Bronze Propeller anode depletion to bonding bronze skin fittings

[vyv_cox]

but presumably complying with ISO 9093 which apparently states that,

“The materials used shall be corrosion-resistant ........”

and defines corrosion-resistant as:

“a material used for a fitting which, within a service time
of five years, does not display any defect that will impair tightness, strength or
function.”

Indeed, and the basis of YM's seacock campaign. I have a statement from Guidi, who supply many upmarket boatbuilders with underwater fittings in the same materials, to the effect that this is excellent material for the duty and they see no problem with it. Presumably the words 'Random Harvest' mean nothing to them.

[Tranona]

My Volvo Penta folding has stainless steel pins (large) holding each of the three blades, the pins are held in place by stainless steel screws with hex head.

What if those were bronze instead of stainless steel?
Would that small mass cause the premature anode depletion?
Could stray current in the marine be causing anode depletion even if the propeller is isolated from the shaft and saildrive?

You might want to ask Volvo why it has happened. Expect they have been asked many times so should be able to give you a good answer!

[haydude]

You might want to ask Volvo why it has happened. Expect they have been asked many times so should be able to give you a good answer!

I have, I will post their answer. It may take a while.

[Boo2]

Proper bronze through hulls are made with 85-5-5-5 bronze and rarely suffer from dezincification.

Interesting. I asked Aquafax what their bronze through hulls were made of and they replied " UNI 7013/8 G-CuSn5Zn5Pb5 frequently referred to as LG2 Gunmetal". Is that the same stuff ?

Boo2

[Tranona]

I have, I will post their answer. It may take a while.

Yes, they probably have a queue to deal with and then they have to decide whether they will give reason number 24 or 86.

[VicS]

Interesting. I asked Aquafax what their bronze through hulls were made of and they replied " UNI 7013/8 G-CuSn5Zn5Pb5 frequently referred to as LG2 Gunmetal". Is that the same stuff ?

Boo2

You appear to be quoting the same analysis as mitiempo!

Admiralty gunmetal contains 10% Sn and only 2% Zn.

LG2 is often used as a substitute for admiralty gunmetal. I imagine the small % of lead improves its machinability. It is sometimes known as red brass

[billmacfarlane]

When I bought my boat new I was told that there was a known problem with the propellor eating anodes and that Volvo was aware of it. The prop was a 3 bladed Volvo folder on a 120S Saildrive. Volvo's solution was to supply me with another propellor made with a different metallic compostion. So maybe the problem is with the Volvo prop. Sorry to disappoint but the new problem actually made the problem worse. It's now in my den acting as a hi-fi headphone stand.

[Chi34]

I have this problem too. I would like to know for sure if the anode is really necessary.
Also, I wonder if the Ambassador rope stripper affects the circuit.
The saildrive anode doesn't erode much. The prop anodes went very quickly during the first year.

[AliM]

We have a similar set-up on a new boat (launched April 2011). After 6 months, the prop anode was about 50% gone, and we replaced it. After 10 months, we've just replaced it again (again about 50% gone). We are keeping the remnants in case we get caught short!

The saildrive anode, after 10 months, was about 30-40% gone. But here lies a problem - it is a standard Volvo anode machined to accommodate a stripper, and we are having to mill away some perfectly good zinc from the Volvo replacement to get it to fit! Again, we'll keep the eroded one just in case.

[haydude]

The prop anodes went very quickly during the first year.

Do you mean that following years were better? If that is the case I read a similar report. Could it be that the new metal is more active and it stabilizes after the initial oxidation?

In the meantime I found out that Volvo Penta decalares that their folding propellers are a nichel+aluminium+copper alloy.