Starting at the Pacific entrance, vessels transiting the Panama Canal climb via the Miraflores and Pedro Miguel Locks then pass through the Gaillard Cut. The Cut comprises 7 separate reaches which slice through the continental divide. By 2001 this cut had been widened to 500 feet to enable 2-way traffic in this section. This widening had the potential to double the capacity of the locks by allowing Panamax vessels to ride the locks both up and down, rather than just up in the mornings and down in the evenings.
But even at 500 feet wide, there was barely 100 feet margin between the passing ships and the banks of the canal. Pilots called for land-based signals which would indicate a lateral deviation of just 20 feet from the “sailing line” even at viewing distances up to 15,000ft away (as in Bas Obispo, the longest reach). 2-station alignment-type signals were already in place on the banks at each end of the reaches, but the steepness of the bank limited the lateral spacing, and the sensitivity. A new solution was required.
The PEL Sector Light is a highperformance single-station light with a resolution better than 1 minute of arc. The optional oscillating boundary gave a signal which varied in proportion to lateral movement over the critical range of 10-50ft from the sailing line.
The dark earth and green jungle background provided favourable daylight viewing conditions (compared to a sky background). The relatively short viewing range (maximum 2.5 nautical miles) meant that the PEL-3-3.5° light had sufficient intensity for day operation. It was automatically dimmed at night.
The individual sectors were configured to give the same signal at the entrance to each reach, regardless of range.
fixed white 20 feet wide
alternating white/colour 42 feet wide (proportional)
fixed colour 208 feet wide
flashing red 42 feet wide
The Panama Canal Authority pilots determined that just 3 feet of lateral movement was sufficient to detect a complete colour change. This was much better that the 20 feet they had set as a minimum, and corresponded to 1.5 minutes of arc at the maximum range of 15,000 feet. The change in the white/colour ratio in the alternating sector was very sharp and enabled constant monitoring of lateral position and speed.