I use it in my plane. It really only lasts about 30 minutes and the ice turns to water.
It works in the plane as I only need it while on the ground. Once I get airborne and a few thousand feet above, the air is naturally cooler and I turn it off. Usually put some drinks in it so when I land they are cold. Upon landing, I turn it back on, while I taxi back to the hangar.
I don't think this will help with a boat.