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Navigation lights: sector, function and state

Rules 20–31 distinguish what a light shows and when an arrangement applies.

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Manual contents
In this guide
Top view with bow upwards: red port 112.5 degrees, green starboard 112.5, white stern sector 135. Separately, white masthead sector 225. Text identifies yellow towing 135 and all-round 360; nominal sectors without installation details.
Horizontal sectors · Rule 21

Original recognition schematic, not to scale; not navigation instruction.

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Top view with bow upwards: red port 112.5 degrees, green starboard 112.5, white stern sector 135. Separately, white masthead sector 225. Text identifies yellow towing 135 and all-round 360; nominal sectors without installation details.

A light has colour, sector, range and position; an arrangement communicates a state or activity. These are different questions.

Rule 21 defines sectors and Rule 22 minimum ranges, while Rules 23–31 address situations. Rule 20 supplies time and condition scope.

One white point does not prove a sailing vessel, and lights should not be selected merely because a lantern fits a bracket. The figure shows defined horizontal sectors rather than an approved installation or complete identification of an actual vessel.

Colour is meaningful only within the relevant arrangement.

Rule 20: nighttime, visibility and display

Part C applies in all weathers. Lights are required from sunset to sunrise; other lights must not be mistaken for them, impair their visibility or distinctive character, or interfere with lookout.

Prescribed lights, if carried, are also exhibited in daytime restricted visibility and may be shown when otherwise necessary. Shapes apply by day.

Lights and shapes must additionally comply with Annex I. Bright deck decoration can interfere with the message even where prescribed lanterns exist.

Time, visibility and technical conformity therefore accompany the question of which arrangement belongs to a vessel’s state.

Rule 21: sectors in plan view

The white masthead light covers 225 degrees, from ahead to 22.5 degrees abaft each beam. The red port and green starboard sidelights each cover 112.5 degrees, from ahead to 22.5 degrees abaft their respective beam.

The white sternlight covers 135 degrees, 67.5 either side of aft. The yellow towing light has the same stern sector.

An all-round light covers 360 degrees. The drawing keeps port on the left with the bow upwards, avoiding any dependence on an observer facing the vessel from ahead.

These are nominal horizontal sectors, not the whole technical photometric specification.

Masthead light is a defined term, not necessarily a lantern at the physical top of a sailboat’s mast. Rule 21 allows combined sidelights for vessels under 20 metres within its stated conditions.

Rule 22 ranges are specified by light and length, not guaranteed detection distances in every weather. For example, below 12 metres the minimum sidelight range is one mile, while masthead, stern and all-round lights have two-mile minima.

The rest of an installation and lawful alternatives cannot be deduced from those numbers alone.

Rules 23–25: propulsion, towing and sail

Rule 23 addresses power-driven vessels underway, including conditional alternatives below 12 metres and below 7 metres with maximum speed not exceeding 7 knots. Rule 24 addresses towing, pushing, composite units and inconspicuous objects, with its own conditions and exceptions.

Rule 25 addresses sail and oars: sidelights and sternlight, a permitted combined mast-top lantern for sailing below 20 metres, and other conditional possibilities. That tricolour combination is not exhibited with the red-over-green all-round lights of paragraph (c).

These distinctions are not optional decorative combinations and do not follow solely from hull type.

Rules 26–31: activity and special circumstances

Rule 26 distinguishes trawling, other fishing and outlying gear; Rule 27 separates not-under-command, restricted-in-ability, dredging, diving and mine-clearance states. Rule 28 permits additional draught-constrained signals, and Rule 29 concerns pilotage duty.

Rule 30 separates anchoring and grounding with length thresholds and conditional exceptions. Rule 31 addresses seaplanes and WIG craft where prescribed arrangements are impracticable.

A one-colour summary would lose state, vertical arrangement, additional signals and important qualifications. This lesson maps the provisions rather than certifying an installation or supplying an exhaustive identification chart.

Concepts in this lesson

Masthead light

Rule 21(a) white light covering 225° from ahead to 22.5° abaft each beam; not simply a light at the physical mast top.

Educational definition; consult the scope of the identified rule.

Sidelight

Red port or green starboard light, each covering 112.5° from ahead to 22.5° abaft its respective beam under Rule 21(b).

Educational definition; consult the scope of the identified rule.

Sternlight

White light near the stern covering 135° horizontally, 67.5° each side of aft, under Rule 21(c).

Educational definition; consult the scope of the identified rule.

Sources and references

  1. RIEAM / COLREGs — Rule 28: Vessels constrained by their draught ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 28, normative Portuguese printed p.48 (PDF p.54); International English cross-check in USCG handbook.

    Rule 28; IH normative Portuguese printed p.48, PDF p.54; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  2. RIEAM / COLREGs — Rule 25: Sailing vessels underway and vessels under oars ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 25, normative Portuguese printed p.39 (PDF p.45); International English cross-check in USCG handbook.

    Rule 25; IH normative Portuguese printed p.39, PDF p.45; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  3. RIEAM / COLREGs — Rule 26: Fishing vessels ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 26, normative Portuguese printed p.40 (PDF p.46); International English cross-check in USCG handbook.

    Rule 26; IH normative Portuguese printed p.40, PDF p.46; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  4. RIEAM / COLREGs — Rule 20: Application of lights and shapes ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 20, normative Portuguese printed p.29 (PDF p.35); International English cross-check in USCG handbook. Rule 21, normative Portuguese printed p.29 (PDF p.35); International English cross-check in USCG handbook.

    Rule 20; IH normative Portuguese printed p.29, PDF p.35; English International column cross-check. Individual provision commencement not established: valid_from remains null. Rule 21; IH normative Portuguese printed p.29, PDF p.35; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  5. Navigation Rules and Regulations Handbook — corrected August 2024 ↗

    United States Coast Guard Navigation Center · International column only, Rules 1–38 and Annexes I–IV. The adjacent U.S. Inland column is excluded.

    Official PDF directly consulted. International/Inland differences are not European rules. Filename says 08-12-2024; landing page says corrected 8 August 2024: no unsupported exact correction day inferred.

    Checked on
  6. RIEAM / COLREGs — Rule 23: Power-driven vessels underway ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 23, normative Portuguese printed p.31 (PDF p.37); International English cross-check in USCG handbook.

    Rule 23; IH normative Portuguese printed p.31, PDF p.37; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  7. RIEAM / COLREGs — Rule 22: Visibility of lights ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 22, normative Portuguese printed p.30 (PDF p.36); International English cross-check in USCG handbook.

    Rule 22; IH normative Portuguese printed p.30, PDF p.36; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  8. RIEAM / COLREGs — Rule 31: Seaplanes ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 31, normative Portuguese printed p.51 (PDF p.57); International English cross-check in USCG handbook.

    Rule 31; IH normative Portuguese printed p.51, PDF p.57; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  9. COLREGs Annex I — Positioning and technical details of lights and shapes ↗

    Instituto Hidrográfico / International Maritime Organization · Annex I; printed p.65, PDF p.71; International cross-check USCG.

    Annex I, IH printed p.65 (PDF p.71); cross-check International annex in USCG handbook. Installation/approval is not taught. International/Inland distinction checked in the USCG PDF: International §3(a) half-length/100m agrees with IH; the quarter-length/50m value belongs to U.S. Inland and is not imported. No dimensional installation prescription is reproduced.

    Checked on
  10. RIEAM / COLREGs — Rule 27: Vessels not under command or restricted in their ability to manoeuvre ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 27, normative Portuguese printed p.43 (PDF p.49); International English cross-check in USCG handbook.

    Rule 27; IH normative Portuguese printed p.43, PDF p.49; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  11. RIEAM / COLREGs — Rule 29: Pilot vessels ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 29, normative Portuguese printed p.49 (PDF p.55); International English cross-check in USCG handbook. Rule 30, normative Portuguese printed p.49 (PDF p.55); International English cross-check in USCG handbook.

    Rule 29; IH normative Portuguese printed p.49, PDF p.55; English International column cross-check. Individual provision commencement not established: valid_from remains null. Rule 30; IH normative Portuguese printed p.49, PDF p.55; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  12. RIEAM / COLREGs — Rule 24: Towing and pushing ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 24, normative Portuguese printed p.34 (PDF p.40); International English cross-check in USCG handbook.

    Rule 24; IH normative Portuguese printed p.34, PDF p.40; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on

Regulatory references

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