Any of the three boats can be taken privately, for a wedding party, a funeral, a football team or a company day. It is quoted by the hour with the fuel in, and the route is yours within sensible limits.
A charter takes a boat off the public timetable, so the more notice the better. We will not cancel a scheduled sailing to take a charter, whatever is offered, because people have bought tickets on it.
Ask at the counter or send a message with your date, the number of people and where you want to go.