Yachtmaster Offshore Standard: Visual Aids

Before a night or reduced-visibility stage, record the expected aid, approximate bearing window, structure or topmark, colour, rhythmic character, complete period, sector, usable range and order in the sequence. Add the current publication or warning source and a decision limit: the last point at which the vessel can hold, turn away or use another route if the cue is absent or inconsistent.

Classify the observation rather than forcing a name onto it. Identified means the measured character and period, bearing, charted context and independent position evidence agree. Provisional means some useful attributes match but a material check is missing. Not identified means the observation conflicts, is too incomplete or could plausibly be another aid. Brightness, colour, one flash group or an approximate bearing cannot carry a close-water decision alone.

An expected light that is not seen does not provide a line of position. The vessel may be outside geographical or luminous range; visibility, background lighting, obstruction, sector geometry or serviceability may intervene; a floating aid may be off station; or the assumed vessel position may be wrong. Test these alternatives with current publications, depth, radar where fitted and operational, bearings, time and distance, and position evidence that does not merely repeat one sensor or chart source.

When visibility is restricted, loss of a visual cue is also a watchkeeping and collision-avoidance condition. Maintain a proper lookout by sight, hearing and all available appropriate means, keep safe speed under continuous review and use radar properly if fitted and operational. The correct Rule 19 action depends on the traffic situation; a light-identification exercise cannot prescribe a live course alteration.