Rule 13 - WHILE TACKING
After a boat passes head to wind, she shall keep clear of other boats until she is on a close-hauled course.
During that time rules 10, 11 and 12 do not apply.
If two boats are subject to this rule at the same time, the one on the other’s port side or the one astern shall keep clear.
It's difficult to actively keep clear while passing head to wind. The idea then is to prevent this situation by not tacking in the path of another boat.
A boat keeps clear of a right-of-way boat
(a) if the right-of-way boat can sail her course with no need to take avoiding action and,
(b) when the boats are overlapped, if the right-of-way boat can also change course in both directions without immediately making contact.
Clear Astern and Clear Ahead; Overlap
One boat is clear astern of another when her hull and equipment in normal position are behind a line abeam from the aftermost point of the other boat’s hull and equipment in normal position. The other boat is clear ahead. They overlap when neither is clear astern.
However, they also overlap when a boat between them overlaps both.
These terms always apply to boats on the same tack.
They apply to boats on opposite tacks only when rule 18 applies between them or when both boats are sailing more than ninety degrees from the true wind.
Examples: Blue (Tacking) must keep clear of Yellow
Blue (Tacking) in front of Yellow
Originally, Blue is on Starboard while Yellow is on Port (Rule 10).
As soon as Blue passes head-to-wind, Rules 10,11,and 12 turn off. It doesn't matter who is Port, Starboard, Windward, or Leeward. Blue has to keep clear of anyone.
Both boats are now on Port, with Blue to Leeward (Rule 11)
In positions 1 and 3, Blue is the right of way boat. However, in position 2, Blue was the keep clear boat, and as such has broken Rule 13.
Blue and Yellow are both tacking.
Both boats have passed head to wind, so both boats are subject to Rule 13.
The boat on the other's port side must keep clear.
Blue is on Yellow's port side, therefore Blue must keep clear of Yellow.