COLREGS Lights and Shapes: The Complete Quiz and Study Guide

Lights and shapes questions appear on every USCG license exam that tests Rules of the Road. They appear on the OUPV (6-pack), the Master 100 GT, the Master 200 GT, and the unlimited master exams. The question formats cycle through three modes: given a vessel type, state the lights it shows; given a described light arrangement, identify the vessel type; and spot the error in a given light configuration.

All three formats draw from the same body of knowledge — COLREGS 1972 Rules 20-31, plus the equivalent U.S. Inland Rules. This guide covers every vessel type, the arc widths in detail, and the identification framework that makes quiz questions faster to answer.

The Four Light Colors and Their Meanings

COLREGS uses exactly four light colors:

• White: Masthead lights, sternlights, all-round lights, anchor lights
• Red: Port sidelight, the port arc of a combined lantern, some fishing/trawling lights
• Green: Starboard sidelight, the starboard arc, some fishing lights
• Yellow: Towing lights (in the sternlight position, same 135° arc), air cushion vessel lights

Any vessel showing a yellow light is either towing/being towed, or is an air cushion vessel operating in the non-displacement mode.

Arc Widths — Memorize These Cold

| Light Type | Arc Width | Notes | |-----------|-----------|-------| | Masthead (white) | 225° | 112.5° each side of dead ahead | | Sidelight (red/green) | 112.5° each | From dead ahead to 22.5° abaft the beam | | Sternlight (white) | 135° | 67.5° each side of dead astern | | Yellow towing light | 135° | Same arc as sternlight | | All-round light | 360° | — | | Flashing light | 360° | Special characteristics: flashes at specified interval |

The sectors that matter for collision avoidance:

A vessel approaching from dead ahead sees your port (red) sidelight, starboard (green) sidelight, and masthead light(s). From the starboard side forward of the beam, she sees green and masthead(s). From the port side forward of the beam, red and masthead(s). From anywhere abaft the beam, only the sternlight.

The 22.5° sector abaft the beam is the overtaking sector — any vessel within it is the overtaking vessel regardless of whether it's technically a sailing vessel or power-driven.

Power-Driven Vessels Underway

Under 50 meters:

• One masthead light forward
• Sidelights (red/green) or combined lantern
• Sternlight (white, 135°)

50 meters and over:

• Two masthead lights — forward lower, aft higher
• Sidelights
• Sternlight

Under 7 meters, maximum speed under 7 knots:

• One all-round white light
• Sidelights if practicable

The two-masthead arrangement for vessels 50m+ creates a vertical "ladder" visible from ahead. If the forward masthead is lower than the aft, the vessel is heading generally away from you. If the aft light is lower, you're looking at her stern. This is the "two mast lights" identification method for power-driven vessels from a distance.

Sailing Vessels Underway

Under 20 meters: May combine red/green sidelights and sternlight in a single tricolor lantern at the masthead (only when under sail). The tricolor shows all three lights in one: forward 112.5° green, forward 112.5° red, aft 135° white. Note: when motoring, even if sails are up, the vessel must show power-driven lights (masthead + sidelights + sternlight), NOT the tricolor.

All sailing vessels: Sidelights and sternlight. A sailing vessel may additionally show two all-round lights at the masthead — red over green — to indicate sailing vessel status (optional signal).

The key exam trap: A sailboat with its engine running shows power-driven vessel lights, not sailing vessel lights. A vessel motorsailing under COLREGS is a power-driven vessel.

Fishing Vessels (Not Trawling)

A vessel engaged in fishing (other than trawling) shows:

• Two all-round lights in a vertical line: red over white
• Sidelights and sternlight when making way through the water
• If gear extends more than 150 meters horizontally, an additional all-round white light in the direction of the gear

Memory device: "red over white — fishing at night"

Trawling Vessels

A vessel engaged in trawling shows:

• Two all-round lights in a vertical line: green over white
• Masthead light abaft and higher than the green all-round light (if 50m+)
• Sidelights and sternlight when making way

Memory device: "green over white — trawling tonight"

When not making way (stopped while trawling), sidelights and sternlight are extinguished.

Vessels Not Under Command (NUC)

A vessel not under command (NUC) — unable to maneuver due to exceptional circumstances, not human negligence — shows:

• Two all-round red lights in a vertical line
• When making way: sidelights and sternlight
• When not making way: no sidelights, no sternlight

The two red all-round lights are the "NUC lights." They are the highest-priority light configuration — they override the normal lights of any vessel type. A NUC power vessel shows two red all-rounds, not masthead lights, though it may add them in addition.

Vessels Restricted in Ability to Maneuver (RAM)

A RAM vessel (dredge, survey vessel working, vessel laying cable, vessel replenishing underway) shows:

• Three all-round lights in a vertical line: red/white/red
• When making way: masthead light(s), sidelights, sternlight

The red-white-red pattern is the "restricted in ability to maneuver" signal. RAM vessels include vessels underway engaged in:

• Laying, servicing, or picking up a navigation mark, submarine cable, or pipeline
• Dredging, surveying, or underwater operations
• Minesweeping operations
• Replenishment underway
• Launch or recovery of aircraft

Constrained by Draft

COLREGS only (not in Inland Rules): A vessel constrained by her draft may show three all-round red lights in a vertical line, or a cylinder, as dayshape. This is a voluntary signal — it alerts other vessels that this ship has limited ability to deviate from the shipping channel due to deep draft.

Exam note: Constrained-by-draft vessels are often confused with NUC vessels (also two red lights) or RAM vessels. Constrained-by-draft = three red lights. NUC = two red lights.

Vessels at Anchor

• Under 50 meters: One all-round white light at or near the bow, and if convenient, an all-round white light at the stern lower than the forward light
• 50 meters and over: One all-round white light forward, one all-round white light aft (lower than the forward light)
• Under 7 meters, not in a fairway or anchorage: Not required to show anchor lights

The "anchor ball" dayshape — a black ball — is displayed forward when at anchor during daylight.

Dayshapes Summary

Dayshapes are displayed instead of lights during daylight hours (30 minutes before sunrise to 30 minutes after sunset). They're black geometric shapes hoisted where best visible.

| Shape | Meaning | |-------|---------| | Ball | Vessel at anchor; also vessel constrained by draft (3 balls) | | Cone (point down) | Vessel under sail AND power (motorsailing) | | Cylinder | Vessel constrained by draft | | Diamond | Vessel being towed (if length of tow exceeds 200m) | | Two cones (point to point, hourglass) | Vessel fishing other than trawling | | Two cones (point up and down, binocular shape) | Trawling vessel | | Ball-diamond-ball | Vessel restricted in ability to maneuver | | Three balls (vertical) | Vessel aground |

The "B-D-B" (ball-diamond-ball) for RAM is tested frequently.

Pilot Vessels

A pilot vessel on pilotage duty shows:

• One all-round white light at the masthead, over one all-round red light
• When underway: sidelights and sternlight
• When at anchor: anchor light, plus white-over-red

"Whites on top — pilot aloft." The mnemonic works.

How to Answer Identification Questions

When a question gives you a described light combination and asks what vessel you're looking at, work through this three-step method:

1. Count the lights. How many total? Are there all-round lights (which means the vessel isn't just moving through the water)?

1. Identify the colors. All-round lights: what colors? Red over white → fishing. Green over white → trawling. Two reds → NUC. Red/white/red → RAM.

1. Check for sidelights and sternlight. If the vessel has sidelights, it's making way. If not, it's stopped (but may still be underway — just not making way through the water).

Most answers fall into place after step 2. All-round light color combinations are the exam's primary distinguishing factor.

Practice with Binnacle School

Lights and shapes questions are completely predictable — every question comes from the NMC question bank, and the question bank is public. What differentiates candidates who pass from those who fail is whether they've drilled these questions enough that the answer is immediate rather than labored.

[Binnacle School](/school) gives you focused lights-and-shapes quiz practice, organized by vessel type and situation, so you build pattern recognition before exam day rather than hoping to remember the details under pressure.

Start your COLREGS lights and shapes practice →

Binnacle AI is not affiliated with the U.S. Coast Guard or the NMC. COLREGS 1972 Rules 20-31 and U.S. Inland Navigation Rules (33 CFR Part 83) are the governing documents. Not legal advice.