COLREGS Rule 6 — Safe Speed

Rule Text

What it means on the water

• →Safe speed applies at ALL TIMES — not just in restricted visibility.
• →The test is: can you stop within a distance appropriate to the circumstances?
• →Factors without radar: visibility, traffic density, maneuverability, night background lights, wind/sea/current, proximity of hazards, draft vs. depth.
• →Additional factors with radar: radar characteristics and limitations, range scale in use, sea-clutter effect, ability to detect small vessels, number and movement of radar targets.
• →Full speed is not safe speed just because visibility is good — traffic density and other factors still apply.

Common exam mistakes

• ✗Thinking safe speed only applies in restricted visibility — it applies at all times.
• ✗Overlooking the radar-specific factors (most exam questions specifically test these).
• ✗Confusing 'safe speed' with 'slow speed' — safe speed is context-dependent and could be high speed in clear, empty waters.

USCG exam questions — Rule 6

These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.

1. 1. Under 72 COLREGS Rule 5, a proper lookout shall be maintained:

   • A.By sight and hearing only when visibility is reduced below 1 nautical mile
   • B.By sight and hearing at all times, using all available means appropriate to the prevailing circumstances✓
   • C.By radar when operating in restricted visibility and by visual means at all other times
   • D.By the officer of the watch, supplemented by radar as required by flag state regulations

   Why: Rule 5 requires a proper lookout by sight AND hearing at ALL times, using ALL available means appropriate to the prevailing circumstances and conditions. This is an absolute, continuous duty — not conditional on visibility conditions — and 'all available means' includes radar, AIS, and other technology.

2. 2. Which factor is NOT listed in Rule 6 as relevant to determining a safe speed?

   • A.The state of visibility
   • B.The maneuverability of the vessel with special reference to stopping distance
   • C.The number of persons on board✓
   • D.The background light at night from shore lights or from backscatter of own lights

   Why: Rule 6 lists specific factors for safe speed: visibility, traffic density, maneuverability (stopping distance, turning ability), background light, sea state, draft versus available depth, radar range/resolution, and whether radar is in use. The number of persons on board is not among the enumerated factors.

3. 3. Rule 6 requires every vessel to proceed at a safe speed at all times. Which factor is specifically listed in Rule 6 for ALL vessels when determining safe speed?

   • A.The state of visibility✓
   • B.The vessel's declared maximum speed
   • C.The distance to the nearest port
   • D.The number of passengers on board

   Why: Rule 6 lists the state of visibility as one of the factors ALL vessels must consider when determining safe speed. Other listed factors include traffic density, maneuverability, the presence of background light at night, wind, sea state, current, and the proximity of navigational hazards.

4. 4. A vessel equipped with a functioning radar is proceeding through dense fog. Under Rule 6, what additional consideration must be taken into account regarding radar when determining safe speed?

   • A.Any constraints imposed by the radar range scale in use✓
   • B.The requirement to broadcast radar contacts on VHF
   • C.The obligation to reduce speed to bare steerageway
   • D.The need to obtain a radar overlay from a VTS station

   Why: Rule 6(b)(ii) of the 72 COLREGS specifically lists 'any constraints imposed by the radar range scale in use' among the additional factors a vessel with operational radar must weigh when determining safe speed. A vessel using a short-range scale may not detect distant targets in time to take avoiding action at higher speeds.

5. 5. Under Rule 6, 'the maneuverability of the vessel with special reference to stopping distance' is listed as a factor in determining safe speed. Which type of vessel would require the most conservative safe speed due to this factor?

   • A.A laden supertanker with limited engine astern power✓
   • B.A small motor yacht with twin screws
   • C.A container ship in ballast condition
   • D.A sailing vessel with auxiliary engine engaged

   Why: Rule 6(a)(iv) lists the maneuverability of the vessel, with special reference to stopping distance in prevailing conditions, as a factor in safe speed determination. A laden supertanker has enormous momentum, extremely long stopping distances, and limited astern power, requiring the most conservative safe speed of any commercial vessel type.

6. 6. Under Rule 19, when a vessel detects by radar alone the presence of another vessel in restricted visibility, what action is required?

   • A.Immediately stop engines and wait for the situation to clarify
   • B.Determine if a close-quarters situation is developing and take avoiding action in ample time✓
   • C.Sound one prolonged blast and proceed at reduced speed
   • D.Alter course to starboard regardless of radar contact bearing

   Why: Rule 19(d) states that a vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing or risk of collision exists, and if so, take avoiding action in ample time.

7. 7. Which of the following is NOT a factor a vessel must consider when determining a safe speed under Rule 6 in restricted visibility?

   • A.State of visibility
   • B.Traffic density
   • C.The flag state of other vessels in the area✓
   • D.The stopping distance and turning ability of the vessel

   Why: Rule 6 lists factors for safe speed including visibility, traffic density, vessel maneuverability, background light at night, state of wind/sea/current, draft relative to water depth, and radar characteristics. The flag state of other vessels is irrelevant to safe speed determination.

8. 8. Under Rule 19(d)(ii), when taking avoiding action to avoid a close-quarters situation detected by radar alone, altering course toward a vessel abeam or abaft the beam is prohibited. This is because:

   • A.It creates a head-on situation increasing closing speed
   • B.It could result in a swinging action that creates additional risk✓
   • C.Such an alteration would be indistinguishable from a course change for port-side passing
   • D.It places the own vessel in the other vessel's restricted visibility zone

   Why: Rule 19(d)(ii) prohibits altering course toward a vessel abeam or abaft the beam because such action could create a dangerous swinging situation and result in a close-quarters or collision scenario as the other vessel's position relative to own vessel changes rapidly.

Frequently asked questions

What factors determine safe speed under Rule 6?

General factors include: visibility, traffic density, vessel maneuverability (especially stopping distance and turning ability), background lights at night, state of wind, sea, and current, proximity of navigational hazards, and draft in relation to depth. Vessels equipped with radar must also consider the characteristics and limitations of that radar, the range scale in use, sea-state effects on radar returns, and the ability to detect small vessels.

Does Rule 6 only apply in restricted visibility?

No. Rule 6 says every vessel shall at all times proceed at a safe speed. Restricted visibility is one of the factors that can lower what counts as safe speed, but the requirement itself applies in all conditions.

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