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

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
---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:
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.

Join to automatically receive all group messages.