Geometry and Hydrostatics
The LCU-501 class of utility landing craft were originally rated as landing craft, tank (LCT(6)). In 1949, they were redesignated as utility landing ships (LSU) to reflect varied employment. In 1952, the designation was changed to utility landing craft (LCU) and they were classified as service craft. There are presently 23 active utility landing craft in the LCU-501 class series, the LCU-509, which was reclassified as YFU-54 in March of 1966, is typical of this class. The total overall length including the stern anchor brace is 119 feet. The actual hull length is 114.5 feet. The length between perpendiculars is 105 feet. Extreme beam is 32.75 feet and the depth to the vehicle deck amidships is 5.5 feet, with a bulkwark extending up to 10 feet above the baseline. The mean design draft is 3.75 feet to the molded baseline. Height to the top of the forward anchor light mast from the design waterline is 21.17 feet and the height to the top of the main mast from the design waterline is 44.08 feet. When the mast is stowed on deck, the highest point is the T.C.S. antenna atop the pilot house. The height of the top of this antenna from the design waterline is 27.08 feet. Light displacement is 140 tons saltwater and load displacement is 310 tons saltwater. Quarters are provided for the 2 CPOs and 11 crew members in three 3-tier berths and two 2-tier berths.
The vessel is constructed of all welded steel. Transverse frames are spaced 2 feet from the fore perpendicular through frame 52 which is 1 foot forward of the transom. The structural support for the cargo deck is provided by eight transverse bulkheads.
Nontight longitudinal bulkheads, 3.5 feet off centerline, run the entire length and watertight bulkheads, 10.75 feet off centerline, run 82 feet through the engine room to the fore peak tank. These ships were constructed in three sections for transportation to advance bases. The forward section extended 30 feet from the fore perpendicular to frame 15, with the bow ramp in the raised position, the total length of this section is 39.5 feet. The midsection extended from frame 15 to frame 39 for a total length of 48 feet. The after section extended from frame 39 to the transom with a total length over the anchor brace of 31.5 feet. It is probably that the joints between sections are permanently welded on all existing vessels of this class.
The stern anchor is stowed over the port side of the transom for ready release and retrieval during beaching operations. The anchor winch is located on the poop deck port side above the crews quarters. The bow ramp is lowered by gravity and raised with a block and tackle arrangement using a hand ramp hoist on the starboard side or a powered ramp winch on the port side. A lever arm, similar to a gaff boom, is welded to the base of the main mast and extends aft where a stay connects the end to the up-port part of the mast and a cable runs down to a hand winch mounted on the poop deck, starboard side, that is used for lowering the mast to a horizontal position along the pi lot house top. A forestay and braces are fitted to support the mast when it is cranked up to the vertical position. A grating walkway at poop deck level connects the port and starboard deck houses for athwartship access. This walkway can be removed for moving vehicles along the main deck aft.
The LCU-501 class landing craft are propelled by three 225-brake-horsepower gray marine diesel engines. The propulsion system drives the ships at a maximum speed of 9 knots. At a cruising speed of 7 knots, the 11.12-ton fuel capacity gives a range of 700 nautical miles.
The LCU-509, which is typical of the LCU-501 class series, is a light but extremely rugged vessel designed for direct "on the beach" loading and unloading. The nature of the vessel also permits loading and unloading at the stern. Having a light draft, it is ideally suited for operation on inland waterways, or on any other shallow water. Equipped with a bow ramp, cargo such as vehicles and livestock can be driven directly from the beach onto the craft. The vessel is capable of transporting a maximum of four tanks or 200 tons of cargo. The bottom is especially designed for "beaching" with a resulting minimization of danger from snags and sandbars. Docking facilities are not required.
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