Anodes....

[Scubadoo]

I'm probably asking a silly question here, but here goes, I have four anodes (Duoprop shaft, Sterndrive, 2xTrim Tabs). What conditions dictate the rate of errosion. My Duoprop anode seems to be the first to completely errode where as the larger stern block anode seems hardly affected and the trim tabs half depleated - this is after 10 months in the water.

If I change to Stainless steel props I read on this forum that the anodes errode quicker. Would hanging another large anode on a wire off the rear cleat (cleat being connected to the engine/mount) save the other anodes? This would save liftouts.

Thanks in advance.

RM.

 

[Trevor_swfyc]

You are talking about the electrochemical series here the rate of loss of Zinc ions from the anode will depend on how much difference there is in the electrode potential of the metal it is protecting, the solution in which both metals are submerged in ( assume its NaCl sea water) and the temperature of this solution.
Note it is usual to use a more reactive anode than Zinc in fresh water.
Can't see why a stainless prop should increase the rate of loss of zinc. Last point will hanging an anode reduce the rate of loss of the permanant anodes yes. It will be proportional to the surface area of the permanant against the subermerged temporary anode. ie if the surface area of both was the same then mass loss would be theoretically equall.

Also many previous postings on this subject.

Trevor.

 

[vyv_cox]

Electrochemical series....

is not the only factor. Relative areas of the anode and cathode are equally important. If you put an aluminium pop rivet in a big steel sheet underwater it will be gone in days. But bolt together some aluminium sheets with steel fasteners and they will last almost indefinitely. Your props may well have a larger surface area than any of the other parts, plus my observation is that props are often something of a mixture of alloys, not always well selected. My Autoprop anode was half gone after only four months.

 

[Miker]

Re: Autoprop anode

As was mine, particularly around the brass (?) fastening bolts. I was advised to put some antifouling around the holding bolts, but I see that the Autiprop anodes are now supplied by Brunton's with plastic holding bolts. I have reconciled myself to getting through upto two prop anodes per season. The shaft anode has been on for two years and could probably last a further year, and the hull anode is untouched. I must check that there is still a decent connection from the hull anode to the prop shaft.

 

[vyv_cox]

Re: Autoprop anode

My Autoprop came with the plastic bolts but I don't know the metal of the anode. It's possibly magnesium but I haven't got around to checking. I am intending putting some zinc from an old anode inside the bolt tube for some extra protection.

 

[Miker]

Re: Autoprop anode

I was advised by Brunton's that the anode was made of "RN quality" zinc, whatever that means.