Originally Posted by ak-guy
I was ready to buy aluminum instead of zinc for the reasons you stated. Then I learned that aluminum wasn't good on a boat that wasn't used a lot. Aluminum is great on for example a commercial vessel that is used daily but not on a yacht that is used occasionally. Here is one exampple:
I have a problem with some of the assumptions made in your attached URL. One is that magnesium will not work in sea water. Here I would suggest that a better statement would be magnesium is unsuitable for sea water use. Yes, it will provide excellent protection but not for long. The metalís higher voltage will result in higher ion flow and quickly destroy the metal. I also do not believe it has a very high amp hour rating/pound or at least not as high as aluminum.
That higher self voltage is ideal for fresh water usage where the waterís resistance is much higher than sea water. Now back to aluminum for boats that see a few trips during a season. The ocean waterís resistance is not going to change very much for a boat moving vs a stationary boat. If anything, I believe a moving boat could have a higher resistance between the metals caused by a disturbance in the ion flow. I yield to others here who may have expert knowledge pertaining to ion flow in a conductive medium.
Our boat most definitely spends far greater hours docked than in motion. My aluminum anode experience indicates that the anode provides excellent protection. I did however have to increase the anodeís mass in order for the anode to perform as needed near the seasonís end. I was using a 6x12x0.5 diverís plate and I doubled the size to 6x12x1....inches of course.
I can get by with one anode only because I made and installed bonding brushes for the boatís prop shafts. I periodically measure the anodeís performance using my silver-silver chloride half cell. When my measurements begin to fall from 0.8 absolute volts it indicates anode trouble.
So I guess it matters not what you anode material you selected to provide galvanic corrosion protection for your boat as long as you remain protected. With that, I am very pleased at how well aluminum has performed for me over the last ten or so years.