Anodes wasting rapidly?

[Fenlander]

I replaced the zinc anodes on my 30 steel motor vessel which I keep in freshwater, with magnesium ones 8 months ago and since then I only spent 6 days in seawater 5 of them whilst connected to a mains hookup.
Today I saw one of them and it was 50% gone, not had a chance to see the others yet but if they are the same then I estimate they will be gone in about 6 months. As this is my first steel boat the question is, is this normal or is ther something seriously wrong with the electrics?

 

[Stork_III]

I replaced the zinc anodes on my 30 steel motor vessel which I keep in freshwater, with magnesium ones 8 months ago and since then I only spent 6 days in seawater 5 of them whilst connected to a mains hookup.
Today I saw one of them and it was 50% gone, not had a chance to see the others yet but if they are the same then I estimate they will be gone in about 6 months. As this is my first steel boat the question is, is this normal or is ther something seriously wrong with the electrics?

Quote from McDuff website:-
"It is therefore very important to check Zinc and Aluminium anodes after any trips into fresh water and if necessary clean off or change the anodes.

Should a vessel move into fresh water for more than two weeks MGDUFF recommend that an alternative anode system is used suitable for fresh water situations. Magnesium Anodes on the other hand have a much higher driving voltage than zinc or aluminium making them highly suitable for use in Fresh Water, they will however become very active in salt water where they will probably only last a matter of months. Protected surfaces can build up a layer of off white calcareous deposit which will be difficult to remove.

Magnesium anodes are not designed for prolonged use in sea water and if you are taking your boat into a salt water location for more than seven days (Fourteen days in any one year) you should consider changing the anodes. Magnesium Anodes should never be fitted to wooden hulled vessels as they can damage the timber.

http://www.mgduff.co.uk/leisure-craft/cathodic-protection.html

 

[VicS]

I replaced the zinc anodes on my 30 steel motor vessel which I keep in freshwater, with magnesium ones 8 months ago and since then I only spent 6 days in seawater 5 of them whilst connected to a mains hookup.
Today I saw one of them and it was 50% gone, not had a chance to see the others yet but if they are the same then I estimate they will be gone in about 6 months. As this is my first steel boat the question is, is this normal or is ther something seriously wrong with the electrics?

Mg anodes are going to disappear quickly in seawater on a steel hull I would think.

The shorepower hookup might be a factor if you do not have a galvanic isolator.

 

[LittleShip]

If you are going to take your boat into salt and fresh water try using Aluminium anodes. They will last longer under those circumstances.

That said, if you have an electrical problem on board you will need to fix it. The advice of a galvanic isolator is worth considering.

Check out the McDuff site, there's loads of information on there and if you need more they will advise you over the phone.

Tom