Volvo Stainless Prop Corrosion - Help

[Yabs]

Hi All,

I am after some help please. I am having corrosion issues with Volvo C3 propellers fitted to 290 DPE drives. I am now on my third set in about two and a half years!

The problem is that the props are suffering corrosion in the centre near to the bush. I believe it is being caused by the plastic washer Volvo are insisting I must use when fitting the props. The corrosion is isolated to the area under this washer, as can be seen in the photo below (A faint line left by the washer can be seen in the image). These props have only been on for 7 months!

I would welcome thoughts on the cause of the corrosion and on refitting the props without the washer?

Also I found that one of the rear props had what I can only describe as a small blister on the surface of the outer hub, which had a small crack visible. On cleaning the props I noticed that the area was soft and as I cleaned it gave way, revealing a cavity filled with black sludge. I think this can only be a floor in the casting?

The set of props from last year, which managed about 10 months were even worse! Again it was isolated to the area under the plastic washer

You help would be appreciated.

Regards

Sacha

 

[vyv_cox]

There is little doubt that this is a good example of crevice corrosion. You can find a good deal of information about the problem on my website at http://coxengineering.sharepoint.com/Pages/Crevice.aspx. Yours is such a nice(!) illustration of the problem that with your permission I will use one of your photos, please.

I'm not quite sure of the function of the washer here but assuming it rotates with the propeller I would add some sealant between the two. Keeping the water out is always a useful measure when dealing with any type of corrosion.

 

[A_8]

Its necessary to electrically isolate the props from the shafts, that's what most of the different plastic stuff is doing however I do not remember a plastic washer on the inner props, there should be a nut, can you post a pic of the plastic washer you refer to?
Also it looks like the "should be" nut is in contact with the metal on the prop, it should only lock the prop bushing. If its in contact with the prop housing than the bushing is not correctly placed. I see the bushings have been replaced, they are not volvo original so someone have changed the center bushings.

 

[Yabs]

Hi,

Thanks for the replies.

Vyv_Cox If you are able to make use of the photos feel free. Sounds like sealant might be a possible solution. What are your thoughts on the other bit of corrosion, on the rear prop?

A_8 I am very interested in your reply about the bushings as these props are brand new (now 7 months old) supplied from Volvo. Therefore I see no reason why the bushes should have been changed, unless they are supplying me with seconds. I will post a picture of the plastic washer I refer to later, when I have had chance to go to the boat and photograph it.

Many thanks

 

[volvopaul]

The latest props to replace the earlier alloy ones to dpe drives are now a one piece manufactured design, it has no centre bush and no isolation from the shaft. There also coated in a special material to stop corrosion. Called the J series when replacing a B series prop. New designs outlaw older style bushed props , also made in Taiwan!

 

[Yabs]

Thanks Paul,

Do you have experience of the J series, would they be a better bet than the ones I am currently using (C series). If they have gone back to not being isolated from the shafts I presume they are back to being protected by the anodes. Does this have implications on frequency of an ode changes and doubling up of the bar anode

Thanks

 

[A_8]

Hi,

Thanks for the replies.

Vyv_Cox If you are able to make use of the photos feel free. Sounds like sealant might be a possible solution. What are your thoughts on the other bit of corrosion, on the rear prop?

A_8 I am very interested in your reply about the bushings as these props are brand new (now 7 months old) supplied from Volvo. Therefore I see no reason why the bushes should have been changed, unless they are supplying me with seconds. I will post a picture of the plastic washer I refer to later, when I have had chance to go to the boat and photograph it.

Many thanks

Don't know how your penta guys operate but thats the same type bushings I got on mine after I had them refurbished by a non penta prop specialist, we discussed the source for the bushings and if I remember correctly they were non penta, US made and considered to be better than the now apparently out of production original bushings. The props you have there still needs isolating from the shaft.

 

[Yabs]

Here is the pictures of the plastic washer. I'm sure from what has already been said that it is this that is causing the issue. I can only imagine it is there to stop the nut contacting with the prop and therefore to ensure isolation of the prop from the shaft.

If as has been suggested I were to bond the washer to the pro what would be the best sealant etc. to use, to provide an effective waterproof seal?

How would the damaged areas best be repaired?

 

[volvopaul]

Thanks Paul,

Do you have experience of the J series, would they be a better bet than the ones I am currently using (C series). If they have gone back to not being isolated from the shafts I presume they are back to being protected by the anodes. Does this have implications on frequency of an ode changes and doubling up of the bar anode

Stainless props eat anodes faster for some reason . No experience yet as they have not been out long enough to test wear of electrolysis.

 

[A_8]

You should not use any sealants etc, make sure your bushings are correctly placed and assemble it right and you should be fine. Where do you put that witheish plastic washer?

A good prop guy will be able to fill the damaged areas and rebalance the props, they will be like new.

 

[Yabs]

The parts are laid out in order in the photo, the plastic washer goes on the face of the prop, it fits around the bush and then the nut does up against the bush with the washer forming between the nut and face of the prop. It is between the prop and washer that the corrosion is occurring.

 

[A_8]

You don't need a plastic washer between the nut and the prop, the bushing is isolating the prop however you need a plastic washer between the cone/spinner and the aft prop. Take a look at this, #46 http://www.marinepartseurope.com/en/volvo-penta-explodedview-7744470-44-7336.aspx
Without it you risk not having isolation and very likely it will eat at metal impurities in your props but also your drives.

 

[GrahamHR]

There is little doubt that this is a good example of crevice corrosion. You can find a good deal of information about the problem on my website at http://coxengineering.sharepoint.com/Pages/Crevice.aspx. Yours is such a nice(!) illustration of the problem that with your permission I will use one of your photos, please.

I'm not quite sure of the function of the washer here but assuming it rotates with the propeller I would add some sealant between the two. Keeping the water out is always a useful measure when dealing with any type of corrosion.

If you want some photos of impressive crevice corrosion on a VP stainless prop, I have a few I can send you ! The surprising thing is that when the corrosion products from a deep, deep pit on that prop were flushed out, the stainless below is remarkably clean with no sign of iron oxides.