If a boat sinks when should the engines be drained?

-It depends on how quickly the engine is going to be serviced. It's worse to pull an engine out of the water and leave it sit than to leave it submerged. Because the metal surfaces inside the engine will start corroding very quickly if they're exposed to air. Pull it out of the water and get started on tearing it down right away. If you leave it sit for more than a few hours it'll be ruined.Immediately upon salvage. The sooner you get the water out of the engine and a fresh coat of oil on everything, the sooner you stop the water damage inside.
ASAP after pulling out of the water.