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/36

 It will be explained further on how the centre of lateral resistance has to be taken into account when the arrangement of the sail-plan is being determined.

ACTION OF THE WIND WHEN THE VESSEL IS CLOSE-HAULED

It is easy to understand how a sailing-boat can travel before a favourable wind, but it would at first sight seem contrary to the laws of dynamics that a boat should be able to sail close-hauled—that is, in a direction opposed to the wind, which serves as the propelling force. A boat, with a sufficiently deep keel to check the tendency to make leeway, can sail within 45° of the wind. In Fig. 2 is represented the deck-plan of a boat sailing close-hauled. The direction of the wind is shown by the arrow W. AB is the sail, so trimmed as just to hold the wind without shaking. Now it can be mathematically demonstrated that the wind, so far as it affects the motion of the vessel, exerts a horizontal pressure on the sail, acting in a direction at right angles to the plane of the sail—that is, in the direction AC. This force, it will be observed, while pressing the boat sideways, tends also to a lesser extent to