The surface water is too hot for cooling, but what is the water temperature 10 feet down? How about 20 feet down?

The original idea might work if you don't have to go too deep to get cool enough water. Getting water from that deep you might need a submersible pump so you push it up rather than pull it.

There is a graph on this page that shows water temps at different depths for Lake Travis. Going 50' down it says the temp only drops from 88F to 80F.

heres your answer use it every weekend!
http://www.homedepot.com/Appliances-...atalogId=10053

and if your boat doesnt have shore power you can get a shore power to regular 110 outlet plug at west marine here

http://catalogs.westmarine.com/guide...atalog/395.asp

But what will you plug that adapter into to get your 120V?

Check out moby-cool,com; they make a cover/conversion shroud for $129.00 to mount a window a/c unit over deck hatch.

Im sure that portable unit does great, im still faced with coming up with 110v ac away from the shore power. either a big converter (lots of house batteries) or a genn on the swim platform. What do you run this portable unit with while ur away from shore power??

Bay air makes a good system that uses ice and a heat exchanger. Claims to use a group 24 batt for 20 hours of run time. Do a search on here for some good info.

Wow, that's a lot less than I would have guessed. With only small temperature drop, that idea goes out the window.