The article presents the theoretical substantiation of using the optimal trim of “river- sea” vessels in order to improve the propulsion of vessels of various types and purposes navigating on seas and rivers. There has been carried out the analysis of the optimal trim for different types of ships in operation. The given calculations prove the possibility of designing new ships with improved sailing characteristics. The scheme of damping the bow shear wave coming from the stem of the “river-sea” vessel is illustrated using the shear wave coming from the bow bulb, with a differential to the bow. It is proved that trimming of a “river-sea” vessel without a bow bulb is effective for slow-moving and high-speed vessels due to the reduction of components and total drag, compared to the resistance to the movement of a vessel with a conventional trim. An integral similar to Mitchell integral for the wave drag of a vessel with a bow bulb is proposed, by means of which the conditions for damping a bow shear wave (coming from the stem) using the bow bulb of a “river-sea” vessel are determined. The elements composing resistance to the vessel propulsion are investigated in detail: total resistance of the medium to the movement of the vessel, resistance of friction, shape, protruding parts, wave, and aerodynamic resistance. There are considered the criteria of the optimal bow draft of the vessel and optimal trim of the vessel, the criteria of the efficient use of the optimal trim for the “river-sea” vessels on the sea sections. An equation is given that determines the value of the optimal length of the wave-forming part of the bow bulb or the condition for the optimal trim. The pictures illustrating a sea vessel bulb, the bow of which is capable of effectively forming a shear wave at a given differential are shown. Conclusions are made about the possibility of using the optimal trim for river-sea vessels on river and sea sections, recommendations are given that contribute to saving fuel and time, increasing the speed to two knots while reducing the total resistance by up to 20%.