Pink prop

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AndrewD

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My propellor is getting a bit pink, which seemed odd because I have a functioning anode (eroding nicely). However on checking I find that when the gearbox is in neutral (most of the time), there is no electrical connection between the engine and the prop shaft. So I need a way of connecting the rotating shaft to the earth bonding system, ie some sort of commutator/brush setup. Clearly it needs to work with a degree of movement/vibration (shaft seal is Deep Sea seal).

Does anyone here know of such a product, or am I into the realms of home engineering?
 
Yes, a pink prop is a sure sign of electrolysis, or at least the potential for it. (No pun intended)

M. G. Duff, the anode people, sell what you are looking for. I think they call it an "Electro Eliminator". Check their web site.
 
As said, but a shaft anode on its own may be sufficient if you have the space to fit one.

I think you should also investigate the possiblity that there is a some other reason why your prop is apparently dezincifying. It may just be that it is not a suitable alloy. Manganeses bronze is the common alloy, although there are better ones eg nickel aluminium bronze.

Manganese bronze is used because it is resistant to corrosion although technically it is a brass not a bronze.

Are you moored in a marina with shorepower connected (not necessarily in use). If so then you need to think in terms of a Galvanic Isolator. Having said that if there is no connection from prop to the earth point it maybe a bit of a red herring.
 
Why don't you just leave the engine in gear when you leave the boat - much cheaper??

FWIW when sailing I always have the engine in gear to stop the shaft rotating so that would maintain your electrical connection.
 
If its a hydraulic box, wont make a difference, the only way is shaft anode or electro eliminator, I'd go for the shaft anode.
 
A local marine engineer has advised me to bridge the flexi coupling with wire, he reckoned if there was no way to bond easily across the coupling then two jubilee clips, one either side connected to the shafts with wire between would do......
Does that make sense?
 
Here we go Again THE GREAT ANODE DEBATE.

As the propshaft is the only bit of stainless in the water it should be fitted with an anode so that it "looks " like a metal lower down the Nobility Table than the propellor
Stainless steel has an electr- potential of -0.2V , Bronze is at -0.25V so stick a lump of Zinc (-1.1V) on the shaft and the zinc will erode preferentially and should protect the prop..
The question about linking the shaft to the engine is only relevant if all the skin fittings are bonded together and as we know, there are two schoo;ls of thought about that one.
You are not perchance in a marina and moored beside an old steel boat or steel piles ? Or have you checked if your boat battery negative is bonded to the incoming mains and is picking up a stray voltage.
Whichever way you look at it ,a pink proellor is de-zincifying and should be given urgent help!!!!!
 
Absolutely right. Don't mess about with shaft brushes, bridging couplings or other fancy ideas. Put a shaft anode on it and it will corrode preferentially ref. the shaft and prop. There's a short note precis of a paper on the subject here. As it says, if the corrosion persists despite the shaft anode it could be worth considering an anode on the prop itself. Shouldn't be too difficult to arrange, Bruntons come with them as standard.
 
A agree that a shaft anode is the best & cheapest way to go BUT unfortunatly the clearance on my boat between outboard end of the stern tube & the prop is not enough to accept a shaft anode. In which I am limited in my options .

Re Not all Bruntons have prop anodes I have a 1 year old Varifold (2 blade) with no prop anode.
 
My prop has recieved some damage over the last couple of years (it's a £2500 Variprop so I'm not too happy about it!), the boat stayed in the water for arounnd 14 months, as it was in the Orwell there wasn't much chance of checking the anodes (one on the shaft, and one on the prop), they'd both completely gone by the time I had chance to take a dive. Hence my interesst in bonding through the shaft across the flexi coupling.

There was also some corrosion to the heat exchanger. I intend to fit two hull anodes both bonded to the heat exchanger and full length of shaft plus the shaft anode and prop anode, see where that gets me.......
 
The Bruntons website says the Varifold is made of nickel-aluminium bronze, which is just about the most corrosion resistant propeller material in existence. An anode should be quite unecessary with it, although a stainless steel shaft may need protection.

And yes, I should have said Autoprop.
 
[ QUOTE ]
There was also some corrosion to the heat exchanger

[/ QUOTE ] If you mean an engine mounted heat exchanger then a hull anode will not do anything to protect that. The only way to protect a heat excahnger is with an anode mounted inside the seawater side of it. Those that need anodes ususally have them fitted but they do need replacing regularly.

Are you moored in a marina with a shorepower connection.
 
No, we're on a swing mooring, Pin Mill, River Orwell. My Variprop has become quite badly pitted, and although pinkish it's not deep (still tings). It was perfect when the boat went in last time and like I say had the prop anode and a ring anode on the shaft. Now it aint /forums/images/graemlins/frown.gif .

I did AF it though with Sea Guardian, do you think that might have caused a problem? Or stray current from my battery bank?
 
[ QUOTE ]
we're on a swing mooring, Pin Mill

[/ QUOTE ] Cant blame the shorepower then!

As Vyv says NiAl bronze should not suffer any corrosion and if it's Bruntons Varifold that's what it is made of.

As for the AF that's a cuprous oxide based one. I think perhaps Bruntons are the people to ask about its suitability on one of their props.

Stray currents from your own batteries might just be the trouble but not if they are properly isolated. To cause your problems you would be looking for a stray positive connection to the prop and shaft and a negative connection to some other underwater fitting in order to create an electrolysis cell.

Zinc anodes on a combination of a stainless shaft and a copper alloy prop will waste away fairly quickly, that's the nature of things.
 
[ QUOTE ]
Variprop are a German make

[/ QUOTE ] I was confused by all these names!

Variprop is made of "NIBRAL" that's a nickel aluminium bronze but it does have its own anode (surprisingly). Sold as something mecahnically stronger than bronze but maybe not as corrosion resistant as we thought. maybe Vyv knows more.

I reckon you will have to keep on top of anode replacement. Regular inspections until you have a feel for its life span and aim to replace when its about 1/2 wasted away I guess. You mentioned shaft anode, like wise. Dont expect either of them to last long.

If you decide to fit a hull anode you will have to be sure that there is a good low resistance path all the way to the prop. That'll mean bridging the flexible coupling but the post that started the thread shows that you still cannot guarantee a connection through the gear box. MG Duffs Electro Eliminator, or a DIY job, is perhaps the only sure answer. (I did not think the Electro Eliminater was all that expensive!)
 
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