COLREGs · Rule 6 · 33 CFR §83.06
Safe Speed
Every vessel shall at all times proceed at a safe speed so that proper and effective action can be taken to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions.
What does Rule 6 actually say?#
Source
Practice this rule#
One real exam question on this rule, cited to source. No sign-up.
Under both the International and Inland Rules, radar may assist in determining safe speed by ______.
Does Inland Rule 6 change anything?#
Inland Rule 6 is 33 CFR §83.06, reproduced above, and carries no exam-relevant divergence from COLREGs Rule 6. One answer serves both the International and the Inland version of a Rules of the Road question on this rule — which is worth knowing precisely because several neighbouring rules do not work that way.
21 of 38 rules differ somewhere; the five the exam leans on are Rule 9, Rule 10, Rule 24, Rule 28 and Rule 34, side by side on Inland vs International Rules.
Why it shows up on the exam#
Rule 6 lists factors to be taken into account — visibility, traffic density, manoeuvrability, lights at night, state of wind/sea/current, draft. Memorise the list.
What does the exam actually test here?#
The standard
Stop in an appropriate distance
A safe speed is one at which the vessel can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions. It is a performance test, not a number.
Factors for every vessel
Six of them
Visibility; traffic density; the vessel's maneuverability, especially stopping distance and turning ability; at night, background light from shore or back-scatter from her own lights; wind, sea, current, and proximity of navigational hazards; and draft in relation to available depth.
Extra factors with radar
Six more
Radar characteristics and limitations; constraints of the range scale in use; the effect of sea state and weather on detection; the possibility that small craft, ice, and floating objects go undetected; the number, location, and movement of contacts; and the more exact assessment of visibility radar ranging can give.
Rule 6 — common exam questions#
What is a safe speed?
A speed at which the vessel can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions (33 CFR §83.06). The rule sets a standard, not a number.
Is there a numerical speed limit in Rule 6?
No. Rule 6 lists factors to be taken into account rather than a maximum speed, which is why a speed that is safe in open water on a clear day can be unsafe in the same vessel in fog or heavy traffic.
What extra factors apply to a vessel with radar?
Rule 6(b) adds six: the equipment's characteristics, efficiency and limitations; constraints of the range scale in use; the effect of sea state, weather and interference on detection; the possibility that small vessels, ice and floating objects go undetected at adequate range; the number, location and movement of vessels detected; and the more exact assessment of visibility possible when radar is used to range objects.
Does safe speed only matter in restricted visibility?
No. Rule 6 requires a safe speed at all times, and it falls inside the Rule 4 block that applies in any condition of visibility.
Authoritative source#
- 33 CFR §83.06 — this section with its neighbours. 33 CFR Part 83 is public domain; checked 2026-05-16.
- COLREGs Rule 6 is published by the IMO and is authoritative internationally.
Practise this rule against the real exam.
Real exam questions. No signup, no card.
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