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