Long winded reply coming...
The "zincs" are what's is known as sacrificial anodes. They are used to protect the steel (or aluminum) structure of a vessel.
The anode is made a of a metal which is more reactive (See galvanic scale:
https://www.mfcp.com/technical-info/galvanic-corrosion) than the metal being protected. Steel hulls typically use aluminum anodes, aluminum hulls use magnesium. Both types used to use zinc as the anode material, but it is less friendly to the environment and has lost popularity - not legal in some waters.
I may not get all the technical terms exactly right, but electrolysis takes place when metal is in water where the metal oxidizes (rusts) - it loses electrons. The sacrificial anode on a boat is essentially the weak link. It will lose electrons more easily than the base metal and protect it from oxidizing until the anode has wasted away.
This is much of a problem in seawater where the salt speeds up the process. Similarly the warmer the water the faster it takes place too.
On the Great Lakes this isn't a huge problem, but anodes are used particularly around the stern of the vessel. At the back of the boat there are usually propeller shafts, rudder shafts and propellers which are made of stainless steel or bronze alloys. Both those metals are further down the galvanic scale and, if unprotected by a "zinc" the hull steel would become the anode and corrode more quickly.
Zincs are installed in a variety of places onboard a vessel, not just the outside of the hull. They're typically found in ballast tanks (seawater mostly), inside seachests, inside piping systems, etc. Anywhere that there's risk of corrosion - a bunch of sacrificial anode are much cheaper to replace than a hull!
Long winded reply coming...
The "zincs" are what's is known as sacrificial anodes. They are used to protect the steel (or aluminum) structure of a vessel.
The anode is made a of a metal which is more reactive (See galvanic scale: https://www.mfcp.com/technical-info/galvanic-corrosion) than the metal being protected. Steel hulls typically use aluminum anodes, aluminum hulls use magnesium. Both types used to use zinc as the anode material, but it is less friendly to the environment and has lost popularity - not legal in some waters.
I may not get all the technical terms exactly right, but electrolysis takes place when metal is in water where the metal oxidizes (rusts) - it loses electrons. The sacrificial anode on a boat is essentially the weak link. It will lose electrons more easily than the base metal and protect it from oxidizing until the anode has wasted away.
This is much of a problem in seawater where the salt speeds up the process. Similarly the warmer the water the faster it takes place too.
On the Great Lakes this isn't a huge problem, but anodes are used particularly around the stern of the vessel. At the back of the boat there are usually propeller shafts, rudder shafts and propellers which are made of stainless steel or bronze alloys. Both those metals are further down the galvanic scale and, if unprotected by a "zinc" the hull steel would become the anode and corrode more quickly.
Zincs are installed in a variety of places onboard a vessel, not just the outside of the hull. They're typically found in ballast tanks (seawater mostly), inside seachests, inside piping systems, etc. Anywhere that there's risk of corrosion - a bunch of sacrificial anode are much cheaper to replace than a hull!