the sail. Originally the curved lines were created by bending a stick and then drawing a line. This was replaced by patterns for one design sails which worked great to insure that they were all the same. A plotter/ cutter machine driven by a computer is the most effective way of doing custom sails and is also used for production sails. Star sails can be done both ways effectively.

Assembly
After the panels are all drawn and cut the batten pockets and windows may be added before the all the seams are sewn. Even some of the corners reinforcement might be added at this point. The seams are then taped together. The taping process is very important because any errors here will cause the shape to change. The current tapes are very aggressive and really just leave the stitching to give a little more peel strength. After the sail is sewn together the corners are finished off followed by the leech and then the luff.

Finishing
In the finishing process often called "handwork" the corners are finished off with grommets, press rings or headboards. Numbers, class royalties and tell tails are applied, battens fitted and the sail is folded up and ready to go!



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