30 might do well with only 12,000 BTU unit. We use 16,000 now. You really are not going ti run A/C on 12 volts and be cool without a generator
. Even then you might still be better with AC power. 12,000 BTU's per hour requires better than 3500 watts of power assuming you had a perfect efficiency unit (nothing is). That would be about 3/4 of the contents in a 4 golf cart battery
bank per hour.
this up takes attention to detail where running the ductwork is mostly vexing. It's worth the money
to get a decent pump
for the cooling water
. March makes about the best and you can buy a spare head
for it should that fail. Cal
pumps are cheap
and tend to act that way and impossible to service
. You want the salt water
supply line as short as possible and it requires it's own sea strainer and through hull
. All the extras may or may not come with the AC unit but the quality of them matter a great deal. These door prizes add up to serious money
as does the labor to install them.
We have a Mermaid now and we had a Cruisair
before. Most all of them use a similar compressor
that is sealed and unserviceable. Both were reverse cycle and heated exceptionally well if the water
is above 50 degrees. You should look for units with a control head
that sets a thermostat. It makes the use just like at home.