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Old 26-11-2011, 16:47
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Default Re: US Navy Floating Dry Docks


Going to start with AFDL47 simply because of a recent enquiry in the USS Laffey thread.

AFDL47 was designed by the Bureau of Yards & Docks, U.S. Navy for the Bureau of Ships. It was built by the Dravo Neville Island Plant, Pittsburgh, Pennsylvania, and launched on Saturday the 10th of August 1946. She was designated as ARD33, but as mentioned in post #1, the docks were re-classified in this year and the dock was known throughout her career as AFDL47.

The Auxiliary Repair Dock was the largest single group of floating drydocks built during the war, and as mentioned in post #1, were designed to accommodate destroyers, submarines, and other craft of comparable size. They were extensively used throughout combat areas and proved among the most useful, flexible, and effective facilities supporting the U.S. fleet.

Like all of the ARDís, ARD33 (AFDL47) had a nominal lifting capacity of 3,500 tons. She was 485 feet 8 inches long and 71 feet wide overall. This gave a usable length of 413 feet, a clear width of 49 feet 4 inches. The depth over the keel blocks was 21 feet.

The hull was an integral unit structure, and was strong enough to resist safely the maximum hogging, sagging, and torsional stresses to which the dock might be subjected in heavy storms at sea, and this made the ARD docks exceptionally rigid when in normal use.

The docks were well compartmented, both for maximum safety at sea or in combat and for optimum control of ballasting during docking operations. The bottom pontoon was divided by one longitudinal and four transverse bulkheads into eight ballast tanks. Each wing wall was divided into five ballast tanks, and, in addition, two tanks were provided in the bow, forward of the head wall of the inner dock. A watertight horizontal safety deck installed in the wing walls and bow precluded immergence below the minimum designed freeboard and helped to prevent undue trim or list at deep draft. These ballast tanks were interconnected by valved piping to two pumping plants, each consisting of two vertical shaft pumps rated at 15,000 g.p.m. at 12 feet head. The flooding and pumping system permitted submerging the dock to minimum freeboard in 50 minutes, and raising the dock and pumping the basin dry in 100 minutes. The ballast tanks were equipped with water-level indicators centralized in the control house, from which all pump and valve operations were also remotely controlled.

Above the safety deck in the wing walls were two machinery decks. The lower, or C, deck accommodated the pump and valve motors, small machines, welding equipment, and storage spaces. The upper, or B, deck accommodated the main diesel generators and other heavy equipment, as well as quarters and messing facilities for the crew. In the bow, the upper deck was omitted in order to provide adequate headroom for the hull repair shop.

ARD docks were equipped with four railway-type diesel engines directly connected to electric generators. As originally designed, provision was made for the installation of low-power electric-drive propulsion machinery, but in fact none of the docks was actually equipped with this propulsion, partly because of the urgent need for such equipment for ships, and partly because of its infrequent use.

All the ARD docks (with the exception of the original ARD1) had bottom-hinged stern gates that were that were closed by an electrically driven sprocket and roller chain device at either side, and opened by gravity. Operating difficulties with this mechanism led eventually to its replacement with hydraulic gate operating gear similar to that used in the ARD1 and providing positive force and control for both closing and opening.

These docks proved to have excellent towing characteristics. Many trans-Pacific movements were made at average speeds of 6 to 8 knots, using fleet tugs and auxiliaries of moderate horsepower. The one particular advantage, was their readiness for immediate service as soon as they were moored.

The need for more auxiliary facilities than could be accommodated on board the docks led to the provision of a covered wooden barge equipped as a carpenter shop for each dock. Keel blocks, cradles, and shoring timbers needed for docking or repairs were fabricated on the shop barge, which was moored alongside the drydock and supplied with power from it.

A vast number of combat vessels damaged in action or requiring graving of the bottom or other hull work below waterline were successfully docked in ARD's in the forward areas. This service to the fleet constituted a significant factor in the success of the Navy, particularly in the later actions in the western Pacific.

AFDL47, later named Reliance, had the unique record of being the largest vessel ever constructed and launched on inland waterways. After completion, it appears she was towed to New Orleans by the 1600 hp tug National (owned by the American Barge Line Co.). I have a record of her being at Guantanamo Bay, Cuba, from 1950 until 1952, and an ex-US Navy servicemanís personal record still placing her there in 1958. Then I find a mention of her being handed over to Groton Electric Boat Works in 1958. Not quite sure what happened next, but it appears that at some stage the U.S. Navy put her into Maritime Administration Reserve, until the 15th of May 1991 when she was leased to Detryens Shipyard, Mount Pleasant, South Carolina. After the lease expired in 2006, the U.S Government took posession of her and towed her to the Naval Weapons Station at Charleston. South Carolina. Detyens have now purchased AFDL47, and is in their yard at Charleston.

AFDL47_1: In 2006 undergoing a structural survey at Goose Creek Naval Weapons Station.
AFDL47_2: US Laffey docking/undocking at Detyens 2009
AFDL47_3: At Detyens with a barge onboard. Date unknown
AFDL47_4: Newspaper cutting announcing the launch

Original sources of photographs not determined. No copyright restrictions evident.
Attached Images
File Type: jpg AFDL47_1.jpg (658.1 KB, 47 views)
File Type: jpg AFDL47_2.jpg (589.0 KB, 41 views)
File Type: jpg AFDL47_3.jpg (624.1 KB, 33 views)
File Type: jpg AFDL47_4.jpg (411.9 KB, 19 views)
Clive Sweetingham

"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce
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