Replacing the rudder bearings on a 39 foot Catamaran

  If your rudder shaft goes through a tube that looks like this one you might have a problem that you aren’t even aware of.
Old tube, sailboat, voyage, wind, mainsail, purchasing a boat, cruising, living on a boat, sailing abroad, at sea, selling a boat,

Original Tube

While fine-tuning a two-year-old catamaran that we had just helped one of our long-time clients to purchase, we noticed that one of the tubes that the rudder shaft passes through was turning within the fiberglass hull. Fortunately only a little water was making its way into the boat, but we all know that the water intrusion would escalate as the gap between the aluminum of the bearing casing and the fiberglass of the hull got bigger. Further investigation showed that the rudder post and the bearing were firmly locked together and nothing we could do while the boat was in the water would free the surfaces. In order to decide what we were going to do to fix this and stop it from ever happening again, we first had to assess what had happened to the bearing, why the bearing would lock itself onto the rudder shaft, and how this whole assembly was able to turn so easily in the hull. A call to the Seezed bearing 2manufacturer of the boat only gave us the information that they had never heard of this problem before and that I should contact the makers of the bearing in France. After several fruitless calls to France and then contacting their distributors in the US, I learned that last year alone they had supplied ten of these replacement bearings to other boat owners. More research and I found a video on YouTube with a boat yard fixing one of these very same bearings on a different kind of boat.

So after all this research I came to the conclusion that perhaps we should use a different kind of bearing system.In the last 10 days I had dealt with and learned more about rudder bearings than in the previous 40 years and over 200,000 miles of off-shore sailing. After all, the rudder bearing is one of the simpler parts of any boat. In my experience it is rare to have to change any part of this system. When we hauled the boat Old and new tubes 2out of the water we found that both of the rudders were seized up into the lower bearings, and what should have been an easy job to lower and remove the rudders was a much longer, more delicate job. Once the rudders had been dropped the removal of the old aluminum tube- and bearing- housing was just a matter of unscrewing the bearing housing from the tube. The tube lifted right off and some gentle coaxing enabled us to push the cone-shaped bearing housing out through the bottom of the hull. The cone was only held to the hull by some form of calking. As we took it out, it was easy to see that the calking, which had adhered to the hull, made a good bond, but none had adhered to the aluminum housing.


This bearing and housing is really very ingenious. Unlike other shaft bearings this bearing can twist and turn within the housing, allowing for movement of the rudder shaft. BUT:
1- It is hard to get anything to stick to aluminum.
2- A round peg in a round hole does not have a lot of resistance to a twisting motion.
3- Aluminum in close proximity to stainless steel that is immersed in salt water is prone to galvanic action.


The bearing housing was not held solidly in place and when the aluminum started to corrode, the bearing stopped turning in its housing. As the rudder shaft started to corrode, more friction was put on the bearing until the aluminum housing started to turn in the fiberglass hull, allowing water to enter between the aluminum housing and the hull. Replacing the old bearings with the same product was not an acceptable option. We purchased two more typical bearings and fiberglass tubes. We enlarged the wholes that the old bearings went through and then fiber glassed the new tubes firmly in place, being careful to keep the new tubes inline with the original upper bearings that were attached to the deck.

After a few weeks and a few hundred miles of sailing we could see that this new system worked perfectly. With it there is little to no friction, no ingress of water, and as there are no dissimilar metals, there can be no galvanic action. This new system should last as long as the boat herself, with little to no maintenance.