So your boat is setting at the dock afloat and you are wondering if your below the water line metals ( props, shafts, thru-hulls, trim tabs ) are being protected from corrosion. Some call it zinc protection.
Are my zincs protecting and doing the job? We use three types of anodes to provide protection. Generally - Zinc for salt water, Aluminum for brackish water and Magnesium for fresh. We can test your vessel in the water and see if your anodes are providing the proper protection.
Call and discuss how this test can be done at your dock. 678.267.9877. Beats diving and or a haul out or worse wait to see damage.