CABRILLO Historic Structures Report

Figure 8. An overall view of Searchlight Shelter No. 15's structure visible above ground.

SEARCHLIGHT SHELTER NO. 15 (Preservation)

Location

This searchlight is located on the west side of Point Loma. The nearby generator that originally supplied power to it is no longer visible or accessible.

History

Constructed during WWII, this structure sheltered a 60-inch coastal searchlight previously mounted on a counterweighted elevator. The structure is similar to other structures at the monument dating c.1916-1921. The searchlight (now missing) and its operating mechanism were salvaged from the defunct, c. 1921 Searchlight No. 4. To prevent vandalism, the metal roof of the shelter was sealed, and the structure remains closed to the public.

Description

Exterior

This is a reinforced concrete, rectangular plan, multi-level underground searchlight shelter. The mechanized, hipped, riveted metal roof (figure 8), painted green, rests on a wooden curb. Metal rails mounted on concrete extend to the north, originally allowing the retracting roof to slide open, exposing the counterweighted searchlight platform and its searchlight. The interior of the shelter is accessed through a riveted metal hatch, also painted green, located in the southwest corner. An above-ground, concrete post formerly supporting a telephone box stands at the southeast corner of the shelter. The roof operating mechanism is located at grade at the northeast corner.

Interior

This multi-level rectangular space features concrete flooring and walls with visible formwork lines. The ceiling is the exposed underside of the steel roof. The shelter is accessed through a manhole at grade located in the southwest corner. Steel rungs embedded into the concrete wall serve as a ladder leading into the personnel portion of the shelter. Nine-feet-six-inches deep, the operator area contains a cable pit that provided electrical service from the nearby generator. The 15-foot, two-inch deep lower space, containing the counterweighted elevator, is accessed by a metal ladder. The elevator is operated manually with a chain sprocket drive (figure 9).

Condition

Exterior

The metal roof vent is missing from the roof of this structure, as is the original square metal entry hatch which was replaced with the current sheet metal one at some point. The roof exhibits heavy overall corrosion with concentrations at the edges. Corrosion appears at all riveted connections and at the metal half-round trim piece that is also bent. Heavy corrosion damage is present on the north and east sides of the roof. Originally retractable, the roof has been sealed closed. The wood curbs supporting the roof are deteriorated, especially to the south where the curb has split horizontally into two pieces. The concrete at the entry hatch exhibits cracks. Spalls are present along the beveled concrete edge that supports the roof assembly, especially on the west side. Reinforcing rod corrosion stains are visible on all concrete surfaces.

Interior

All steel elements exhibit corrosion. The base of the elevator framework is severely corroded. The concrete is generally in sound condition, although efflorescence is visible at the ceiling near the elevator gear traces and rust stains run down the west wall below the entry hatch. Graffiti on the south wall includes some appearing to date from 1946.

Structural Analysis

Similar to Searchlight No. 19, the concrete surfaces exhibit some spalling and cracking, which is relatively minor and does not at this time appear to compromise the structure's capacity. The concrete deterioration at this searchlight appears slightly worse than at Searchlight No. 19. The spalling at the concrete post appears to be the result of inadequate concrete cover to the reinforcing during the original construction.

Also similar to Searchlight No. 19, 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 9. Interior view of the elevator platform operating mechanism.