When the sailor throws overboard a lifebelt from next to the door at 35 min. in, a moment later the lifebelt is hanging there again.
The ship's doors, even the external ones, are simple wooden ones with house doorknobs.
The opening shots show a ship enclosed in heavy fog, yet a close up of the ship's fog horn show it with no fog at all.
When Charlie fires three times at Erickson, his gun is pointed at the floor, but Erickson grabs his wrist, where he has presumably been hit.