Hull Anode

[DaveW]

On inspection of the anodes after haul out I discovered that the propshaft anode was well 'sacrificed' - which shows that it was doing its job. However the hull anode showed very little evidence of 'wasting'. After looking at the bolt that secures the anode to the hull and to which two wires are connected (inside the engine compartment), it was very rusty.
The wires attach one to the P-bracket and one to the engine block.

I believe that the hull anode was fitted 4 years ago.

My question is: Will the fact that the anode securing bolt is corroded explain why the anode has not wasted?

I realise that due to the corrosion it requires replacing, but is this the cause of the anode not wasting away.

Advice required, please - thanks in advance.

Dave

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[dickh]

When I bought my boat seven years ago, it had both a shaft and a hull anode. The hull anode had obviously not been working and all the internal bonding wire was useless. The surveyor recmmended removing the hull anode and rely on the shaft anode. This I did and the shaft anode seems to last a season. Boat laid up last week and the anode was about ½ gone, so it's been doing it's work.
The hull anode bolts should be a good electrical contact onto the anode itself - MG Duff supply a serrated washer to ensure this.

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I'd rather be sailing... /forums/images/icons/smile.gif

 

[anabel]

Connect digital meter between hull anode and prop shaft (assuming shaft is making perfect electrical contact with engine). Be sure to make good contact with both. Resistance reading should not be more than about 2 or 3 ohms. Forget exact figure MCDUFF give as info is on the boat. If it is more, then it can't work properly. If it is less, then there is no need to worry. I only get 1 season out of my shaft anode, whereas the hull anode will last at least 3 or 4 seasons.
Rgds.
E
PS: If you getting large reading I would check that the shaft is making good connection with the engine. There should be an electrical bonding wire bridging the gearbox coupling & the connections here should be A1.

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[Evadne]

The only anode I have is in my engine, but I do know a little bit about electrickery. The anode nearest the item to be protected will waste away preferentially, so your shaft anode is probably protecting your propeller from corrosion and is best placed for the job. The effect of an anode falls off as it is removed from the scene of the celectrolytic action. Poor contact would prevent the second anode from working but it is unlikely to have been installed in a rusty state, so if it is untouched, it may not be protecting anything at all. It is unlikely in the extreme that it is accelerating the wasting of the shaft anode. GRP boats with all bronze or plastic underwater fittings, moored away from any other boats or sources of stray current may not need any protection at all, and many do without. By all means clean it up (wire brush any oxide off the exterior as well as cleaning the connections) but if it still doesn't corrode, then it is surplus to requirements.


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[DaveW]

Thanks for all the advice

Dave

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