Rules 11 to 18 apply to vessels in sight of one another. In restricted visibility, Rule 19 applies instead.
Rule 12 - Sailing vessels
When two sailing vessels approach: if each has the wind on a different side, the vessel with the wind on the port side keeps out of the way. If both have the wind on the same side, the vessel to windward keeps out of the way. A vessel with the wind on the port side that sees another vessel to windward and cannot determine whether the other has the wind on the port or starboard side shall keep out of the way.
Rule 13 - Overtaking
Any vessel overtaking another shall keep out of the way. A vessel is overtaking when it comes up with another from a direction more than 22.5 degrees abaft her beam. If in doubt, assume you are overtaking.
Rule 14 - Head-on situation
When two power-driven vessels meet on reciprocal or nearly reciprocal courses so as to involve risk of collision, each shall alter course to starboard so that each passes on the port side of the other.
Rule 15 - Crossing situation
When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and, if circumstances allow, avoid crossing ahead of the other.
Rule 16 - Action by give-way vessel
The vessel required to keep out of the way shall take early and substantial action to keep well clear.
Rule 17 - Action by stand-on vessel
- Where one vessel must keep out of the way, the other shall keep her course and speed.
- She may take action to avoid collision as soon as it becomes apparent that the give-way vessel is not taking appropriate action.
- When so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take the action that best aids to avoid collision.
- In a crossing situation, a power-driven stand-on vessel shall not alter course to port for a vessel on her own port side.
Rule 18 - Responsibilities between vessels
Except where Rules 9, 10 and 13 otherwise require: a power-driven vessel gives way to a vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel engaged in fishing and a sailing vessel. A sailing vessel gives way to NUC, RAM and fishing vessels. A fishing vessel gives way to NUC and RAM. Any vessel other than NUC or RAM shall, if circumstances allow, avoid impeding the safe passage of a vessel constrained by her draught.
In short: Rules 13-17 decide who gives way between two vessels; Rule 18 decides between vessel types.