For a short term backup, maybe. I have to agree with the others. Very inefficient and not very effective. But you would have ice for frozen margaritas and stuff. I say get it and use it when you need actual ice. Use a proper reefer setup for keeping food
cold. There are ways to do it fairly cheap
. Especially if you run your engine
a lot. I always thought a compressor
from a car air conditioner would make a pretty good engine
driven small reefer compressor. I'm sure it would work great on a motorboat. But the figures I am seeing on 12V systems look pretty good, except maybe the price
could be a little lower.
A cheap way to keep a few drinks or a couple days worth of food cold would be a 12v fridge like what they sell at truck stops. They are cheap as dirt but painfully small, usually. I don't know how much current
they draw but probably more than a purpose built boat reefer.