Corrosion in the marina
Whether or not to bond through hulls to the rest of the boat''s underwater metals is one of the great debates. Nigel Calders, Boatowner''s Mechanical and Electrical Manual, 1990 ed, p. 107 discusses this and calls bonding the conventional wisdom.
Recognize, however, that a through hull in a fiberglass hull with rubber hoses is electrically isolated and unlikely to corrode significantly in the absence of strong stray currents in the water. There''s simply no circuit for the electrons to flow through to balance the copper and other ions which leave the through hull and dissolve in the seawater. Of course, the lack of bonding means they probably aren''t connected to a zinc to protect them either. But, connections can go bad and zincs can erode to nothing.
I feel safer with all underwater metals isolated.