COLREGS Rule 4 — Application

Rule Text

What it means on the water

• →Section I of Part B (Rules 4–10) applies in ANY condition of visibility — clear weather, fog, rain, snow, or darkness.
• →These rules apply whether or not vessels are in sight of one another — unlike Section II (Rules 11–18), which applies only to vessels in sight of each other.
• →The Section I conduct rules covered are: Rule 5 (look-out), Rule 6 (safe speed), Rule 7 (risk of collision), Rule 8 (action to avoid collision), Rule 9 (narrow channels), and Rule 10 (traffic separation schemes).
• →Because Rule 4 has no visibility precondition, a proper look-out and a safe speed are required in clear daylight just as much as in fog.
• →Contrast with Section III (Rule 19, restricted visibility), which adds extra duties when vessels are NOT in sight of each other — but the Section I baseline still applies underneath.

Common exam mistakes

• ✗Thinking the safe-speed and look-out rules only apply in restricted visibility — Rule 4 says they apply in any condition of visibility.
• ✗Confusing Section I (any visibility, Rules 4–10) with Section II (vessels in sight, Rules 11–18) — the application clauses are different.
• ✗Overlooking Rule 4 entirely because it is short — it is the gateway that makes Rules 5–10 universal.

USCG exam questions — Rule 4

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. A vessel equipped with radar determines by radar plotting that risk of collision may exist. Under Rule 6, this is relevant because:

   • A.A radar-equipped vessel must proceed at reduced speed whenever a contact is detected within 10 miles
   • B.The state of weather and sea conditions alters the interpretation of radar returns
   • C.Radar characteristics, efficiency, and limitations are a factor in determining safe speed✓
   • D.A radar-equipped vessel is always deemed to have complied with the lookout requirement

   Why: Rule 6(b) specifically lists factors relevant to safe speed for radar-equipped vessels, including the characteristics, efficiency, and limitations of the radar equipment. A vessel must account for what radar can and cannot detect when choosing a speed that allows stopping in time.

3. 3. A sailing vessel sees another sailing vessel to windward but cannot determine whether that vessel has the wind on the port or starboard side. Under Rule 12, the vessel to leeward shall:

   • A.Sound five short blasts and maintain course and speed
   • B.Keep out of the way of the vessel to windward✓
   • C.Assume the other vessel is on starboard tack and give way accordingly
   • D.Reduce speed until the windward vessel's tack can be determined

   Why: The keyed answer is correct: under Rule 12(a)(iii), if a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether that vessel has the wind on the port or starboard side, she shall keep out of the way of the other. This is a safety default for the leeward (port-tack) vessel, requiring her to give way to the windward vessel. (Note: Rule 12(b) is the separate definition of the "windward side" — the side opposite that on which the mainsail is carried — and does not govern this ambiguous-tack situation.)

4. 4. Two power-driven vessels are meeting on reciprocal or nearly reciprocal courses such that there is a risk of collision. Each vessel shall:

   • A.The vessel on the port side shall give way; the starboard vessel shall stand on
   • B.Alter course to port so as to pass on the port side of the other
   • C.Alter course to starboard so that each passes on the port side of the other✓
   • D.Reduce speed and wait for the other vessel to take action first

   Why: Rule 14(a) requires both vessels in a head-on situation to alter course to starboard so they pass port-to-port. This is a bilateral obligation — both act simultaneously. Altering to port would increase the closing rate on the collision course and is explicitly wrong.

5. 5. Two power-driven vessels are in a crossing situation so as to involve risk of collision. Under Rule 15, which vessel is the give-way vessel?

   • A.The vessel that is making the greater speed
   • B.The vessel that is smaller in length
   • C.The vessel which has the other on her starboard side✓
   • D.The vessel which has the other on her port side

   Why: Rule 15 requires the vessel that has the other on her starboard side to keep out of the way. Memory aid: the give-way vessel sees a red (port) light on the crossing vessel — a reminder to stop. Speed and size are irrelevant to this determination.

6. 6. Under Rule 17(a), the stand-on vessel in a crossing situation shall:

   • A.Immediately alter course to port to open the CPA
   • B.Immediately reduce speed to allow the give-way vessel more time
   • C.Maintain her course and speed✓
   • D.Sound five short blasts and then take independent action

   Why: Rule 17(a)(i) obliges the stand-on vessel to maintain course and speed. This predictability is essential — the give-way vessel plans its maneuver based on the stand-on vessel continuing unchanged. Unpredictable early action by the stand-on vessel can negate the give-way vessel's avoidance.

7. 7. Rule 17(c) states that a stand-on vessel taking action in accordance with Rule 17(a)(ii):

   • A.Becomes the give-way vessel for the remainder of the encounter
   • B.Shall not alter course to port for a vessel on her own port side✓
   • C.Must first reduce speed before altering course
   • D.Must sound the appropriate maneuvering signal before acting

   Why: Rule 17(c) prohibits the stand-on vessel from altering course to port for a vessel on her own port side when she decides to act under 17(a)(ii). Turning toward a give-way vessel approaching from the port bow would increase closing rate. Turning to starboard (away from the give-way vessel) is the correct action.

8. 8. US Inland Navigation Rules apply to:

   • A.All vessels upon the inland waters of the United States and to vessels of the United States on the Canadian waters of the Great Lakes✓
   • B.All vessels navigating within the 12-nautical-mile territorial sea of the United States
   • C.Only US-flagged vessels operating on US inland waterways
   • D.All vessels operating within state waters, as defined by each individual state

   Why: The US Inland Rules apply to all vessels on US inland waters and extend to US-flagged vessels on the Canadian waters of the Great Lakes, reflecting the bilateral navigation agreement with Canada.

Frequently asked questions

What does Rule 4 of the COLREGS cover?

Rule 4 is the application clause for Section I of the Steering and Sailing Rules. It states that the rules in this Section apply in any condition of visibility. This makes Rules 5 through 10 — look-out, safe speed, risk of collision, action to avoid collision, narrow channels, and traffic separation schemes — applicable at all times, regardless of weather.

Do the Section I rules apply when vessels cannot see each other?

Yes. Rule 4 specifies any condition of visibility, so the Section I conduct rules apply whether or not vessels are in sight of one another. This is the key difference from Section II (Rules 11–18), which applies only to vessels in sight of each other. In fog, the Section I rules still apply, and Rule 19 adds further duties on top.

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