Direct Propulsion

<b>Direct Propulsion</b> With direct propulsion, the drive power of the engine is transmitted directly to the propeller via a rigid shaft that is guided outboard through the so-called stern tube. This type of propulsion is usually used in so-called “slow-steaming” diesel engines with speeds between 60 rmp and 250 rmp. The direction of rotation of the propeller can e.g. for reversing, can only be changed here by reversing the motor. The engine must then be stopped while driving ahead, reversed by moving the camshaft and restarted for reversing. Another possibility for changing the speed and direction of travel is to use a controllable pitch propeller: to change the ship's speed as well as for the prerequisite or reverse travel, the angle of attack (pitch) of the individual propeller blades is changed. The motor rotates at a constant speed. The shaft is usually flanged directly to the crankshaft of the engine by means of a flexible coupling. So-called medium-speed 4-stroke diesel engines with a speed range of up to 1200 rmp are primarily used on small-bit medium-sized cargo ships, passenger ships and in naval shipbuilding. High-speed runners with speeds> 2000 rmp can be found in inland shipping and in sport and leisure shipping. These speed ranges often require a gear reduction, also in connection with controllable pitch propellers.