HarryKrause wrote:

I have two boats with refrigerators. One is a 25' Parker with a 12V
refrigerator/freezer unit. It has never been used.

The refer or the boatBG?

Damn thing hooks into the two batteries on
board, and even though it is supposed to shut itself off if the voltage
drops below a certain level. Who knows if it will? And of course, I
could switch off one battery and run it off the other, but will I
remember? What it needs is its own dedicated battery with isolaters, but
I haven't gotten around to doing that bit of wiring.

The boat I'm presently involved with has an older ('78?) Norcold
dual-voltage refer of the usual size. This is the sort that has its
own internal inverter & changes over to 12vdc whenever it's available
at its terminals. During delivery trials I noted that on 12v it only
draws a little over 1 amp. I have little exp using 12v refers other
than an RV 3-way I didn't like, so to me this indicates 1 of 4 things:

- the refer is slightly hosed though it cools OK even with its no-good
door gasket (big gap at bottom in the usual place); or,

- it is unbelieveably efficient; or,

- the monitoring instrumentation (Link 2000) is lying (I haven't been
through that panel and verified its setup yet); or,

- you could run the sucker with only a small solar panel charging the
bank almost indefinitely.

But as for water chilling, it'd seem a natural for a cruising boat in
hot climates to obtain it part-time via a 2nd exchanger from
engine-driven A/C, particularly since most who can afford such boats
consider "roughing it" to mean badly-dressed line handlers & slow room
service. Or for the rest of us, fulltime via the
compact/simple/poor-man's route of routing DW through a little fin-tube
exchanger in the refer, perhaps using up the usual otherwise-cramped
space up high next to its freezer (evap).

Of course, once someone begins fabbing & selling the little exchanger
to boaters, it won't be a poor-man's route anymore. ;-) But finned
tubing is common enough that you could roll your own, and poking 2
holes in the rear to plumb it is a no-brainer for a careful person.
You might enjoy having a 5gal tank of nice well water piped to a small
DW-dedicated handpump spout that'd give you one big cold glass at a
time. This DW tank might also be an ordinary springwater carboy
secured with a 2-hole stopper - you could chuck it for a new one
anytime it got suspicious, or rinse it out easily, or even have 2 for
home filling/swapout. Finally, there'd be a lot more room in the
already-small refer.