I've checked some of these out before, and played with some ideas myself...but have not tried to use one in a boat or car yet.
There are some...no, lots...of YouTube videos about how to make one of these cheaply, which I would personally suggest doing and testing on your boat in your weather before investing any significant $$ into a "production" model. Here I've included a link to another "production" add-on for your existing cooler, plus you can search for "ice chest air conditioner" or "cooler air conditioner" or "DIY air conditioner" or "homemade air conditioner"...you get the idea...in YouTube and you will find many people who have made these out of regular stuff...
Check out this one for the basic idea...
http://youtu.be/D4Pyr5YJfew
Here's an official one:
http://www.kooleraire.com
ChuckieTodd wrote:It takes 144 btu to melt one lb of ice into water. From that, we can calculate that 5000 btu (small air conditioner equivalent) would be almost 35 lb of ice. And that's just for one hour!
This may be true, but what matters is how much cooler the air in your boat gets by taking that many BTU's of heat out of the air to melt the ice! That's the main point anyway...removing some of the heat from the air. You don't have to make it 68-degF in the boat to improve the comfort level...changing the air temp from 92F (here in Florida) to 85F can feel like a North Wind when you're hot and sweaty and sticky!
So if you use frozen water bottles (which, by the way, more smaller bottles will work better than fewer larger bottles), and you keep the air flow low so it stretches out to a little bit of cooling for a couple hours, that can make it nice enough to get to sleep and sleep long enough comfortably that you don't notice that it isn't cooling much anymore... I think using something like this might work fine for one night out, but you can't carry enough ice for this to be feasible for many nights.
Also, for better results I would suggest a centrifugal type "blower" (like the one in the pic in the first post which is a squirrel-cage fan or other centrifugal blower) rather than the axial-flow "room fan" types used in many of the video's...may not be cheaper, but you need a little pressure, and axial-flow fans don't do that very well. Just some random thoughts...