When the ship is sailing, the stern bearing and sealing device are easy to heat, and must be lubricated and cooled. Although there are many types of stern tube devices, there are only two kinds of lubricants: water and oil. Different lubricants have different lubrication and cooling methods, which are described below.

① Water lubricated stern tube

In the water lubricated stern tube (such as iron pear wood and birch laminated stern bearing), as the stern tube is located below the water surface, bearing clearance and longitudinal groove are left in the stern bearing, and the stern tube is not equipped with a tail sealing device, so the space between the stern shaft and the stern bearing is always full of outboard water, which is a good lubricant and coolant for these bearing materials. The stern tube usually passes through the stern peak tank, which is often used as a fresh water tank or ballast tank on the ship. The friction heat of the stern bearing in operation is directly transmitted to the outboard water by the metal at the stern, to the fresh water or sea water in the stern tip tank, and to the outboard water flowing freely through the longitudinal channel and clearance of the stern shaft into the engine room. In general, the packing gland of the first sealing device should not be pressed too tightly, so it can operate reliably. However, as it is easy to deposit mud and sand at the stern bearing and the bow sealing device in the bow, which will make the cooling effect worse or even form stagnant water, the water lubricated stern tube (especially on large ships) is generally set with cooling water inlet and outlet pipes at the bow bearing or near the stuffing box (see Figure 5-66) to achieve the purpose of flushing mud and sand, dirt and strengthening the bow cooling. For the rubber stern bearing with large and continuous cooling water volume, the installed piping system can send pressure water for lubrication and cooling.

② Oil lubricated stern tube

Lubrication system shall be installed on oil lubricated stern tube. The lubrication system used on small and medium-sized ships is relatively simple, consisting of a gravity oil tank, a hand pump and oil inlet and return pipes. The lubrication system shown in Figure 5-71 is widely used in large ships. Inject lubricating oil into the gravity oil tank with a hand pump or an electric pump, and monitor whether the oil tank is full with an observation glass. Low oil level alarm is set in the gravity oil tank. Under normal conditions, the stern tube is always filled with lubricating oil, which is automatically replenished by the gravity oil tank after consumption. The lubricating oil in the stern tube can flow to the oil return tank through the stop valve, which also plays a role in regulating the speed of oil return.