While on the ghost ship, you'll have to quickly move and manage your inventory at the same time. The trickiest point comes when getting the feather and using it.

To do so, start by getting the key and, while walking through the room with the sleeping ghost crew, open the inventory and hold your down arrow key until the key gets the yellow box and, at the same time, position the cursor where the ghostly feather will be in the next room. Then, pick up the feather, click on the passage so Guybrush starts walking towards it, open the inventory and press the right arrow key while, at the same time, you move the cursor so it will appear on the ghost's feet when entering the next room.