ON THE SAILS OF SHIPS.
The principal object in the formation of a ship, is its motion through the water, and the action of the wind on the sails is the great source from which that motion is derived. The degree in which this action is exerted, is dependent in a great measure on the size of the sails, and therefore the right determination of their forms and dimensions, is a subject of much importance to naval architecture.
To obtain as great a degree of velocity as possible, the dimensions of sails are sometimes carried beyond those limits which the safety and stability of a vessel sanction; but there must be some proportions and sizes for sails, which shall ensure to every class of ships, the maximum conditions of the very important elements of stability and velocity. This, however, is one of the many important elements yet to be determined by the future cultivators of naval architecture.
Let us in the first place attend to a few simple consi derations connected with this very important subject. Suppose, in the first place, the line AB, Fig. 3, Plate CCCCXCII. to represent the water section of a vessel ; and, in it, let DG be assumed as the measure of the fluid's horizontal action against the head of the ship ; and since from the assumed theory of resistances it is TT T r known, that when a ship is in motion, the action of the water on the after part of the vessel is distinguished by a sign opposite to that which characterizes the fluid's action on the bow ; let IE in the same horizontal line be assumed as the measure of its action, and in its proper numerical relation to DG. Let GI1, also at right an
gles to the water section, denote the vertical force of the water upon the head, the direction of which is from G to LI ; and K1 the direction of a similar force acting on the after part, the direction of which is from K to I. Join DH, which will be the resultant of the first pair of forces acting in the direction DH. Join also KE, which will be the resultant of the second pair of forces, and the action of which will be exerted from K to E.
Produce these resultant forces to meet in F, and make FN and FO respectively equal to them; and let these forces, in their new condition, be supposed to change their character from resultant to component forces, and complete the parallelogram FNPO, and draw its diago nal PF, and let it also be produced to Q. From the cen tre of gravity C of the ship, let fall CL, CM, and CQ perpendicular respectively to DH, EK, and PP. Then by a well-known theorem in mechanics, we have the following equation :