Re: battery bank dual charger or triple charger?
No one has mentioned the more modern approaches.
A common setup these days is to have chargers only charge the house battery, then to charge the starting battery off of the house battery.
On my boat there 3 batteries in the same configuration as yours and 3 multi-phase chargers: shore power based one, alternator-based, and solar. All of these are charging the house batteries.
The starting battery is charged off of the house battery using a Xantrex Echo Charger.
The battery switch is a Bluesea 5511e which has 3 positions: Off, On, and Combine(Emergency). Off turns everything off. On connects the starting battery to the engine circuits, and the house battery to the house circuits. Combine will combine all circuits should I need to start the boat off of the house batteries.
The advantage of this setup is that my house and starting batteries are never combined (unless there is an emergency) and all batteries get the best quality charging possible. It also allows me to safely mix battery technologies, my house batteries are AGM while my starting battery is a wet cell.
My shore power charger is a Xantrex Trucharge 20+ that can handle two battery banks, but I only have one attached to it.
1986 Pearson 28-2 "Elena"