Auxiliary floating drydock


Auxiliary floating drydock are US Navy floating dry docks that are able to submerge under water and be placed under a ship in need of repair below the water line. Floating drydocks then rise up under the ship raising the ship out of the water. The ship is now blocked on the deck of the floating dry dock for repair. Most floating drydocks had no engine and are towed by tugboats to locations. Floating dry docks come in a different sizes to accommodate varying ship sizes. The large floating drydocks come in sections and can be assembled together to increase the size and lift power. Ballast pontoons tanks are flooded with water to submerge or pumped dry to raise the ship.

World War 2

When World War 2 started the US Navy had only three steel auxiliary floating dry docks:
To reduce travel time for repair work, over 150 auxiliary floating dry docks of different sizes were built during World War 2, between 1942 and 1945. These new floating dry docks built had a 400 to 100,000 ton lift capacity. Without these forward repair bases, ships would have to return to the states for repair. Between 1 October 1944 and 17 October 1945 7,000 ships were repaired in auxiliary floating dry docks. After World War 2 some of the auxiliary floating dry docks were sold for private use and a few were scrapped. Timber floating dry docks were built also for World War 2. These Timber floating dry docks had a lift capacity from 400 to 20,000 tons. These were not towed across the open ocean and were not given a US Navy class.

Role

Ships in continuous use during war need repair both from wear and from war damage such as naval mines, kamikaze attacks, dive bombs and torpedoes. Rudders and propellers are best serviced on dry docks. Without remote on location dry docks, months could be lost in a ship returning to a home port for repair.
Most auxiliary floating drydock had provisions for the repair crew, such bunk beds, meals, and laundry. Most had power stations, ballast pumps, repair shops, machine shops, and mess halls to be self-sustaining. Some of the auxiliary floating drydocks also had provisions for the ship under repair, but when possible, the crew of the damaged ship remained on their ship while repair was being made. Many had cranes able to lift tons of material and parts for removing damage parts and install new parts.

Armament

Most auxiliary floating drydocks only have anti-aircraft guns for defense, as space would not allow for large guns. Typical armament were 40 mm and 20 mm machine guns. Japanese pilots sometime mistook empty auxiliary floating drydocks for a type of aircraft carrier.

Large Auxiliary Floating Dry Docks (AFDB)

Auxiliary Floating Docks, Big, came in sections that are 3,850 tons and are 93 feet long each. Each Section had a 165 feet beam, a 75 feet molded depth and had 10,000 tons lifting capacity each. They are also known as Advance Base Sectional Docks. Sections could be put together to lift larger ships. AFDB were needed to repair battleships, aircraft carriers, cruisers, and large auxiliary ships. AFDB-1 Artisan had 10 sections for a total lift of 100,000 tons and was 1,000 feet long with all 10 sections installed. AFDB-1 to 7 were built between 1943 and 1945 and then towed to remote navy bases. An AFDB would have a crew of 600 to 1000 men, have a fresh-water distilling plant and be self-sustaining. They had a rail traveling 15-ton capacity crane with an 85-foot radius and two or more support barges. To pump out the water in the tanks there were two 24-inch discharge pumps on each section, each pump rated 15,000 gpm. For power there were two 350-kw diesel AC generators on each section, producing 440 volts 3-phase 60-cycle power. Had steam plants to run the pumps. Each section could store 65,000 gal. of fuel oil, this was to supply the ships under repair. For the crew to live next to the AFDB the Navy had barracks ships called APL, that dock next to the AFDB.
AFDM are from 6,800 to 8,000 tons and are from 528 to 622 feet long. AFDM has crew of 140 to 200 men. AFDM had a lift capacity 18,000 tons and armed with two 40mm and four 20mm guns. Had two 7 1/2 tons cranes with 16 ballast tank compartments. AFDM were built in three pieces, a long center section and two shorter sections at each end. All AFDM had Yard Floating Docks class numbers also.
Mobile are 5,200 tons and are 489 feet long. ARD had a ship form hull and lifting capacity of 3,500 tons. ARDM were used to repair destroyers, submarines, and small auxiliaries. ARDM has a crew of 130 to 160 men.
Auxiliary Floating Docks, Light. Also called Auxiliary Floating Docks. AFD were 288 ft long, had a beam of 64 ft, and draft of 3 ft 3 in empty and 31 ft 4 in flooded to load a ship. A normal crew was 60 men. AFDL displacement 1,200 tons and could lift 1,900 tons. AFDL were built as one piece, open a both ends. A few were AFDL has a crew of 30 to 130 men, living in a barge alongside the AFDL. Used to repair small crafts, PT boats and small submarines. All AFD were reclassified AFDL after the war in 1946.
Built by Pacific Bridge Company in Alameda, California, and are 483 feet long, beam of 71 Feet, and draft of 5 Feet. Ship displacement 4,800 tons. Crew complement 6 Officers and 125 Enlisted. Armament of Two single Oerlikon 20 mm cannon. ARD had a crew of 100 to 160 men. ARD have a bow and are sea worthy. They are self-sustaining with a rudders to help in tow moving and have two cranes with a 5-ton capacity. Normal also had stowage barge for extra space. Used to repair destroyers and submarines. Class 2 could repair Landing Ship, Tank. The stern of ship is open to have the ship in need of repair enter.
Auxiliary Repair Dock, Concrete were mobile drydock made of concrete, due the shortage of steel during the war. ARDC had a 2,800 tons lifting capacity. ARDC were 389 feet long, 84 feet wide, and 40 feet deep. ARDC has a crew of five officers and 84 enlisted men. Each had a 5-ton crane, with a 42 feet reach. Eight were built at Wilmington, North Carolina, and five at San Pedro in Los Angeles, California.
Yard Floating Dock was used for many types of floating docks. These were mostly used for harbor or shipyard use. YFD normally had no or little crew space and were serviced from shore. Some auxiliary Repair Dock were converted to YFD. Types of YFD were: 400-ton concrete docks, 1,000-ton, 3,000-ton and 5,000-ton wood docks; sectional wood docks from 7,000 to 20,000 tons lifting capacity and a three-piece self docking steel sectional docks with 14,000 to 18,000 tons lifting capacity. All Medium Auxiliary Floating Dry Docks were converted to YFD after the war.