I took the day off and spent most of it on the boat with my wife and some
friends. We decided to do some swimming so we anchored at our favorite
swimming hole.

While in the water I noticed that the paint is starting to let go along the
edges of my outdrive. The outdrive has magnesium anodes in all the
correct places but there is no tab anode on the back end of the cavitation
plate.

This is the first time this boat has ever spent life in the water at a
marina........it was always a trailered boat in the past and the outdrive
was in pristine condition cosmetically when I purchased the boat last
summer.

Shore power is available at my dock but I do not use it other then when
working on the boat. The boat does not have a galvanic isolator.

I am planning on adding the tab anode on back end of the outdrive cavitation
plate. I am also considering adding a galvanic isolator to the boats DC
electrical system.

Is this a good decision or am acting prematurely before doing other trouble
shooting (and what would that trouble shooting include?)

If the galvanic isolator is a good add on ($150 on a Guest 50 amp on Ebay),
what amp size should I consider? 30? 50?

TIA for your help!