Fermat's principle, Huygens' principle, Hamilton's optics and sailing strategy

Fermat's principle asserts that light takes the path of minimum (actually extremal) time. Sailors often wish to find paths of minimum time. Thus by thinking of a sailboat as a light ray, a sailor can use Fermat's principle to describe the optimum sailing strategy. Huygens' principle and Hamiltonian optics follow from Fermat's principle, so a sailor can use Huygens' principle to visualize least-time paths, and Hamilton's optics provides a mathematical description of these paths. In especially simple cases, the optics-based formalism can be used to describe and quantify the basic tactics of sailboat racing.