The Ghost Ship is a haunted vessel the cruises the Wind Waker ocean according to the phases of the moon. It's filled with undead monsters. To enter it, simply approach it. If you have the Ghost Ship Map in your possession, you will automatically board it.

Beat the enemies inside (utilizing the moonlight to defeat the Poes) and you will collect the Triforce Shard 4 (Wii U) or the Triforce Chart 4 (GameCube).

Ghost Ship Location

The locations of the Ghost Ship follow the phases of the moon, according to the Ghost Ship Map. They are, starting with the full moon, clock-wise: