The M147 double bitt (fig. 10-19) consists of two 8" steel pipe posts, 20" long, welded to a 13" x 40" base and capped on the upper ends.

PROPULSION UNITS

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 shown in figure 10-20 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. Each unit has a steering wheel and an indicator that show direction of

Figure 10-19. - ;M147 double bitt.

Figure 10-20. - Model L-295 diesel outboard propulsion unit.

travel. The tail section, with the propeller, is mounted on the vertical housing assembly that can be elevated outward and backward to raise it out of the water for inspection or repairs. As new equipment and techniques for amphibious operations developed, performance requirements for all components increased accordingly. As a result, propulsion units have increased in power and thrust capability.

PONTOON STRING ASSEMBLY

After the first two assembly angles have been placed on the ways, the pontoons are placed in the angles (figs. 10-21 and 10-22). The pontoons are positioned on their sides with all deck surfaces on the same side. The first pontoon will ordinarily be placed in the center of the angles with the assembly bolt holes aligned; placement of the remaining pontoons from the center toward each end can be accomplished without difficulty.

Bolting Lower Angles

As each pontoon is placed in the assembly angles, the A6B assembly bolt holes in the pontoon nut receptacles are aligned with those in the angles, using spud wrenches or driftpins as necessary. The A6B bolts are then inserted through the assembly angles

Figure 10-21. - Pontoon positioned on assembly