SM Prop Shaft Seal direction and Bush***RESPONSE TO *** IMPORTANT RESPONSE***
I don't want to make this a major issue and I appreciate your comments, knowledge, and experience with our boats but I have several issues with your RESPONSE.
1) I am ONLY reporting the result of my experiment, NOT recommending anything to owners. I would not recommend anybody without knowledge of mechanical engineering, seals, and lubrication to conduct experiments on their own but I thought that reporting my results to the group could be helpful to promote discussion about the topic.
2) My reason to conduct the experiment was motivated by TWO consecutive situations where water entered into the transmission before the 2 years. In both cases, I had followed carefully AMEL's recommendations and used original parts.
3) The last incident of water ingress into the transmission happened as I was sailing back from Cartagena to the Bahamas and I was forced to run the engine for several hours during a bad storm north of Cuba with milky oil. It was very stressfull to have to run hard the engine knowing that salt water was reducing the lubrication of the gears.
4) I agree that catastrophic loss of oil from the transmission leads to a very expensive damaged of the gears as much as catastrophic replacement of oil by saltwater would lead to the same type of damage.
However, experience tells us that seal damage is not catastrophic but gradual and shown by a change in color of the oil (with the seals in the recommended AMEL configuration), or a slow drop of a few mm per week in the oil level from the tank which can be refilled with a heavier oil as I did, totally eliminating the oil loss until the next haulout. In contrast, watery oil cannot be replaced until the boat is haulout, potentially forcing you to do it in less than desirable places.
5) My rationale for experimenting with the seal's direction was based on the physics of how seals work. A seal without lubrication will wear out faster than one with lubrication, and the AMEL recommended directions leave ALL seals unlubricated, THAT is a FACT. So I don't know how you can be so sure that the change in seal direction was not the reason for the difference in seal and bushing wear.
6) THE REAL QUESTION IS WHETHER IT IS WORSE TO LOSE A LITTLE OIL THAT CAN BE REPLACED OR RUN THE ENGINE WITH SALT WATER IN THE TRANSMISSION WHICH KEEPS BRINGING THE LEVEL OF THE OIL TANK HIGHER AS WATER LEAKS IN.
7) THERE IS NO QUESTION THAT THE SEALS SHOULD BE REPLACED AT LEAST EVERY TWO YEARS AS recommended, but WITH THE PROPER SEAL DIRECTION it is likely that the bushing my last much longer if the seals are ALLOW proper lubrication.
Finally, let me suggest that if losing a little oil is thought to be worse that adding salt water, or EVEN WORSE fresh water with silt in rivers, to the gears, one could reverse the direction of the central seal to face away from the propeller. That would have the two outer seals preventing oil from leaving and the inner one preventing water from entering. Here ALL seals would still be lubricated.
AMEL has made fine cruising boats with incredible advantages for cruising and the Amel School Book is extremely helpfu to new and old owners. However, that does not mean that their original designs cannot be improved as knowledgeable cruisers gain experience and try different approaches to improve on the few issues that remain unresolved. Just see how many changes were done as the SM evolved over time. AS FAR AS THE SEALS CONFIGURATION, I am now certain that the one proposed by AMEL is not ideal.