Sailboat navigation lights: a working COLREG guide

A light that glows is not necessarily a compliant light. At night, a yacht’s pattern tells another watchkeeper what kind of vessel is approaching, which way it lies and how it is being propelled long before hull details become clear. This guide turns the COLREG framework into a usable onboard method, while leaving the governing text, local rules and equipment instructions as the final authority.

Treat the pattern as a message

COLREG Part C contains the rules for lights and shapes, spanning Rules 20 to 31. Rule 20 applies the lighting provisions from sunset to sunrise and also calls for prescribed lights in restricted visibility during daylight. It also excludes other lighting that could be mistaken for navigation lights, degrade their distinctive character or interfere with a proper lookout.

Red and green sidelights reveal the port and starboard aspects, while the sternlight marks the after sector. Their boundaries matter because an observer uses the visible combination to infer relative heading. That inference should remain cautious: heel, waves, an obstructing sail or a deteriorated lens can change the pattern actually seen.

No light pattern awards an unconditional right of way. Lookout, safe speed, collision-risk assessment and the steering rules still govern the encounter, as the IMO summary of Parts A and B makes clear. Batoo’s analysis is that lights should be treated as one observation to test against bearing, relative movement and the surrounding traffic picture.

Switch the identity when propulsion changes

A sailing vessel underway under sail displays sidelights and a sternlight. Rule 25 allows a boat below 20 metres to combine those sectors into one lantern carried at or near the masthead where it can best be seen. This tricolour is an alternative arrangement, not another layer to display alongside the equivalent lower sidelights and sternlight.

Rule 25 offers a separate optional signal: two all-round lights in a vertical line near the masthead, red above green, shown in addition to separate sidelights and sternlight. Those red-over-green lights must not accompany the combined tricolour. A sound switchboard therefore needs to prevent mutually inconsistent combinations, rather than expecting a tired crew member to remember every exclusion.

Sails set do not preserve sailing-vessel status when machinery is also propelling the yacht. Rule 25 requires a cone, apex downward, forward by day, although vessels below 12 metres are not required to carry it; at night the displayed lights must identify a power-driven vessel under Rule 23. The operational trigger is propulsion, not merely whether the engine is running to charge batteries.

This distinction should be visible on the electrical panel. Separate selections for sailing, power-driven operation and anchoring, backed by a clear status indication, reduce mode errors. The exact interlock and circuit design remain boat-specific, but Batoo regards intelligible controls as a practical layer of risk reduction rather than cosmetic labelling.

Match visibility range to vessel length

Rule 22 sets minimum ranges for compliant lights, not guaranteed detection distances in every sea state. On vessels below 12 metres, sidelights have a 1-nautical-mile minimum while masthead, stern and all-round lights have 2-nautical-mile minima. From 12 metres to below 50 metres, sidelights, sternlights and all-round lights require 2 miles; the masthead light requires 5 miles, except that the figure is 3 miles below 20 metres.

Those numbers assume the full installation meets the applicable technical provisions. Brightness judged from a pontoon cannot establish compliance, because colour, horizontal and vertical sectors, placement and separation all affect the signal. Annex I supplies positioning and technical detail, so a replacement should be checked against the approved lantern and the yacht’s actual dimensions.

Rule 25 gives a limited alternative for a sailing vessel below 7 metres. Where the normal lights or combined lantern are not practicable, it must show an all-round white light or keep a white torch or lighted lantern ready to show in enough time to prevent collision. “Ready” should mean immediately reachable, charged and operable—not buried under gear.

At anchor the yacht presents another identity. Rule 30 permits a vessel below 50 metres to show one all-round white light where it can best be seen instead of the forward and after lights required in the basic arrangement for larger craft. Local designated-anchor-area exceptions may differ, so the skipper still has to check the waters being used.

Do not turn an LED retrofit into guesswork

An LED inserted into an incandescent lantern is not automatically an equivalent navigation light. The UK Maritime and Coastguard Agency warns that retrofitting a new source may invalidate the lantern’s type approval and advises consulting its manufacturer. Light source, coloured lens, optics, thermal behaviour and supply voltage work as one photometric system.

IMO Resolution MSC.253(83) defines a lamp broadly enough to include incandescent sources, LEDs and other non-incandescent technologies. More importantly, its definition of a navigation light includes the source, housing, position and the means that delimit the lighting angle. A component advertised as brighter may therefore make the assembled signal worse by shifting colour or bleeding across a sector boundary.

Before changing technology, record the lantern manufacturer, model, rated voltage, approval and permitted replacement. If the documentation does not establish compatibility, the fail-closed choice is the specified source or a complete approved fixture for the intended duty. Circuit protection, conductor sizing, watertight entries and voltage drop also need to remain consistent with the yacht’s design and manufacturer guidance.

No universal service interval can be responsibly invented for every light. Exposure, fixture construction and electrical architecture differ, so the maker’s inspection and replacement instructions control. A boat file containing manuals, approval markings, wiring diagrams and purchase records makes the next inspection far more reliable than an unlabeled spare-bin assortment.

Inspect the signal from outside the boat

The MCA guidance recommends checking every navigation light before leaving port, about an hour before use, periodically during the voyage, and especially at night or in poor visibility. A glowing indicator on the panel proves only part of the circuit. Someone outside should confirm the expected colour, sector and apparent output without obstruction in every selected mode.

Start with the optical surfaces. Salt, cracks and clouding reduce performance; ultraviolet exposure can yellow acrylic or polycarbonate, and lamp heat can craze plastic and diffuse the beam. Continue through seals, moisture, corroded contacts, mounting security, cable entries and loaded voltage, following the manufacturer’s safe test procedure.

A sailing yacht also needs a realistic obstruction check. Furled headsails, booms, tenders, solar panels and wind generators can conceal a sector that looked clear during installation. Batoo suggests an observation circuit from a safe distance with a helper, explicitly as a screening test: it can reveal gross shadows but cannot certify luminous range, colour coordinates or approval.

Operate every logical mode in turn: sail alone, machinery propelling, anchored, and off. Compare the actual fixtures with the panel labels and the wiring diagram, then record defects rather than working around them. A spare is useful only when it is the permitted replacement and can be fitted without compromising sealing or electrical safety.

Make uncertainty a reason to stop

Even a correct installation cannot make a congested night unambiguous. Shore lights, rain, fog, vessel motion and blind sectors can hide or distort a signal, which is why a proper lookout and safe speed remain fundamental. Electronics may support the watch, but they do not change what the yacht must exhibit or excuse a doubtful visual assessment.

The most useful handover is a small mode matrix beside the switchboard: vessel state, required selection, expected fixtures and independent visual confirmation. Build it from the applicable COLREG text, local provisions, approved equipment documents and the yacht’s wiring plan. If these sources conflict with what is installed, postpone night operation, document the discrepancy and have a competent marine electrician or surveyor resolve it.

That is the durable habit behind reliable sailboat navigation lights: identify the vessel truthfully, make incompatible settings difficult, and inspect what other mariners will actually see. Compliance is not the moment a bulb illuminates; it is the continuing integrity of the complete signal.