The P19 can't luff at all.
"17 ON THE SAME TACK; PROPER COURSE
If a boat clear astern becomes overlapped within two of her hull
lengths to leeward of a boat on the same tack, she shall not sail above
her proper course while they remain on the same tack and overlapped
within that distance, unless in doing so she promptly sails
astern of the other boat. This rule does not apply if the overlap
begins while the windward boat is required by rule 13 to keep clear."
That applies only to the overtaking boat - the F16 with spinnaker in this case. It means that you can't sail from behind and under someone and then take them up. It doesn't say that the ROW boat who is being overtaken from windward can't alter course to defend.
I'm with Dave on this one, you need to plan way ahead if you are the spinnaker boat and be prepared to drop the kite quickly if the leeward boat starts to engage his rights and you haven't been able to get enough height to negate his advantage. I agree that it's a risky and not terribly beneficial maneuver on part of the non-spin boat...but it's within his rights.
