Merc BIII, Zinc vs Aluminium anodes

[makkers]

I need to replace the anodes on my Bravo III and have always replaced with zinc. However hunting around for replacements it would appear that I can replace with Aluminium ones now.

I always understood this to be ok on the newer BIII issued legs but I have come acoss Aluminium anode sets for the older legs so this would imply its ok.

For ref I am salt water based.

Does anyone have any views or can qualify this?

Thanks

 

[trying]

I believe, although i am not an expert, that zinc will not last as long as aluminium although both can be used in salt water.

 

[Alrob]

As far as Im aware Ali anodes have super-seeded Zinc, I have had ali for 2.5 seasons now - no probs

part here

 

[VicS]

Aluminium anodes:

Are an aluminium - indium alloy to the US military specification MIL-A-24779 (SH).

They cost less than zinc, are claimed to give the level of protection as a similar sized zinc anode and to last for approximately a third longer.

Like zinc they are suitable for use in salt water and also in brackish water where zinc is not suitable.

 

[BrendanS]

Mercruiser stopped supplying Zinc anodes on their drives, and supply Aluminium as standard on their drives for salt water use some years ago, after some problems with corrosion on drives with Zinc anodes. I'd take that as all the evidence you need, though you can contact their customer support to verify.

 

[makkers]

Thanks everyone for the replies, aluminium it is!

 

[Alrob]

just as a point of interest - my previous boat with a B3 lived in fresh water (summer moored) from 2000 - 2004 and the anodes were 100% intact, my current boat on its 3rd season (salt water) is on its 3rd set of anodes and it is not permanently on shore power either

 

[trying]

Again no expert but I think you should use magnesium in fresh water.

I believe aluminium can stop working in fresh water.

 

[Alrob]

good point -dont actually know what anodes they were - but certainly no damage to leg, in fact what a differance fresh water makes, the legs were as shinny after 5 years as they were new (well nearly)

/forums/images/graemlins/tongue.gif

 

[whisper]

Presumably these work with Volvo kit as well.
If so, any suggestions as to where I can buy them?

 

[VicS]

[ QUOTE ]
I think you should use magnesium in fresh water.
I believe aluminium can stop working in fresh water

[/ QUOTE ]

From MG Duff's website:[ QUOTE ]
FIT THE CORRECT ANODE MATERIAL FOR THE WATERS YOUR VESSEL IS OPERATING IN

As a general rule owners should fit the anodes suitable for the environment they most regularly berth in and the following table provides a useful guide:

Salt Water Fit Zinc or Aluminium Anodes
In Brackish Water Fit Aluminium Anodes
In Fresh Water Fit Magnesium Anodes

Some vessels will from time to time move between salt and fresh water, others are berthed within marinas and behind tidal barriers where the water is enclosed and likely to be brackish or even virtually fresh. Owners must be aware of the effects that this may have on their boats and fit the correct cathodic protection system to avoid corrosion.

Not all anodes are suitable for every environment, for example the surface of a zinc or aluminium anode will if left in fresh water for some time become covered with an off white crust of oxide which effectively seals the anode and stops it working even when returned to salt water. Zinc Anodes suffer a similar problem even in brackish conditions whereas Aluminium will continue to operate effectively in river estuaries and other areas of brackish water indefinitely. The consequences of this passivation of the anode are that the next most anodic item within the anode bonding system will start to sacrifice itself which could of course be very serious.

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.


[/ QUOTE ]

 

[Alrob]

mercruiser man said use mercruiser parts or loose the warranty !!!
/forums/images/graemlins/frown.gif

 

[VicS]

[ QUOTE ]
mercruiser man said use mercruiser parts

[/ QUOTE ] but Mercruiser should be able to supply zinc, aluminium or magnesium to suit the water in which you are operating.