This is getting complex - how about that for a comment on the obvious?
Going first to the lightning issue, keep in mind that the best minds I believe now agree that lightning does not "strike". What happens is a huge positive charge can accumulate on a high point (a person's head, a tree, or a masthead). The overhead negative charge from the clouds is attracted to the strong positive charge and shazamm. The electricity goes up, not down. The purpose of a bottle brush, and a large ground plate under water is to dissipate any positive charge buildup at the masthead. If the masthead is maintained at ground level electrically, it will not attract the negative tracers from the overhead cloud/passing air.
The issue of having a common connection for the internal electrical system ground and the hull ground is one I have mused about at length. However, my conclusion is that the experts opine that if you don't do that, a lightning hit will wipe out your entire electrical system - instruments, motor starter, everything. It will jump over to the second electrical system ground in other words. Very risky - at least.
Perhaps the worst alternative is to have multiple earth grounds (the seawater is effectively earth ground for a boat) because then you do have a loop, and electrical currents can flow. For example, if the system electrical ground is connected to the motor (which is then in the water), you have a loop with the masthead ground. That is not good, in my opinion. Everything has to be commoned to a common point closest to the ground dissipation point. In my boat the wire from the electrical system meets the ground from the masthead at the through hull plate.
When you hear about a boat that has been "hit" by lightning and winds up with areas of pin holes, that is because, lacking a clear low impedance path to the water, the current goes right through the fiberglass creating a myriad of pinholes and the boat can sink. Wood plugs don't work for those small pin holes. I have noticed that many west coast built boats do not have lightning protection/water ground, and it seems those are the ones that get hit and blown apart (I should mention that a laminated hull, which the Ariel/Commander does not have, is a big part of the problem).
Bill: I have been considering your concerns and putting a zinc on the rudder post(s). As I recall you have an outboard that you pull out of the well when you are not using it. In such case, the rudder post(s) may be the only metal connection to the water/ground. If that is the case, the posts are grounding posts and are subject to significant galvonic action (the shoe is part of the rudder post assembly for this discussion since it is electrically connected) In such event, a zinc sacrifical plate would be mandatory, but, based on my possibly flawed reasoning, one zinc plate should be adequate for the assembly - the preferable location being the shoe.
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