The Author, looking into the rules defining the sailing ship efficiency in steady motion, delineates a number of mathematical equations that have proven to be accurate in practice. The equation of the sailing ship efficiency in a downwind (full wind) sector are defined by the curves of the Wulff grid, while the equation in an windward (sharp wind) sector is a new fourth degree curve, developed by the author . The book presents the basic assumptions as well as the derivation of the new formulas as well as conclusions and suggestions of new definitions of terms to be used in the sailing vocabulary.