The article devoted to the analytical studies of torsion oscillations of propeller shaft during changes in rotational speed, including going over the resonant frequency. It is assumed that diesel in only reason of periodically variable torque and that torque amplitude is proportional to the square of the speed of rotation. Case where the rotation frequency varies linearly is viewed. Found that amplitude of torsional oscillations don’t change smoothly during change of rotation speed. The maximum value of oscillation amplitude is noticeably before resonant frequency both if frequency increase, and if decrease. Significant increase of oscillation amplitude is also before stopping.