Every marina or environment will be different. Squalicum in Bellingham is a "hot" marina and the average service life of the typical "license plate" zinc is about six to eight months. The marina often has a layer of fresh water on top due to nearby streams and the river that empties into the bay. So many boaters including us hang a zinc on a heavy cable down about six or eight feet off the boat. The other end of the cable is attached to the boat's bonding system.
We and the boaters I know (and boats I see hauled out) never have any slime or algae on the zincs. I was told by people in the business ess that this is because the tiny current in the anode prevents growth from occuring. If there is slime or growth on an anode, it means the anode is not doing a very good job for some reason.
People have tried aluminum anodes in our marina and in every case I have been aware of they soon went back to zinc as they found the aluminum was not providing as effective a level of protection as the zinc does. But this probably varies wiith the environment the boat Is in.
We and the boaters I know (and boats I see hauled out) never have any slime or algae on the zincs. I was told by people in the business ess that this is because the tiny current in the anode prevents growth from occuring. If there is slime or growth on an anode, it means the anode is not doing a very good job for some reason.
People have tried aluminum anodes in our marina and in every case I have been aware of they soon went back to zinc as they found the aluminum was not providing as effective a level of protection as the zinc does. But this probably varies wiith the environment the boat Is in.