which zinc to use

[mudmanjw]

I have an anode question for ya.
I'm repairing a mudboat(flat-bottomed shallow draft boat similar to one pictured in a post a few down in this forum"Building a 15' Mudboat"). Its plywood with an outer layer of polyester fiberglass. I've rebuilt the bottom and still have some work to do. When I pulled off the old aluminum strut, there was a descent amount of electrolysis on it. Mostly between the aluminum and the fiberglass bottom. The boat spends only about 3 weeks a year total in the water either on hunting trips or parked in front of our camp. I was going to put a magnesium anode on the new strut to protect the boat but after doing some reading, I came across some info that said the magnesium in salt or brackish water "overprotects" the aluminum and a zinc anode should be used instead. I think I read that in a post on this forum and I'm not shure how you can "overprotect" something. Eating up the strut is one thing but the motor is an aluminum block 35Hp Briggs & Stratton that i would like to see last and if its getting to the strut, it must be getting to the engine/clutch, etc...

My question is... Which anode should I be using in this mostly brackish environment?