A collection of common situation explained in terms of:

The references rules are the Racing Rules of Sailing 2021-2024 rules. They are referenced throughout to give the reader an option to study them in more detail. Also referenced are the Case Book 2021-2024 and the book "Elvstrom explains The Racing Rules" for the 2021-2024 edition.

Rule 14 (avoiding contact) is not discussed here as it applies at all times.

1. Running Boats On Starboard Tack

Green is running with the wind on starboard tack and meets red beating on port tack. Often red is joined by a train of red boats line astern.
Green boat has right-of-way according to rule 10. Note in particular that rule 11 (windward boat keep clear) does NOT apply as they are on opposite tacks.

The safest action for red boat is to luff and go behind green boat (see picture).

Red may choose to fall down and go in front of green, but this is risky as running boats often cover more distance than you think and judging the distance from the shore is difficult.

Green has to trust red to do the right thing and runs the risk of hitting red, so this is not a situation green particularly likes. In this situation it is in greens best interest to turn slightly to starboard such that green goes behind all red boats. This has to be done early and preferably communicated to red ("I will go behind you!"); if green turns to starboard just as red luffs to clear green, then green has violated rule 16.1 by altering course and not giving the other boat (time and) room to keep clear.

2. Gybing In The Zone

Green and Red were overlapped when the first of them reached the zone, so Red has to give Green mark room. Green gybes while in the zone before they reach the mark. Does Red still have to give Green mark-room?

Red still has to give Green mark room. Rule 18 does not say that Green loses mark room if he gybes. See specifically Elvfstrom, page 173.

3. Tacking To Starboard

Red tacks to starboard in front of Green, who was already on starboard. Green has to change course just as Red comes to a close-hauled course. Green objects that "red tacked right in front of me".

Red violated rule 15 ("acquiring right of way"). Red acquired right-of-way over Green by tacking to starboard, at which point rule 12 would have stopped Green from sailing into Red. However, for a short moment after Red came to a close-hauled course she still had to give Green the time and room to keep clear. This is a very short moment in radio-controlled sailing.

4. Tacking In The Zone After Passing The Mark

Red was entitled to mark room. Green provided that room, but rounded the mark tighter. Red, still in the zone, tacks onto starboard in front of Green claiming mark room. Contact would have occurred before Red was closed hauled on starboard tack.

Reds mark room does not entitle Red to tack in the face of Green. Reds mark-room ends as soon as Red leave the mark (rule 18.1 and definition of "mark-room"), position 1 in the picture. The fact that Red was still in the zone is irrelevant.

5. Calling Room To Tack To Another Port Tack Boat

Yellow is on starboard tack, Red and Green on port. Green will have to change course to avoid Yellow. Can Green force Red to tack?

Yes. Green can hail Red "Room to tack" followed by Greens sail number, at which point Red must tack and Green must follow immediately. Yellow has right-of-way over Red and Green and is therefore an Obstruction. Rule 19.1.a gives Green the right to choose which side she will pass the Obstruction on. If she chooses to tack away, then rule 20.1 ("Hailing") gives Green the right to force Red to tack. It is no different to the situation when Green is approaching land and has to tack away; Yellow is as much an obstruction as land.

If Green choose to duck behind Yellow, then she must give Red room to do the same (rule 19.2.b).

6. Running On Different Tacks

Green and Red and running on port tack on Blues starboard side. Blue is on starboard tack. Red is pushing Green towards Blue invoking rule 11 (windward boat keep clear).

Red must give Green room to keep clear of Blue. Rule 19.2.b limits what Red can do under rule 11. Specifically, Red must give Green room between Red and the obstruction (Blue).

7. Catching Port Tack Boat

Green on starboard tack is sailing faster than Red on port tack. Both boats sail a straight line. Green sails into the stern of Red.

Red must keep clear of Green according to rule 10. There is no rule that says that overtaking boats must give way regardless of tack. Rule 12 would protect Red if they were on the same tack.

Note that Green cannot chase Red indefinitely when Red manoeuvres to keep clear without violating rule 16.1. When Green changes course, she must give Red time and room to keep clear.

8. Mark Room Rights

Green and Red were overlapped with multiple other boats when the first of them reached the zone. Green is unable to turn into Blue and Yellow boats to provide Red mark-room.

Red is not entitled to mark-room according to rule 18.2.f, which says that Green does not need to provide mark-room if he has been unable to do so from the time the overlap began. See specifically Elvfstrom, page 173 and this video at 3:48.
Red will have to take evasive action and not barge inside Green. The fault lies with Yellow, who is required to give Blue enough room to give Green enough room. Red can protest, but cannot sail in between the mark and Green.

Red must start asking for mark room as soon as possible to make sure the other boats move over. Red could also gybe to starboard well before the mark and use rule 10 to push the others boats out. Red would have to be careful not to violate rules 15 and 16.1.

9. Sailing Too Close

Green and Red are close-hauled with a small (a boat-width or two) gap between them. Is either boat violating a rule?

Red is violating rule 11 (windward boat keep clear) due to the definition of "keep clear". Red is keeping clear only if Green is able to change course in either direction without immediately making contact.

If Green made a quick and large course change she may violate rule 16.1, which says that Green must give Red room to keep clear. So Red must be far away from Green so that Green can make a moderate course change, no more.

Green may luff Red all the way up to head-to-wind and enjoy the protection of rule 11, but cannot pass head-to-wind and tack; Green would then have to give Red right-of-way under rule 13.

What should Green do? Keep luffing Red until Red has had enough and tacks away.

10. On Port Tack At A Mark

Red has to give way to Green and Blue boats. What should Red do?
Tacking onto starboard is unlikely to help as Red is unlikely to fetch the mark and is still to the left of the Green and Blue boats.

Also, if Red tacked onto starboard inside the zone, then Red cannot force Green or Blue to sail above close-hauled according to rule 18.3. If Green and Blue boats were just fetching the mark, then Red won't be able to fetch.
Red must acknowledge that his situation is bad and give up any notion of saving placings. Red should duck and go behind Blue. Trying to sail through Green and Blue boats is difficult and Red risks incurring a penalty and get tangled up.

11. Tacking To Starboard In The Zone

Green tacks onto starboard inside the zone and is fetching the mark. Red is sailing well below closed-hauled. Does Red have to give Green mark-room?

No, but Red has to keep clear of Green (rule 11).

Rule 18.2.b does not apply at any time because the boats were on opposite tacks when the first boat reached the zone (see rule 18.1.a). So initially Red has right-of-way under rule 10 while Green is on port tack.

When Green tacks to starboard, rule 13 and rule 18.3 applies as soon as she passes head-to-wind. Once on a close-hauled course rule 13 stops and rule 11 starts along with rule 15 (briefly). Rule 18.3 remains in effect so Green cannot force Red to sail above close-hauled before the boats have left the mark at which point 18.3 is no longer in effect.

The intent of this scenario is to show that just because Green tacked in the zone doesn't mean that Red can ignore Green at the mark.

12. Ample Room At Obstruction

Green and Red are approaching the shore line. Red hails for room to tack and Green responds "you tack". Red tacks, but have to bear away to avoid Green. Did Green have to tack to avoid Red?

No. Green must respond, either by tacking or responding "you tack". Green must also give Red room, but is not required to keep clear of red. The room Red is entitled to is the space Red needs to comply with her obligations under Part 2 and rule 31. In this case there was enough room for Red to duck under Green. No rule was broken. See Case 35.

13. Hailing

Green and Red are approaching the shoreline. Red calls "Water!". Is Green required to respond?

No. Unlike full-size sailing, "water" is not a valid hail. Appendix E1.3.b and E2.1.c states that the hail must contains the words "room", "tack" and the sail number (as individual digits) of the hailing boat (Red).

14. Outside Mark Room

Green and Red are approaching a leeward gate. Both have decided to turn left. Green is well behind Red when Red enters the zone. Red sails past and wide of the mark but still in the zone before turning up. Red on port tack sails into Green on starboard tack inside the zone. The gate was within meters of the skippers on land and easily visible. Who was at fault?

Red violated Rule 10. Red did not enjoy the protection of Rule 18 at that time.

Green was required to give Red "mark room" (RRS definition). "Mark room" is defined as the "room" (RRS definition) needed to sail to the mark and to round and leave the mark without touching it (see RRS definition of "mark room"). "Room" (yet another RRS definition) is the space a boat needs in the existing conditions while maneuvering promptly in a seamanlike way.

This gate was close to shore right in front of the skippers, so a seamanlike rounding would see Red sailing straight to the mark and rounding it tightly. Red did not do that and at that point Rule 18 does not apply because Red is sailing outside her "mark room". When Red turns up she is trying to get back to her mark room, but she violates Rule 10 by sailing into a starboard tack boat while on port tack before reaching her mark room and will not be exonerated by Rule 43.1(b).

As this was a gate, Green was not limited by Rule 18.4.

The key point here is that Rule 18 only protects a boat sailing in her "mark room", no matter how much in front she was when she entered the zone. That "mark room" is a lane straight to the mark and the space needed to round it, no more.

It is also worth noting that Rule 18 or applicable definitions do not say "keep clear" (RRS definition) at any point.