User:Mliu92/sandbox/Hunter's Point gantry crane

The unnamed Hunters Point gantry crane at the San Francisco Naval Shipyard in the Bayview-Hunters Point neighborhood of San Francisco was the world's largest crane at its completion in 1947. It was designed with sufficient capacity to remove a battleship gun turret intact, but since battleships had become obsolete by the end of World War II, was instead used to refit aircraft carriers and later, to restrain Polaris missile airframe tests. After the Navy withdrew from the shipyard in 1974, the crane has been left as a prominent landmark, where it is easily visible for several miles in each direction.

History
In 1947 an enormous gantry crane with a 450 LT capacity was completed at the site by the American Bridge Company. It was the largest crane in the world, and was intended to be used to remove the turrets of battleships so the guns could be quickly replaced while the old set was being refurbished on land. The Hunter's Point crane succeeded YD-171, better known as Herman the German, as the largest crane in America.

Operation Crossroads decontamination
Following Operation Crossroads, radiologically contaminated ships were initially brought to Bikini for decontamination. As Bikini itself was radiologically contaminated, the ships were moved to Kwajalein Atoll, where the most heavily contaminated ships were scuttled. Preliminary decontamination was conducted at Kwajalein, but a shipyard was needed for more extensive decontamination procedure development, and Hunters Point was chosen in part for its access to academic facilities at Berkeley and Stanford.

Six target vessels were towed to Hunters Point following their participation in Crossroads: ex-USS Independence (CVL-22), ex-USS Gasconade (APA-85), ex-USS Crittenden (APA-77), ex-USS Skate (SS-305), ex-USS Skipjack (SS-184), and ex-USS Hughes (DD-410)

Operation Skycatch
In 1959, the crane was used for Operation Skycatch, where Polaris missiles were fired and caught via a string of arresting cables, before being lowered to the ground for testing. Previous versions of the test launched the missiles into San Francisco Bay where they would be later retrieved. Subsequently, the crane was modified for the UGM-73 Poseidon missile test facility by adding a 230 ft tall trapezoidal tower was added to the top of the crane, bringing its total height to nearly 500 ft. This made the crane the tallest man-made structure in San Francisco until the completion of 44 Montgomery in 1967. The structural members were lifted by Marine Boss in 1967.

The crane dominates the landscape in the area as it is easily visible from miles around.

Design
As completed in 1947, the crane had two independent hoists running along the gantry. The deck of the gantry on which the hoists ran is 182 ft above ground level, and the gantry is 730 ft long and 142 ft wide. The deck is built with the ends slightly elevated (by 12 in) to accommodate sag in the structure under full load. Levelling of the structure is accomplished through hydraulic jacks in the base of each tower.

Each hoist ran on rails on the gantry deck, and each hoist had a main and auxiliary hook. Each main hook had a individual capacity of 245 LT and could travel from 25 ft below sea level to 160 ft above (limited to 130.5 ft at maximum load). Each auxiliary hook had a capacity of 50 LT and could travel from 35 ft below to 191 ft above sea level. The two hoists combined weigh 1593 LT, and the gantry structure weighs 5700 LT. Power for the hoists is supplied through a substation located in one of the tower bases; incoming 11.5kV power is stepped down to 480VAC.

To reach its maximum capacity of 450 LT, the two hoists were coupled together and the main hooks were tied to an equalizing beam. The beam itself weighed 40 LT in addition to the combined 5 LT "biggest hook" attached to the middle of the equalizing beam. The maximum load can be lifted to 78.5 ft above the water. The hoist brakes are designed to slip when the load exceeds 150 to 170% of the rated capacity, to accommodate the rising and falling tides.

Gun Mole Pier
A new mole was built to accommodate the large crane, which is installed at the end of the mole. The mole is 1700 ft long by 405 ft wide, and required 3000000 cuyd of fill. Each end of the crane is cantilevered 162.5 ft over the water, allowing ships to tie up next to the mole for repairs facilitated by the crane. The concrete foundations for each tower rest on H-piles driven 100 ft deep.

The formal name for this mole is the Gun Mole Pier. The Navy has designated this area as Parcel D (sub-parcel D-1) at Hunters Point, and has identified it as radiologically impacted, meaning that it has the potential for, or is known to contain or have contained radioactive contamination, according to a radiological assessment conducted in 2004.