A Guppy, (or any other anode), can protect ONLY the underwater metal that is bonded to it, (inside or out), and then... that metal needs to be close, like within 6' or so. In other words... The clamp end of the Guppy wire must of be clamped to the interior
My shaft zinc protects the nearby strut, even though they appear to be electrically separated by the rubber cutlass bearing. This is because the strut has an interior
bonding wire, that connects it to the shaft at the engine, by a "shaft brush".
It is best in many respects, (excepting ABYC compliance), to isolate the mast
and its lightning
ground, from any bonding wire and anode protection system.
It is also advisable, to have the mast's lightning
ground AND the galvanic corrosion prevention system, isolated from each other, AND the boat's DC- wire, which requires some effort, like rubber mounting the VHF
antennae's base bracket, putting in a main battery switch for the engine's - wire, etc...
While still staying isolated, you can use the boats underwater metal in your SSB's ground plane, by connecting them (by way of diodes), that pass RF energy, but not AC or DC current... (see photo). NO galvanic corrosion induced!
If you have no "issues" with corrosion, or REALLY fast zinc consumption
, by all means use the ABYC's suggested "common negative" ground buss, and connect everything to it, I was a member
when I built our boat, and I did... but if you later find that you eat zincs like crazy, and don't actually have a substantial leak from the DC or AC system, then your dissimilar metals have created a battery from all of that bonding, and it has combined with the inevitable trickle charges from the boat's systems. In this case, if you ever accidentally go unzinced, you could loose metal FAST!
If you have this problem, ISOLATE the systems! Then protect those that need it, separately. After making the necessary changes, my problems all went away. I went from 5 small zincs, changed every few weeks, to just the ONE on the shaft. I now change it every 6 months or so, still halfway in tact.