Page:Small-boat sailing; an explanation of the management of small yachts, half-decked and open sailing-boats of various rigs; sailing on sea and on river; cruising, etc (IA smallboatsailing01knig).pdf/39

 tendency to blow either the vessel's bow or stern round, if the sails are not properly balanced. If, for example, a boat sailing with the wind abeam carry too much sail forward—and more especially if the leverage of the head sail, as is the case with a jib, be increased by setting it at the end of a long bowsprit—the boat's bow will be driven off the wind, and the steersman will have to counteract this tendency with the rudder.

Now, the wind exerting a side pressure on a boat's sail, or sails, acts through a point known as the centre of effort of the sails—a point which is, roughly speaking, in the centre of the total sail area. It has already been explained that the resistance of the water to a vessel's leeway acts through a point in the centre of the submerged section of the ship's side, known as the centre of lateral resistance. These two horizontal forces act in opposite directions; consequently, unless as in Fig. 6, A, the centre of effort of the sails, and B, the centre of lateral resistance, are in the same vertical line, so that the opposing forces balance each other, the vessel will have a tendency to turn either her bow or her stern towards the wind.

In Fig. 7 we have a vessel sailing close-hauled. Here B, the centre of lateral resistance, is further aft