CABRILLO Historic Structures Report

Figure 12. Only the metal roofs and a concrete post are visible above ground.

SEARCHLIGHT SHELTER NO. 19 (Preservation)

Location

This structure is situated on a bluff above the Bayside Trail, near Searchlight Shelter No. 18 and the Generator Station.

History

Constructed in 1918-1919, this World War I structure sheltered a 60-inch searchlight mounted on a counterweighted elevator. Originally named Searchlight No. 6, the searchlight shelter was renamed No. 12 in 1936 when additional searchlights were added to the coastal defense system. The searchlight was renamed No. 19 during WWII. This structure no longer contains a searchlight. The shelter remains closed to the public.

Description

Exterior

This reinforced concrete, multi-level underground structure features a square, mechanized roof that moves north on metal tracks embedded in concrete curbs. The riveted, metal hipped roof, painted green, rests on a wooden structure (figure 12). The roof slides north to completely expose the main room of the structure and the counter-weighted elevator platform below. A single, solid, riveted metal hatch, located at the south end provides access to the structure. A cog and chain roof opening mechanism is located at grade, west of the roof. An above-ground, single concrete post situated also to the west of the roof, originally supported a communications control box.

Interior

The interior is bi-level. The southern third of the space comprises the operator area, while the remainder drops down to house the searchlight lift. The space features concrete slab floors and walls with visible formwork lines. The exposed underside of the steel roof cover forms the ceiling (figure 13). The shelter is accessed through a manhole at grade. Steel rungs embedded into the concrete wall serve as a ladder leading into the upper, personnel portion of the shelter. Nine-feet, six-inches deep, this space contains a cable pit that provided electrical service from the nearby generator station, and a wood tongue-and-groove closet located in the southeast corner. The closet features a five-panel wood door and shelving. The 14-foot deep lower space containing the counterweighted elevator is accessed from the personnel area by a metal ladder. The elevator is operated manually with a chain sprocket drive. Traces of gray-green paint remain on the walls.

Condition

Exterior

Deterioration includes minor cracking at the concrete walls; rotting wood at the roof base; corrosion at the metal roof and platform mechanism; and cracking, spalling and exposed reinforcing rod at the concrete post. The metal cover is sound with some corrosion evident at the edge, although it is no longer firmly attached. Invasive vegetation covers part of the structure and the roof tracks.

Interior

The concrete walls exhibit minor deterioration including spalling concrete over the control area.

Structural Analysis

As noted above, the concrete surfaces have some spalling and cracking, which is relatively minor and does not at this time appear to compromise the structure's capacity. The spalling and exposed reinforcing rod at the concrete post appears to be the result of inadequate concrete cover to the reinforcing during the original construction.

As noted above, the steel elevator platform and frame for the searchlight, and the steel roof cover, are corroded. For the most part, this appears to be primarily superficial and is unlikely to have compromised the structural capacity of the main steel members. However the capacity of the bolts and brackets connecting the members together may have been reduced significantly.

Figure 13. The underside of the elevator platform viewed from the pit.