Let’s look at what Rule 11 says:
(* Emphasis added)
As opposed to Rule 10 where boats are on opposite tacks, Rule 11 deals only with boats that are on the same tack and overlapped. Ie, both on a port tack or both on a starboard tack and neither is clear ahead or clear astern. Rule 10 doesn’t go any further than looking at opposite tacks. It generally doesn’t really matter what boat is on the windward side or which is on the leeward side or if boats are overlapped.
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.
Note that when the rules talk about “in normal position” it simply means that you are not allowed to manipulate your equipment to gain a tactical advantage. For example, letting out your spinnaker in order to establish an overlap.
The below example 2 reinforces 2 issues:
- Green is overlapped with yellow because green is no longer clear astern when her spinnaker (in normal position) is behind a line abeam of yellow’s aftermost point.
- If green was not in the picture, yellow and blue would not be overlapped. Blue’s spinnaker is not in a normal position.
- However, blue and yellow are overlap because the green boat in between blue and yellow overlaps both.
A boat’s leeward side is the side that is or, when she is head to wind, was away from the wind. However, when sailing by the lee or directly downwind, her leeward side is the side on which her mainsail lies. The other side is her windward side. When two boats on the same tack overlap, the one on the leeward side of the other is the leeward boat. The other is the windward boat.
In essence, it is that side where the wind comes from or the opposite side to where the mainsail is deployed when sailing downwind.