thing about a pool is it's only a few feet deep. you sink in the ocean, you just keep sinking. you get lost in the ocean, there's a whole lot of ocean and you're moving from the point that you fell into. it's night in the ocean? no one is finding you, even if they pass by a few dozen feet away. all this, and you're constantly fighting the whole time you're in there without food or fresh water. Between that and temperature shock, you're losing consciousness in 12 hours in the best case scenario and, depending on the temp of the water, maybe only a few minutes. Once you're lost in the open ocean you are ggggoooooonnnnneeee.

The ocean is kinda like mountain climbing in Antarctica, even if youre good at mountain climbing and dealing with extreme temps combong the two is an exponential increase in difficulties.

For any sailor in open sea especially rough seas of you go overboard it's generally presumed you will not be recovered. Even carriers in smooth seas have the occasional overboard loss, somebody will slip no one notices and by the time they go dropping zodiacs and getting helos in the air they might be miles away leaving a search area of several miles.

They might be able to stay alive for days even in cold ocean water, but that doesn't mean you'll find them in time

Fuck, this is yet another reminder I really really need to watch The Lighthouse.

Seals can drown. They are mammals and as such don't have gills. They may be able to hold their breath for a long time, but eventually they have to come back up to breathe.