Anodes

[Adaero]

On our boat we have Yanmar 54hp engines with SD50 saildrives. We only collected it from Cape Town in October last year and it has been in the water from Aug 08. The boat is now in Tenerife and when snorkelling the other day we noticed the anodes on the end of the folding props had completely disappeared. The ring anode on the saildrive behind the prop was ok but still starting to go. We replaced the outer dome anodes on the props but I am wondering what is causing this problem.
The marina is pretty new with (what looks like) good electrics but I have two boats beside that look like they haven't moved for a while both plugged in to shore power.
I was looking at dangling a couple of lumps of zinc I have over the side beside the saildrives if this might help but do I need to connect them to something or just hang them off a rail.
Any help would be appreciated.

 

[Quandary]

There have been a lot of threads on this subject so it is worth going back to them. I have a saildrive, al. alloy with a bronze folder, the small anodes on the prop do not last a season but those on the leg hardly reduce at all. When tied up I put a hanging anode over, this is wired back to a bolt on the top of the leg. (Volvo say that the leg is galvanically isolated?) I suspect that the hanging anode is protecting the alloy leg but the bronze prop. being a dissimilar metal is having to depend on the integral ring anodes. I plan to stock up on these and not being a diver to dry out somewhere every six months to check them. I have not painted the leg but coat it and the prop with lanolin grease (Propshield) which stays on for about one season.
All this is a pain and expensive but so is sterngear

 

[VicS]

Frankly small anodes on brass (or bronze) props are going to disappear pretty quickly. Simply the result of the two dissimilar metals being in contact in salt water.

The ring anode on the leg, all being well, will not be consumed at such a high rate because the zinc (or aluminium/indium alloy if its an aluminium anode) is not so dissimilar to the aluminium leg.

A hanging anode must have a good low resistance electrical connection to the item it is to protect. That means somewhere on the leg to protect that and hopefully extend the life of the ring anode. I am not familiar with the engine and drive in question so I cannot say how you would connect a hanging anode to protect the prop and extend the life of the prop anodes, or even if it is possible.

Must add that for the ring anode to be effective it must also be making a good electrical connection with the leg and must not be painted over.

In a marina it is all but vital to have a galvanic isolator fitted if you leave shorepower connected even if not actually in use. It is merely the earth connection that causes the problems although a sail drive may be electrically isolated and therefore not at risk itself.

 

[Adaero]

Thanks guys for the advice.
So if I take say a 6mm earth wire from the saildrive casing in the engine room and somehow connect it to my dangling zinc that might hopefully help to protect the other anodes?

 

[oldsaltoz]

I have noticed a few boats use old standing rigging or safety stainless steel cable rather than copper.

 

[samwise]

I was advised that galvanised wire was the best stuff from which to dangle your anodes -- cheaper than copper.

 

[VicS]

[ QUOTE ]
So if I take say a 6mm earth wire ...... might hopefully help to protect the other anodes

[/ QUOTE ] Possibly.
I would not use copper wire. The hanging anodes MGDuff supply have a stainless steel wire.

Remember this hanging anode will have to be close to the sail drive to be effective. You can do that with stern drives but a sail drive is tucked right under the hull.