They do whatever is needed whenever it's needed. Wiper Entry level position. Wipers provide labor and cleaning in the engine room under the supervision of the engineer. These are the guys that make the deck department hum. ABs are responsible for general upkeep and painting of the vessel and its equipment, including mooring equipment, anchors, chains and lines, and lifeboats and safety equipment.
ABs usually supervise the deckhands.
Oiler One promotion level above wiper. The next promotion level above oiler, the AE usually stands watch while the engineer sleeps. Just like you'd guess, the Chief is in charge of everything that makes the vessel work. Engines, engine room, and any and all electrical or mechanical equipment. He stands his watch while the captain sleeps.