Even if your dock does not have electricity running to it, smart boaters regularly inspect the condition of their engine zincs. These sacrificial anodes are the only real protection against galvanic action that very quickly can destroy your motors and underwater fittings.
All it takes is for someone nearby to drop a hot shore power cord in the water, or have an improperly wired shore power system on a dock, or even have a problem with a 12 volt system and the galvanic activity begins. In as little as a day the damage may be done.
We here at the marina have seen cases where you actually could see the water bubbling around metal items, such as trim tabs, as they were being eaten up by the electrical action. (Never fear SMP slip tenants, that was eventually traced to a problem with that boat’s own 12 volt system).
Should you notice any abnormal wear on your zincs, have them replaced immediately and take steps to find out why that situation is occurring.