2-speed gears and gearboxes - Wärtsilä

The Wärtsilä 2-speed gear enables vessels that operate regularly with varying propeller loads to be designed with a propulsion system that is highly efficient. The losses from the prime mover to the controllable pitch propeller are small, and the introduction of a gear with a choice of two propeller speeds at a constant engine speed results in excellent propulsion efficiency at varying loads. Thus, by reducing the speed and increasing the pitch of the propeller, at reduced loads greater propeller efficiency is achieved. By operating the ship’s propeller at low speed when maximum vessel speed or propeller thrust is not required, fuel consumption can be reduced by as much as 15% compared to a single mechanical propulsion system. At the same time, nitrogen oxide (NOX) and sulphur oxide (SOX) emissions are similarly lowered. Despite the low propeller speed, the engine speed is kept constant, thereby allowing the electric power generation from the Power Take-Off (PTO) on the gear to remain uninterrupted.