Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/454

App. VIII. In practice, the two reactions (under and above water) not being in one plane, there is a resultant torque which has to be taken by the moment of heel due to the stability of the vessel. This results in a necessity for added surface and resistance due to the motion of the hull, both above and below water, especially the latter; the actual course is in consequence at a greater angle.

It seems to the author that by taking the present view many points hitherto but partially understood appear in a new light. For example, the bulging or filling of sails beyond the line of relative wind direction, a phenomenon well known to yachtsmen and other sailors, is the strict analogue of the arched section with dipping front edge of the aerofoil so amply demonstrated in the foregoing pages.

Further, the "dagger plate," the well-known expedient of the designer of light- draught racing craft, evidently "scores" over the ordinary centre-board by reason of its greater aspect ratio.