Zinc, alumium, or magnesium anodes?

Addis

Petty Officer 3rd Class
Joined
Oct 19, 2005
Messages
83
I a'm confused on what type of anode to purchase. My houseboat is kept in fresh water and has twin Volvo Penta AQ200/280. I have another anode from other houseboat of mine and it seems very heavy for its size (zinc?) compared with a larger aluminum one that I have. I imagine that magnesium also is very light. Does it realy mater if A zinc or aluminum anode is used. After all the unit is kept in fresh water? Thanks.
 

Dunaruna

Admiral
Joined
May 2, 2003
Messages
6,027
Re: Zinc, alumium, or magnesium anodes?

General rule of thumb is magnesium for fresh, zinc for salt. Sacrificial anodes are made up of a cocktail of alloy, the best people to advise you as to the exact type you need is the outdrive manufacturer.

There should be a direct correlation between the size of the anode and the material that needs protection.

For example, my boat has a pair of 45ft alloy toons. I have a 10 pound magnesium anode attached to each pontoon.
 

Addis

Petty Officer 3rd Class
Joined
Oct 19, 2005
Messages
83
Re: Zinc, alumium, or magnesium anodes?

Thank you for the reply.
I found the mfgr.of one of the anodes and it is zinc. So I guess someone put the wrong type on. I guess I'll have to wait for a couple more weeks untill the covers come off to check to see what type of material the second dog bone type is made of so I don't mix zinc/magnesium or what ever. Thanks again.
 

Jeepster04

Chief Petty Officer
Joined
Jan 5, 2009
Messages
481
Re: Zinc, alumium, or magnesium anodes?

Went to a houseboat show a couple weeks back and talked to some vendors about anodes. Seems aluminum is the best thing to get for a boat in fresh water. I was kinda curious how an aluminum anode would do any good on a house boat that is made of aluminum and he said the anodes are much softer than the hull of the boat so electrolysis sets up in the anodes before the hull, etc.
 

204 Escape

Ensign
Joined
Nov 17, 2007
Messages
909
Re: Zinc, alumium, or magnesium anodes?

:confused:

O.K., I'm not mechanical, so I will ask. What is an anode, and what does it do ??

:confused:
 

wkb2460

Petty Officer 2nd Class
Joined
May 4, 2008
Messages
146
Re: Zinc, alumium, or magnesium anodes?

I've always been told Magnesium is best for fresh water.
Aluminum was for brackish and zinc for salt.
 

Dunaruna

Admiral
Joined
May 2, 2003
Messages
6,027
Re: Zinc, alumium, or magnesium anodes?

204,

An anode is a alloy that will sacrifice itself in place of the surrounding alloys (such as outdrive legs, props, toons etc etc).

A sacrificial anode must be towards the bottom (or at the bottom ) of the 'Nobility Table'.

I am currently blocked from posting pictures but someone (hopefully!) will post a copy of the 'Nobility Table' to clarify what I am talking about.
 

Addis

Petty Officer 3rd Class
Joined
Oct 19, 2005
Messages
83
Re: Zinc, alumium, or magnesium anodes?

Thank you Super Daddy! Great site for a super explanation of both salt and fresh water applications plus other components affected also.
 
Top