COLREGs Lights and Shapes: Rules 20 to 31

Background

Purpose of the Lights and Shapes system

The Lights and Shapes system serves multiple purposes in collision avoidance:

• Vessel identification: distinguishing power-driven vessels from sailing vessels, fishing vessels, anchored vessels, etc.
• Activity recognition: identifying what a vessel is doing (towing, fishing, dredging, etc.).
• Manoeuvrability assessment: indicating whether a vessel can manoeuvre normally or has limitations.
• Direction indication: showing the vessel’s orientation relative to the observer.
• Day-night equivalence: shapes by day, lights at night, with consistent meanings.

The visual identification system is the foundation for applying the Steering and Sailing Rules, without it, mariners would have to determine vessel status by other (less reliable) means.

Day shapes vs night lights

The distinction between shapes (day) and lights (night) reflects practical visibility:

• Day shapes: visible in daylight; typically black to contrast with sky.
• Night lights: visible in darkness; coloured or white as prescribed.
• Restricted visibility (fog, heavy rain, snow): lights also displayed by day to maintain visibility.

The day shapes use combinations of balls (spheres), cones, diamonds, and cylinders to convey information equivalent to the night light patterns. For example:

• Power-driven vessel: no day shape required (the vessel itself is the indication).
• Sailing vessel under power and sail: cone, point downward (Rule 25).
• Vessel not under command: two black balls vertically.
• Vessel restricted in ability to manoeuvre: ball, diamond, ball vertically.
• Vessel constrained by draught: cylinder.
• Anchor: black ball forward.
• Aground: anchor ball plus three black balls vertically.
• Fishing: basket or cone.
• Mine clearing: three black balls in triangular configuration.

Major amendment history

The Lights and Shapes have been refined through COLREG amendment cycles:

• 1981: clarification of Rule 26 fishing vessel lights.
• 1987: refinements to several rules.
• 1989: WIG craft lights added.
• 1993: WIG craft refinements.
• 2001: comprehensive update including high-speed craft considerations.

The amendment cycle has been measured, reflecting the foundational nature of the visual identification system and the conservatism toward changes that affect mariner training globally.

Rule 21: Definitions of lights

Masthead light

The masthead light is:

• Colour: white.
• Position: on or near the centreline of the ship.
• Visibility arc: 225 degrees, from right ahead to 22.5 degrees abaft the beam on either side.
• Visibility range: 6 nm for vessels of 50 m or more, 5 nm for 20-50 m, 3 nm for 12-20 m, 2 nm for less than 12 m.

The masthead light is the principal forward identification light, allowing observers to identify a power-driven vessel approaching head-on or from the bow quadrant.

Sidelights

The sidelights are:

• Colour: green on starboard, red on port.
• Position: at the side of the vessel, near the bow.
• Visibility arc: 112.5 degrees each, from right ahead to 22.5 degrees abaft the beam.
• Visibility range: 3 nm for vessels of 50 m or more, 2 nm for 12-50 m, 1 nm for less than 12 m.

The sidelights identify the vessel’s heading: red on the observer’s left (own ship’s port) means the target is showing her port side; green means starboard side; both visible means head-on or near head-on.

The mnemonic “red right returning” applied in IALA Region B is for buoyage, not for navigation lights, nav lights have a consistent global colour convention.

Sternlight

The sternlight is:

• Colour: white.
• Position: on the stern centreline.
• Visibility arc: 135 degrees, from 67.5 degrees on each side of dead astern.
• Visibility range: 3 nm for vessels of 50 m or more, 2 nm for less.

The sternlight is the principal identification when overtaking; an overtaking vessel sees only the sternlight of the vessel being overtaken.

Towing light

The towing light is identical to the sternlight but yellow rather than white. Used by towing vessels (Rule 24) above their sternlight to indicate towing operations.

All-round light

The all-round light:

• Position: above other lights so that 360-degree visibility is achievable.
• Visibility arc: 360 degrees.
• Used in: anchor lights, NUC lights, RAM lights, fishing lights, pilot lights.

Flashing light

The flashing light:

• Yellow flashing.
• Frequency: 120 or more flashes per minute.
• Used by: WIG craft, certain hovercraft.

Rule 22: Visibility ranges

The minimum visibility ranges for navigation lights are specified by vessel length:

For vessels of 50 metres or more in length:

• Masthead light: 6 nautical miles.
• Sidelights: 3 nautical miles.
• Sternlight: 3 nautical miles.
• Towing light: 3 nautical miles.
• All-round light: 3 nautical miles.

For vessels of 12 to 50 metres in length:

• Masthead light: 5 nautical miles, except where length is less than 20 metres, 3 nautical miles.
• Sidelights: 2 nautical miles.
• Sternlight: 2 nautical miles.
• Towing light: 2 nautical miles.
• All-round light: 2 nautical miles.

For vessels of less than 12 metres in length:

• Masthead light: 2 nautical miles.
• Sidelights: 1 nautical mile.
• Sternlight: 2 nautical miles.
• Towing light: 2 nautical miles.
• All-round light: 2 nautical miles.

The navigation light visibility range calculator returns the required range for a given vessel and light type.

The visibility ranges are minimum requirements; lights may be brighter for greater visibility. The required range depends on light intensity (in candelas) and atmospheric conditions; the COLREG Annex I provides the conversion formulas.

Rule 23: Power-driven vessels underway

A power-driven vessel underway shall exhibit:

• Forward masthead light at the bow.
• Sidelights (port red, starboard green).
• Sternlight at the stern.
• Second masthead light for vessels of 50 metres or more, abaft and higher than the forward masthead light.

For vessels less than 12 metres, alternative arrangements are permitted (combined masthead/sternlight, all-round white, etc.).

The two-masthead-lights pattern for larger vessels enables observers to determine the vessel’s relative course and length more accurately.

For air-cushion vessels (hovercraft) operating in the non-displacement mode, an additional all-round flashing yellow light is required.

For Wing-In-Ground (WIG) craft taking off, landing, or in flight near the surface, a high-intensity all-round flashing red light.

The vessel identification by lights calculator implements the recognition logic.

Rule 24: Towing and pushing

A power-driven vessel towing or pushing exhibits:

• Two masthead lights in a vertical line in addition to the standard masthead lights (or three masthead lights vertically when the length of the tow exceeds 200 metres).
• Sidelights.
• Sternlight.
• Towing light in a vertical line above the sternlight (yellow).
• Diamond shape by day where the length of the tow exceeds 200 metres.

The vessel being towed (the tow) exhibits:

• Sidelights and sternlight as appropriate to her status.
• Diamond shape by day where the length of the tow exceeds 200 metres.

A vessel pushing ahead or towing alongside:

• Two masthead lights in a vertical line.
• Sidelights and sternlight.

The towing rules support recognition of the difficult-to-manoeuvre tug-tow combination, which requires special handling under the Steering and Sailing Rules.

Rule 25: Sailing vessels under sail and vessels under oars

Sailing vessels exhibit:

• Sidelights.
• Sternlight.
• Optional: at the masthead, two all-round lights (red over green) for sailing vessels.

A sailing vessel of less than 7 metres in length shall, if practicable, exhibit the lights but is not required to.

A vessel under oars (rowing): may exhibit lights as for a sailing vessel, or shall have an electric torch ready to show in sufficient time to prevent collision.

The sailing vessel pattern (no masthead lights) is the principal distinction from power-driven vessels under Rule 23. A power-driven vessel observing only sidelights and sternlight (no masthead light) recognises a sailing vessel and applies Rule 18 priorities.

Rule 26: Fishing vessels

Fishing vessels engaged in fishing have specific lights and shapes:

Trawling

A vessel trawling exhibits:

• Two all-round lights vertically: green over white.
• Sidelights and sternlight when making way.
• Day shape: two cones with their points joined together (basket).

When the trawler’s gear extends more than 150 metres horizontally from the vessel, an additional all-round white light or cone with apex upward is exhibited in the direction of the gear.

Other fishing (longlining, gill-netting, etc.)

A vessel engaged in fishing other than trawling exhibits:

• Two all-round lights vertically: red over white.
• Sidelights and sternlight when making way.
• Day shape: same basket as for trawling.

When the gear extends more than 150 metres horizontally, the additional white all-round or cone is exhibited.

Significance for other vessels

The fishing vessel lights identify a vessel that has reduced manoeuvrability when fishing gear is deployed. Other vessels must keep clear under Rule 18.

The vessel identification by lights calculator covers the fishing vessel identification.

Rule 27: Vessels not under command or restricted in ability to manoeuvre

Vessel Not Under Command (NUC)

A vessel not under command (i.e. the vessel cannot be manoeuvred due to circumstances such as engine failure or steering damage) exhibits:

• Two all-round red lights vertically in the most visible position.
• Sidelights and sternlight when making way through the water (showing the vessel still has motion).
• Day shape: two black balls vertically.

A NUC vessel cannot give way to others; other vessels under Rule 18 must keep clear.

Vessel Restricted in Ability to Manoeuvre (RAM)

A vessel restricted in her ability to manoeuvre (e.g. cable-laying, dredging, mine-clearance, surveying) exhibits:

• Three all-round lights vertically: red, white, red.
• Sidelights and sternlight when making way.
• Day shape: ball, diamond, ball vertically (three shapes).

Specific RAM activities have additional indications:

• Underwater operations (diving): two all-round red lights to indicate side on which obstruction exists, two all-round green to indicate side where another vessel may pass.
• Mine clearing: three all-round green lights or three black balls in a triangular pattern.
• Vessel engaged in towing where the towing operation severely restricts the towing vessel and tow in their ability to deviate from their course: same as RAM lights and shapes.
• Vessel engaged in dredging: same RAM lights with additional all-round red on side of obstruction and all-round green on side a vessel may pass.

A RAM vessel has reduced manoeuvrability and is given priority under Rule 18.

Rule 28: Vessels constrained by their draught

A vessel constrained by her draught (a power-driven vessel which because of her draught in relation to the available depth of water is severely restricted in her ability to deviate from the course she is following):

• Three all-round red lights vertically in addition to the lights for power-driven vessels under Rule 23.
• Day shape: a cylinder.

The constrained-by-draught designation is increasingly relevant for very large container ships and bulk carriers in port approaches and shallow channels. Other vessels under Rule 18 should avoid impeding her passage.

Rule 29: Pilot vessels

A pilot vessel on duty exhibits:

• Two all-round lights vertically: white over red.
• Sidelights and sternlight when underway.
• Anchor lights when at anchor, plus the white-red identification.

A pilot vessel not on duty shows lights as a vessel of similar size in the same role (e.g., as a power-driven vessel underway).

The pilot identification supports recognition of pilot vessels by approaching ships expecting to embark a pilot.

Rule 30: Anchored vessels and vessels aground

Anchored vessel

A vessel at anchor exhibits:

• Forward: an all-round white light.
• At or near the stern, lower than the forward light: another all-round white light.
• Day shape: a black ball forward.

For vessels of less than 50 metres, only the single forward all-round white light is required (no second light or shape).

For vessels of less than 7 metres, only required if anchored in or near a narrow channel, fairway, or anchorage where other vessels normally navigate.

In addition, if practicable, the vessel may use the working lights to illuminate the deck (especially for large vessels with crew working).

Vessel aground

A vessel aground exhibits:

• The anchor lights as above.
• Two all-round red lights vertically.
• Day shape: three black balls vertically.

The aground signals identify a stationary vessel that may be in shallow water and that other vessels must avoid.

Rule 31: Seaplanes and WIG craft

A seaplane on the water exhibits, where practicable, lights similar to those required of vessels of similar size, with adaptations for the specific configuration. Where compliance is impractical, lights as nearly similar as possible to those required for vessels of her size and type.

A WIG craft on takeoff, landing, or in flight near the surface exhibits, in addition to the lights prescribed for power-driven vessels, a high-intensity all-round flashing red light.

The seaplane and WIG provisions have been refined through 2001 amendments to address the operational realities of these unusual vessel types.

Annex I: Positioning and technical details

COLREG Annex I provides detailed technical specifications:

• Vertical positioning: spacing between vertical lights, height above hull.
• Horizontal positioning: longitudinal placement of masthead lights.
• Sidelight positioning: angle and shielding to ensure correct horizontal arc.
• Light intensity: in candelas, with conversion to visibility range.
• Colour specifications: chromaticity coordinates for white, red, green, yellow.
• Vertical sectors: ensuring lights remain visible at heeled conditions.
• Manoeuvring light: optional all-round white forward of the masthead light for indicating intended manoeuvres.

Modern technology and navigation lights

LED navigation lights

LED (light emitting diode) navigation lights have largely replaced traditional incandescent and halogen lights in new construction:

• Energy efficiency: 50 to 80 percent less power consumption than equivalent traditional lights.
• Long lifetime: 50,000 to 100,000 hours typical.
• Reliability: solid-state with fewer failure modes.
• Colour stability: better adherence to chromaticity specifications over lifetime.
• Initial cost: higher than incandescent but offset by lower lifecycle cost.

LED nav lights must meet the same COLREG visibility ranges and chromaticity specifications as traditional lights. Type approval through the relevant certification bodies (USCG, MED, IACS, etc.) verifies compliance.

Light failure detection

Modern navigation lights typically include:

• Failure detection: monitoring whether each light is operating.
• Bridge alarm: alerting the watchkeeper if a light fails.
• Backup lights: especially for masthead and sidelights in some installations.
• Reduced power mode: for power conservation in battery-supply situations.

Light failure during operations requires immediate corrective action under Rule 5 (lookout); a failed light essentially makes the vessel “not under command” or restricted in normal operation.

Type approval

Navigation lights must be type-approved by recognised authorities:

• MED (Marine Equipment Directive) in EU waters.
• USCG for US flag and US ports.
• Class society approvals under various flag states.
• IALA standards for some applications.

Type approval ensures the light meets the COLREG visibility, chromaticity, and durability requirements.

Sound and Light Signals interaction

Lights and Shapes interact with the Sound and Light Signals (Rules 32-37), collectively the COLREG visual and audible communication system. Specific interactions:

• Manoeuvring light under Rule 34 may be used to indicate intended course changes.
• All-round flashing yellow for hovercraft and WIG.
• Distress signals under Rule 31 in conjunction with Annex IV.

The combination provides redundant visual and audible communication for collision avoidance.

Rule 19 (restricted visibility) interaction

In restricted visibility, the Lights and Shapes are used together with the sound signals of Rule 35:

• Lights at all times (not just at night) when in or near restricted visibility.
• Fog signals under Rule 35 supplement the visual identification.
• AIS and radar become primary identification with lights as supplementary.

The fog procedure is particularly demanding in mixed-visibility conditions where some traffic is visible and other traffic is not.

Specific scenarios and lights

Tanker cargo operations

Tankers in cargo operations:

• Underway with cargo operations: standard Rule 23 power-driven vessel lights.
• At anchor with cargo operations: anchor lights plus possibly RAM lights if cargo system creates manoeuvrability restrictions.
• Berthed: working lights for personnel safety; navigation lights typically off when alongside.

Container ship operations

Container ships:

• Underway: standard Rule 23 power-driven vessel.
• High deck cargo: may obstruct line-of-sight to certain lights, requiring specific positioning.
• Engaged in container handling at anchor: anchor lights plus working lights.

Ro-ro and cruise ship operations

Ro-ro and cruise ships:

• Underway: standard Rule 23.
• At anchor with passenger operations: anchor lights plus illumination.
• Berthed: working lights for passenger embarkation and disembarkation.

Naval and government vessels

Naval and government vessels:

• Generally exempt from civil light requirements when on military operations.
• Subject to COLREGs when in routine transit and not on operations.
• Adapted lights for some military operations (mine clearance, etc.).

Lights and shapes in unusual conditions

Heavy weather operations

In heavy weather:

• Light visibility may be reduced due to spray, rain, sea spray on glazing.
• Light positioning may shift due to ship motion, with ships heeling beyond design assumptions.
• Background motion of waves and weather creates visual clutter.
• Reduced confidence in light identification, increasing reliance on radar/AIS.

The mariner’s response in heavy weather is increased vigilance, slower speeds where appropriate, and tighter integration of visual identification with other observation methods.

Night vision considerations

Night vision considerations:

• Bridge lighting: red night lighting maintains crew dark adaptation.
• Light glare: own ship’s deck lights can blind the watchkeeper to distant navigation lights.
• Adaptation time: 20 to 30 minutes for full dark adaptation after exposure to bright light.
• Eye strain: prolonged watch in low light fatigues vision; rotation supports continued vigilance.

The night vision considerations affect both Rule 5 (lookout) and the practical effectiveness of the lights and shapes system.

Ice operations

Ice operations have specific lights and shapes considerations:

• Icing on light fittings: can obscure light or alter chromaticity.
• Heating systems: navigation lights in polar service typically include de-icing.
• Limited daylight in polar winters: lights may be required for extended periods.
• Polar Code provisions: under Polar Code Part I-A.

Restricted visibility operations

Restricted visibility (fog, heavy rain, snow):

• Lights at all times even by day.
• Sound signals supplement visual identification.
• Radar becomes primary: lights are still relevant but secondary.
• AIS supplements: identification of nearby vessels by name.
• Reduced effective range: lights may be visible at less than rated visibility range.

The fog procedure is the principal application where lights and shapes integration is most challenging, and where bridge resource management discipline is essential to maintain situational awareness through coordinated use of multiple observation methods including visual, radar, AIS, sound signals, and continuous communication with potential targets identified through the available means, with the master assuming primary responsibility for collision avoidance decisions in restricted visibility scenarios.

Lights and shapes evolution

Switch-on procedures

Navigation light switch-on:

• Sundown: lights typically switched on at sunset or when approaching sunset.
• Restricted visibility: lights also displayed during fog, heavy rain, snow regardless of time.
• Approaching restricted visibility: lights switched on in anticipation.
• Departing port at night: lights on before leaving berth.
• Arriving port at night: lights remain on through approach and berthing.

The switch-on is typically integrated with bridge automation, with photocell detection of ambient light or with manual control by the watchkeeper.

Light maintenance during operations

During voyage operations:

• Daily verification of all navigation lights operational.
• Watch handover: outgoing watchkeeper confirms light status.
• Failure response: immediate spare light installation or repair.
• Spare lamp inventory: maintained on board with sufficient quantity.
• Battery condition: for emergency-power lights.

The maintenance discipline prevents light failures from compromising collision avoidance.

Bridge light controls

Modern bridge light control panels include:

• Master switch for all navigation lights.
• Individual light switches for masthead, sidelights, sternlight, anchor, etc.
• Failure indicators for each light.
• Automatic dimming/brightening for night vision considerations.
• Remote control from various bridge positions.
• Integration with general bridge automation.

The control panel layout follows IMO ergonomic guidelines under SOLAS Chapter V Regulation 15.

Light positioning verification

Light positioning is critical for COLREG compliance:

• Survey at construction: positioning verified during shipyard construction.
• Periodic verification: typically at periodical surveys.
• After modifications: re-verification when ship is modified (extension, conversion).
• After collision damage: re-verification after collision repairs.
• Documentation: positioning recorded in ship’s drawings.

Incorrect positioning can affect light arc visibility and lead to misidentification by other vessels.

Lights and shapes training

STCW provisions

Crew training under STCW:

• Section A-II/1: officer in charge of a navigational watch on ships of 500 GT or more must demonstrate competence in identifying lights and shapes.
• Section A-II/2: master and chief mate similar.
• Section A-II/4: ratings forming part of a navigational watch.
• Bridge resource management: includes lights and shapes recognition as part of situational awareness.

Practical training

Practical training methods:

• Simulator-based: bridge simulators with realistic light patterns.
• Charts and diagrams: classroom learning of light combinations.
• Live observation: at-sea training during routine watches.
• Quiz and assessment: periodic verification of recognition ability.

The training ensures officers can rapidly identify other vessels and apply the correct COLREG rules.

Refresher training

Refresher training at intervals:

• STCW certificate validity: 5-year cycle requires refresher.
• Operator-specific: many operators require additional refresher training.
• Post-incident: after any collision or near-miss involving recognition issues.

Specific vessel light combinations

Tug with tow combinations

A vessel towing exhibits combinations depending on the tow length:

• Tow under 200 m: two masthead lights vertically + sidelights + sternlight + towing light + diamond shape.
• Tow over 200 m: three masthead lights vertically + sidelights + sternlight + towing light + diamond.
• Pushing alongside: two masthead lights vertically (without towing light).
• Tow being towed: sidelights + sternlight + diamond if over 200 m.

The complexity of tow combinations reflects the variety of tug-tow operations and the need for clear identification.

Mine clearance vessels

Mine clearance vessels under Rule 27 exhibit:

• Standard power-driven vessel lights under Rule 23.
• Three all-round green lights at the foremast and at each side of the foremast yardarm.
• Day shapes: three black balls in triangular configuration (one at the foremast, one at each yardarm).

The lights and shapes warn other vessels of the mine clearance operation and the need to keep clear by at least 1,000 metres.

Diving operations

Vessels engaged in underwater operations (diving, salvage, etc.) under Rule 27 exhibit:

• Three all-round lights vertically: red, white, red.
• Two all-round red lights to indicate the side on which obstruction exists.
• Two all-round green lights to indicate the side on which another vessel may pass.
• Day shapes: ball, diamond, ball; plus rigid replicas of code flag “A” (white-blue) at least 1 m high (small vessels).
• Diving flag (code A): traditional indication of “diver below, keep well clear”.

Pilot vessels in different operating modes

Pilot vessels exhibit different lights depending on operational status:

• On duty, underway: white over red all-round + sidelights + sternlight.
• On duty, at anchor: white over red all-round + anchor lights.
• Off duty: lights as for similar-sized vessel in same role (typically power-driven vessel under Rule 23 if underway, anchor lights if at anchor).

The pilot identification supports the post-arrival pilot embarkation procedure under SOLAS Chapter V Regulation 23.

High-speed craft and WIG

High-speed craft (HSC under SOLAS Chapter X):

• Standard Rule 23 power-driven vessel lights.
• Optional all-round flashing yellow when operating in displacement mode.
• Speed-of-light considerations: at very high speeds, identification time is reduced.

WIG craft:

• Standard Rule 23 power-driven vessel lights.
• High-intensity all-round flashing red when in flight near surface, on takeoff, or landing.
• Day equivalent: special considerations for WIG operations.

Submarines

Submarines on the surface:

• Standard Rule 23 power-driven vessel lights when surfaced and underway.
• Yellow rotating light in some navies (national variant).
• Day shape: typical for power-driven vessel.

Submarines submerged: not subject to surface vessel light requirements but typically identified through other means (sonar, radio communication).

Lights and shapes in PSC inspection

Inspection focus

PSC inspection of lights and shapes covers:

• Type approval certificates for installed navigation lights.
• Visual inspection of light fittings for damage, fading, soiling.
• Operation test of each light from the bridge control panel.
• Failure detection system functional test.
• Spare lights carriage as appropriate.
• Day shapes carriage and condition (typically stowed but accessible).
• Crew familiarity through interview and demonstration.

Common deficiencies

Common Annex V deficiencies in PSC inspection include:

• Light failure: navigation light not operating, often discovered during night-time inspection.
• Sidelight obstruction: equipment, mast structure or cargo blocking light arc.
• Wrong colour: degraded lens producing off-spec colour temperature.
• Failure detection inoperative: bridge alarm not functioning.
• Day shapes missing or damaged: black balls, cones, diamonds not on board or unusable.
• Crew unfamiliar with light operation: from bridge or with manual operation.

A serious lights and shapes deficiency can result in detention, especially if the vessel is about to depart for a night transit.

Detention triggers

Specific detention triggers:

• All masthead lights inoperative.
• Both sidelights inoperative.
• Sternlight inoperative when no overtaking situation exists.
• All anchor lights inoperative when at anchor.
• Day shapes for NUC, RAM, anchor, or aground vessels missing.

The detention reflects the safety-critical nature of the visual identification system.

Lights and shapes in casualty investigation

Recognition failures

Casualty investigations frequently identify recognition failures:

• Failure to identify a fishing vessel as engaged in fishing under Rule 26.
• Failure to identify a NUC vessel under Rule 27.
• Failure to identify a tug-tow combination under Rule 24.
• Misinterpretation of light pattern leading to wrong COLREG application.

The investigations emphasise the importance of crew training in light recognition and bridge resource management in identifying observed targets.

Light condition factors

Condition factors affecting light recognition:

• Background lighting: shore lights, harbour illumination, other vessels’ lights creating visual clutter.
• Weather: rain, fog, snow reducing visibility and chromaticity perception.
• Ship’s motion: rolling and pitching affecting light alignment.
• Distance: light intensity reduces with distance per inverse-square law.
• Atmospheric clarity: dust, haze, smoke reducing transmission.

Each factor can lead to misidentification or failure to identify a target.

Lights and shapes evolution

Historic development

Navigation lights evolved through:

• Pre-1850: no standardised lights; collisions common in busy waters.
• 1840s-1860s: regional adoption of red-port green-starboard convention.
• 1889: first International Conference on Navigation Lights and Rules.
• 1910 conference: formalised international system.
• 1948 conference: refined post-WWII shipping context.
• 1972 COLREG: current system adopted.

Future evolution

Future evolution of lights and shapes likely includes:

• AIS supplementation as the primary identification mechanism for some categories.
• Enhanced LED features (intensity adjustment, condition monitoring).
• Specific WIG and high-speed craft adaptations as those vessel types proliferate.
• MASS (autonomous ship) provisions as autonomous shipping develops.
• Drone and unmanned surface vehicle (USV) provisions for emerging maritime operations.

The evolution will continue through IMO MSC consideration in coming decades.

Documentation

Every vessel maintains:

• COLREG copy on board.
• Navigation light specifications in the ship’s manual including type approval.
• Light maintenance records.
• Crew training records in nav light recognition under STCW.
• PSC inspection records.

Related Calculators

• COLREG - Vessel identification by lights Calculator
• COLREG - Navigation light visibility range Calculator

See also

• COLREGs Convention parent article
• COLREGs Steering and Sailing Rules: Rules 4 to 19
• SOLAS Chapter V: Safety of Navigation
• AIS and ECDIS
• STCW Convention

References

• IMO, Convention on the International Regulations for Preventing Collisions at Sea (COLREG), 1972, as amended.
• IMO COLREG Annex I (Positioning and technical details of lights and shapes).
• IALA Maritime Buoyage System.
• IEC standards for navigation light specifications.
• MED (Marine Equipment Directive) approval documentation.
• USCG navigation light type approval documentation.