This got removed, you can not longer fight vs enemys, only vs the ghostship, you have to shoot 1-2x with a cannon and then it's dead.

Spawning on your ship after some seconds when the ghostship appears in Margoria (also Ross Sea)
When it starts to get dark you will be stopped and the ship comes out of the water.
The spectre is dropping Gold Ingots 1g, Golden Pearl and Shiny Golden Seal
But only get every 4th one loot.
He sometimes stuck and is not attackable for me.
With more players on your ship there are more spectres but at same spawnlocation (stucked in each other)

I got 1 of these from the ghost once -> Sealed Golden Treasure Chest

I have also recieved the same item as glarty. Sealed Golden Treasure Chest
This Item also dropped 1 Oberin's Gold Bar