On the inertial propulsion of floating objects using contra-rotating masses

•We analysed an inertial drive on a floating object without propeller.•We explained the mechanical reasons for which limited propulsion is possible.•We clarified the role of the initial polar angle.•We clarified the role of the motor speed.•We proposed the conditions under which indefinite motion could be possible.

This paper demystifies the mechanics involved in the propulsion of a floating object in the water due to attached rotating masses. It is shown that a device made of contra-rotating masses may induce adequate water resistance that is capable of offering support to move the object in calm water. The resistance is split into two main components, the former being due to Blasius effect and the latter due to harmonic oscillation. Neglecting the wave-making resistance, a computer model reveals that the maximum distance travelled by the floating object is proportional to the square root of motor speed and highly depends on the cosine of the initial polar angle of the eccentric masses.