Part B – Steering and sailing (rule 4-18)

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4. Application
The rules apply in any condition of visibility (e.g., in sight or in restricted visibility).
5. Look-out
Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.
6. Safe speed
Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions.

In determining a safe speed the following factors shall be among those taken into account:

(a) By all vessels:

  • (i) the state of visibility;
  • (ii) the traffic density including concentrations of fishing vessels or any other vessels;
  • (iii) the maneuvrability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions;
  • (iv) at night the presence of background light such as from shore lights or from back scatter of her own lights;
  • (v) the state of wind, sea and current, and the proximity of navigational hazards;
  • (vi) the draught in relation to the available depth of water.

(b) Additionally, by vessels with operational radar:

  • (i) the characteristics, efficiency and limitations of the radar equipment;
  • (ii) any constraints imposed by the radar range scale in use;
  • (iii) the effect on radar detection of the sea state, weather and other sources of interference;
  • (iv) the possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range;
  • (v) the number, location and movement of vessels detected by radar;
  • (vi) the more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.
7. Risk of collision
Vessels must use all available means to determine the risk of a collision, including the use of radar (if available) to get early warning of the risk of collision by radar plotting or equivalent systematic observation of detected objects. (e.g. ARPA, AIS).
If the distance of any vessel is reducing and her compass bearing is not changing much or it is a large vessel or towing vessel at close distance, or if there is any doubt, then a risk of collision shall be deemed to exist.[11][page needed]
8. Action to avoid collision
Actions taken to avoid collision should be:

  • positive
  • obvious
  • made in good time
9. Narrow channels
  • A vessel proceeding along a narrow channel must keep to starboard.
  • Small vessels or sailing vessels must not impede (larger) vessels which can navigate only within a narrow channel.
  • Ships must not cross a channel if to do so would impede another vessel which can navigate only within that channel.
10. Traffic Separation Schemes
Ships must cross traffic lanes steering a course “as nearly as practicable” at right angles to the direction of traffic. This reduces confusion and enables that vessel to cross the lane as quickly as possible.
Vessel entering a traffic separation scheme should do it at an angle as small as practicable.
A traffic separation scheme does not relieve any vessel from complying with other rules.

Section II (Conduct of vessels in sight of one another)[edit]

11. Application
The following rules 11–18 applies to vessels in sight of one another. (Section III has specific requirements for restricted visibility)
12. Sailing vessels
Two sailing vessels approaching one another must give-way as follows:

  • Port gives way to starboard. When each has the wind on a different side, the vessel which has the wind to port must give way;
  • Windward gives way to leeward. When both have the wind on the same side, the vessel which is windward must give way to the vessel which is leeward;
  • Ensure port gives way. If a vessel, with the wind on the port side, sees a vessel to windward and cannot determine whether the other vessel has the wind on the port or the starboard side, they must give way.
For the purposes of this rule, the wind is considered to be coming from the side opposite the mainsail boom, or if the vessel is square rigged, opposite the largest fore-and-aft rigged sail, regardless of which side the true or apparent wind is on.
13. Overtaking
Notwithstanding anything contained in the Rules … … an overtaking vessel must keep out of the way of the vessel being overtaken. “Overtaking” means approaching another vessel at more than 22.5 degrees abaft her beam, i.e., so that at night, the overtaking vessel would see only the stern light and neither of the sidelights of the vessel being overtaken.Note that the opening words of this rule make clear that this rule overrides all other rules.
14. Head-on situations
When two power-driven vessels are meeting head-on both must alter course to starboard so that they pass on the port side of the other. “Head-on” means seeing the other vessel ahead or nearly ahead so that by night her masthead lights are actually or nearly lined up and/or seeing both her sidelights, or by day seeing a similar aspect of her. “If you see three lights ahead, starboard wheel and show your red.”

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15. Crossing situations when

two power-driven vessels are crossing, the vessel which has the other on the starboard side must give way and avoid crossing ahead of her. The saying is “If to starboard red appear, ‘this your duty to keep clear.
16. The give-way vessel
The give-way vessel must take early and substantial action to keep well clear.
17. The stand-on vessel
The stand-on vessel shall maintain her course and speed, but she may take action to avoid collision if it becomes clear that the give-way vessel is not taking appropriate action, or when so close that collision can no longer be avoided by the actions of the give-way vessel alone. In a crossing situation, the stand-on vessel should avoid turning to port even if the give-way vessel is not taking appropriate action. These options for the stand-on vessel do not relieve the give-way vessel of her obligations under the rules.
18. Responsibilities between vessels
Except in narrow channels, traffic separation schemes, and when overtaking (i.e., rules 9, 10, and 13)

  • A power-driven vessel must give way to:
    • a vessel not under command;
    • a vessel restricted in her ability to manoeuvre (this may include vessels towing one another);[20]
    • a vessel engaged in fishing;
    • a sailing vessel.
  • A sailing vessel must give way to:
    • a vessel not under command;
    • a vessel restricted in her ability to manoeuvre;
    • a vessel engaged in fishing.
  • A vessel engaged in fishing when underway shall, so far as possible, keep out of the way of:
    • a vessel not under command;
    • a vessel restricted in her ability to manoeuvre.
  • Any vessel other than a vessel not under command or a vessel restricted in her ability to manoeuvre shall, if possible, not impede the safe passage of a vessel constrained by her draft, exhibiting the signals in Rule 28.
  • A vessel constrained by her draft shall navigate with particular caution having full regard to her special condition.