An upwind vessel is able to manoeuvre at will toward any downwind point, since in doing so the relative wind moves aft . A vessel downwind of another, however, in attempting to attack upwind, is constrained to trim sail as the relative wind moves forward and cannot point too far into the wind for fear of being headed.
42.
Given these inputs, the Mark 1 automatically computed the lead angles to the future position of the target at the end of the projectile's time of flight, adding in corrections for gravity, relative wind, the magnus effect of the spinning projectile, and parallax, the latter compensation necessary because the guns themselves were widely displaced along the length of the ship.
43.
The rapid change in shape of the boot is designed to break the adhesive force between the ice and the rubber, and allow the ice to be carried away by the relative wind flowing past the aircraft . However, the ice must be carried away cleanly from the trailing portions of the surface, or it could re-freeze behind the protected area.
