BOOM DERRICK

The BOOM DERRICK consists of a mast with a boom attached, as shown in figure 6-12. It may be used to move weight in any direction. You will find the boom derrick useful for loading and unloading trucks and flatcars when the base of weight-lifting equipment cannot be set close to the objects to be lifted. It is also used to advantage on docks and piers for unloading boats and barges.

For medium loads, the boom may be rigged to swing independently of the mast, as shown in figure 6-12. For heavy loads, the boom may be set on a turnplate or turn wheel and it and the mast rigged to swing as a unit. On more permanent installations, it is good practice to rig the mast separately and to strap another pole or

Figure 6-12.\Boom derrick.

mast to it. In such a case, one mast is fixed; the boom is rigged to the other mast, which is set on a turnplate. This provides rigid guying with a swing of more than 180 on the boom.

In case the proper size of line is not available, a set of tackle reeved with the same size line as that used in the hoisting tackle may be used as a guy by extending the tackle from the top of the derrick to the anchorage. See that the block attached to the derrick is lashed at that point where the other guys are tied and in the same manner.

Rigging

In fieldwork, you may be called on frequently to assist in rigging a boom derrick. For medium loads, follow the rigging procedure given below.

The first step is to rig a mast and lash the tackle on, which is used as the topping lift. If the hauling part of the topping lift tackle comes from the movable block, lash a fairlead block to the mast 2 or 3 feet (60 or 90 centimeters) below the topping lift lashing.

For your boom, select a pole, timber, steel pipe, beam, or laminated plank of the same diameter as the mast, but only about two thirds of its length. Attach two cleats to the butt end of the boom and lash them with small stuff to form a fork, as shown in figure 6-12. This fork is to keep the boom from getting away from the mast while a load is being moved from side to side. Use cleats long enough to extend from the butt end of the boom past the mast. About 4 feet (1.2 meters) above the point where the boom meets the mast, attach two cleats into the mast, and place a lashing of at least four turns of small stuff above the cleats, keeping two ends free.

Using a sling attached to the topping lift, raise the butt end of the boom as high as you want it. With the free ends from the lashing on the mast, make a sling to support the butt end of the boom.

Lash the movable block of the topping lift to the top end of the boom, and lash the fixed block of the boom tackle at the same point. The boom tackle is reeved so that the hauling part comes from the fixed block and passes through a fairlead block lashed at the base of the mast.

Erecting

Raise the boom into position after the above rigging is completed. When working with heavy

loads, see that the base of the boom rests on the ground at the foot of the pole. When working with light loads, you may use a more horizontal position, thus providing a greater radius. In no case should the boom bear against any part of the upper two thirds of the mast.

To swing the boom, push directly on the load or pull the load with bridle lines or tag lines. The angle of the boom to the mast is adjusted by hauling on the hauling part of the topping lift. The load is raised or lowered by the hauling part of the boom tackle. A fairlead block (snatch block) is usually placed at the base of the mast. The hauling part of the boom tackle is led through this fairlead block to a hand- or power-operated winch for the actual hoisting of the load.