I don't think you waited long enough. I've drowned. When your screen starts getting black around the edges you know its only a matter of seconds. It even warns you in the field manual

Try again... you drown, actually sounds really intense... :) Good job Bohemia!

yea i have drowned

I waited 3 minutes and i was a boat operator. I dont know if its a glitch or something. ill do what i did again and if it works then well thats a good thing.

Unable to reproduce. Could you please provide more specific repro? I mean fraction, type of boat, exact position of unit on the boat (commander, driver,...), etc. Thank you.

Takes quite some time before you drown (fatigue has no effect on how long you can stay under water), but eventually you will drown.

Closing as unable to reproduce.