A method is explained for calculating fuel expenditure necessary to obtain one ton of distillate in seawater evaporators. Using this method, a program of calculation on a digital computer is compiled. Results of investigations into the selection of an optimal variant of including a high-vacuum evaporator into the cycle of the steam turbine plant on a vessel are presented. It is found that economically the most efficient is the inclusion of a high-vacuum evaporator into the cycle which provides for direct heating of the heating battery by the bleed steam.