Do I need a reservation for the boat?
Boat trips in Switzerland do not need to be booked in advance, unless stated otherwise in the timetable. Exceptions are special cruises like dinner cruises or music cruises. You would book these through the shipping company. Boats on the Swiss lakes are like city transport: you can just hop on and off as you like with a valid ticket or a rail pass (many "rail" passes are actually public transport passes and thus also include boats).
We recommend the SBB ticketshop