Part C — Lights and Shapes
COLREGS Rule 22 — Visibility of Lights
Rule 22 specifies the minimum visibility distances that lights must be visible to the naked eye in a clear night. The required range depends on vessel length and type of light.
Rule Text
Lights shall have an intensity as specified in Section 8 of Annex I so as to be visible at the following minimum ranges: Vessels 50 meters or more in length — masthead light 6 miles, sidelight 3 miles, sternlight 3 miles, towing light 3 miles, white/red/green/yellow all-around 3 miles. Vessels 12 to 50 meters — masthead light 5 miles, sidelight 2 miles, sternlight 2 miles, towing light 2 miles, all-around 2 miles. Vessels under 12 meters — masthead light 2 miles, sidelight 1 mile, sternlight 2 miles, all-around 2 miles. Vessels under 12 meters: if not practicable to show lights of these ranges, lights of lesser range may be shown. Inconspicuous, partly submerged vessels or objects — all-around white 3 miles.
What it means on the water
- →Vessels 50m or more: masthead 6 miles, all others 3 miles.
- →Vessels 12–50m: masthead 5 miles, all others 2 miles.
- →Vessels under 12m: masthead 2 miles, sternlight 2 miles, sidelight 1 mile.
- →Sidelights consistently have shorter range requirements than masthead/stern lights.
- →Inconspicuous/partly submerged objects: all-around white at 3 miles.
Common exam mistakes
- ✗Confusing the 5-mile masthead range (12–50m vessels) with the 6-mile range (50m+ vessels).
- ✗Applying the same range to sidelights as masthead lights — sidelights have lower requirements.
- ✗Missing the special provision for partly submerged or inconspicuous objects.
USCG exam questions — Rule 22
These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.
1. According to the COLREGS, what is the minimum required visibility range for a masthead light on a vessel 50 meters or more in length?
- A.2 miles
- B.3 miles
- C.5 miles
- D.6 miles✓
Why: Rule 22(a) requires masthead lights on vessels 50 meters or more in length to be visible at a minimum range of 6 miles. Sidelights on the same vessels require 3 miles, and the sternlight requires 3 miles — masthead lights have the greatest range requirement.
2. What is the minimum visibility range required for sidelights on a vessel of 12 meters or more but less than 50 meters in length?
- A.1 mile
- B.3 miles
- C.5 miles
- D.2 miles✓
Why: Rule 22(b) requires sidelights on vessels 12 meters or more but less than 50 meters in length to be visible at least 2 miles. Sternlights and towing lights on the same size vessels also require 2 miles.
3. A 'masthead light' under the COLREGS shows over an arc of how many degrees?
- A.112.5 degrees
- B.135 degrees
- C.225 degrees✓
- D.360 degrees
Why: Rule 21(a) defines a masthead light as showing an unbroken arc of 225 degrees, from dead ahead to 22.5 degrees abaft the beam on each side. This distinguishes it from an all-round light which covers 360 degrees.
4. What arc does a sternlight cover?
- A.112.5 degrees centered on dead astern
- B.225 degrees from dead astern
- C.135 degrees centered on dead astern✓
- D.180 degrees from dead astern
Why: Rule 21(c) defines the sternlight as showing a white light over an arc of 135 degrees (67.5 degrees on each side of dead astern). Together with the sidelights' 112.5-degree arcs each, these three lights collectively cover 360 degrees.
5. Rule 20 states that lights required by the COLREGS shall be exhibited:
- A.At all times when underway
- B.From sunset to sunrise only
- C.From sunset to sunrise and during restricted visibility at all times✓
- D.Whenever another vessel is within sight
Why: Rule 20(b) requires prescribed lights to be exhibited from sunset to sunrise and during restricted visibility — and may be exhibited at other times when the mariner considers it necessary. This ensures safety in both darkness and poor visibility.
6. What color is a towing light under the COLREGS and where is it positioned?
- A.Yellow; in a vertical line above the sternlight showing over the same arc as the sternlight✓
- B.White; at the stern above the sternlight
- C.Yellow; at the masthead showing all-round
- D.Yellow; on the port side of the stern
Why: Rule 21(f) defines the towing light as a yellow light having the same characteristics as the sternlight (135-degree arc, centered on dead astern), positioned in a vertical line above the sternlight. Yellow over white at the stern identifies an astern tow.
7. Under Rule 20, which statement regarding the use of prescribed lights and shapes is CORRECT?
- A.Shapes need only be displayed from sunrise to sunset✓
- B.Lights may never be shown during daylight hours
- C.Shapes shall be exhibited from sunrise to sunset and may be shown at night if necessary
- D.Lights shall be shown at all times, including daylight hours
Why: Rule 20(d) specifies that shapes shall be exhibited during daylight (sunrise to sunset). Rule 20(b) covers lights from sunset to sunrise and during restricted visibility. The two regimes are complementary: lights for darkness/poor visibility, shapes for daylight.
Frequently asked questions
- How far must masthead lights be visible under COLREGS?
- The required visibility range depends on vessel size: vessels 50 meters or more must show a masthead light visible for at least 6 miles; vessels 12 to 50 meters, at least 5 miles; vessels under 12 meters, at least 2 miles. These are minimum ranges in a clear dark night.
- Do sidelights need to be as visible as masthead lights?
- No. Sidelights have lower visibility requirements. On vessels 12 meters and over, sidelights must be visible at 2 miles (compared to 5–6 miles for masthead lights). On vessels under 12 meters, sidelights need only be visible at 1 mile.
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