Why
then, do vessels go to windward as well as they do? is a fair question to ask. Suppose, as an ideal condition, that a vessel has no fore and aft resistance, and has complete lateral resistance; assume, further, that there are no spars, rigging, or hull above water to hold wind, that the sail is a perfectly flat plane, and that the frictional value of the wind on the surface of the canvas is nil. In such a case the excesses of the angles under consideration over 90 degrees will be infinitesimal, and the ship would go nearly head to wind. It follows, therefore, that the closewindedness of a vessel depends mainly upon the relative proportion of lateral to fore and aft resistance, upon the effect of windage upon hull, spars, and rigging, upon the friction of wind upon the surface of the sail, and upon the curvature of the sail.
A smooth surface is very important, hence the superiority of Egyptian cotton over flax as a material for racing canvas. A flat sail is also important, but as elsewhere explained, a certain form of hull is a condition precedent to getting full value from a flat sail. Both these conditions help a vessel to windward, and other factors come under consideration which produce the same happy result.