Re: [Amel Yacht Owners] SM Prop Shaft Seal direction and Bush*** IMPORTANT RESPONSE***
Well said. We have followed the guidelines posted by you and have never had an issue with any intrusion of water or leakage of oil. It is an easy process to follow. We have always purchased parts for this from Amel. As you say, to replace the drive would be costly. Why risk it.
With best regards,
Sailing Vessel - Cream Puff - SM2K - #275
Currently cruising - Bonaire
From: amelyachtowners@... [mailto:amelyachtowners@...]
Sent: Monday, May 7, 2018 3:59 PM
Subject: Re: [Amel Yacht Owners] SM Prop Shaft Seal direction and Bush*** IMPORTANT RESPONSE***
Jose, I really appreciate all of your participation in this Group. Thank you very much.
My following response is not intended to be an argument to you, but, it is intended to give those people in the Group who are "new-to-Amel" the reasons NOT to follow your advice. Remember there are a number of things that can go wrong with the installation of the wear bushing and seals. I am absolutely positive that changing the seal orientation from what Amel recommends was NOT the reason for your changing results.
Let's make this simple:
What is more important? Oil leaking out, or water leaking in? The answer to the question is obviously oil leaking out, and that is probably the reason Amel recommends a redundancy of seals (2 instead of 1 to hold oil in) to protect your 35,000 euro C-Drive from melt down because of no oil.
To not service a 35,000 euro C-Drive for 8 years (4 times the manufacturers recommended service interval) is not a RISK that I would take and is one that I do not recommend any of my clients taking. Afterall, you are going to haulout every 2 years anyway, why try to save a few hundred euro and risk 35,000 euro?
Let me share with you a summary of a page in my Amel School Book:
Amel has stuck with the same C Drive Bushing, seals and procedures for over 25 years and today recommends the same procedures in new 55s and 64s, which have the same wear bushing and seals. The only change Amel has recommended is the change to 80/90 gear oil. I know for a fact that Amel has experimented with several options and may be close to making a change to the wear bushing which may give it a longer life. But, I assume rather than busing wear with a harder bushing the seal will wear. This may be an insurmountable issue because with a very hard bushing good seals will eventually leak because they wear rather than the bushing.
I want to report my experience with the shaft seals and bushing.
When I bought my SM2000 278, It had its seal and bushing replaced and the seals oriented as recommended by AMEL. In less than 2 seasons it was leaking water into the oil and I replaced it again in that spring finding substantial wear in the bushing, as you will see in the pix I have uploaded in face book. After trying again the same scheme and less than two years later, as we were returning from Cartagena to Florida, just before reaching the windward passage between Cuba and Española, the transmission oil showed again the dreaded white color and I had to sail with no wind around the eastern tip of Cuba. In Fort Lauderdale, I decided to experiment with the shaft seals direction based on my Mechanical Engineering background: single lip seals are designed to prevent fluid from crossing the seal in only one direction; Fluid from the side facing the lip apply a pressure on the lip and it that prevents it from crossing to the other side. Fluid coming from the other side can expand the lip and move across. This motion of the fluid is helpful as it serves to lubricate the surface of contact between the seal and the shaft.
Based on this idea I realized that having the two inner seals facing in prevented oil leaving and to outer seal facing out prevented water coming in. As a result, none of the seals is lubricated and as the grease is worn out the outer seal will start leaking water in, which is not prevented to get into the transmission by the two inner seals. The heavy wear and corrosion can be seen in the bushing surface of the outer seal. So, even if the two inner seals are still viable they will not prevent water entry into the transmission.
My solution was to have the outer seal lip face into the transmission, preventing oil from leaving but allowing water to lubricate it. Also, the two inner seals were oriented with the lip facing the shaft, preventing water from entering the transmission but allowing oil to move and lubricate them.
After 5 years of use, I noticed a small amount of oil loss ( < 2 cm drop in the tank) which I replaced with a heavier gear oil that completely stopped the oil loss.
Last week I decided to replace the seals and bushings. I noticed that the oil was perfectly clean and the two inner seals and corresponding bushing surfaces were intact but, as expected some wear was present in the outer bushing surface. My guess is that with the heavier oil the outer lip began to work again, this time allowing a small amount of oil lubricating it.
Since after the outer lip function deteriorates the oil loss is very gradual and can be easily replaced with heavier oil, my recommendation is that the two inner seal lips should face the prop and the outer seal face the transmission. Based on the wear pattern and total lack of wear in the inner seal I estimate that the seal/bushing system would have worked preventing water entrance into the transmission for another two or 3 years. So my next experiment is to only replace the seals 8 years from now unless I begin to see a drop in oil level which is not fixed with heavier oil which I will report immediately.
Ipanema SM2k 278