Boat rudder shaft seal

The sealing system is one of the most important parts of the rudder system. A leaking sealing system is irritating and dangerous. A lot of development is done in the last decade to guaranty a problem free system. Some designers still draw old-fashioned systems based on on O-rings or stuffing boxes. O-rings should not be used as they don't allow any misalignment ore movement of the rudder shaft. As O-rings are always located between 2 bearings, and the shaft will bent under rudder load, the O-ring will be pushed in on one side and create a gap at the other side and water will enter the boat. Stuffing boxes don't allow the shaft to bend and will act, unwontedly, as a third bearing. They also cause a lot of friction as the grease cord is pressed under high load on the shaft surface. Eventually the shaft will run in and more pressure will have to be put onto the cords to achieve a proper sealing, creating more friction. With the modernisation of the rudder system by the introduction of self-aligning bearings a big problem arose for the sealing systems: As the bearing houses don't have to be fully aligned with the shaft, and the rudder shaft can freely bend between the bearings, the precise position of the sealing system is unknown. The only solution for these modern solutions is a sealing system that isn't critical for the position of the shaft (like a gaiter) or to use a seal or tube in the inner housing that will move together with the shaft.