SM Prop Shaft Seal direction and Bush***RESPONSE TO *** IMPORTANT RESPONSE***


Jose Venegas
 

Dear Bill,

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.  

Jose 

 




rossirossix4
 

A bit of a twist on this issue.  Like many of us I am now using 90w oil vs 15-w40 and it is lighter colored.  Used to be that it was lighter and then milky.  Just curious, has anyone noticed how 90w looks when it starts to get mixed with salt water?
Bob, KAIMI SM429


Craig Briggs
 

Hi Bob, 

The 90w gear oil behaves pretty much like the old 15w-40, turning progressively more white-ish. Like the 15w-40 in emulsifies into a pretty thick white grease, like cold creme, but still flows to lubricate the gears, that is, there is simply no pure salt water against the gears, so the urgency of changing milky oil is likely not high, ie., a few months won't make a difference. It may not flow out the drain hole on its own so you need to rinse it out with lots of diesel fuel - 5 gallons does it nicely. Put the plug back in, fill the drive, run the engine in gear a bit to swish it around, drain again. Repeat a few times until the diesel comes out clear. 

Jose,

An SKF seal engineer reviewed this for me some years ago - the post is still around, but bottom line of his evaluation was that Amel's selection of brass bearing material was not nearly hard enough. (Duh, Amel calls it the "wearing-out bearing".) SKF offered to machine a proper bearing and several folks went to a hard stainless (not 316) and had good success. Others get 6 years on the original Amel configuration. Hmmm.

Cheers, Craig


---In amelyachtowners@..., <rossidesigngroup@...> wrote :

A bit of a twist on this issue.  Like many of us I am now using 90w oil vs 15-w40 and it is lighter colored.  Used to be that it was lighter and then milky.  Just curious, has anyone noticed how 90w looks when it starts to get mixed with salt water?
Bob, KAIMI SM429


Jose Venegas
 

Thank you, Craig,
That makes sense.  What did the SFK expert tell you about the orientation of the seals?

Good winds

Jose


Craig Briggs
 

Hi Jose, see my original post under your question below.  Bottom line from the SKF engineer, inner seal facing oil, two outer ones facing the water. Use MUCH harder metal for the bearing than Amel used.
Cheers, Craig, SN68 Sangaris, Ft. Pierce, FL
---In amelyachtowners@..., <jvenegas@...> wrote :
Thank you, Craig,
That makes sense.  What did the SFK expert tell you about the orientation of the seals?
Good winds
Jose
---In amelyachtowners@..., <sangaris@...> wrote :

As we've all experienced, the bronze "wearing-out bushing" (as Amel refers it) gets, well, worn out and grooved from the lip seals. Then water leaks into the oil and we see the tell-tale "chocolate milk" colored oil that says it's time to haul out and replace the seals (cheap) and the "wearing-out bushing" (typically dear in price if supplied by Amel.)
I've had two thoughts on this: switch to a harder bushing of stainless steel and/or try a new (to me) lip seal design by SKF called the Wave Seal. It has the lip in a sinusoidal pattern that spreads the wearing area on the bushing. (SKF is "the world leader in bearing technology.")
I ran this by SKF's engineering department who were most responsive. Here's what their take was on the issue:
"Craig, 
My educated guess is that the seals are not an issue in this application. The problem is with the Bronze bushing that is being used as a sealing surface. Bronze is generally quite soft and might not have the required hardness of Rockwell C 30 or higher. You have a few options to solve this issue:
• You can put SKF speedi-sleeve gold on the shaft (P/N 99830). You will probably have to install multiple sleeves as you have 3 seals next to each other.
• You can replace the bronze bushing with a hardened wear sleeve for better abrasion resistance. We can offer you a custom wear sleeve if needed.
• You can plate your bushing with a harder material (Chrome, ceramic, etc) to make it wear resistant.
Essentially, the harder the shaft is, the less grooving it will see. I also suggest you to make sure that you grease pack the area between the seals to make sure that the seals not in contact with the oil are well lubricated. A lack of lubrication can cause the seal and surface to wear quicker. Finally I would arrange the seals with 2 facing the water and one facing the oil as long as there is no pressure difference. 
Best regards, Jaydeep Laljani, Application Engineer, SKF USA

I wrote back and said:
"Many thanks for your analysis. Frankly, I have wondered why the manufacturer used Bronze in the first place and not stainless - they actually call it a "wearing-out bushing" (but then they do charge a lot for replacements :-). 
Next month I'm returning to the boat, which is in Turkey, and I can easily have a local shop turn a new bushing in 316 Stainless (the same material as the shaft and propeller, so no electrolysis issues.) I think that would solve the problem without going to sleeves or plating. 
As for the orientation of the seals, I like your suggestion of two facing the water and will do that the next time I change the seals. After all, we're really trying to keep the water out more than keeping the oil in. And, yes, indeed, I always pack the seals with a good water-proof grease and that helps, I'm sure. "

Jaydeep replied with:
"I think you might not get as much life as you want with 316 SS as it is still not up to the required hardness. If you want to go Stainless I recommend 17-4 Stainless steel which is harder. If you are going with the 316 SS I would recommend you to passivate it to improve corrosion resistance. "

So that's the story which I thought might be of interest to the group. I hauled last year and only haul every three years, plus the new seals I put on then only have 300 hours and are not yet leaking so I'll report back in 2015 when I haul again and install a new 17-4 Stainless Steel "Not Wearing-Out Bushing" with two seals facing out!

Cheers, Craig Briggs
s/v SANGARIS, 1992 Santorin #68, Didim Turkey

PS; Update in 2018; never did get around to the 17-4 SS bearing, but used SKF speedie sleeves with inconclusive results; Next tried centrifugal rebabitting of the WOB; again, not much difference. Just last week installed a new Amel bronze bearing, "by-the-book" with two seals toward oil and one toward water. We'll see.


Ian Park
 

Craig
I am waiting in anticipation. Amel Martinique’s replaced mine 2 years ago (but we missed last season’s cruising). However I already had the parts which included a phosphor bronze copy of the wearing out bushing. An engineer friend of my son had looked at the schematic drawings of the whole set up and suggested£ that it would work better with a harder material. The seals were put in the way you stated with two facing the water.
In the meantime I’m keeping an eye on the colour of the oil........
Still don’t know whether changing to SAE 90 would slow down the prop shaft alternator. Anyone got a professional view?

Ian
Ocean Hobo SN96 Isles des Saintes


Craig Briggs
 

Ian,

I hadn't though about the prop shaft alternator, as I removed mine some time ago (have a genset), but it certainly seems reasonable that the heavier SAE90 oil will present more resistance and likely slow the shaft alternator.  
I'd say stick with the 10w40.

Cheers, Craig
(PS. I think Bill Rouse's comment was that the C drive oil viscosity wouldn't materially affect the engine speed, with which I agree -  but your comment was about the SN shaft alternator, with which Bill isn't familiar.)


---In amelyachtowners@..., <parkianj@...> wrote :

Craig
I am waiting in anticipation. Amel Martinique’s replaced mine 2 years ago (but we missed last season’s cruising). However I already had the parts which included a phosphor bronze copy of the wearing out bushing. An engineer friend of my son had looked at the schematic drawings of the whole set up and suggested£ that it would work better with a harder material. The seals were put in the way you stated with two facing the water.
In the meantime I’m keeping an eye on the colour of the oil........
Still don’t know whether changing to SAE 90 would slow down the prop shaft alternator. Anyone got a professional view?

Ian
Ocean Hobo SN96 Isles des Saintes