Using a winch and some type of rigging, a vehicle can pull itself or another vehicle through such obstacles as muddy or rough terrain. This is the primary reason for providing winches on military vehicles.

In the Naval Construction Force (NCF), an in-depth management program for maintenance and use of all rigging gear is required to ensure all operations are performed safely and professionally. These guidelines are outlined in the COMSECOND/ COMTHIRDNCBINST 11200.11, Use of Wire Rope Slings and Rigging Hardware in the Naval Construc-tion Force and the NAVFAC P-307, Management of Weight Handling Equipment.

WINCHES
Most winches that you will encounter are used on tactical vehicles and construction equipment. On tactical equipment, the winch is mounted behind the front bumper and is secured to the front cross member of the frame or between the two side frame rails. In some cases, it may be mounted behind the cab of the vehicle. The typical front-mounted winch is a jaw-clutch worm-gear type (fig. 6-31).

The jaw-clutch winch consists of a worm gear that is keyed to a shaft. A bushed drum is mounted on the worm-gear shaft, which is controlled by a hand-operated sliding clutch. The worm shaft is driven by power from the power takeoff through a solid drive shaft and universal joints. The universal joint yoke, connected to the worm shaft of the winch, has a provision for a shear pin that is made of mild steel. This pin has a predetermined breaking strength that allows it to shear when the winch is overloaded.

A hand-operated sliding clutch is keyed to the worm-gear shaft outside of the winch drum and must be engaged with the jaws on the side of the winch drum when the winch is to be operated. Disengagement of the sliding clutch permits the drum to turn on the worm-gear shaft.

Figure 6-31.- Jaw-clutch worm-gear winch.

The two brakes that provide control of the winch drum are as follows:
NOTE

The WORM BRAKE SHAFT prevents the winch drum from rotating under load when the power takeoff is disengaged. will occur when overloaded.

The SHIFTER BRACKET BRAKE prevents the drum from overrunning the cable when the cable is being unreeled.

Some winches may be equipped with an automatic level-winding device to spool the cable on the drum in tight, even coils, and layers. This prevents crushing of the cable due to loose, crossed coils and layers, and it allows off leads of the cable while maintaining level winding.

A broken shear pin usually causes faulty operation of winches. Internal damage of the winch can be caused by the use of a shear pin that has too high a breaking strength. Internal winch failure, resulting from overload, is commonly found to be sheared keys or a broken worm shaft. Often, when the cable is wound unevenly under tension, the winch housing will be cracked or broken. This will require replacement of the assembly.

The winch that you will most likely encounter on construction equipment is the one attached to the rear of a crawler tractor, also known as a dozer. It is mounted on the rear of the dozer (fig. 6-32) and is directly geared to the rear power takeoff. This arrangement permits development of a line of pull that is 50 to 100 percent greater than straight dozer pull. The winch is used for uprooting trees and stumps, hoisting and skidding stress, freeing mired equipment, and support amphibious construction operations.

When performing maintenance on a winch, ensure that the gear case has the recommended amount and type of lubricant. Should disassemble of the winch be required for repairs, follow the procedures given in the manufacturer's manual.

Figure 6-32.- Winch attachment on a dozer.