If Davy Jones copied the ability of Namazu:
Give this sea monster a shoot action. A wave S wide and 2L long leaves the sea monster in one direction. Up to 2 masts of every ship in the path of the wave are eliminated. Eliminate one of this sea monster’s masts.
Would the ship he’s on be able to use the ability? Or would the text refering to a “Sea Monster” prevent the usage of the ability?
Copying an ability doesn’t change a ship’s type, so because it refers specifically to “this sea monster” in the text, Davy Jones can’t use it unless he’s riding on a sea monster at the time (via Chariot, etc.).
Behemoth can copy it and use it normally.