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AI-assisted editorial review · version 3 ·

Yacht lights: sailing, machinery and anchoring

The same hull can require different sets; a tricolour lantern is not a masthead light.

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Function map for a fictional10m yacht. Sail only: sidelights and sternlight, combinable under25(b). Machinery:23(d)(i) alternative, all-round white and sidelights. Anchor:30(b) alternative, all-round white and daytime ball. Functions are not all visible in one photograph; sectors and installation are not drawn.
The same yacht · three states

Original interpretation schematic with declared functions and references. No scale, approved installation or operational track.

insideSailOriginal insideSail artwork — all rights reserved
Enlarge the diagram
Function map for a fictional10m yacht. Sail only: sidelights and sternlight, combinable under25(b). Machinery:23(d)(i) alternative, all-round white and sidelights. Anchor:30(b) alternative, all-round white and daytime ball. Functions are not all visible in one photograph; sectors and installation are not drawn.

Consider a fictional ten-metre yacht. Sailing without machinery, using machinery for propulsion and anchoring change the relevant status.

Lights must correspond to that status. Switching on every lantern to be more visible can confuse the message, and some combinations are expressly incompatible.

Start with Rules 3, 20 and 21, then identify the provision in 23, 25 or 30. The drawing represents sets of functions, not wiring or an approved installation.

Under sail alone: sidelights and sternlight

Rule 25(a) prescribes sidelights, red to port and green to starboard, and a white sternlight. For a sailing vessel under twenty metres, 25(b) permits their combination in a lantern at or near the mast top where best seen.

It is commonly called a tricolour, but its three colours remain in sectors: they are not three all-round lights. One physical lantern can provide three defined functions.

The additional arrangement in 25(c) is red over green, both all-round, at or near the mast top, alongside the set in 25(a). It must not be used with the combined lantern in 25(b).

Red over green does not replace sidelights and sternlight on its own. Below seven metres, 25(d)(i) requires prescribed lights if practicable; otherwise a white electric torch or lighted lantern must be ready at hand and exhibited in sufficient time to prevent collision.

That alternative cannot be transferred to a ten-metre yacht.

Under machinery: a function change is not all lights on

Under Rule 23(a), a power-driven vessel underway shows masthead, sidelights and sternlight; the second masthead abaft and higher becomes compulsory from fifty metres and optional below. Masthead here means a white 225-degree light, not its location at the physical mast top.

A sailing tricolour does not provide that function. Rule 23(d)(i) allows an all-round white light and sidelights instead of 23(a) below twelve metres.

That is not the ordinary alternative at exactly twelve metres.

Anchoring and the figure’s limits

Rule 30(a) prescribes all-round white forward and another lower aft, but 30(b) permits one all-round white light below fifty metres where best seen. The ball is the day shape.

The under-seven-metre exception in 30(e) depends on location as well as length. Being aground differs and can add signals.

Minimum ranges come from 22; positioning, separation, sectors and approval come from Annex I.

The schematic’s colours and functions are exact for the stated cases; dot size is not intensity, range or lantern size. Not all sectors are visible from the same viewpoint.

This reading prepares checking an individual vessel’s light plan against technical documentation and the competent authority. It neither certifies an installation from a photograph nor derives encounter responsibility from one observed white light.

Sources and references

  1. 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
  2. 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
  3. USCG amalgamated rules — International current web cross-check ↗

    United States Coast Guard Navigation Center · International/shared Rules 3,20–30,32–35; International Annexes I–III. International-only wording identified by angle-bracket legend; all Inland insertions excluded. Rule35(j)/(k) compared with IH normative Portuguese printed55/PDF61 and English appendix89–90/PDF95–96.

    Directly read 11 October2026 alongside freshly fetched corrected-August2024 official handbook. Current page confirms under12 paragraph(j) and pilot(k); Portuguese IH agrees; its English appendix differs. Access is not qualified legal approval. No unsupported exact consolidation date assigned.

    Checked on
  4. 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
  5. RIEAM / COLREGs — Rule 2: Responsibility ↗

    Instituto Hidrográfico / International Maritime Organization · Rule 3, normative Portuguese printed p.3 (PDF p.9); International English cross-check in USCG handbook.

    Rule 3; IH normative Portuguese printed p.3, PDF p.9; English International column cross-check. Individual provision commencement not established: valid_from remains null.

    Checked on
  6. 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
  7. 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
  8. RIEAM / COLREGs — Rule 29: Pilot vessels ↗

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

    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

Regulatory references

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Sailing vessel under COLREGs

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