speculation on light-and-dark adepts.

[Rolina]

Lied about not being an Adept?  No, if he was one, he'd have taken the boat himself, remember?  That's the whole reason he was searching for adepts - so someone could drive the boat.

[Aile~♥]

Correction:
Babi CAN command the boat, but was the only one of them to be able to do so. He is now too old and can't go anywhere without easy access to his Mystic Draught, and has a responsibility to his city that cannot be ignored. So he needs to recruit someone else to do it.

[Rolina]

Wait, really?  Where was this?  I'm still a ways away from that section in my WiiU playthough - could you maybe hunt it down in one of the many scripts online?

[Aile~♥]

Kraden    : Unfortunately, Babi was the only one of us who could use the ship.

So there you have it. It's not mentioned in GS1, though.