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Navy Lighterage (NL)

The idea to use hollow, sheet steel boxes as pontoons and pontoon-assembled structures originated in 1935. The standard pontoon unit and the principle of stringing such units together was developed in 1939 by Captain John N. Laycock of the Bureau of Yards and Docks and subsequently tested during 1940 and 1941.

When the United States entered World War II, the Navy was faced for the first time with the problem of landing and supplying large forces where conventional harbor facilities were occupied by the enemy. Navy Lightered (N.L.) pontoons were developed in 1942 to meet this difficult situation. They were designed for erection by naval personnel and shipment aboard Navy vessels. Naval officers conversant with invasion landing problems foresaw that many problems could be solved with assemblies of pontoon strings and conceived that they might be used for wharves, docks, piers, lighters, tugs, and special-duty barges. The importance of the contribution to the war effort made by the Seabees and their pontoons cannot be overemphasized. These pontoons proved to be an invaluable asset and were used extensively in operations during World War II, the Korean conflict, and again in Vietnam.

During World War II, PHIBCBs were designated Naval Construction Battalions, Pontoon, and were generally called Pontoon Operating Battalions. Pontoon-barge-mounted 75-ton booms unloaded PT boats from carriers under the noses of the Japanese in the Solomons. Pontoon-floating drydocks serviced damaged small craft in many parts of the world. Barge-mounted cranes deepened harbors, and loaded and unloaded vessels. In the campaigns of Sicily, Normandy, Italy, and the Philippines, causeways were indispensable in the rapid unloading of vehicle-borne cargo from LSTs. Rhino and smaller barges ferried cargo ashore, and pontoon tugs retrieved broached craft from the beaches, helped tow barges, and assisted in the installation of piers and wharves. All over the world, pontoon piers, wharves, and bridge units were used to create harbors or to increase the facilities of existing ones. It was learned during the invasion of Sicily that pontoon causeways provided an excellent method of rapidly unloading vehicle-borne cargo from LSTs. The shallow water of the southern beaches of Sicily effectively prevented LSTs from moving in close enough to shore to discharge troops and cargo. Consequently, the enemy made preparations for an assault from the North where the water was deeper. By using causeways between LSTs and the shore, allied troops and cargo were landed on the southern beaches and achieved the element of surprise.

The versatility of the Navy Lightered (NL) pontoon causeway system was shown during World War II. The system played a pivotal role in many amphibious operations, having been successfully used to build wharves, docks, piers, lighters, tugs, special-duty barges, causeways and other structures at locations around the world. Though various improvements were made to the pontoon gear after World War II, it wasn't until after the Korean War that the basic design was reviewed. Studies conducted from 1953 to 1955 resulted in an improved pontoon system design, known as the P-series, that was less costly, easier to fabricate, required fewer parts, and was more quickly assembled than the existing T-series pontoon system. It is this basic P-series design, with improvements, that is still in use today by the Navy.

Another significant improvement to the T-series causeway was providing a method of securing causeway sections end-to-end thus eliminating the overlapping of causeways as previously required. A series of end connection systems was developed and used over the years, including the Anderson-Nichols connector, the P-5 pontoon-link and padeye connector, and finally the P-8 pontoon-flexor causeway connector, which was adopted in the mid-1970's. Causeway width was also increased from 14- to 21-ft to create two traffic lanes.

Navy lighterage structures, when joined together, form a roadway to permit movement of vehicles, personnel and supplies from ship to shore during amphibious operations. In addition to bridging the gap between ships and the beach, floating causeways may be used as lighterage barges to transport vehicles and supplies to a wharf or to a beach, or may serve as piers for unloading small craft.

Self-propelled pontoon barges and tugs are powered by outboard propulsion units. These units have been specially designed for this purpose and readily installed on tugs or barges of any size. The propulsion unit is essentially a heavy-duty outboard motor, consisting of a propulsion mechanism and a marine diesel engine mounted on a heavy structural base. Propulsion power is carried from the engine through a right-angle housing and a vertical-drive housing to the propeller. Steering is affected by shifting the propulsion-force direction; the propeller can be turned around a vertical axis in either direction through a complete circle.

A barge is any of several pontoon string assemblies connected together to form a complete unit used for transporting cargo, including vehicles and personnel, and used primarily in their transfer from landing craft to amphibious vehicles or for lighterage duties in ship-to-shore movement of cargo. Barges, designed for lighterage operations, either self-propelled or towed, can be built in various sizes and, with modifications as required, can be used as a diving platform for salvage operations, as a tugboat, as a gate vessel, for fuel storage, or for mounting cranes.

A floating pontoon causeway consists of three distinct sections: a beach section, which provides a ramp to the beach; one or more intermediate sections, used to achieve the required length; and an offshore section, which provides the connection between the ship and the causeway.

NLS is a floating dock system designed to reach locations where conventional port facilities may be damaged, inadequate or non-existent. The system assembles at sea and connects together like building blocks to form ferries, causeway piers, or ships' ramp roll-off discharge platforms. NLS was developed during World War II as a method of moving equipment from ship to shore.

Beginning in the mid-1970's, significant improvements to the NL causeway system were made. New pontoon facilities, such as the Elevated Causeway (ELCAS) and Roll-On/Roll-Off Discharge Facility (RRDF) were developed. The outboard propulsion units on the warping tugs and causeway ferries were replaced with waterjet powered propulsion units.

Other improvements have been designed and tested, but not fielded. Some examples include providing the ELCAS with a RO/RO capability and replacing the beach causeway section's finger ramps with an articulated ramp.

The Navy Lighter (NL) section consists of 5 feet x 5 feet x 7 feet watertight welded steel pontoons permanently welded together to form 21 feet wide by 90 feet long causeway sections. The standard NL section displaces approximately 67.5 short tons.

NL sections are constructed out of 5 feet x 5 feet x 7 feet welded steel modules or pontoons which are bolted onto angle irons. Two angle irons are used to form a channel into which the pontoons will be secured. A string is completed by bolting angle irons along the upper edges of the pontoons. Strings are then bolted side-to-side to form the causeway section. A standard NL causeway section consists of three parallel strings, 15 pontoons long.

Typically, NL sections are constructed vertically on land. The pontoons are assembled on their sides so that one string can be assembled on top of the first string, and so forth, until the desired width of three strings is attained. Sections as wide as four strings have been successfully assembled using this vertical construction technique. Factors that control the size of the pontoon structure that can be sucessfully assembled on land include the capacity of available launching equipment and the stability of the structure. The site selected for the assembly must be close enough for a floating crane to reach, or located on the edge of a dock or pier so that it can be tipped into the water.

Deficiencies relating to the physical characteristics of the NL originate from the inherent qualities of the construction material and several basic elements in the design. The steel used in the construction of current causeways, when subjected to the harsh marine environment, suffers severe corrosive attack. Regardless of the care taken in surface preparation and painting, rust is a perpetual problem and the primary factor in the short seven to ten year lifespan of the current causeway sections.

Design deficiencies create special repair problems for the NL. The buoyancy provided by the individual watertight pontoons or "cans" contained in each NL section is often lost due to puncture. In such instances, the entire NL section must be removed from the water and the damaged individual pontoons must be torch-cut from the causeway for rehabilitation and repair. In discussing these problems, several causeway end-users expressed an interest in modularity - - specifically the capability to remove damaged portions of the causeway while the section is still in the water.

Further design deficiencies relate to deck fixtures. The large bolts used in the NL system to secure the pontoons are a design problem which creates a trip hazard, particularly during night operations. Additional trip hazards are presented by openings resulting from missing gratings on the NL surface inflicting what are described by causeway users as "gator-bites" (lacerations about the lower leg, knee and mid-thigh, incurred as a result of stepping into the opening presented by the missing gratings). Sailors aboard USS Comstock (LSD 45) successfully loaded a 270 ft. section of the Navy Lighter System (NLS) into the ship's well deck 09 December 2005, making it the first ship on the west coast to do so. NLS was never loaded onto a ship until recently in support of Hurricane Katrina. The operation went off without a hitch. There's a lot of capacity on the dock to carry vehicles, construction equipment and pallets of food and water. A craft like this makes it possible to get big loads ashore. Moving the system by ship will make it much more mobile. Comstock is a fully-capable amphibious ship with a well deck that allows them to take on a variety of different craft. A well deck is an open bay with a large opening at the back of the ship which allows amphibious vehicles to deploy and be retrieved. The ship's primary mission is to transport Marines.

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Page last modified: 07-07-2011 12:50:25 ZULU