ISAF – Rule 18 rely on "mark-room".
The 18 rules apply in mark-zone - (start) when the first boat enters the zone - and that have nothing to do where it ends.
The rules in section B also apply inside the mark-zone, i.e. Rule 17 is still valid.
The rule 18 rights are not valid in hole mark-zone as many sailors believe (unfortunately even some PC - judge with less Knowles). The definition of Proper course also prevents a vide turn in tactical purpose against other boats.
Mark-Room -rights by definition applies with rule 18.xx but mark-room ends when the stern passed the mark in 90 degree to the direction of leaving leg (see "while at the mark" below).
Some people believe that Mark-Zone is a Definition where Mark-Room apply - and that is not in the book!
The rules in chapter 18 integrate and rely on definitions where the major is Mark-Room!
Rule 18.xx have not any other own Definitions such i.e. saying "while at the zone"!
Rule 18.xx rely on definitions as Proper Course-, Room-, Mark-Room-, Mark-, and Leg-. All rules in the book is integrated with the definitions!
The rulebook also have it's own definition telling that all definition is in the book with the meaning of that no other definitions exist!
The fact is that Rules 18, by it selves, become a "empty" when the stearn has passed the mark, by reason of that Mark-Room ends. The rights regarding Mark-Room, ends at the point where the Mark is passed by stearn! (and rule 18 has no definition by it selves on where it ends - only where it apply).
The Mark is passed when the stern leaving the Mark, in the 90 degr, direction to new leg (leg to next mark or finish line).
At that point:
1. The Mark is no longer a Mark - it is a obstruction - ref. Definitions on mark.
2. The old leg is ended - and you sailing on a new leg - ref Definition on mark.
3. You are not "while at the mark" - ref. Definition on mark-room below - and judge-book, chapter: 39.12 and 39.18 (a).
4. Rule 18.xx is "empty", all it's right's of room is related to Definitions.
Where the Mark-Zone ends is by that completely irrelevant!
One exception is when a leg ends at finish line. Then mark is passed when the finish line is completed ("clears the finishing line" - below).
(When stern passed the finish line, without any contact to Mark. - P.S. at that point boat no longer racing and rule 25 apply).
VSK sailors have been misled "to a bad standard" of that mark-room-rights going on meanwhile hull is in mark-zone, in Races and even in some VSK competitions, maybe because of "lack of knowledge" of the cooperation and synergy between the ISAF rules and its definitions.
P.S. - In real life the discussion is more common on what point a boat "clears the finishing line" if there after a boat is in contact to a mark (on what point a mark become to be an obstruction)
In the ISAF judge-book is described "crystal clear" that the 18 rights ends when stearn passed the mark, chapter: 39.12 and 39.18 (a).
(The judge book is a quality guideline for judges, to ensure right decisions.)
ISAF RULE & Definitions
(essentials are underlined by Lazy.se sometimes with comment)
Terminology
A term used in the sense stated in the Definitions is printed in italics or, in preambles, in bold italics (for example, racing and racing).
Definitions
Rules
• (a) The rules in this book, including the Definitions, Race Signals, Introduction, preambles and the rules of relevant appendices,but not titles;
• (b) ISAF Regulation 19, Eligibility Code; Regulation 20, Advertis- ing Code; Regulation 21, Anti-Doping Code; and Regulation 22, Sailor Classification Code;
• (c) the prescriptions of the national authority, unless they are changed by the sailing instructions in compliance with the national authority’s prescription, if any, to rule 88;
• (d) the class rules (for a boat racing under a handicap or rating system, the rules of that system are ‘class rules’);
• (e) the notice of race;
• (f) the sailing instructions; and
• (g) any other documents that govern the event.
Mark-Room
Room for a boat to sail to the mark, and then room to sail her
proper course while at the mark*. However, mark-room does not include
room to tack unless the boat is overlapped to windward and on the inside of
the boat required to give mark-room.
* = Observe - Mark-room definition does NOT say "while at the zone" - it say' "while at the mark"
Mark
An object the sailing instructions require a boat to leave* on a specified
side, and a race committee boat surrounded by navigable water from
which the starting or finishing line extends. An anchor line or an object
attached temporarily or accidentally to a mark is not part of it.
* = after you left a mark - you are sailing on the new leg, so here is the "leg"-definition, included - because "to leave" become "left" at the point stearn passed the mark, in 90 degr. direction to leg. who also explain the point where "while at the mark" ends.
Proper Course
A course a boat would sail to finish as soon as possible in the absence of the other boats* referred to in the rule using the term. A boat has no proper course before her starting signal.
*= Prevents a to wide turn, or a tactical purpose behind how the turn is done - against how it should have been done "in the absence of the other boats".
Racing
A boat is racing from her preparatory signal until she finishes and
clears the finishing line and marks or retires, or until the race committee
signals a general recall, postponement or abandonment.
Never forget that the rule book has its own definition, telling that Book "including the Definitions", who also prevents all other definitions!
