On Saturday racing starts from the Clubhouse line formed by the transit marks on top of the clubhouse. Perhaps simpler to picture it's an imaginary line between ourselves and Royal Cornwall Yacht Club which passes through both signals masts.
Courses are taken from the SI handbook, from the section Inner Harbour Cubhouse Starts. The courses are grouped by prevailing wind direction. Each of the eight groups has about a dozen numbered potential courses. Typically each fleet will have its own course.
There is a ninth group should sailing be constrained in some way, perhaps by commercial shipping, or very low water.
The group (1 to 8) is selected by a numeral pennant flying from the signals mast. The individual course is given on boards on the quayside wall. Each course is preceded by the class, e.g. Q2U3VW4C6G1B7 expands to Q-class, course 2; U-class, course 3; V- and W-class, course 4, and so on.
Normally the course is set over 2 rounds, where the boats come back up the harbour to a turning mark, a buoy with a green flag positioned on the approach to the club finishing line. This mark is left to starboard (except when finishing).
B-class start at a mark displaying a FSC burgee and the committee boat (with an orange flag) moored in the inner harbour. If B-class sails two rounds, their turning mark is the pin end of the B-class start line. This mark should be taken to starboard, except when finishing.
If the race is shortened or altered the changes will be indicated on the course boards along with flag and sound signals. B-class will also be informed by radio on Ch 72.
The finish line is the imaginary line through the transit marks on the clubhouse roof.
A definitive set of SIs, which takes precedence over this informal description, is available