Facing in or out--- SM Prop Shaft Seal direction and Bush*** IMPORTANT RESPONSE***

Eric Freedman


Just to clarify things about this discussion.

I assume that when you say the lip seal is facing in you mean that the rubber side is facing towards the C drive  and when you say out you mean the spring side is facing the C drive.

Fair Winds


Kimberlite Amel Super Maramu #376



From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Thursday, May 10, 2018 6:36 PM
To: amelyachtowners@...
Subject: Re: [Amel Yacht Owners] SM Prop Shaft Seal direction and Bush*** IMPORTANT RESPONSE***



Danny and Bill,


First, I don't take it personally our interaction and also respect and by-enlarge agree with your conservative approach to keeping the boat as close as possible to the original design.  I also agree that the safest approach for new owners, particularly those without background or experience should stay within the original specs.  So I don't see as a personal argument but more as an open discussion that may or may not lead to a better solution for some of the small issues of our boats. 

For example, adding grease ports to the furling gears can prolong the life of these very expensive parts for a long time.  The "amel way" resulted in the replacement of two gears by the previous owner and onece by me.  This is a clear example of how the "amel way" COULD BE can be improved.


Now, we all know that milky oil in the C-Drive is something common in most of our boats in spite of trying to strictly follow the "amel way".   We also know that Amel has been experimenting with ways to reduce the premature entry of water by making harder bushings and that in Martinique they have been changing the scheme having two seals to prevent water in and only one to prevent oil out.  You also told me that they now recommend heavier oil and that they had worked on a  hardened bushing surface that seems to work but Maud told me that they did not plan to sell them it in the future.  So even Amel has recognized the need to work on reducing the incidence of water leaking into the C-Drive which may not kill it but even you would agree is not good.  And that has been my motivation to write these posts.


As for Danny statement that oil cannot leave because it is lighter than water, it all depends on which direction the seals are oriented. With the Amel way, water is only prevented to come by the outer seal. Once it is gone, water can flow up along the two other seals that are not preventing that motion. In my experiment I had both the inner and central seals with the lips facing the propeller (preventing water from coming in but allowing oil to move out)  The outer seal was facing the C-drive, thus acting to prevent the oil from leaking out but allowing some lubrication by the water.  My experience was that after 4 and 1/2 seasons there was a very slow reduction of the oil level when the outer seal/bushing wore out.  However, this leak was eliminated by adding the additive that made the oil heavier.  So, water or oil can move in or out depending on the direction of the seals that remain working.  


With my approach, the outer seal was the only one preventing oil from leaving and, just as I observed, oil began to flow out very slowly when that seal/bush surface wear developed a leak since the two inner seals did not prevent the flow of oil out.  The good news was that the leak was very very slow and that making the oil heavier acted to make that last seal work again since the additional viscous pressure drop forced the seal lip towards the shaft preventing or minimizing a further oil leak.  Note that from there on the seal was well lubricated by a minimal oil leak and likely would have kept working for a long time before oil began to flow out again.  


The good news is that this approach allows you to keep sailing until you find the proper place to do the repair and, as in my experience of 5 seasons without damaging the C-Drive.  Note that I kept the bushing/seals in place as an experiment and not as a recommendation to the general user, BUT MY EXPERIENCE LEADS ME TO RECOMMEND THE ALTERNATIVE SEAL ORIENTATION to eliminate the milky oil and give you the time to find a proper site for repairing it 


Of course, everyone is free to take it or not my recommendation and I hope that within the coming years we compare notes to see how things are going.  I do promise that I will immediately report if my C-Drive freezes ;)


No hard feelings and this closes my chapter FOR this topic until at least 2 years.


Fair winds



Ipanema SM2K 278






Join main@AmelYachtOwners.groups.io to automatically receive all group messages.