Power-Driven Vessel Lights (Rule 23)

Introduction

Rule 23 (Power-driven Vessels Underway) is the most foundational of all the specific light configurations. Found in 33 CFR 83.23, this rule establishes the baseline lighting pattern from which all other configurations are derived. Understanding power-driven vessel lights is essential because they are the most common lights you will encounter on the water.

A "power-driven vessel" is defined by Rule 3 as "any vessel propelled by machinery." This broad definition includes:

• Vessels with inboard or outboard engines
• Vessels with stern drives or jet drives
• Sailing vessels when they are also using their engine (motorsailers)
• Personal watercraft (PWC)
• Commercial vessels, tugs, and ferries
• Even kayaks or canoes with electric trolling motors

An operator who can quickly identify a standard power-driven vessel can more easily identify the variations that signal special operations such as towing, fishing, or restricted maneuverability.

The "Big Ships": Vessels 50 Meters (164 ft) and Over

The lighting configuration for large vessels is the most complete and serves as the "full" expression of Rule 23. A power-driven vessel of 50 meters or more in length, when underway, shall exhibit:

1. A masthead light forward: A 225° white light placed over the fore-and-aft centerline
2. A second masthead light: A 225° white light, abaft of and higher than the forward one
3. Sidelights: Red (port) and green (starboard) 112.5° lights
4. A sternlight: A 135° white light

The Purpose of the Second Masthead Light

The mandatory second masthead light is not merely decorative or for increased visibility. Its positioning, dictated by 33 CFR 84.02 and 84.03, provides critical passive information to other mariners. The rules require both vertical separation (the aft light must be higher) and horizontal separation (the horizontal distance must be at least one-quarter of the vessel's length, though it need not be more than 50 meters).

This separation of the two white masthead lights creates a "range system" that serves multiple functions:

Scale and Identification: An observer seeing two masthead lights in vertical alignment instantly knows the vessel is either:

• A power-driven vessel over 50 meters in length, OR
• A vessel engaged in towing (which will be discussed in Lesson 4)

This immediate visual cue signals a large, less-maneuverable vessel that should be given a wide berth under Rule 18 (vessel hierarchy).

Aspect and Turn Indication: When viewing a large vessel head-on, the two masthead lights will appear vertically aligned, one directly above the other. As the vessel begins to turn, the two lights will "open up" or separate horizontally. This change in alignment provides a much earlier and more perceptible indication of a course change than waiting to see the sidelights switch from both-visible to only-green or only-red.

This visual "ranging" is a critical tool for collision avoidance in crossing or meeting situations, particularly at distances of 3-6 miles where the vessel's hull may not yet be visible but the bright white masthead lights are clearly visible.

The "Baseline": Vessels 12 Meters (39.4 ft) to < 50 Meters (164 ft)

This category represents the vast majority of commercial vessels, charter boats, and larger recreational vessels. For a power-driven vessel in this size range, the lighting requirements are nearly identical to their larger counterparts, with one key difference.

A power-driven vessel of 12 meters to less than 50 meters shall exhibit:

1. A masthead light forward
2. Sidelights
3. A sternlight

The second masthead light (abaft and higher) is optional for vessels in this size range. While it is permitted, it is less common to see it on vessels at the smaller end of this range (e.g., a 40-foot vessel) due to the significant vertical separation required, which is often structurally impractical.

Practical Identification: An operator seeing a single masthead light combined with sidelights and a sternlight should assume they are viewing a power-driven vessel under 50 meters in length, or a vessel over 50 meters viewed from a position where the second masthead light is obscured or not yet visible.

The "Small Craft": Vessels Under 12 Meters (39.4 ft)

This category includes the vast majority of recreational powerboats in the United States. The rules, recognizing the practical limitations and structural constraints of small craft, provide significant simplification.

Rule 23(d) states that a power-driven vessel of less than 12 meters in length may, in lieu of the masthead light and sternlight, exhibit:

1. An all-round white light: A single 360° white light
2. Sidelights: Separate or combined into a single bi-color unit

This is the most common configuration for recreational powerboats. The all-round white light is typically mounted on a post, Bimini top frame, or T-top structure high enough to be visible over all structures and the heads of standing passengers.

The "Bi-Color" Option: Small vessels may also combine the red and green sidelights into a single "bi-color" lantern mounted on the centerline. This reduces the number of separate lights from three (red, green, white stern) to two (bi-color, all-round white), simplifying installation and reducing power consumption.

Special Case: Very Small, Slow Vessels (< 7m and < 7 knots)

The rules provide a further simplification for very small, very slow vessels. Rule 23 (International) allows a power-driven vessel of less than 7 meters whose maximum speed does not exceed 7 knots to exhibit:

• One all-round white light, and
• If practicable, sidelights

Practical Impact: This means a small inflatable tender with a 5-horsepower outboard motor is legally lit with a single all-round white light (such as a battery-powered LED light clipped to a fishing rod or pole). The "if practicable" language for sidelights means sidelights are recommended but not mandatory for these very small, slow vessels.

The Problem of the "Ambiguous White Light"

The various simplifications for small vessels, while practical and necessary, create a significant and dangerous ambiguity on the water that every mariner must understand.

Consider the following legal configurations:

• PDV < 12m: May show an all-round white light and sidelights
• PDV < 7m & < 7 knots: May show only an all-round white light
• Sailboat < 7m: May show only an all-round white light (or handheld flashlight)
• Vessel at anchor < 50m: Shall show only an all-round white light

The Dangerous Reality: An operator on a dark night who sees a single all-round white light on the water has no way of knowing, from that visual signal alone, what they are looking at.

Is it:

• A 20-foot center console making 25 knots and approaching head-on?
• A 15-foot sailboat drifting slowly under oars?
• A 150-foot vessel anchored in the channel?
• A small fishing boat dead in the water?

This ambiguity places a heavy burden on all mariners:

For the Observer (seeing a single white light):

The mariner must:

1. Slow to a safe speed immediately (Rule 6)
2. Assume risk of collision exists (Rule 7)
3. Use every available means to determine the vessel's status:
   • Radar (if equipped) to determine range, bearing, and movement
   • Binoculars to look for additional lights, vessel outline, or motion
   • Spotlight to illuminate the other vessel (if safe to do so)
   • VHF radio to attempt contact
4. Default to giving way and taking early, substantial action to avoid collision
5. Sound the danger signal (5 short blasts) if in doubt

For the Operator (showing only a single white light):

The mariner must recognize their ambiguity and understand they are "legally lit" but "practically invisible" from a status and movement standpoint. They must:

1. Be hyper-vigilant and maintain an enhanced lookout
2. Operate at a reduced safe speed
3. Be prepared to maneuver aggressively to avoid other vessels who may not understand their movement
4. Display additional lights when practical (such as sidelights even when optional)
5. Use a searchlight or spotlight to illuminate their vessel for approaching traffic
6. Sound appropriate signals to alert nearby vessels of their presence

Best Practice: Even when the rules allow a single all-round white light, prudent seamanship dictates using the more complete set of lights (sidelights + masthead or all-round white) to eliminate ambiguity and maximize visibility.

Special PDV Cases and Variations

Air-Cushion Vessels (Hovercraft)

When operating in the non-displacement mode (hovering on its air cushion), an air-cushion vessel must exhibit, in addition to the standard power-driven vessel lights for its length:

• An all-round flashing yellow light

This distinctive yellow flashing light warns other mariners of the hovercraft's unique characteristics:

• High speed capability
• Unconventional handling and stopping distances
• Ability to operate over water, ice, mud, or land
• Unpredictable maneuvering

The flashing yellow light serves as a caution signal equivalent to "give me extra room."

Personal Watercraft (PWC)

A PWC is legally classified as a "power-driven vessel." However, the vast majority of PWC are not manufactured with the navigation lights required for night operation. Most PWC have only a single all-round white light with minimal range, and many lack proper sidelights entirely.

As a result, the vast majority of U.S. states and territories flatly prohibit PWC operation between sunset and sunrise. State regulations typically read: "No person shall operate a PWC from sunset to sunrise" or "PWC operation is prohibited during hours of darkness."

Exception: In the rare event a PWC is properly equipped with USCG-approved navigation lights and state law permits night operation, the PWC must display the lights for a power-driven vessel less than 12 meters:

• An all-round white light, AND
• Sidelights (separate or combined)

Safety Note: Even where legal, night PWC operation is extremely dangerous due to the low profile of the craft, minimal freeboard, high speed, and reduced operator visibility from the low seating position.

Great Lakes Special Rule (Inland Only)

33 CFR 83.23(e) provides a regional variation applicable only to the Great Lakes. A power-driven vessel operating on the Great Lakes may:

• Carry an all-round white light in the position of the second masthead light and in lieu of the sternlight

This configuration creates a visible all-round white light aft instead of the standard sternlight. This Great Lakes exception is a historical carryover from pre-1980 rules and is not applicable in any other Inland or International waters.

Important: This exception applies only to vessels operating on the five Great Lakes (Superior, Michigan, Huron, Erie, Ontario) and their directly connecting waters. It does NOT apply to rivers, coastal waters, or inland lakes even within Great Lakes states.

Identifying Power-Driven Vessels: Practical Scenarios

Scenario 1: Head-On Approach

You see:

• Two white lights (vertical alignment) or one white light (depending on vessel size)
• Both red and green sidelights visible simultaneously

Identification: Power-driven vessel approaching head-on. This is a potential collision situation.

Your Action: Both vessels must alter course to starboard for port-to-port passing (Rule 14).

Scenario 2: Crossing from Starboard

You see:

• One or two white masthead lights
• Green sidelight only (no red visible)

Identification: Power-driven vessel on your starboard side. You are the give-way vessel.

Your Action: Take early, substantial action to keep clear (Rule 15, 16). Alter course to starboard to pass astern if possible.

Scenario 3: Crossing from Port

You see:

• One or two white masthead lights
• Red sidelight only (no green visible)

Identification: Power-driven vessel on your port side. You are the stand-on vessel.

Your Action: Maintain course and speed (Rule 17), but be prepared to maneuver if the other vessel fails to give way.

Scenario 4: Overtaking

You see:

• White sternlight only (no red or green visible)

Identification: You are overtaking a power-driven vessel from astern.

Your Action: You are the give-way vessel and must keep clear until finally past and clear (Rule 13).

Summary

Power-driven vessel lights form the foundation of the navigation light system. Vessels 50 meters and over display two masthead lights in vertical alignment, sidelights, and a sternlight. Vessels 12-49.9 meters display a single masthead light, sidelights, and sternlight (second masthead optional). Vessels under 12 meters may substitute an all-round white light for the masthead and sternlight.

The simplified single all-round white light, while legal, creates dangerous ambiguity. Operators seeing a single white light must slow down, assume risk, and use all available means to determine the vessel's status and movement. Operators showing only a single white light must recognize they are practically invisible and exercise extreme caution.

Special variations include air-cushion vessels (flashing yellow), PWC (usually prohibited at night), and Great Lakes vessels (all-round white in lieu of sternlight).

Understanding these configurations allows mariners to instantly identify vessel type, size, and aspect, enabling proper application of the navigation rules for collision avoidance.

Key Takeaways

• Power-driven vessels are any vessels propelled by machinery, including motorsailers
• Vessels ≥50m must display two masthead lights (aft one higher) for size identification and aspect indication
• Vessels 12-49.9m display single masthead light, sidelights, and sternlight
• Vessels <12m may use simplified all-round white light and sidelights
• A single white light is dangerously ambiguous-could be underway vessel, sailboat, or anchor light
• Operators seeing single white light must slow, assume risk, and determine vessel status
• PWC operation is prohibited at night in most states due to inadequate lighting
• Air-cushion vessels display flashing yellow in addition to standard PDV lights
• Proper identification of aspect (head-on, crossing, overtaking) depends on which lights are visible