See RRS 28

28 SAILING THE COURSE
28.1 A boat shall start, sail the course described in the sailing instructions and finish. While doing so, she may leave on either side a mark that does not begin, bound or end the leg she is sailing. After finishing she need not cross the finishing line completely.

28.2 A string representing a boat’s track from the time she begins to approach the starting line from its pre-start side to start until she finishes shall, when drawn taut, (a) pass each mark on the required side and in the correct order, (b) touch each rounding mark, and (c) pass between the marks of a gate from the direction of the previous mark.

She may correct any errors to comply with this rule, provided she has not finished.

See also Case 106 

 
The definition of finish provides you with the answer.

Finish
A boat finishes when any part of her hull, or crew or equipment in normal position, crosses the finishing line from the course side. However, she has not finished if after crossing the finishing line she 
(a) takes a penalty under rule 44.2, 
(b) corrects an error under rule 28.2 made at the line, or 
(c) continues to sail the course. 

You must loop around an end to satisfy the string rule. It's OK if your string also touches the wrong side of one or both finish marks, but it must, when drawn taut, touch the correct side. A "reverse dip" fails that test. 

This is a dancing on the head of a pin question/answer. The boat does finish correctly but has not sailed the course. The race cttee must give her a finishing position but can protest her for not sailing the course. 

Mr. Hohman has answered correctly. Ten points to Gryffindor! See Case 106

Actually I missed the part that Charles pointed out, that the boat could meet the definition of finish without having sailed the course correctly and absent a protest would have to be scored in her finishing place. 

Case 128

I'd only add that care and attention is required by both the RC and the competitors in this situation.  When wind dies and currents prevail, depending upon how long the line is compared to the how much anchor line is let out, strange line orientations to the last mark can be created and competitors .. far from the last mark .. can loose orientation as they drift and spin.

If the line started skewed and then the RC swings in such a way to exasperate that skew, Case 82 might start to come into play .. Case 82  - Ang

Reviving this based on an actual on-the-water scenario from last weekend. Random leg course, "L" is the last mark before the finish (distance reduced to keep it in the diagram).

When did the boat finish and comply with rule 28?

The boat finished and complied with RRS 28 at position 2 .

A horn at the finish line or go around gestures are not part of the RRS.

True about the horn and gesture. But it's a PHRF race so finishing time can matter and the RC has a practice of sounding a horn when boats finish so they can compare time with competitors.

Tim and Peter,

I think the issue here for Blue is that it appears that she continued to sail the course.

By Tim's drawing, it's not shown but I think Blue probably clears the line the first time at 2.75 when she turns parallel to it.  At this point, she is also far enough from the marks that they are not influencing her course, therefore if she had stopped there, she would have finished [and finished racing].

That said, Blue appears to me to continue to sail the course, by unwinding her first crossing and crossing from the other side.  I think the RC should have recorded both [all 3] times, but I think there is a good case to be made that it is her 2nd [final] crossing that should count, not her first.

Also, I think this is close enough to Case  82 that a boat could cross from either side.

I think this is similar to a situation we discussed on another thread where a boat entitled to mark-room is compelled to touch a mark as they crossed the line.  Unsure if they will be exonerated, the boat decides to do a turn around the pin and cross a second time.  This was their choice and I think in this case the 2nd finish is what counts as the boat decided upon themselves to take the penalty.

Angelo, thanks, I hadn't thought about that aspect. I think I assumed that "continuing to sail the course" meant proceeding to another mark (a "twice around" scenario). But I guess we were correcting a perceived 28.2 error (based on lack of a horn and the RC's gesture) so we didn't finish at 2.

At the time I did feel like it was a Case 82 situation and I suspect that if we'd headed in after position 2 we'd have been able to get our score based on our finish at position 2 on redress. But if the RC felt that the bottom of the diagram was "from the course side" then I don't think awarding us a finish at 3 was correct, I felt like we had to unwind and pass the pin on what the RC felt was the "correct" side.

And I can't figure out why the RC didn't just move the finish pin to make it more square to the last leg of the course and remove the ambiguity.

So how about this: the RC erred in setting the finish line ambiguously parallel to the direction from the last mark making it unclear which was the course side. This is an error of the race committee and the RC should have recorded finishes in either direction (Case 82). The RC further erred in communicating to Blue that she had not finished at 2, which caused Blue to continue to sail the course to correct the perceived 28.2 error.

So if Blue's continuing to sail the course and finish at position 7 rather than 2 made her score worse (allowing one or more competitors to correct over her), would she be entitled to redress?

Angelo, I considered case 82, but position 2 is the first time the boat crossed the finish line and the boat probably should have been recorded as finished in the case of crossing for the first time from the other side.   I don't agree that this is a case of continuing sailing the course, but it could be correcting a perceived RRS 28.2 error.  I hope that in these cases the RC records all the times that the boat crosses the finish line.  Yes Tim, squaring up the finish line would have been more sailor friendly.

Here is a link to the 2021-2024 Draft RRS:   https://www.dropbox.com/s/1iwbo8dwu43rd86/WorldSailingRRS2124draft1Jan2019-%5B25233%5D.pdf?dl=0
There are significant changes proposed regarding the "finishing"  definition and new definition of  "sail the course".