The boat sails up and down the river through the centre of Turku from the afternoon until the early hours of the morning
There is a charge to board, but then you can hop on and off as much as you like for the rest of the day
The main purpose of the boat is as a floating bar so there is a bit of an expectation that you'll buy at least one drink.
There is no guiding and no real timetable, but the website has a live map to show where the boat is so you can head to the most convenient stop