Keel(s)?
Even if it were a sailing boat, generally keels do not need anodes - and if they were fitted would be bolted direct to the keel rather than to the "earth"
Well, strictly speaking, the line "There is normally nothing else other than perhaps rudders that need anodes.", which I was responding to, doesn't mention earth bonding, though the OP does.
That may be true, but they were fitted at a time when there was little understanding of galvanic action and there was a tendency to just slap anodes on as a cure for "corrosion" when most of the corrosion on steel and iron is simple rust from contact with salt water.. only real cure for rust on steel bilge plates is what I have done with mine - blast to a high standard and then immediately coat with epoxy. Can also be done with iron ballast keels and works reasonably well, although it is very difficult to get old iron keels really clean, particularly the bottom face. Isolate the metal from the water and hey presto the rust cannot start.
Reasonable to have anodes close by and connected to rudders - common when rudders are made of a mixture of bronze and stainless. Are yours? How are your propellers protected? They are usually the only thing that need anodes. Galvanic isolators are to protect against possible electrolysis, not galvanic action. Two different things.
Dont quite understand your implied distinction between "simple rust" and corrosion that could be addressed by anodes. "Simple rust" is oxidation, which involves the loss of electrons, so I'd have thought it should be addressable by sacrificial anodes as well as by isolation with paint.
"simple" rust is iron oxide formed by the reaction between steel or iron and moisture - absolutely nothing to do with galvanic action. Electricity has nothing to do with it. Only way of preventing this type of corrosion is to isolate the steel/iron from moisture. Iron castings such as used for ballast keels are slightly different from mild steel sheet as used in bilge plates in that there are often traces of other metals with different potential to iron in the casting. This can set up localised galvanic circuits usually evidenced by pock marks on the surface of the casting. While in theory an anode might reduce this, but the size and volume of a typical keel in relation to the anode limits its effectiveness. What often happens is that the pock marks break the paint covering exposing iron to water which then rusts and the rust spreads under paint. The difficulty with preparing such castings for better protection is getting the craters clean of all traces of corrosion. Hard work doing it manually but blasting makes it easier.
This is wrong, in fact more or less the opposite of what is correct.
These two statements are not incompatible, alternatives, or mutually exclusive. Both statements are true
The anodes should be connected to whatever they are protecting, rudders, shafts, props etc. There is no point connecting them to the batteries. Shore power should go to the GI and then to the onboard protective Earth circuit, with a single connection to one of the anodes.