MSC Texas, one of the world’s largest container ships, was intending to visit the Port of Long Beach and required access up the “back channel” to berth. The back channel is 315 feet wide and about 7,000 feet long. The vessel is 140 feet wide, leaving just 88 feet each side (on the surface) at the narrowest section. Some minor dredging was proposed to increase the side clearance in specific places, but this was not completed in time for the first visit.
The main challenge was to provide a visual aid to navigation which would be accurate enough for the pilots to assess the exact position and movement of the vessel during transit. Two-station ranges were not an option because of the cost of new towers, and nowhere to place them.
The proposal was to place a PEL Sector Light on a 120ft tower at each end of the channel, one to be used by the pilots for entering and the other for exit. The locations are marked by the red arrows. Each light was fitted with 7 distinct sectors using just 3 colours. Vega’s “oscillating boundary” system was used to provide the four alternating sectors – in which the signal alternates sharply between two colours in a 3-second cycle. The closer the mariner is to the white sector the longer the white flash, etc. The time for each colour varies in proportion to the distance across the sector. The relatively short viewing range (1 mile) meant that the PEL-3-5° model had more than enough intensity for day operation. The intensity of each light is automatically reduced at night. Properly configured, a PEL Sector Light can give greater precision than a typical 2-station range.
A demonstration confirmed that PEL Sector Lights were capable of providing an extremely accurate visual signal suitable for guiding very large vessels into the most confined spaces.
The technique for using a PEL Light is for the pilot to take a couple of steps to one side, until a sector boundary is encountered. A complete colour change will occur in less than half a step sideways across a boundary - even when the light is more than 1 mile away.
The lateral distance back to the centre of the vessel can be assessed at a glance. The position of the vessel relative to the channel centre-line can be quickly estimated to within 2-3 feet. This transit was so tight that the vessel had to be held rigidly on a fixed bearing and only moved sideways with tugs and thrusters. There was no room to angle the vessel in the channel to adjust lateral position.
Initially the white sector was made exactly the same intensity as the colour sectors, but the white sector was later doubled to make the PEL Light easier to see against a bright blue sky background.