Mainsail Shrinkage
Many Macgregor mainsails, as they get older, suffer from shrinkage of the bolt rope. The bolt rope is the rope that is sewn into the edge of the sail along the mast and boom. When the bolt rope shrinks the sail will not set the way it was designed to. If the shrinkage is extreme there will be creases starting at the mast and traveling parallel to the leach. The shrinkage makes the sail too full(to much belly). This reduces the sail performance and makes the boom hang too low over the cockpit. It gives less drive and more healing force.
Fortunately, correcting the problem is not difficult. The rope is in a sleeve of sailcloth and is only fastened to the sail at the head, foot, clew, and reef points. To fix the sail along the mast it necessary to cut the stitching at the reef points and the tack. This will allow the sail cloth to extend to its original size. when the cloth is pulled the rope will slide up in the sleeve. Then the rope can be sewn to the sail in its new position. The boom can be done in a similar manner.
Many sails have had the rope shrink 8 to 10 inches. The rope wants to be tight when the sailcloth is smooth with no wrinkles.
The diagram shows what I am describing. The points "A" are where the stitching is removed and re sewn to cure the mast side. The point "B" is where the stitching is removed and re sewn to cure the boom.
The examples shown here is a picture of extreme shrinkage and one of moderate shrinkage.
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