0

NAUTICAL CHART LIGHTS DEPICTION- INTRODUCTION

Written on 20 July 2017

Since the incorporation of the Royal Charter in 1514, the seaman welfare has been placed at the forefront of the safety at sea. The correct depiction of Lighthouses, beacons and related aids to navigation, regulating initially the pilotage of the River Thames became the prime responsibility of Trinity House with its statutory duty as a General Lighthouse Authority. Queen Elizabeth’s Seamarks Act of 1566 enabled Trinity House:

at their wills and pleasures, and at their costs, (to) make, erect, and set up such, and so many beacons, marks, and signs for the sea… whereby the dangers may be avoided and escaped, and the ships the better come into their ports without peril.”

Now Trinity House works jointly with several highly-specialised national and international organisations, including the Maritime & Coastguard Agency, the UK Hydrographic Office and the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA). The established co-operation between these organisations and their historical knowledge on the hazards, channels and coastline features contributes to the delivery of reliable, efficient and cost-effective aids to navigation, services and products such as nautical charts, pilots and Admiralty Lists of Lights for the benefits of all mariners.

To make an introduction to what a Light Symbol looks like on a nautical chart and visualise a typical example of a full Light Description on a metric chart as per UK Hydrographic Office publication 5011, below is the depiction:

⋆ Fl(3)WRG. 15s13m7-5M

Fl(3) Class or Character of light: in this example a group-flashing light, regularly repeated a group of three flashes.
WRG. Colours of light: white, red or green, exhibiting the different colours in defined sectors.
15s Period of light in seconds, i.e., the time taken to exhibit one full sequence of 3 flashes and eclipses: 15 seconds.
13m Elevation of local plane above height datum: 13 metres.
7-5M Luminous range in sea miles: the distance at which a light of a particular intensity can be seen in ‘clear’ visibility, taking no account of earth curvature. In those countries where the term ‘clear’ is defined as a meteorological visibility of 10 sea miles, the range may be termed ‘normal’. In this example, the ranges of the colours are: white 7 miles, green 5 miles, red between 7 and 5 miles.

An example of a light description on a fathoms chart using international abbreviations is shown below:

⋆ Al.Fl.WR. 30s 110ft23/22M

AL.Fl. Class or Character of light: in this example exhibiting single flashes of different colours alternatively.
WR. Colours of light shown alternatively: white and red all-round (i.e. not a sector light).
30s Period of light in seconds, i.e., the time taken to exhibit the sequence of 2 flashes and 2 eclipses: 30 seconds.
110ft Elevation of local plane above height datum: 110 feet.
23/22M Range in sea miles: Until 1971 the lesser of geographical range (based on a height of eye at 15 feet0 and luminous range was charted. Now, when the charts are corrected, luminous (or normal) range is given. In this example, the luminous ranges of the colours are: white 23 miles, red 22 miles. The geographical range can be found from the table of Admiralty List of Lights (for the elevation of 110 feet, it would be 16 miles).

 

Add comment