At the risk of writing one of those smugly ignorant HN comments with a poorly thought out "why don't you just" solution in it... That actually sort of does. An

At the risk of writing one of those smugly ignorant HN comments with a poorly thought out "why don't you just" solution in it... That actually sort of does. An observer hits a MOB alarm, like a fire alarm point, and that causes the deployment of a few drones with infrared cameras that start circling the ship in an outward spiral. Even in the warm waters of the Carribean a (live) human is significantly warmer than the water and I think should stick out. Tracking a light blob on a dark background feels like it ought to be fairly basic CV (though I don't know for sure). The drones can take it in turns to loiter, tracking the MOB. Perhaps a larger drone might then be launched to fly out and drop a flotation device. At the very least something like this may help to provide a better location fix on the victim. But again I don't know - probably there are all sorts of complications to spotting people in the water using infrared. I am sure a former Coast Guard SAR pilot will be along in a minute to tell me why I am wrong - I look forward to being educated :)