For those who like mast abeam, Rule 13 is the one rule you hate to see go away. The new rules no longer places the mast-abeam restriction on the leeward boat. Along with that rule (also Rule 16, see previous Sailing Tips), they do not prohibit the leeward boat from "obstructing" the boat which is tacking on her. It all boils down to the point that it makes it harder for the starboard tacker to "slam dunk" a port tacker.
Rule 13 After a boat passes head-to-wind, she shall keep clear of other boats until she is a close-hauled course…
Under the old rules, the slam dunker could hail mast abeam, or claim she is being obstructed from keeping clear, to prevent the leeward boat from luffing when she is completes her tack. With the new rules, the boat being dunked can liff as soon as she crosses the starboard tacker's stern, as long as she give the dunker room to keep clear.
So now, if you are being "dunked", and once you have crossed the tacker's transom, you can now luff the dunker! If the dunker declares, "Mast abeam! You can now respond, "Leeward, there is longer a mast abeam, so I can luff you so long I give you room to keep clear."