Look-out, safe speed, risk of collision and action to avoid it

The rule in plain words

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.

The same ship, two situations: open sea and good visibility on the left; fog and nearby traffic on the right, where a safe speed is much lower. It depends on the conditions, not on a fixed number.

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Before you read on: what would you do?

Question 1/1

What must safe speed allow a vessel to do?

Frequent 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.

Exam keys & interpretation

"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.

Key points

Goal: act effectively and stop within an appropriate distance.
6(a): six factor groups apply to all vessels.
6(b): operational radar adds six checks.
Prevailing circumstances and conditions decide the speed.

Test your knowledge

3 questions to check it. Pick an answer to see why.

Question 1/3

Which factor is taken into account by all vessels?

Official text

IMO COLREG 1972 U.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)