I lived in Amsterdam a few years ago, and there were multiple startups for boat rideshares (more for tourists to cruise around than actual transportation). It actually worked well because it's €20-ish for an hour long canal cruise on the tourist boats, and fuel costs were minimal as it was no wake everywhere, so if you got 5-6 people in your boat you could really clean up.
I do remember one startup that was supposed to be a boat Airbnb, in the sense of let people come and use your boat for a few hours. That one didn't last long because there's no way in hell anyone who actually owns a boat is going to let some drunks use it without them around.