I think the term I should've used is "pilot boat captain", or "harbor pilot" actually. The ones by me work for the government. They don't need to provide their own boats.

A lot. But most tug captains work for someone that owns the boat and over time might buy into the boat ownership or buy their own. You can still make a big salary while running someone else’s boat though.

I had a friend who got into working on boats like this. She worked her ass off, but made really good money for someone just starting out.