Why Did The OOD Shorten Course?
The OOD can declare "Shorten Course" for several reasons. The most common is a change of wind conditions. Another reason may not be so well understood.
Typically if during a race the wind increases excessively creating safety risks or fades to the point where the time limit may be exceeded, the OOD may shorten course in a way that is as fair as possible to all competitors.
To understand the other reason for shortening course, we first need to understand how pursuit race starting time offsets are calculated by TopYacht. After the course is set on a pursuit race day, the OOD makes an estimate of the elapsed time for the lowest HC boat in the fleet considering the length of the race and predicted weather conditions. Based on this time and each boat's HC, TopYacht calculates theoretical Start times (to the nearest minute) for all boats to finish together. If wind strength is less than predicted and the race takes significantly longer than in the TopYacht calculation, the backmarkers would gain an advantage.
In such circumstances, the OOD may shorten the course by declaring an earlier finishing line to achieve an elapsed time closer to the day's predicted value and so maintain the fairness of the starting offsets used that day.