As Rambler 88 rounded the Fastnet Rock they took a hard left and left the Fastnet Traffic Separation Scheme (TSS) to Starboard.
Unfortunately not only was the TSS an obstruction, it was also a mark of the course. This is allowed – see Racing Rules of Sailing Rule 19.
From the tracker replay, Rambler 88 very clearly avoids the TSS as an obstruction so no cause for alarm or protest there. However, the TSS was ALSO a mark of the course as per the Rolex Fastnet Race 2021 Sailing Instructions Appendices. It had to be left to port.
From the tracker is it clear that Rambler virtually gybed at the mark (The Fastnet Rock) and left the next mark (the TSS) to Starboard and therefore DID NOT SAIL THE COURSE.
The correct action is the one they took which was to finish. They clearly didn’t immediately realize their error otherwise they would have turned around and made sure the bit of string went around all the marks.
It is pointless speculation as to when they realized, all that matters is that when they did realize the error they posted a retirement, they had to sail back anyway so why not push the bat and see what she could do.
A great shame for them and hands up for them for taking the correct and sportsmanlike action.