Rule 6: Safe Speed (COLREGS)

Last reviewed October 21, 2026

The short answer

Rule 6 says every vessel must always proceed at a safe speed, one that lets her take proper and effective action to avoid collision and stop within a distance appropriate to conditions. Factors include visibility, traffic, maneuverability, background lights, wind, sea, current, hazards, draft, and radar limits.

The rule 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.
International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 6

What it means on the water

No fixed number. Safe speed depends on conditions.
All vessels consider visibility, traffic density, maneuverability, background light at night, wind, sea, current, hazards, and draft vs depth (6(a)).
Vessels with operational radar also consider its limits, range scale, interference, small targets, and contacts (6(b)).

International vs Inland

Same in both International and Inland.

Common exam traps

Picking a specific knot value. Rule 6 sets none.
Forgetting radar factors apply only to vessels with operational radar.

Try 3 questions on Rule 6

Does Rule 6 set a maximum speed?
1. Yes, 10 knots
2. No, it depends on conditions
3. Yes, 6 knots in fog
4. Only Inland
Show answer
B. No, it depends on conditions Rule 6.
Which is a Rule 6(a) factor for all vessels?
1. Radar range scale
2. State of visibility
3. Number of radar contacts
4. Radar interference
Show answer
B. State of visibility Rule 6(a)(i).
Background shore lights at night are:
1. Irrelevant
2. A safe speed factor
3. Only Inland
4. A Rule 5 issue only
Show answer
B. A safe speed factor Rule 6(a)(iv).

Frequently asked questions

What is safe speed?

A speed that lets you take proper and effective action to avoid collision and stop within a distance appropriate to conditions (Rule 6).