Second alternator needed?

My vessel is primarily 24 v, starter, alternator, lights and pumps, but I have a few 12v accessory items that I currently operate off of a 24x12v converter which only makes about 20 amps, not quite what I need at times.
The obvious solution is to add a second alternator at 12v and a 12 v battery, but all the bracketing, and drive belt mods to make that work are both complex and expen$ive, so I’m wondering if it might be more feasible to install a 24x12v charger and battery?
Electrics are not my forte, would appreciate thoughts from those more knowledgeable in the field.
Also would a 3 bank shore power battery charger be able to charge all 3 batteries since two of them are wired together to make the 24 v side?
Thanks!