Table 22-7 - Intensity Requirements of LampsThe International Maritime Organisation (IMO) and National Authorities prescribe the number, position and power rating of navigation lights aboard ships. By far the most common arrangement is to have five specially designed navigation 'running' lights referred to as Fore mast, Main mast (or Aft mast), Port, Starboard and Stern. Two anchor lights fitted forward and aft, may also be controlled from the Navigation Light Panel. The sidelights are red for port and green for starboard while the other lights are white. Special incandescent filament lamps are used each with a power rating of 65W, but 60W and 40W ratings are permitted in some cases. Due to the essential safety requirement for navigation lights, it is becoming a common practice to have two fittings at each position, or two lamps and lamp-holders within a special dual fitting. Each light is separately supplied, switched, fused and monitored from a Navigation Light Indicator Panel in the wheelhouse. The electric power is provided usually at 220V a.c. with a 'main' supply fed from the section of the main switchboard that is meant for the essential services. (Refer Figures 3.9 and 4.2). An 'alternative' or 'stand by' power supply is fed from the emergency switchboard. A changeover switch on the Navigation Light Panel is used to select the main or standby power supply. The Navigation Light Indicator Panel has indicator lamps and an audible alarm to warn of any lamp or lamp-circuit failure. Each lamp-circuit has an alarm relay which monitors the lamp's current. The relay may be electromagnetic or electronic. A basic double navigation light's schematic circuit with alternative power supplies is shown in Figure 22.10. A similar circuit is shown in Figure 22.11.
Obviously the light fittings are in exposed positions, so during maintenance checks, one should concentrate on water-tightness and on the condition of the supply cable.
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