A boat clear ahead rounds a leeward mark leaving it to starboard and sails four, five lengths upwind before tacking. While she's luffing the trailing boat arrives at the mark, rounds it and heads up. She's changing course around the mark and is now heading straight for the tacking boat. That boat - passed head to wind - is now keep clear boat either under 13 (tacking) or under rule 10 (Port Starboard), but cannot do anything until she's gained speed.

Meanwhile the other (starboard) boat is sailing three, four lengths in a straight line toward her. A clear port / starboard issue, you say? No, it is not, in my opinion.

Again, because of the type of boats, the definition room must include more. Rule 16.1 dictates that Starboard, who initiated the collision course, must provide the room to the other boat to keep clear. Once Port is passed head to wind and tacking, that includes room to finish that tack. Port has no other way to keep clear. Going back is not going to work, that would only take more time.

The space a boat needs in the existing conditions while manoeuvring promptly in a seamanlike way.