Prop shaft abrasion

[Farey]

Coming along the Leeds and Liverpool last month I developed a leak from the stern gland - a Volvo Penta rubber seal. The leak was significant - a steady drip amounting to 2 - 3 buckets of water a day and it started quite suddenly.  I tried greasing it to no avail, so assumed the stern gland needed replacing - it was last done around 5 years ago. However, when the engineer looked at it he said the cause of the leak was wear on the prop shaft, which he showed me. Moving the prop shaft forward or back an inch or two stopped it. So the boat is waiting to have a new prop shaft fitted.

 

What I'm wondering is what could have caused the prop shaft abrasion? Presumably sand ot grit must have somehow got into the seal, but how?

[Tony Brooks]

I am very tempted to use a rude word to describe that diagnosis IF your description is correct.

 

The propshaft should not be able to move in and out by than a fraction of a mm, if at all. The shaft is held in place by either a thrust bearing of some type or the gearbox coupling, so unless he undid the coupling he should not have been able to move the shaft in and out. Exactly what was done and what you have needs clarifying.

 

Later Penta seals seem to be very like Vetus ones and need regular greasing AND descaling the shaft where the seal runs. have you been doing that, this is based on Vetus instructions).

 

Does your gland have a water feed into it? Often from the weed hatch trunk?

 

Was the shaft checked for wear and smoothness at the last replacement?

 

Was/is the shaft and engine properly aligned.

[blackrose]

3 minutes ago, Tony Brooks said:

The propshaft should not be able to move in and out by than a fraction of a mm, if at all. The shaft is held in place by either a thrust bearing of some type or the gearbox coupling, so unless he undid the coupling he should not have been able to move the shaft in and out. Exactly what was done and what you have needs clarifying.

 

I assumed the coupling had been loosened in order to move the prop shaft. That's how I read it.

[Farey]

Sorry - I should have been clearer. The boat has a Aquadrive fitted, which fixes the shaft alighment. The movement only occurred after removing the Aquadrive so the shaft was then free to be slid in and out. The Volvo Penta seal does not have a water feed; it's one of these: https://www.yachtboatparts.com/volvo-penta-stern-glandspropeller-glands-5291-p.asp.

 

I've greased it regularly, using a drinking straw to get the grease under the seal. I've no idea if the shaft was checked when the seal was replaced, but I would assume so. It was done by Calcutt Boats, who seem to know what they're doing. I wans't aware of the need for descaling; I presume that would require the removal of the seal?

 

I'm not sure if it could be a factor, but last year I took the boat from Bristol to Sharpness, so it was in salt water for a while.

 

What surprised me was how suddenly it happened - nothing one day then a steady drip the next.

[Tony Brooks]

1 minute ago, Farey said:

Sorry - I should have been clearer. The boat has a Aquadrive fitted, which fixes the shaft alighment. The movement only occurred after removing the Aquadrive so the shaft was then free to be slid in and out. The Volvo Penta seal does not have a water feed; it's one of these: https://www.yachtboatparts.com/volvo-penta-stern-glandspropeller-glands-5291-p.asp.

 

I've greased it regularly, using a drinking straw to get the grease under the seal. I've no idea if the shaft was checked when the seal was replaced, but I would assume so. It was done by Calcutt Boats, who seem to know what they're doing. I wans't aware of the need for descaling; I presume that would require the removal of the seal?

 

I'm not sure if it could be a factor, but last year I took the boat from Bristol to Sharpness, so it was in salt water for a while.

 

What surprised me was how suddenly it happened - nothing one day then a steady drip the next.

 

As long as the shaft was properly aligned at the boat building stage, the Aquadrive means it should still be properly aligned.

 

Penta may not say the shaft needs descaling, and in any case it will depend on the dissolved solids in the water that you are boating in.

 

It almost sounds as if the seal has got grit embedded in it that has worn the shaft. It might be an idea to look at the PSS seal that uses a carbon ring and may not need a new shaft because the carbon ring runs on a rotor fitted to the shaft.

[Ryeland]

I had the same experience,  apart from the leak not starting suddenly. I replaced the shaft bearing, a rubber cutlass type in my case, prop shaft and seal in a few hours with a single day pull out on Stafford Boat Club slipway. And yes, moving the prop shaft slightly gave a temporary improvement. 

Richard 

[Bee]

The shaft is probably stainless steel which is hard stuff but it will wear, Bee's shaft is secondhand and has some worn bits but they are right inside the stern tube. If you have a bit of spare shaft inside the Aquadrive or maybe a bit of spare between the outboard bearing and the prop you might be able to get the rubber seal to run on a good bit of shaft . I think you'd be unlucky to get grit in there but I'm a bit concerned that the heap of nylon fishing line that I removed from my prop and shaft has wound its way into and damaged the cutless bearing .

[Steve56]

On 11/06/2023 at 19:04, Farey said:

 

 

I'm not sure if it could be a factor, but last year I took the boat from Bristol to Sharpness, so it was in salt water for a while.

 

Whether it's had any bearing or not I wouldn't know. But what I do know as most of my boating is done in the Bristol channel is that you are running in almost liquefied mud most of the time. Hence if you looked at the water on yor trip you would have seen it was brown.