On Mon, 01 Oct 2007 19:25:48 -0500, Molesworth
wrote:

And there's not a lot of load ampere-wise - florescent lights, mast
lights, hot water (on occassion), laptop, depth meter, GPS, anchor winch
.. that's about it, apart from the 4cyl 51HP Yanmar. Oh and I just
bought a portable AC unit and an inverter (3000 amp). I already have a
charger set up. Oh, and a refrigerator and the Lectra-San.

Blimey. it adds up doesn't it?

Sigh. Any guesses on my amperage requirement?

You won't be able to run an AC unit or hot water heater very long from
batteries, regardless of size. You need a generator or shore power
for that. The only reason to buy a 3000 watt inverter is to get the
extra charging capacity that usually comes with it. To charge at a
150 amp rate you will need a battery bank of at least 600 to 800 amp
hours. The cheapest way to do that is with 6 to 8 golf cart batteries
in series-parallel. Do you have a high capacity alternator on your
Yanmar of at least 100 to 150 amps? If so you can use it as a
generator of sorts, powering your inverter with DC and getting 1000 to
1500 watts of AC out. That will power a small AC.