the following: 3x7, 3x12, 4x7, 4x12, 5x12, 6x18, and 10x30 barges. The conventional pontoon barge, in sizes up to and including the 6x18 barge, is designed to carry its rated load with 1' of freeboard or a load concentrated at the center point that is heavy enough to bring the deck awash.

The 3x7 pontoon barge is a general-purpose structure that can be used as necessary in lighterage and ferrying operations. Cargo transport can be accomplished by tow, or the barge can be self-propelled by mounting a propulsion unit on the end without fenders. A 3x7 barge with a propulsion unit is shown in figure 10-27.

The 3x12 pontoon ramp barge is ordinarily used for transporting cargo and equipment and has proved suitable for general use in amphibious operation. The sloping bow end with ramps attached permits beaching the barge under its own power. And also it helps to unload tractors and equipment that will be used to assist in forming a causeway pier. Four 3x12 barges can be side-loaded on an LST for side-carry to the assault area, or the barges can be loaded in the well deck of an LSD or deck-loaded on an LST.

The 4x7 pontoon barge is similar in all respects to the 3x7 barge, except it is one string wider. Although this is a general-purpose barge used principally for lighterage operations, it is suitable for any transportation task within its capacity.

The 4x12 pontoon barge is a general-purpose structure that can be used in lighterage operations either by towing or as a self-propelled structure by the addition of propulsion.

The 5x12 pontoon barge is one string wider than the 4x12 barge but similar in all other respects. It is particularly suitable for mounting a crawler crane with a lifting capacity ranging from 20 tons at a 12' radius to 7 tons at 55'. This barge can also be used as a general-purpose structure and can be used in lighterage operations as a self-propelled structure by the addition of propulsion units.

The 6x18 pontoon barge is the second largest barge in the P-series pontoon system. Installation of propulsion units permits its use in lighterage operations for transporting loads (cargo, vehicles, and personnel) up to 250 tons. By the addition of accessories and equipment, the barge can be converted into a 1,500-barrel fuel storage barge (fig. 10-28). Also, by installing heavy-duty hinges, the barge can be converted into a wharf or used for outfitting and repair of smaller structures when placed on its deck.

The 10x30 pontoon barge is the largest barge in the pontoon system. It was developed primarily for mounting a 100-ton derrick (See fig. 10-29.) The barge, however, is adaptable to other uses. With propulsion units attached, it can serve as a lighterage barge in transporting over 800 tons of cargo at one time from ship to shore or dock. The barge can also be

Figure 10-27. - A 3x7 pontoon barge with a propulsion unit.