Rule 6 requires every vessel to 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.
Factors for all vessels include:
Additional factors for vessels with operational radar include:
- 2constraints imposed by the radar range scale in use
- 3the effect of sea state, weather and interference on radar detection
- 4the possibility that small vessels, ice and other floating objects may not be detected at an adequate range
- 5the number, location and movement of vessels detected by radar
- 6the more exact assessment of visibility that radar can provide when vessels or objects are detected nearby
IMO COLREG 1972Official text
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 manoeuvrability 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.Reproduced verbatim from the IMO COLREG 1972 Convention (as amended).
STCW Bridge Watch Lens
Decide applicability before manoeuvring: Rules 4-10 apply in any visibility, Rules 11-18 only when vessels are in sight, and Rule 19 governs radar-only encounters in restricted visibility.
Build the traffic picture with sight, hearing, radar/ARPA and chart context.
Do not let AIS or one isolated bearing replace systematic observation.
Safe speed is judged by what the ship can actually do in the moment: stop, turn, reduce exposure and avoid collision within the available sea room.
Exam Focus
Start every scenario by classifying the encounter: overtaking, head-on, crossing, narrow channel, traffic separation, or restricted visibility.
If two rules seem to conflict, check the order carefully: overtaking duties still apply, and Rule 2 still requires ordinary seamanship.
If schedule, fuel economy or comfort appears in the options, it is not a Rule 6 factor.
Points clés
Safe speed is whatever allows timely, effective collision-avoidance action in the actual conditions
Stopping distance, turning ability and available sea room are part of the decision
Radar does not justify higher speed; it adds more factors that must be considered
Commercial pressure, schedule and convenience are never Rule 6 factors
Erreurs courantes
Keeping too much speed in restricted visibility or dense traffic
Looking only at engine speed instead of the ship's actual stopping and turning performance
Assuming radar removes the need to slow down
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