A guide to the way sails work, and how to design, make, repair and modify them. It is suitable for boats measuring up to 40 feet. The author describes the differences between each type of rig, its handling and its performance out on the water. He discusses the choice of sailcloth and sail care, and covers the principles of sail design and the use of a basic home computer for DIY sail-making. There is a free computer-aided design disk with the book to assist sailors in designing and modifying their sails by plotting the panel shapes.