<b>Marine Shaft Device</b> The “Marine shaft device” is used to transfer the rotary motion / rotary power of the propelling engine to the propeller and to absorb the propeller thrust and its transfer to the hull. The shaft position can consist of one or more parallel drive trains (multi-propelled vessels). If the propelled engine is not located very far aft, the shaft system is usually a system divided into several segments. The shaft system includes the propeller shaft, also known as the tail shaft, which is guided through the stern tube, the line or drive shaft, the pressure wave, the shaft coupling, the bearings and the stern tube with the stern tube seal. The ship's propeller sits on the propeller shaft, which is guided in the stern tube by means of a water-lubricated slide bearing. At least on the inside of the ship, the stern tube is provided with a seal to prevent water from penetrating the ship's interior. The drive or line shaft, mounted on bearing blocks in plain, ball or roller bearings, is flanged to the pressure shaft. This is provided with a pressure flange and initiates the propeller advance into the ship's hull via the pressure bearing. The pressure wave in turn is connected to the crankshaft of the prime mover. In the case of ships with a continuous shaft, the thrust bearing can also be integrated in the drive machine or in an optionally available gear; then there is no pressure bearing. For maintenance and assembly reasons, long shaft systems are made up of several partial shafts. Correct alignment of the drive shaft is important to ensure optimal operating conditions for ship propulsion. Improper alignment of the drive shaft can cause the ship to vibrate and damage the shaft bearings. In the case of very long wave systems, a walk-in wave tunnel surrounds the wave system when crossing cargo holds or other ship spaces. Gearboxes are often part of the shaft system. These are used to reduce the engine speed, since speeds below 200 revolutions per minute, if possible even below 100 revolutions per minute, are aimed for a favorable drive efficiency in large shipping. In addition, the gearboxes often have additional drives for operating auxiliary machines such as generators or pumps. In complex drive systems, the gearboxes of the shaft system play a central role, since several motors and possibly turbines with very different speeds have to be switched to one or more shafts.