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/37

propel her in a forward direction. The old friend of our youthful studies, the parallelogram of forces, enables us to resolve the force AC into its two component forces, and to estimate their relative magnitudes. Let GF be the line of the keel. From C draw CD perpendicular to GF, and complete the parallelogram ADCE. Then if DC represents the magnitude of the force driving the vessel sideways, AD will represent the magnitude of the force propelling her forward in the direction FG. The closer to the wind a vessel sails, the greater will be the disproportion between these two forces; and the tyro will soon discover that if he flattens his sheets too close and attempts to squeeze his craft too near the wind, so small a proportion of the wind's force will be exerted in propelling his vessel in a forward direction that she will practically stand still. A comparison of Figs. 2 and 3 will demonstrate this. In Fig. 2 the boat is sailing as near the wind as she can, so that the force DC is far greater than the force AD, and she will have little headway. In Fig. 3 the boat is sailing with the wind a little before the beam, so that the propelling force AD is about equal to DC, and she will be travelling fast. As has already been explained, a boat is so constructed as to offer the least possible resistance to the propelling force AD, and, on the other hand—by giving her as large an immersed horizontal section as possible—to offer the utmost resistance to the lateral force DC.