I think my alternator's shot, based on the tests I've done, but I'm
still running around the lake with no problem. . . . . yet!

Boat's got a '78 5.7litre Mercruiser with a two-bank, four battery
system. Batteries are two week's new, basic crankin' batteries. I've
had it out four times, with about 8 total running hours. Bank 2, the
only one I've used, is reading about 12.2v on one of the on-boat
meters, bank 1 shows about 12.8v. Alternator tester showed similar
numbers, and no increase in voltage when engine was running. Ammeter
on flying bridge shows 0 - no draw or charge, other meter (don't
remember if volt or amps) shows in red, discharge state for both banks
when running.

I'm taking the alternator to the shop on Monday, but I'm wondering if
this is unusual. Should I be able to run around this long on a
two-battery bank with what appears to be a shot alternator?

Thanks,
Speedo