I mean, it's not a boat specific job, but neither are Zoro or Robin's.
Like I mentionned many time, Robin act as the metaphorical destination, the cap. The guiding light. The point on the map. She is the "road" (literally the name of the chapter when she was introduced) that point the strawhats toward a destination. That's her role on the seas, its linked to her skill as a archeologist. Note how are called the 4 most important poneglyph..
Spy is not really relevant on the sea, its doesn't bring any symbolical or literal value. Its just something that most strawhats have done, its something requiered by a mission not really. That could change if Oda puts more care into the "post" but right now I don't see it. Its more of a Robin bis..