Publisher's Synopsis
Excerpt from Contract for Construction of Concrete Base for Light and Fog-Signal Station, on Mile Rock, at Entrance to San Francisco Harbor, California
The object of the contract to be entered into under these specifications is to construct the concrete base or pillar of a light and fog-signal station, to be erected on Mile Rock, entrance to San Francisco Harbor, Cal. This station is to consist of a monolith concrete base, enclosed by steel plates, resting on the rock at the level of mean, high water. This monolith is to be 34 feet high, and will cover an area of 704 square feet. On the top of this there will be a four-story tower made of structural steel, and surmounted by a lantern} The station will be provided with machinery, in duplicate, for a 10-inch fog whistle, to be operated by compressed air. The motive power of the compression machinery will be some form of mineral oil engine. Accommodations are to be provided for three keepers. The focal plane of the light will be 84 feet 3 inches above the datum plane, which is at the mean of lower low water.
Location - Mile Rock is about one half a mile inside a line joining the outer heads of San Francisco Harbor, and three eighths of a mile from the nearest point on the south Shore. It rises nearly vertical out of the water, which is from forty to fifty feet deep. It has an area at the level of mean high water of about square feet, and its highest point is sixteen feet above datum plane.
About one hundred and Sixty feet from the rock, on the inshore side, there is another smaller rock extending above high water, which may be found useful in the course of construction, for mooring purposes. Between these there is navigable water. The mean rise and fall of the tide in this locality is about six feet. The tide on both ebb and ?ood is very swift, and the duration of slack water small.
The ordinary summer afternoon winds of the locality will interfere with the construction work during its early stages - that is, until a height of five or Six feet above the foundation is reached.
Parties intending to submit proposals for the construction of this station should visit the locality and study the difficulties to be contended with.
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