How it works
First, an important factor is the intended lubrication medium. Oil-lubricated stern tube systems are the most common and occasionally ship owners require a water-lubricated or grease-lubricated stern tube system.
Second, depending on the ship design, the stern tube can be supported with struts or can be positioned within the ship’s hull. Often the surrounding sea water will suffice for dissipating the heat from the stern tube oil. The heat generated by bearing friction is then transferred through the shaft and the stern tube inner surfaces towards the outer surfaces of the stern tube, adjacent to the sea water. If the natural heat dissipation doesn’t suffice and the oil temperature needs to be controlled, an external lube oil unit can be acquired for circulating and cooling the stern tube lube oil. Circulating the oil also provides the means to separate water from the oil, in case of water ingress.
Third, it is inevitable that stresses occur in the stern tube during installation and operation due to thermal growth. To prevent internal stresses, the forward end of the Lagersmit stern tube is free to extend in an axial direction, without compromising the strength and stiffness, or the attachment to the hull.