How much zinc anode is enough?

[Traskmilemrk11]

How much zinc anode is enough and not too much? I have a 20 ft smokercraft 2072 jon boat. The main outboard and kicker have the zinc on them. I plan on taking this boat in the bays and maybe in the bubble out of Tillamook bay at times. I have heard that too much zinc can cause problems too, so how much is enough? Thanks in advance for info.

[StickFish]

Don't know that answer. but here is a good one on zinc all together

Zincs (http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=36;t=000031)