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 do not apply to boats on opposite tacks unless rule 18 applies
Best explained with pictures:
A part of Blue is in front of the line abeam Yellow, therefore they overlap;
With Blue windward and Yellow leeward;
Rule 11 applies.
Again: both boats on the same tack.
The same situation as in 2, but again boats are on different tack;
Blue and Yellow are NOT overlapped, but on Port and Starboard;
Rule 10 applies.
One more difference: at a mark (about to round);
Rule 18 comes into effect;
Blue is overlapped and on Port;
Yellow is overlapped and on Starboard;
Because there is a conflict between 18.2(a) and rule 10, rule 18 takes precedence.
Yellow must give Blue room to round the mark as inside boat.
Finally a three boat picture with a question:
Do Purple and Red have an overlap?
This concludes the series of weekly posts about Definitions.
If you have a different insight or want to ask about my scribbling's, don't hesitate to comment or send an E-mail. I'm thinking about turning the series into an E-book.