Talking of anodes

[Enya]

I have an Albin Vega. When I sanded off the propellor I was surprised to see that it was rather pink with some brassy circular bits. No obvious pitting. I then read Andrew Simpsons RYA Electrics Handbook and concluded that the propellor is probably managanese bronze with 40% zinc. A galvanic cell all on its own. The prop shaft anode was suitably corroded too. I used trilux antifoul last year. This propellor has probably been attached to its shaft for 40 years.

I was a little more bothered to find some pinky colour where the through the hull anode is electrically connected to the tiller shaft. I now do not have time to renew the fixings on the hull anode or replace it. Would cleaning them up with a soft wire brush help? Will kurust be any good? I am unsure how the electrons flow in this situation and how tolerant they are of rusty bolts.

The hull anode is corroding but has still more than half left after 3 years.

 

[VicS]

Make sure there is a good low resistance electrical connection between the anodes and what they are fitted to protect. I.e. good bonding of the hull anode and good contact between shaft anode and shaft

Manganese bronze is a copper/zinc alloy with small amounts of other elements including lead, tin and of course manganese It is perhaps technically a brass and some suppliers do in fact call it manganese brass, I think you will find.
Normally it does not suffer from dezincification and has been widely used for props because of its high resistance to seawater corrosion.

If the pink colour is only surface deep it is no problem but should be of concern if deeper. See Vyv Cox's website

I'd not use a rust remover like Kurust on the anodes . Maybe wire brush but be careful not to leave bits of wire embedded in them.
The anode should protect its own fixing bolts when in the water but they tend to rust when the boat is out of the water. Provided there is good metal to metal contact between anode and fastening all should be well. The continuity check mentioned above will confirm it.

 

[Enya]

Thank you for that advice. I connected my multi meter to each bolt in turn on the anode. The lowest scale on my multimetre is 200 ohms. The connection between the bolt on the anode and the tiller shaft gave readings under 200 but I could not say what the lowest was. The reading seems to start around 150 and fade out to a fixed 1.

I could get no reading between the other bolt and the engine fixing point. Does that signify no resistance?

For all those reasons, I am wondering how to clean up the anode bolts. The zinc anode is actually well cleaned.

I guess I should actually probe with one point of the multi meter on to the actual Zinc on the anode and fix the other end to the part being tested but my multimeter seems fairly limited or else I do not know how to use it properly. Any thoughts?

 

[VicS]

Thank you for that advice. I connected my multi meter to each bolt in turn on the anode. The lowest scale on my multimetre is 200 ohms. The connection between the bolt on the anode and the tiller shaft gave readings under 200 but I could not say what the lowest was. The reading seems to start around 150 and fade out to a fixed 1.

I could get no reading between the other bolt and the engine fixing point. Does that signify no resistance?

For all those reasons, I am wondering how to clean up the anode bolts. The zinc anode is actually well cleaned.

I guess I should actually probe with one point of the multi meter on to the actual Zinc on the anode and fix the other end to the part being tested but my multimeter seems fairly limited or else I do not know how to use it properly. Any thoughts?

200 ohms is a typical lowest resistance range . I'd expect it to have a resolution of 0.1 ohms.
Familiarise your self with the reading when there is no circuit ...ie infinite resistance ... mine shows a 1 on its own on the LHS ... and also what raeding you get when the prods are shorted together ie the closest you can get to zero ohms ... mine reads about 00.4 .

Check what you get between the zinc ( clean a bit to get a good contact if necessary) and the fixing studs and between the zinc and the item being checked. The closer you get to the reading with the leads shorted the better.. the higher the reading the poorer the connection is somewhere.

You say you get no reading between anode and engine block. Is that because the anode is not connected to the engine block? There is no need for it to be if you rely on the shaft anode to protect the prop.
If there is a connection but you get no reading ( or a reading significantly above the zero reading) the connection is not good.
Remember that if the hull anode is to protect the prop via a connection to the engine or gearbox any flexible shaft coupling must be bridged to complete the circuit.