The definition of finish says, “A boat finishes when after starting, any part of her hull crosses the finishing line from the course side.”
The diagram actually shows two different but common course configurations. These two boats are not actually racing against each other. If we start with the Blue boat, the course in the sailing instructions says “Start – 1 – 2s/2p – 1 – Finish”. They say that the start and finishing marks are Blue. They also say that “The finishing line will be between a staff displaying a blue flag on the race committee vessel and the course side of the finishing mark.” The race committee uses the same mark for the start and the finish. Notice that when Blue finishes just before position 10, she leaves the blue mark to starboard. The side she leaves it on will depend on where it is. Even though the windward marks (or even all other marks) are left to port, she finishes by crossing from the course side, which is in the direction from the previous mark, mark 1, rather than by leaving the finish mark to port. It is also important to understand that marks 2s and 2p are not marks on the first leg or the last leg. Blue can go either side of either mark – or between them, though this may be crowded if another fleet is rounding them at the same time.
 
For Yellow there are similar sailing instructions, but the course is “Start – 1 – 2s/2p – 1 –2p – Finish” and the finish mark is Yellow. This course, which is quite common for ILCAs and Optimists, has the boats reaching across the finishing line. The race committee uses this since it is easier to read the sail numbers from the mainsail when the boats are on a reach. This is sometimes called a “Hollywood Finish” since the boats put on a good show going by. This time, Yellow leaves the finish mark to port since this allows her to finish by crossing in the direction from the last mark. In this second case, 2p is a mark of the course on the last downwind leg. Boats must leave it to port before finishing. Read the instructions carefully to see if 2s is a mark of the course here. Some instructions require boats to pass through the gate between 2s and 2p, others just require 2p to be left to port. Boats with very wide gybing angles might leave 2s to port as well.


The next diagram was from a youth regatta that I judged in 2022. They had set up a separate finish boat. The course was “Start – 1 – 2s/2p – 1 – 2p – Finish”. As in the previous example the finishing line was defined as being, “……between a staff displaying a blue flag on the race committee vessel and the course side of the finishing mark.”  The race committee was using a separate finish boat even though the finish was fairly close to the start line. The Green boat understood this and finished correctly. The Yellow boat did not see which committee boat was flying the blue flag and crossed between the finish mark and the starting signal boat. The starting signal boat was not displaying a blue flag, so Yellow had not crossed the finishing line and did not finish.


In the third diagram the course is defined as “Start – 1- 2 -3 -1- 2- 3- 1- 2 – Finish”. The sailing instructions list the finish mark as green. The race committee has deliberately used a different mark for mark 3 and for finishing to separate the fleets who are still on an earlier lap from those that are finishing. Grey has just finished. Purple has not finished. She has either sailed across the wrong line or she is still racing on an earlier lap. This is again a “buoys to port” course but the finishing mark is left to starboard.


Many of the same principles apply when the race committee decides to shorten the course. For the next two scenarios the course is “Start – 1- 2- 3- 1- 2- 3- 1- 2- Finish”. In the diagram, the orange signal boat is in the normal position to signal shorten course. The finish line is between the mark the boats were supposed to round (mark 1) and flag S. Green finishes between position 1 and 2.
Sometimes, often for logistical reasons, the committee sets up on the other side of the mark where the white boat is in this diagram. This moves the line to the other side of the mark. Remember that to finish, a boat must cross from the course side, that is, coming from mark 3. Red finishes correctly between position 1 and 2. Green, who rounds the mark leaving it to port, as she would if the course was not shortened, crosses the line at position 3, but she is not crossing from the course side, so she does not finish.


The fifth diagram is based on a situation that I also saw in 2022. The course was “Start – 1- 2 -3 -1- 2- 3- 1- 2 – Finish”. The wind died so the race committee moved up close to mark 1 and signalled that the course was being shortened. The wind had also shifted significantly so boats could sail directly from mark 3 to mark 1. This time however, the finish boat was further upwind and further to the left of the diagram. The only way to finish from course side was to leave the mark to starboard as Blue does in the diagram. Other boats followed the path shown by Yellow. They did not finish according to the definition of finish.



There is an exception to the rule about finishing between flag S and the mark. If the mark is a gate mark such as the leeward gate in the third diagram, rule 32.2(c) says that the finish is between the two gate marks. Purple is finishing, Grey is not. Many race committees will set up very close to one of the marks to make it obvious that there is no room. This applies at gate marks. The rules don’t define gate marks, but I would say that gate marks are a pair of marks that you have to pass between. A windward offset mark such as 1A in this diagram is not an gate mark, even though I have heard some people describe it as one.
 
The final exception listed in 32.2(b) “a line the course requires boats to cross” is not one that I have seen. It would probably apply to long distance races which have a particular line that has to be crossed as part of the course.
The lesson here is that when you see flag “S” indicating a shortened course, always be careful about which side of the mark the signal boat is sitting on, as it may not be the side that you expect.