Lights and Fog Signals

Lights and Fog Signals

• Lights are shown on Admiralty paper charts and ARCS charts as a light star with a magenta flare.
• The greatest detail will usually be found on the largest Scale paper / ARCS charts.
• The amount of detail reduces as the Scale of the chart decreases.
• Electronic Navigation Charts (ENCs) may be interrogated to display full details.
• The ALLFS (NPs 74-84) provides additional information not shown on paper / ARCS charts.
• The Admiralty Sailing Directions (‘Pilots') usually only provide the height and description of important light structures.
• The appearance of a light is called its ‘Character' or ‘Characteristic'.
• Lights may be Fixed, Rhythmic and Alternating.

Fixed Lights

• Fixed lights are those exhibited without interruption.

Rhythmic Lights

• Rhythmic lights show a sequence of intervals of light and dark, the whole sequence being repeated at regular intervals.
• Period: The time taken to exhibit one complete sequence.
• Phase: One element (e.g., Flash, Eclipse) of a sequence.
• Flashing: A Flashing light has a Phase of illumination shorter than that of darkness.
• Quick, Very Quick and Ultra Quick Flashing lights have flash rates per minute of 50-80, 80-160 and ‘over 160' respectively.
• Eclipse: A Phase where no light is visible.
• Group Flashing: A Flashing light in which a group of flashes, specified in number, is regularly repeated.
• Isophase: An Isophase light has a Phase of illumination the same length as that of darkness (Eclipse).
• Occulting: An Occulting light has a Phase of illumination longer than that of darkness (eclipse).
• Group Occulting: An Occulting light in which a group of eclipses, specified in number, is regularly repeated.
• Composite Group Occulting: Similar to a Group Occulting light except that successive groups in a Period may have different numbers of eclipses.

Alternating Lights

• Alternating lights are Rhythmic lights showing different colours during each sequence.
• Period: The Period of an Alternating light is the time taken to exhibit the complete sequence, including the change of colour.

Nomenclature of Lights

• See ALLFS for full details of nomenclature of lights.
• Intensity: The intensity of a light is its brightness, expressed in candelas or converted to Nominal Range.
• Elevation: The vertical distance between the focal plane of the light and the level of Mean High Water Springs (MHWS), Mean Higher High Water (MHHW), or Mean Sea Level (MSL).
• Luminous Range: The maximum distance at which a light can be seen, determined only by its intensity and the prevailing visibility.
• Luminous Range takes no account of Elevation, observer's height of eye or the curvature of the Earth.
• Nominal Range: Its Luminous Range for a meteorological visibility of 10 miles.
• Geographical Range: The maximum distance at which a light can reach an observer as determined by the height of the observer, the light's Elevation, and the curvature of the Earth.
• Loom: Diffused glow observed from a light below the horizon or hidden behind an obstacle, due to atmospheric scattering.
• Main Light: The major of two lights on the same or adjacent supports.
• Subsidiary (Auxiliary) Light: One placed near a Main Light and having a special use in navigation.
• Sector Light: Presents different colours or Characteristics in different directions. Sector limits are stated in true bearings (0°-360°) from seaward.
• Leading Lights: Two or more lights forming a Leading Line; their alignment is stated in true bearings (0°-360°) from seaward.
• Direction Light: Shows over a very narrow sector, forming a single Leading Light.
• This sector may be flanked by sectors of greatly reduced intensity, or by sectors of different colours or Character.
• Moiré Direction Light: Gives a yellow background to a screen on which a vertical black line is seen when on the centre-line. When off the centre-line, the vertical black line changes to black arrows indicating the direction to turn to regain the centre-line.
• Vertical Lights: Two or more lights disposed vertically, horizontally, or in a geometric shape, to distinguish them from single lights.
• Occasional Lights: Only exhibited when needed.
• Structure Descriptions: Heights, Bands, Stripes & Diagonal Stripes.

Admiralty List of Lights & Fog Signals

• Positions: Positions of lights are referenced to WGS 84 unless otherwise stated but may be approximate.
• Charts should be consulted for more authoritative positions.
• Aeromarine Lights: Aeromarine Lights included are marine-type lights in which part of the beam is deflected 10°-15° above the horizon for aircraft use.
• Aero Lights: Primarily for aircraft use; they are often of great intensity and Elevation.
• Obstruction Lights: Mark radio towers, chimneys etc.
• Daytime Lights: Daytime Lights are operated throughout 24 hours.
• Fog Lights: Lights shown only in Fog are marked accordingly.
• Fog Detector Lights: Fog Detector Lights are often bluish in colour.

Maximum Ranges of Lights

• Two criteria for determining the maximum range at which a light can be seen: the light must be above the horizon, and the light must be powerful enough to be seen.
• The range at which a light will be seen by the observer will be either the Geographical or the Luminous Range, whichever is the less.
• The ranges quoted in ALLFS for nominated countries is the Nominal Range, but for other countries Luminous Range is used instead.

Calculating Ranges

• Geographical Range: Can be calculated from a table in ALLFS.
• Luminous Range: May be calculated from a diagram in ALLFS.

Using Lights - Aide Memoire

• Check the Characteristics of a light on initial sighting.
• The ‘Rising or Dipping Range' of a light can only be approximate and must be used with particular caution if being used as a Position Line.
• Lights placed at high Elevations are often obscured by cloud.
• Distances: The distance of an observer from a light cannot be estimated from its apparent brightness.
• The distance at which lights are sighted varies greatly with atmospheric conditions.
• Ranges at which lights first appear can only be approximate.
• Sector Limits: The limits of light sectors should not be relied upon and should always be checked by compass bearing.
• Arcs of Visibility: The limits of arcs of visibility of lights are rarely exact, especially at short ranges.
• Glare from background lighting may considerably reduce the range at which lights are initially sighted.

Fog Signals

• Diaphone: Uses compressed air to issue a powerful low note, usually with a characteristic 'grunt' at the end of the note.
• Horn: Uses compressed air or electricity.
• Siren: Uses compressed air.
• Reed: Uses compressed air and emits a weak, high-pitched sound.
• Explosive: Produces short reports by firing explosive charges.
• Bell, Gong & Whistle: May be operated by machinery, by hand, or by wave action.
• Morse Code: Consist of one or more letters of the Morse Code.

Using Fog Signals - Cautions

• Fog signals should never be relied upon implicitly.
• Fog signals may be heard at greatly varying distances.
• The apparent direction of a Fog signal is NOT always a correct indication of its true direction.
• If a Fog signal is a combination of high and low notes, one of the notes may be inaudible in certain atmospheric conditions.
• There are occasionally areas around a station in which the Fog signal is quite inaudible.
• Fog may exist a short distance from a station and not be observable from it, so that the signal may not be operated.
• Some Fog signals cannot be started immediately Fog is detected.

Buoy and Beacon Types

• Buoys: Floating structures moored to the sea bed, used to mark channels and fairways, shoals, banks, rocks, wrecks and other dangers to navigation.
• Beacons: Navigational marks, erected as an aid to navigation, placed on or in the vicinity of danger, or onshore.

IALA Maritime System of Buoyage

• Consists of Lateral Marks, Cardinal Marks, Isolated Danger Marks, Safe Water Marks, Special Marks and Emergency Wreck Marking Buoys.
• Region A and Region B differences include color usage for port and starboard lateral marks.
• Lateral Marks are generally used for well-defined channels with a Conventional Direction of Buoyage, which indicates the port and starboard hand sides of the route to be followed.

Lateral Marks - Region A

• Used in well-defined channels with Direction of Buoyage and indicate the port and starboard sides of the route to be followed.

IALA Cardinal Marks

• Indicate that safe navigable water lies to the named side of the mark.

IALA Isolated Danger Marks

• Placed at isolated dangers of limited extent surrounded by navigable water.

IALA Safe Water Marks

• Indicate that there is navigable water all around the mark.

IALA Special Marks

• Used to indicate a special area or feature, the nature of which is apparent from a chart, used for ‘Ocean Data' marks, Traffic Separation Schemes (TSS).
• Emergency Wreck Marking Buoys are fitted with alternating Occulting blue and yellow lights, a Racon (Morse Code 'D') and an AIS transponder.

Using Buoys and Other Floating Structures for Navigation

• They must always be treated with caution, even in narrow channels.
• Buoys may quite easily drag or break adrift.
• Fix from charted shore objects or high accuracy electronic systems, and in Pilotage also run a Headmark / Sternmark with Clearing Lines.
• Always monitor the Echo Sounder and correlate it to the charted position.
• Always check the DR / EP against the other positions indicated.
• The concept of cross-checking all available sources of positional information applies to buoys; use buoys, but do NOT rely implicitly on them.

Automatic Identification System (AIS)

• AIS was introduced in 2002 and is a shipboard broadcast transponder system, using common digital VHF channel(s).
• AIS Class A provides full maritime functionality and must be carried by all vessels over 300 grt, from 1 July 2007.
• AIS may be used to assist collision avoidance decision making, but only as an additional source of information; decisions should be based primarily on visual and/or radar data.