Planejammer Campaign Setting
Crown of Stars
This cannot be made by conventional enchantment. They do not normally have a rated AC, hardness, hit points or break DC, but you could use an AC based on its size, and +22 save bonus.
Caster Level: 19th; Weight: -.
Arcane Price: a king’s ransom, at least
This magical item distills the abilities of a minor helm into a portable item that can be worn, allowing the helmsman to move normally in addition to commanding his ship.
If the crown is used to power a ship for one week or more, it becomes bonded to that ship. It cannot be used to power a different ship unless it has been away from its bonded ship for at least one week, thereby severing the bond.
The Crown of the Stars is effective up to one mile away from the ship it is bonded to, so a helmsman can operate the vessel even if he is not on board.
A Crown of the Stars will not affect a ship with an active helm (or equivalent) on board. It can provide spelljamming ability to ships that would otherwise lack it (such as a viking longship). Often a crown is discovered on the ground where they befuddle the local sages, who do not know of the worlds spinning above their heads.