Section B
GENERAL LIMITATIONS
14
AVOIDING CONTACT
A boat shall avoid contact with another boat if reasonably possible.  However, a right-of-way boat or one entitled to room or mark-room
  1. need not act to avoid contact until it is clear that the other boat is not keeping clear or giving room or mark-room, and
  2. shall be exonerated if she breaks this rule and the contact does not cause damage or injury.
15
ACQUIRING RIGHT OF WAY
When a boat acquires right of way, she shall initially give the other boat room to keep clear, unless she acquires right of way because of the other boat's actions.
16
CHANGING COURSE
16.1
When a right-of-way boat changes course, she shall give the other boat room to keep clear.
16.2
In addition, when after the starting signal a port-tack boat is keeping clear by sailing to pass astern of a starboard-tack boat, the starboard-tack boat shall not change course if as a result the port-tack boat would immediately need to change course to continue keeping clear.
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.
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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.
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
  1. between boats on opposite tacks on a beat to windward, 
  2. between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack.
  3. between a boat approaching a mark and one leaving it, or
  4. if the mark is a continuing obstruction, in which case rule 19 applies.
18.2
Giving Mark-Room
  1. When boats are overlapped the outside boat shall give the inside boat mark-room, unless rule 18.2(b) applies.
  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.
  3. When a boat is required to give mark-room by rule 18.2(b),
    1. she shall continue to do so even if later an overlap is broken or a new overlap begins;
    2. if she becomes overlapped inside the boat entitled to mark-room, she shall also give that boat room to sail her proper course while they remain overlapped.
  4. Rules 18.2(b) and (c) cease to apply when the boat entitled to mark-room has been given that mark-room. or if she passes head to wind or leaves the zone.
  5. If there is a reasonable doubt that a boat obtained or broke an overlap at the time, it shall be presumed that she did not.
  6. If a boat obtained an inside overlap from clear astern or by tacking to windward of the other boat and, from the time the overlap begins, the outside boat has been unable to give mark-room, she is not required to give it.
18.3
Tacking in the Zone
If a boat in the zone of a mark to be left to port passes head to wind from port to starboard tack and is then fetching the mark, she shall not cause a boat that has been on starboard tack since entering the zone to sail above close-hauled to avoid contact and she shall give mark-room if that boat becomes overlapped inside her. When this rule applies between boats, rule 18.2 does not apply between them.
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 not further from the mark than needed to sail that course.  Rule 18.4 does not apply at a gate mark.
19
ROOM TO PASS AN OBSTRUCTION
19.1
When Rule 19 Applies
Rule 19 applies between boats at an obstruction except
  1. when the obstruction is a mark the boats are required to leave on the same side, or
  2. when rule 18 applies between boats and the obstruction is another boat overlapped with each of them.
However, at a continuing obstruction, rule 19 always applies and rule 18 does not.
19.2
Giving Room at an Obstruction
  1. A right-of-way boat may choose to pass an obstruction on either side.
  2. When boats are overlapped, the outside boat shall give the inside boat room between her and the obstruction, unless she has been unable to do so from the time the overlap began.
  3. While boats are passing a continuing obstruction, if a boat that was clear astern and required to keep clear becomes overlapped between the other boat and the obstruction and, at the moment the overlap begins, there is not room for her to pass between them, she is not entitled to room under rule 19.2(b),. While the boats remain overlapped, she shall keep clear and rules 10 and 11 do not apply.
20
ROOM TO TACK AT AN OBSTRUCTION
20.1
Hailing
A boat may hail for room to tack and avoid a boat on the same tack. However, she shall not hail unless
  1. she is approaching an obstruction and will soon need to make a substantial course change to avoid it safely, and
  2. she is sailing close-hauled or above.
In addition, she shall not hail if the obstruction is a mark and a boat that is fetching it would be required to change course as a result of the hail.
20.2
Responding
  1. After a boat hails, she shall give the hailed boat time to respond.
  2. The hailed boat shall respond even if the hail breaks rule 20.1.
  3. The hailed boat shall respond either by tacking as soon as possible, or by immediately replying "You tack" and then giving the hailing boat room to tack and avoid her.
  4. When the hailed boat responds, the hailing boat shall tack as soon as possible.
  5. From the time a boat hails until she has tacked and avoided the hailed boat, rule 18.2 does not apply between them.
20.3
Passing On a Hail to an Additional Boat
When a boat has been hailed for room to tack and she intends to respond by tacking, she may hail another boat on the same tack for room to tack and avoid her. She may hail even if her hail does not meet the conditions of rule 20.1. Rule 20.2 applies between her and the boat she hails.