Restaurant is on board so you need to arrive at the appropriate depature time to board the boat. You haven't specified time of day or date, or event, so you need to call them and ask about your specific request. You also need to allow for time to park, get a ticket if necessary and get on board. Sounds like a lot of messing about but it will be worth it. There is no other or better way to see the cities and sites while having an enjoyable meal in a unique venue.
You need to purchase your tickets and they depart on the time your cruise is and start serving shortly afterwards
The boat leaves the dock most of the time, so you need to see what latest to boars time is on ticket
They depart at certain times and dinner is served during sailing.
You have to purchase a ticket for one of the cruises. Your best bet is to just call them directly and see what times they depart.
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