The Skull and Bones ghost ship, the Maangodin, doesn’t directly drop any cosmetics for your ship. However, defeating the Maangodin grants you Ethereal Ashes, a special currency you can use to purchase unique cosmetics from the Mysterious Rogue vendor located at The Oubliette outpost.
Here are some of the cosmetics you can buy using Ethereal Ashes:
Keep in mind that the specific items available for purchase may vary, and the Mysterious Rogue’s inventory might change periodically. Additionally, Ethereal Ashes are not guaranteed drops from the Maangodin, so you might need to defeat it multiple times to acquire enough currency for your desired cosmetic.