Synchronous motors for ship propulsion

SINCE the inception and development of the idea of electric ship propulsion, the question of the possibility of using synchronous motors for such service has often been raised. Such a motor could be designed for unity power factor with a resulting saving in cost, weight, and efficiency, of both motor and generator. So far as mechanical design was concerned, the answer was, of course, that the same substantial mechanical features could be obtained with a synchronous motor as with an induction motor. In addition, the synchronous motor would have greater clearance between rotor and stator and repairs could be more easily made since it would not be necessary to remove the rotor to replace either field or armature coils. The question, therefore, was whether or not satisfactory electrical characteristics could be obtained with this type of motor. The affirmative answer to this question is attested to by the fact that the S. S. Cuba, a fast passenger and express boat belonging to the Miami Steamship Company, and the first vessel of any kind to be propelled by a synchronous motor, has been in successful operation since November 1920, and five more equipments are under construction. Four of these are to drive cutters being built for the U. S. S. Coast Guard Service and one for a fruit steamer.