I've asked a few people about this personally, but I'd like to throw it open to the larger group as well.
I'm trying to cool the boat for a few days at a time...
A normal 5000 BUT marine air conditioner can pull up to 30 amps of 12 volt power. If my house battery were new and fully charged, that's 4 or5 hours. That won't get it for even for a weekend.
If we had a diesel engine (and ran it all day) we could use an automotive approach. But we don't - and can't.
So, quoting Kelly Johnston (one of my favorite heroes), "Simplicate, and add lightness".
Statement of Problem: I want to air condition the boat for up to 3 or maybe 4 days at a time. Independent of dock power. With as low of a battery load as possible.
A cooler type container with a load of dry ice and a way to move large amounts of air across the cooler.
A sketch at:
But what to make the rest of it from? Cheap, off the shelf stuff preferred! A pump that can handle antifreeze? High torque low power 12 volt DC motors? What to use for the heat exchangers? Coils of tubing? Or auto parts?
Other than a drip pan (and a handful of brain cells), what am I missing?