Do the exterior doors on a ship (ocean liner) open inward or outward?

They would open outward , to be sure.........to prevent from being blown open.

If anything............they might be sliding doors, that retract into the walls.

Generally, on a ship, doors and hatches that open to the weather open outward or upward. This is so water cannot push them open in heavy seas.

Inside doors generally open into the room from passageways so people traveling in the passageway do not get hit by doors.

They open outward, the impact of a wave would act to lock it tighter shut.