Anode Replacement - How often?

Tim Good

Tim Good

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Ok so I replaced a prop shaft anode in December with a bigger expensive one and I was snorkeling at the weekend and noticed it was gone. Do they really corrode off in only 8 months?

It's the only anode on the boat just for reference.
 
northcave said:
Ok so I replaced a prop shaft anode in December with a bigger expensive one and I was snorkeling at the weekend and noticed it was gone. Do they really corrode off in only 8 months?

It's the only anode on the boat just for reference.
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Shaft anodes have very small volume - so if you have a big prop you are protecting it may well disappear quickly. Suggest you consider a hull anode, bonded to the shaft through the gearbox, with a bridge across the coupling if it is the flexible type. Good information on anodes on the MG Duff site.
 
Shaft and prop anodes often disappear because their smallest section is around the fastener which holds them on. When this erodes, the anode falls off. Painting this area (I've heard nail varnish recommended but almost anything will do) can delay that effect.
Of course painting the whole thing will make it last even longer, although it won't be very effective :rolleyes:
 
macd said:
Shaft and prop anodes often disappear because their smallest section is around the fastener which holds them on. When this erodes, the anode falls off. Painting this area (I've heard nail varnish recommended but almost anything will do) can delay that effect.
Of course painting the whole thing will make it last even longer, although it won't be very effective :rolleyes:
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It is NOT good advice to put any kind of paint on an anode!!
 
If you are connected to the marina's power for extended periods, galvanic corrosion may be the culprit.

Many report that a Galvanic Isolator solves it.
 
Very many shaft anodes have a steel inner part to which the bolts are attached. If the anode has corroded away this steel strap will still be attached to the shaft. If the bolts have loosened and the anode has fallen off it will not.

The best way to attach an anode to the shaft is to bang each half together with two hammers, or one hammer and a heavy weight, tighten the bolts and repeat until it is no longer possible to turn any further. The anode will then remain in place.
 
macd said:
But it is perfectly OK to paint a small area of an anode in the manner I described. Now which do you think is the more effective: an anode with two small spots of paint on it, or one lying on the sea bed because it's fallen off?
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No paint on any part of an anode. If paint is there the anode cannot work and will corrode RAPIDLY.
 
rivonia said:
No paint on any part of an anode. If paint is there the anode cannot work and will corrode RAPIDLY.
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Another, sorry you are wrong. The paint stop the anode working in the immediate area so prevents the boilt holes from getting larger and the anode falling off. If the rest of the anode is firmly on the shaft or the prop it will continue working. When it is fully eroded there will be little pillars with the bolts through them, so the remains do not fall off.
 
northcave said:
That's interesting. No reason that wouldn't be as good as a hull anode when leaving the boat for a period right?
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In some situations, particularly saildrive installations, where it is useful to use this technique as wear on the saildrive anode can be rapid and a hull anode is difficult to arrange. It is, however less effective because of the distance between the anode and the saildrive.

Much easier on a shaft drive boat to fit a hull anode if there is not room for a big shaft anode. If you have both, the shaft anode is likely to go first because it is closer to the prop, so when it is eroded the hull anode takes over.
 
11 months after putting my boat in the water for the first time I was swimming under the boat and noticed my anodes (shaft/pear/prop) were either gone or down to a scrap. Cue haul out for emergency replacement and discovery of how much faster a boat goes after a pressure wash. I guessed my error was leaving the boat plugged in in a marina when I wasn't there. Galvanic isolator got put on the shopping list but never purchased, so in the mean time I disconnected the power and turned everything off (bilge pump bypasses the battery isolator) when I left the boat. After another year we hauled out for a scrub and anode check and all were in fairly good condition. I replaced the prop anode but thought the others could last another 3 months til an autumn haul out. When that came round 8 months later the anodes need replacing but were still in one piece.

So the moral of the story is either buy a galvanic isolator or don't leave your boat plugged in when you leave it in a marina for a week or more. The latter has become much easier since the forum made be aware of contralube 770 but that's another story...
 
laika said:
So the moral of the story is either buy a galvanic isolator or don't leave your boat plugged in when you leave it in a marina for a week or more. The latter has become much easier since the forum made be aware of contralube 770 but that's another story...
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I agree, never leave a boat plugged in without a GI.

But (as the original poster regarding ContraLube770) I'm curious about what has become easier? Reminds me, time to get some more:

http://www.amazon.co.uk/exec/obidos/ASIN/B007OUZDPG/dolcetto-21
 
Ok so my anode lasted all of about 6 months. When i snorkel under the boat again in a couple of weeks is it worth fixing two? Will they corrode half as quickly?
 
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