Saildrive anode and corrosion

[nigelmercier]

If you had a small leakage to earth ... [the GI] would then not have protected you from the "galvanic" effects that it otherwise should do...

If you are measuring 1.4 volts across the GI that is worrying .. thats the level at which it will conduct. Maybe thats not quite what you mean though.

I'm starting to like the idea that the faulty immersion heater was the cause, it is the only thing that has changed in the last few months. An boat-earth to neutral fault of a few volts could have easily caused electrolysis.

No, that's not what I meant I didn't measure the GI in situ before replacing the heater, but I did check it out of circuit using a 12V battery and a series light bulb to provide a current limit.

Ground plane issues are a red herring, but my Bavaria does have a lightning strap between the mast and the keel. I'm not sure if this is bonded to the battery terminal, but I suspect it gets there via mast fittings.

 

[PabloPicasso]

yes yes

I know when we bought our boat and had it surveyed the previous owner had it taken from the Med back to the UK. It may have been the end of the season so it was in the water for longer than its usual haul out and anode change. As a result the saildrive leg anode had worn so much that there was pitting on the prop and saildrive. The surveyor said both prop and saildrve needed replacing otherwise there was a risk of failure.
This cause problems as they do not make 120 legs anymore. They are now the 130 which has different gearing making it difficult to match a prop.

I was told the saildrive anode should be changed each year. At least with the 130 it can be done in the water as it comes in two half's where as the 120 was a one piece thing.

Why don't they make an oversized anode that last longer than a year?

Yes yes that is what we need. Why oh why doesn't an enterprising annode maker market some?

 

[Tranona]

Yes yes that is what we need. Why oh why doesn't an enterprising annode maker market some?

Because there is no need. If you want to increase your anode capacity then use a hanging anode. Boats spend most of their time stationary so no problem to hang an anode over the side. Alternatively you can buy a retractable through hull anode. For some reason, neither of these sell in any great numbers, even though they have been on the market for years. Wonder why?

However, for saildrives, most have no problems with the standard anode, particularly the newer Volvo 130 which is almost twice as big as the earlier ones. Most of the corrosion problem is related to fancy props rather than the saildrive itself.

 

[farmer.leo]

If you want to increase your anode capacity then use a hanging anode.

Never heard of that before. My understanding is that the anode must be electrically connected to the piece of metal that you are protecting, otherwise it does not help.

What would you connect the hanging anode to, and how would you connect it?

 

[johnphilip]

Avoid VP Prices

I have used a couple of times the 3 part propellor anode from these people instead of the Volvo part and for about half the price. Both this and the Volvo anodes virtually disapear in a season, no discernable difference. Unfortunately they did not sell the two part leg anode.
http://www.zinetianodes.co.uk/product.php?shopprodid=42

 

[Tranona]

Never heard of that before. My understanding is that the anode must be electrically connected to the piece of metal that you are protecting, otherwise it does not help.

What would you connect the hanging anode to, and how would you connect it?

You can buy them ready made from MG Duff. Of course they have to be connected electrically to the component you want to protect. A wire to the gearbox for example to protect the stern gear, just as in a connection to a hull anode. Some people take the wire up to a pushpit mounting and connect the anode to that. You can, of course make your own. My neighbour uses an old anode which is perhaps too eroded to leave on the hull, but can be easily replaced if it disappears.

 

[farmer.leo]

I'm going to look into doing that myself.

Thanks

 

[sailaboutvic]

When I brought my Dufour in 2009 I was told by the dealer that it was best not to bond my sea cock , so I didn't and so far I have not had a problem , my sail drive anode last two years but the three around the prop need to be changed every year . Any thoughts on not bonding the sea cock ?