In the first diagram, Blue and Yellow are both on starboard tack approaching the starting line. At position 1, Blue is clear ahead of Yellow, but luffing her sail to slow down since she is early for the start. At position 2, Yellow gains an overlap to windward of Blue.  Rule 11 says that Yellow must keep clear of Blue. At about position 4, the starting signal goes. Just as in last month’s article, Yellow expects Blue to bear off and go to the next mark, which after all, is Blue’s proper course. At the least, Yellow expects mark-room at the committee boat. Blue, though, can stay up and deny mark-room to Yellow for almost the same reason as we saw last month – there is no mark-room at a starting mark surrounded by navigable water. The only difference is the application of Rule 17. This time, instead of the overlap being established more than two boat lengths apart, Yellow did so while to windward, and from clear astern. Rule 17 still does not apply, so Blue is allowed to shut Yellow out.

The second diagram, like the first, shows Green and Red both approaching on starboard tack. This time at position 1, Green is clear ahead of Red and luffing her sails to slow down. Red establishes an overlap to leeward from clear astern. This is exactly the situation that is described in rule 17. According to rule 17, Red is not allowed to sail above her proper course. However, if we look at the definition of proper course, it says “a boat has no proper course before her start signal” so at this time there is no restriction imposed by Rule 17 on Red. When the start signal goes at position 4, Red must go down to her proper course, which is probably directly towards the mark.  There is room for Green to pass between Red and the committee boat, so she does, and we have a very different race.
 
The simple way to think about this is that in the first diagram today and last month, Yellow had the option to go astern of Blue and end up on the leeward side. When she didn’t do this, she became vulnerable. In the second diagram today, Green as the windward boat did not get the choice. Red came up from astern. Green is given more protections once the starting signal has gone.