A Stock Alt even if it is a 100 amp or so will only output 13.8 To 14.2 volts, essentially trickle charging
the battery. That is fine to keep a battery that is fully charged from discharging, but won't charge one well at all.
If your regularly at the slip plugged in, you'll be fine until the kitty can afford a real Alt and external regulator, if your only charge source is the Alternator, then you'll need to do something, may even be more cost effective to buy a Honda
to charge batteries and run other AC devices than a high output alt and external regulator.
I believe many have successfully used an external reg with an ambulance or other automotive larger than normal alternator.
I'm going out on a limb here, but I believe almost all Marine
high output alternators are based on automotive ones.
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