The radial bearings of shafting between gearbox and tailpipe or between engine and tailpipe usually use several journal bearings instead of ordinary sliding bearings or roller bearings. The number and arrangement of bearings are determined by the length and diameter of the shaft, the bending vibration performance of the shaft, the static bending line of the shaft, the bending stress and the strength of the bearing seat. In order to reduce the cost and drive flexibly, it is suggested to use bearings as little as possible. Ordinary sliding bearings are mainly used for larger propulsion devices, while roller bearings are mainly used for smaller devices. The bearing and seal of the stern tube are special and much stronger than other bearings, because it has to bear not only a great load, but also the sudden impact force brought by the propeller (such as in rough waves and accidents). There are various technical solutions to seal the tailpipe. Most ships adopt single barrel structure, and the stern shaft seal protects the stern tube from entering the seawater. The internal pressure of the stern tube depends on the draft of the ship, and the stern tube is oil-filled. Raising the oil tank can adjust the oil pressure to be higher than the external water pressure. A particularly important development related to the environment is the simple and compact airspace liner seal. In addition, the pressurized and adjustable intermediate cavity separates the oil from the seawater, so that even in the event of an accident, the seawater will not enter the ship and the oil will not overflow the ship.