All pointless speculation unless you add a few factors that have not been mentioned here. In the Florida Keys
you can go down 30' and still not hit a thermocline, so that water is at 85-88F exactly like it is on the surface.
Go to the NE US and you hit that thermocline at 10-20' and the water usually is 10-20F colder than the surface.
Now, is you hull
deep enough so that your intake is sucking in COLD water from below a thermocline? Or are you using a drop hose to suck from below the thermocline?
And even if you conjure it up and get it right, really? Seawater cooling
systems with pumps and intake strainers and filters and cooling pipes to clean out as the critters grow in them? Oh, what, you don't have little crusty things growing in your waters, because they are so toxic? (Ain't always a bad thing.)
Yeah the little things don't make any difference at all. Swamp coolers have been around for a long time and like anything else, they only work in the right places when they're correctly engineered. Won't find 'em in the movie
theatres in Dallas though, will you?