The Wärtsilä 2-speed gear enables vessels that operate regularly under varying propeller loads to be designed with a highly efficient propulsion system. The losses from the prime mover to the controllable pitch propeller are small, and the introduction of a gear able to select from two propeller speeds while the engine speed remains constant results in excellent propulsion efficiency at varying loads. Thus, by reducing the speed and increasing the pitch of the propeller, greater propeller efficiency is achieved, even at reduced loads.  At the same time, the carbon dioxide (CO₂), nitrogen oxide (NO_x) and sulphur oxide (SO_x) emissions are correspondingly lowered.

By reducing the propeller speed the underwater radiated noise is significantly reduced. This is of great importance for fishing vessels and seismic vessels, while less noise and vibration in the living quarters is also highly appreciated by the crew. Measurements show the reduction in sound pressure to be at a maximum of 20 dB when the propeller speed is decreased from 125 rpm to 100 rpm. Note that a 10 dB reduction in the noise level is perceived as being 50% quieter.