In this paper some analytical developments concerning the possibility of generating a rectilinear motion of vessels subject to vibration, without the use of propellers are presented. The motion is obtained by a device equipped with counter rotating masses installed in the boat which vibrates along the longitudinal direction. The hull has a suitably shaped stern. The study considers an analysis for evaluating the energy that the propulsion system consumes in relation to its performances. A further aim was to increase the speed of the system. This result is obtained by using elliptical gears to transmit the motion from the driving motor to a two or more pairs of counter rotating masses. This solution allows one to reach the variability of the angular velocity of the counter rotating masses during each revolution in accordance with certain laws that maximize the thrust applied to the vessel preferentially along a direction with respect to the opposite one, all things being equal. A formulation to compute the propulsive efficiency of the device study is developed. Some remarks in relation to practical applications and critical issues of the proposed approach are shortly discussed. In the second part of the paper the results relative to a vessel 13 m long are illustrated.
