CHAPTER 10 PONTOONS

When the United States entered World War 11, our Navy was faced for the first time with the problem of landing and supplying large forces in areas where traditional harbor facilities were controlled 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. These pontoons pro-veal to be an invaluable asset and were used extensively in operations during World War II, the Korean conflict, and again in Vietnam.

P-SERIES PONTOONS

P-series pontoons were used throughout the Republic of Vietnam in combat conditions. Although originally designed to meet the requirements of the Advanced Base Functional Component (ABFC) System, they have been used successfully in many other fields due to their inherent versatility and ease of erection. Large structures are easily and quickly disassembled then made into smaller structures, and then the smaller structures can be quickly and easily reassembled into larger structures. The light draft, structural strength, mobility, and adaptability of pontoon structures made them extremely useful for shallow water passage and tactical deployment in the Mekong Delta. They allowed movement of heavy weapons and shifting of firepower throughout otherwise remote areas. Many structures not discussed in this manual, such as armored barges, helicopter pads, mortar barges, and barracks barges, were constructed in the field for use in special situations throughout the waterways of South Vietnam.

TYPES OF P-SERIES PONTOONS

Five basic types of P-series pontoons are in use today, designated Pl, P2, P3, P4, and P5. These pontoons are specially designed, internally reinforced, welded steel cubes. They are tested to withstand an internal pressure of 20 pounds per square inch (psi). All pontoons have plain deck plates covered with a nonskid coating, and all are, fitted with a 2" plugged hole for air, drain, or siphon connections at the top and bottom of one of the end plates.

The P1 pontoon is cubicle in shape. (See fig. 10-1.) The deck of the P1 is 5'3/8" x 7', and the sides are 5'3/8" high. The side, end, deck, and bottom plating is 3/16" thick. The P1 is the most common and widely used pontoon in the P-series. Its usage is required in every structure of the pontoon system.

The P2 pontoon has the same depth (5'3/8") as the PI, but it has a 7' square deck and a straight-line sloping bow. (See fig. 10-2.) The side, end, and deck plates are 3/16" thick. The sloping bow plate is 3/8" thick. P2 pontoons are used on the bow and stern of various pontoon structures.

Figure 10-2.-P2 straight-line sloping bow pontoon.

The P3 pontoon has an inclined deck5'1 3/4" long and 7' wide. (See fig. 103.) The deck slopes from 4' 11 3/8"to3'8 1/4" high. The bottom is horizontal. All plating is 3/16" thick The sloping deck is fitted with five 1" square ribs 5/6" long, evenly spaced and secured by welding, with a covering of nonskid paint applied between the cleats. The P3 is used in conjunction with the P4 to form a gradually sloped ramp for causeway ends and ramp barge bows.

The P4 pontoon has a deck 5'1 3/4" long and 7' wide inclined at the same angle as that of the P3 pontoon. (See fig. 10-4.) The after end is 3'6" high; the forward end, 1'. The bottom is horizontal for 8" on the after end, then slopes upward. The deck, side, and back plates are 3/16" thick; the bottom, or bilge, plate is 3/8" thick. Five evenly spaced, 1" square ribs are welded to the sloped deck, and a coat of nonskid paint is applied between the cleats. Used in conjunction with the P3 pontoon, the P4 forms a continuous ramp for causeway ends and ramp barge bows.

Figure 10-4.-P4 ramp-end pontoon.

P5 pontoons consist of P2 pontoons with quick-lock hinge connectors fixed to the bow. The P5M is a P5 with a male connector; the P5F is a P5 with a female connector. (See fig. 10-5.) P-series 3 x 15 pontoon causeways are connected end-to-end by alternate P5M and P5F pontoons; so are barge sections that are used as wharves where end-to-end connection is required. These pontoons are constructed by welding hinge connectors to P2 pontoons that are then assembled in male and female sequence, forming causeways of any required length. These pontoons are also used for enlarging or extending wharf structures. The center section of the P5F hinge is made from a section of extra strong pipe. When joined, these two parts resist the torsion, compression, and vertical shear forces in the joint.

Making end-to-end connections with P5M and P5F pontoons is not a difficult task (fig. 10-5). When the mating ends of two causeway or wharf sections are brought together, the male pipe connection is simply guided into the female and held in place by pad eyes and links. The resulting pipe joint then prevents vertical movement of either section. A short chain-locking device completes the connection and secures the links in the pad eyes. Each set of hinges is capable of withstanding 300,000 pounds of pull. Closure plates are welded on either side of each connection to bridge open spaces between pontoons.

A wide variety of structures-wharves, barges, causeways, and so on-can be assembled from pontoons. In the assembly of pontoon structures, the pontoons are first joined into strings and the strings are launched; the floating strings are then attached to each other. Structures of not over three strings in width can be entirely assembled on land and then launched as a unit. The number of pontoons in each string and the number of strings attached to each other depends upon the size and type of structure being assembled. The manner of assembly is similar in each case with variations depending largely on the intended use of the completed structure. The size of each pontoon structure is designed by indicating the number of strings in the assembly and the number of pontoons in each string, Thus a 3 x 15 causeway section is three strings wide and fifteen pontoons long. Pontoon gear is usually shipped with the parts required to complete a specific structure.

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