Go to the chocobo forest to closest to edeas house from there go north into the water and in between the two islands where there is water once you have gone betweend them go to the cover to the west and follow it around towards the north and make sure you go right along the coast and you will find the ship.

sheep? i dont know go to a farm. baaah baaa!
na, just kiddin anyway its between the two islands north of
edea's house...baaaaaaaa

Yes, this part was exceedingly frustrating! If you want to find it without knowing exactly where it is, then just keep checking your subscreen to make sure that you are exploring around the Centra continent. If you want to know just where it is, look at your world map. You will see what looks like an imperfect ring of land surrounding a body of water closer to the south edge in the middle. The lower edge of this ring appears to have three fingers on the right and a long finger on the left. The white ship is to the left of the long finger. There are three inlets pointing down, and the ship is in the western most inlet.