Rule 18

Section C: At marks and obstructions

Section C rules do not apply at a starting mark surrounded by navigable water or at its anchor line from the time boats are approaching them to start until they have passed them. When rule 20 applies, rules 18 and 19 do not.

18 Mark room

18.1 When Rule 18 Applies

Rule 18 applies between boats when they are required to leave a mark on the same side and at least one of them is in the zone. However, it does not apply

(a) between boats on opposite tacks on a beat to windward,

(b) between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack,

(c) between a boat approaching a mark and one leaving it, or

(d) if the mark is a continuing obstruction, in which case rule 19 applies.

See also: mark-room thumb|300px|left|Rule 18 Mark Rounding

Rule 18.1 illustrated

	File:Rule18.1b applies.gif	File:Rule18.1b na.gif
File:Rule18.1c na.png	File:Rule18.1 barging at start.png	File:Rule18.1d na rule19 applies.png
	static and animated images wanted

The VSK auto-umpire can be especially quick to judge when a boat first begins to be leaving a mark.

Barging at the start

A boat is said to be barging at the start when it is sailing below close hauled and to windward of the outside layline to either starting mark. (In practice this appears most often for starboard tack boats at the committee boat or right-hand end of a start line however it is also applicable to the symmetrical situation for the port tack layline to the left hand end of the start line.)

• The barging boat has no right to "mark room" because the entire set of Section C rules expressly do not apply a starting mark.
  FYI: this exclusion used to be expressed as Rule 18.1(a) in the 2005-2008 RRS.
• Any boat sailing close-hauled and to leeward of the barging boat may push the barging boat to windward and the barging boat must keep clear (per Rule 11) even if this means missing her start altogether.
• The barging boat may use intimidation to trick an inexperienced skipper into allowing them to round the start mark. Do not let yourself be intimidated. It is better to politely teach the barging skipper the correct rules of sailing.

18.2 Giving mark-room

(a) When boats are overlapped the outside boat shall give the inside boat mark-room, unless rule 18.2(b) applies.

(b) If boats are overlapped when the first of them reaches the zone, the outside boat at that moment shall thereafter give the inside boat mark-room. If a boat is clear ahead when she reaches the zone, the boat clear astern at that moment shall thereafter give her mark-room.

(c) When a boat is required to give mark-room by rule 18.2(b), she shall continue to do so even if later an overlap is broken or a new overlap begins. However, if either boat passes head to wind or if the boat entitled to mark-room leaves the zone, rule 18.2(b) ceases to apply.

(d) If there is reasonable doubt that a boat obtained or broke an overlap in time, it shall be presumed that she did not.

(e) If a boat obtained an inside overlap from clear astern and, from the time the overlap began, the outside boat has been unable to give mark-room, she is not required to give it.

These rules are among the most difficult to fully understand and anticipate whilst approaching and rounding a mark. This is due in part to 18.2c "head-to-wind" canceling 18.2b but also due to some differences between 2005-2008 RRS and 2009-2012 RRS. This wiki is focused on the 2009-2012 RRS whereas the auto-umpire was designed to emulate the 2005-2008 RRS. The broad intentions are similar but the specific rule numberings have changed enough to become confusing. See also #Comparison (2005-2008) vs (2009-2012)

The best advice for the VSK skipper is to be sure to monitor the ISAF window (top right of game's UI) for any limitation rule numbers displayed and anticipate change as soon as either boat tacks or gybes.

Rule 18.2 illustrated

File:Rule18.2a wo 18.2b.gif	File:Rule18.2a with 18.2b.gif	File:Rule18.2b overlap.gif
File:Rule18.2b no overlap.gif	File:Rule18.2c overlap broken.gif	File:Rule18.2c new overlap.gif
File:Rule18.2c headtowind.gif	File:Rule18.2c leave.gif	File:Rule18.2e unable.gif
	animated images wanted

Comparison (2005-2008) vs (2009-2012)

The auto-umpire was designed to emulate the ISAF RRS (2005-2008) and there are rule numbering differences between (2005-2008) and (2009-2012).

Rule 18.2 mapping (2005-2008) vs (2009-2012)

Auto-umpire (2005-2008)	(2009-2012)
18.2a When boats are overlapped the outside boat shall give the inside boat room to round or pass the mark or obstruction, and if the inside boat has right of way the outside boat shall also keep clear. Other parts of rule 18 contain exceptions to this rule.	18.2a When boats are overlapped the outside boat shall give the inside boat mark-room, unless rule 18.2(b) applies.
18.2b piece 1 If boats were overlapped before either of them reached the two-length zone and the overlap is broken after one of them has reached it, the boat that was on the outside shall continue to give the other boat room. If the outside boat becomes clear astern or overlapped inside the other boat, she is not entitled to room and shall keep clear.	18.2b piece 1 If boats are overlapped when the first of them reaches the zone, the outside boat at that moment shall thereafter give the inside boat mark-room. If a boat is clear ahead when she reaches the zone, the boat clear astern at that moment shall thereafter give her mark-room.
18.2b piece 2 If boats were overlapped before either of them reached the two-length zone and the overlap is broken after one of them has reached it, the boat that was on the outside shall continue to give the other boat room. If the outside boat becomes clear astern or overlapped inside the other boat, she is not entitled to room and shall keep clear.	18.2c piece 1 When a boat is required to give mark-room by rule 18.2(b), she shall continue to do so even if later an overlap is broken or a new overlap begins. However, if either boat passes head to wind or if the boat entitled to mark-room leaves the zone, rule 18.2(b) ceases to apply.
18.2c piece 1 If a boat was clear ahead at the time she reached the two-length zone, the boat clear astern shall thereafter keep clear. If the boat clear astern becomes overlapped outside the other boat, she shall also give the inside boat room. If the boat clear astern becomes overlapped inside the other boat, she is not entitled to room. If the boat that was clear ahead passes head to wind, rule 18.2(c) no longer applies and remains inapplicable.	18.2b piece 2 If boats are overlapped when the first of them reaches the zone, the outside boat at that moment shall thereafter give the inside boat mark-room. If a boat is clear ahead when she reaches the zone, the boat clear astern at that moment shall thereafter give her mark-room.
18.2c piece 2 If a boat was clear ahead at the time she reached the two-length zone, the boat clear astern shall thereafter keep clear. If the boat clear astern becomes overlapped outside the other boat, she shall also give the inside boat room. If the boat clear astern becomes overlapped inside the other boat, she is not entitled to room. If the boat that was clear ahead passes head to wind, rule 18.2(c) no longer applies and remains inapplicable.	18.2c piece 1 When a boat is required to give mark-room by rule 18.2(b), she shall continue to do so even if later an overlap is broken or a new overlap begins. However, if either boat passes head to wind or if the boat entitled to mark-room leaves the zone, rule 18.2(b) ceases to apply.
18.2c piece 3 If a boat was clear ahead at the time she reached the two-length zone, the boat clear astern shall thereafter keep clear. If the boat clear astern becomes overlapped outside the other boat, she shall also give the inside boat room. If the boat clear astern becomes overlapped inside the other boat, she is not entitled to room. If the boat that was clear ahead passes head to wind, rule 18.2(c) no longer applies and remains inapplicable.	18.2c piece 2 When a boat is required to give mark-room by rule 18.2(b), she shall continue to do so even if later an overlap is broken or a new overlap begins. However, if either boat passes head to wind or if the boat entitled to mark-room leaves the zone, rule 18.2(b) ceases to apply.
18.2d When after the starting signal rule 18 applies between two boats and the right-of-way boat is changing course to round or pass a mark, rule 16 does not apply between her and the other boat.	deleted
18.2e If there is reasonable doubt that a boat obtained or broke an overlap in time, it shall be presumed that she did not. If the outside boat is unable to give room when an overlap begins, rules 18.2(a) and 18.2(b) do not apply.	18.2d If there is reasonable doubt that a boat obtained or broke an overlap in time, it shall be presumed that she did not.
did not exist	18.2e If a boat obtained an inside overlap from clear astern and, from the time the overlap began, the outside boat has been unable to give mark-room, she is not required to give it.

The auto-umpire only gives penalties for 18.2a, 18.2b and 18.2c.

18.3 Tacking When Approaching a Mark

If two boats were approaching a mark on opposite tacks and one of them changes tack, and as a result is subject to rule 13 in the zone when the other is fetching the mark, rule 18.2 does not thereafter apply. The boat that changed tack

(a) shall not cause the other boat to sail above close-hauled to avoid her or prevent the other boat from passing the mark on the required side, and

(b) shall give mark-room if the other boat becomes overlapped inside her.

Rule 18.3 illustrated

18.3(a) shall not cause the other boat to sail above close-hauled to avoid her		18.3(a) shall not cause the other boat to sail above close-hauled to avoid her
18.3a .. or prevent the other boat from passing the mark on the required side		18.3(b) shall give mark-room if the other boat becomes overlapped inside her
thumb|300px|left|Rule 18.3a tacking boat shall not interfere with fetching boat

In each case notice that the yellow boat passes head to wind inside the zone and this triggers rule 18.3 because yellow "changes tack, and as a result is subject to rule 13" while blue is fetching the mark.

18.4 Gybing

When an inside overlapped right-of-way boat must gybe at a mark to sail her proper course, until she gybes she shall sail no farther from the mark than needed to sail that course. Rule 18.4 does not apply at a gate mark.

Rule 18.4 illustrated

File:Rule18.4 overstand.gif	File:Rule18.4 proper.gif	File:Rule18.4 overstand gate na.gif
	animated images wanted

18.5 Exoneration

When a boat is taking mark-room to which she is entitled, she shall be exonerated

(a) if, as a result of the other boat failing to give her mark-room, she breaks a rule of Section A, or

(b) if, by rounding the mark on her proper course, she breaks a rule of Section A or rule 15 or 16.

Rule 18.5 illustrated

File:Rule18.5 rule10.gif	File:Rule18.5 rule11.gif	File:Rule18.5 rule12.gif
File:Rule18.5 rule13.gif		File:Rule18.5 rule15.gif
File:Rule18.5 rule16.1.gif	animated images wanted	File:Rule18.5 rule16.2.gif