Originally Posted by Mr. Blu
Why do you want aluminium anodes in stead of zinc anodes? The diference in electrical potential between aluminium and other metal sorts is larger than the difference between zinc and other metal sorts. This is important to know because the electrical resistance in fresh water is higher than in salt water. Aluminium anodes are for fresh water. When you are on salt water the zinc anodes are preferable.
Based on the research I've done, Aluminum provides the following advantages:
1. Lasts longer than Zinc
2. Better for the environment
3. Protects in any type of water
You might choose Zinc if either of the following are true:
1. Boat is in tropical (very warm) waters, as Zinc will actually last longer than Aluminum in such environments
2. Boat will sit at anchor or in a slip for extended periods, as Zinc "sloughs" better than Aluminum, which can form a "crust" that inactivates the anode.
Zinc anodes have historically been cheaper than Aluminum anodes, which is likely why they have been much more popular. More recently, Aluminum prices have come down and in some cases Aluminum anodes are less expensive, which is driving up their popularity.