Visual Aids to Navigation

Reading Light Descriptions on Charts

Read Fl(2) WR 10s 15m 12M as one repeated group of two flashes, white and red sectors, a complete period of ten seconds, an elevation of 15 metres above the chart's stated height datum, a...

• Decode character, colour, period, elevation and nominal range in order
• Period is the complete cycle from one repeat point to the next

Light Sectors

IALA notes that a sector or sector limit may mark a fairway, turn, channel junction, hazard, deepest water, anchorage or another feature. A white fairway sector is commonly flanked by gre...

• A sector supplies directional information over a charted arc
• White often covers a fairway but is not universally safe at every range or draught

Lighthouses and Other Structures

Major fixed lights may be recognised by charted structure, daymark, light character, elevation and sometimes a fog signal. A fixed structure is useful bearing evidence once positively ide...

• Fixed aids support bearings after positive identification
• Floating aids can move within the mooring or be off station

Fog Signals

Charted audible aids include horns, sirens, bells, gongs and whistles. Horn(2) 30s describes two blasts in a complete 30-second period. Time the full character and compare it with current...

• Time the complete charted sound character
• Apparent loudness and direction do not give precise range or bearing

Range of Lights

Nominal range is the luminous range in a homogeneous atmosphere when meteorological visibility is 10 nautical miles. It is the value generally published on charts and in light lists. IALA...

• Nominal range uses the standard 10-nautical-mile meteorological-visibility convention
• Luminous range depends on intensity and prevailing atmosphere

Using Lights for Navigation

For each critical light, record the expected bearing window, sector or colour, character, period, detection range and surrounding sequence. Add the charted hazard or channel information t...

• Predict bearing, sequence, character, period and detection gate
• Promote provisional to identified only after independent agreement

Yachtmaster Offshore Standard

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 an...

Advanced Scenario: Visual Aids

A yacht is approaching a fictional harbour at night as rain reduces visibility. The plan expects an east cardinal mark followed by a white sector. An intermittent group of three white fla...