angles of the strings. On the other hand, end-condition angles connect P2, P3, or P4 pontoons to the ends of strings, and each is designed for a specific orientation-top or bottom and right or left. Basic angles can be shortened or lengthened to make up modified configurations, and end-condition angles can be cut and formed from basic angles to meet abnormal operating requirements.

The A6B ASSEMBLY BOLT is a 1 1/2" diameter x 3 3/8" long, hexagonal head, steel bolt (fig. 10-8). Three radial grooves on the head, spaced 120 degrees apart, are the code for grade 5 steel rated at a tensile strength of 105,000 psi. In addition to its use in securing assembly angles to pontoons ate each comer, the A6B bolt is also used to connect strings into structures, to secure deck fittings and accessories, and to pin hinges on dry dock stabilizer towers.

The forged FNl FLANGED NUT (fig. 10-9) is designed to fit into a pontoon pocket with sufficient clearance to allow positioning on the A6B assembly bolt. The flange of the nut is large enough to prevent the nut from turning in the pocket when the bolt is tightened; it is formed near the midline of the nut to clear welds in the pocket and allow positive se sting of the nut boss when the A6B bolt is tight.

Figure 10-8. - An A6B assembly bolt.

Figure 10-9. - AII FNl flanged nut.

The KPl KEEPER PLATE (fig. 10-10) is made from a plate 3 3/4" long, 2 1/8" wide, and 3/16" thick. The plate is cut out to fit over four of the hexagonal flats on the A6B bolt head. After final tightening of a bolt in a pontoon structure, the keeper plate is positioned around the bolt head and skip-welded to the underlying assembly plate or angle. This prevents the bolt from working loose during operations. To reduce maintenance problems, you should use the keeper plate on the bottom of pontoon structures where daily inspection is impractical. Keeper plates should not be welded to the bolt head.

Steel PLATES of various shapes are used in the assembly of pontoon structures mostly to reinforce those areas that are subjected to maximum stress and shear. A number of different types of assembly plates are shown in figure 10-11. Each of the plates shown is designed for a specific application, as indicated below.

APl CONNECTING PLATE: The AP1 is a steel plate with four drilled holes for A6B assembly bolts. It reinforces the A6B bolts that hold pontoon strings to each other in completed structures that use either 6" or 8" angles.

AP3 LAUNCHING ANGLE PLATE: When pontoon structures are to be side-loaded on an LST, an accessory known as an LA1 launching angle is attached. The AP3 is a steel plate that is used to attach the LA1 to the structure. The AP3 has four drilled holes for A6B bolts, and a curved plate is attached to form a semicylindrical pad. The pad serves as a fender to protect the hull of the LST on which the pontoon structure is side-loaded.

Figure 10-10. - A KPl keeper plate being installed on an A6B bolt.