According to international navigational laws, navigation lights are the most important lights fitted onboard a ship. They help in safe manoeuvring of the ship, preventing accidents and collisions. As there are no signals or road-signs in the open sea, the navigational laws of ships are demonstrated using these navigational lights, which are strategically arranged on ship. They are differentiated on the basis of colours, visibility, range, angle and locations. The type of navigational lights used depends on the size and type of the vessel and rules specified by international conventions also known as rules of the road.
The international regulation for preventing collisions at sea (COLREGS 1972) describes the operation of navigational lights from sunset to sunrise and during time of low or poor visibility so that nearby ships can navigate safely after seeing the navigation lights.
Types of Navigational Lights
Five separate specially designed navigational lights are fitted at different positions on the ship as per the navigational rules. This gives easy identification of ships size, direction of travel, anchorage of the ship. Following are the different colours and positions where these navigation lights are fitted:
1.Foremast - Bright White
The foremast light has a horizontal arc range of 225 degrees.
2.Mainmast- Bright White
The mainmast light which is also known as all-round light has a horizontal arc visibility of 360 degrees.
3.Port side - Bright Red
The port side light horizontal arc visibility is 112.5 degrees.
4.Starboard side - Bright Green
The starboard side light horizontal arc visibility is 112.5 degrees
5.Stern of the ship- Bright White
The aft or stern light horizontal arc visibility is 135 degrees.
Apart from these five mandatory navigation lights, two anchor lights are fitted forward and aft and are bright white in colour. These lights are operated from the navigational bridge of the ship.
The power for the navigational lights is supplied from a separate distribution board which has no other supplies attached to it. This is done so that they cannot be put off by inadvertent operation of a wrong switch.
For vessels of length more than 50 m, the visibility range of the mast head lights is 6 N.M and all the other lights should be visible from a distance of 3 N.M. To achieve such visibility special incandescent filament lamps are used and the normal power rating is of 65 KW. In some cases 60 KW and 40 KW rating lamps are also permitted.
Due to the critical nature and essential safety requirement of navigational lights, they are fitted in duplex manner at each position. Two separate lamps or a lamp holder with dual fitting can also be used.
It is also to be noted that each light is separately supplied, switched, fused and monitored from the navigational wheel house. The supply is usually of 220 V and is fed from essential service section of main switch board and from emergency switch when there is a power failure. A changeover switch on the navigation light panel in wheel house selects the main or standby power supply.
The navigational light panel has indicator lamps and an audible alarm to warn off any lamp circuit failure. Each lamp circuit has alarm relay which monitors lamp current and in case of fault, sounds it on the bridge.
You may also read What is collision of a ship?.
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