6Safe Speed
1The rule in plain words
Proceed at a safe speed so you can take proper, effective action to avoid collision and stop within an appropriate distance.
What must it let you do?
Choose a speed that lets you take proper and effective action, avoid collision and stop within an appropriate distance.
What counts for all vessels?
Check visibility and traffic: all these factors count alongside your maneuverability, stopping distance and turning ability; background light, such as shore lights that dazzle you at night; wind, sea, current, hazards and draft against available depth.
What does operational radar add?
With operational radar, radar still has limits: add its characteristics, efficiency and limitations; the range scale; sea, weather and interference; and the possibility of missing small vessels, ice or other floating objects, among other factors.
Is there a fixed number?
No. Rule 6 lists factors among those taken into account and requires the prevailing circumstances and conditions to be assessed; so speed changes with the situation.
2Key points
- 1
Goal: act effectively and stop within an appropriate distance.
- 2
6(a): six factor groups apply to all vessels.
- 3
6(b): operational radar adds six checks.
- 4
Prevailing circumstances and conditions decide the speed.
3Frequent mistakes
Wrong: "If radar works, you can go fast."
Right: Radar adds factors; its limits and the situation still matter.
Wrong: "Safe speed is always the same."
Right: It depends on the prevailing circumstances and conditions.
Wrong: "Only stopping distance matters."
Right: You must also take proper, effective action to avoid collision.
4Exam keys & interpretation
Exam keys
- "All vessels" = paragraph 6(a); do not confuse its factors with the radar additions.
- "Additionally" + "operational radar" = 6(b): look for limitations, range scale and undetected targets.
- "Among those taken into account" + "prevailing circumstances" rules out a fixed or universal speed.
How to read it
- If conditions worsen, reassess speed: respond to the real situation rather than memorising a number.
- With radar, use it to refine ranges, but remember that some objects may not be detected.
5Official text
IMO COLREG 1972U.S. Coast Guard — International Navigation Rules (2024)
Full wording of the rule, reproduced from the official source below.
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 maneuverability 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 draft 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.Source: U.S. Coast Guard — International Navigation Rules (2024)
Finish this unit
When you've read it, match the terms, then answer three questions. Get them all right to finish the unit; opening the page alone doesn't count.
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