. The combinations shown in a sail-plan almost always include three configurations: A light air sail plan. Over most of the Earth, most of the time, the wind force is Force 1 or less. Thus a sail plan should include a set of huge, lightweight sails that will keep the ship underway in light breezes. A working sail plan. This is the set of sails that are changed rapidly in variable conditions. They are much stronger than the light air sails, but still lightweight. An economical sail in this set wi… (More on Sail-plan)