We shall look at the mainsail first. In many ways it is the most important, and the most difficult to get right. Its the most important because of how it affects the jib, and the heel and the rudder angle. The most difficult because we only have one mainsail, and it has to do all wind speeds.
It may be best to think of the mainsail as a huge rudder itself, as many of the principles of rudder trim apply equally well to the mainsail.
The mainsail has to be well designed and well made to perform all its tasks well. It has to be able to perform on a straight or initially pre-bent mast, and then when the mast is progressively more bent, until at maximum bend the sail is fully “bladed-out”.
The fabric has to be strong enough to withstand the loads, but not so heavy that it weighs too much.