Lesson 4-3 HOISTING EQUIPMENT
You must know how to tie simple knots, use block and tackle, and operate hoisting equipment efficiently and safely.
4-3. Knots and Hitches
Knots and hitches are used in many ways to tie equipment, materials, scaffolds, and many other items to block and tackle in order to raise or lower items, as needed. Some of the most commonly used knots and hitches are discussed below:
a. Square Knot. A square knot (Figure 4-22) is used to tie two ropes of equal size together so they will not slip and are easily untied. Note that the square knot, the running end and standing part of one rope come out on the same side of the bright that is formed by the other rope. The square knot will not hold if the ropes are set or if they are of different sizes. It tightens under strain but can be untied by grasping the ends of the two brights and pulling the knots apart.
Figure 4-22. Square knot
b. Bowline. The bowline (Figure 4-23) is used to form a single loop that will not tighten or slip under strain and can be easily untied. It is one of the most common knots and has a variety of uses, one of which is the lowering of men and material.
Figure 4-23. Bowline
c. Running Bowline. The running bowline (Figure 4-24) forms a strong running loop. It is a convenient form of running an eye. The running bowline provides a sling of the choker type at the end of a single line. Use it when tying a handline around an object at a point that you cannot safely reach, such as the end of a limb.
Figure 4-24. Running bowline
d. Double Bowline. The double bowline (Figure 4-25) forms three nonslipping loops. Use this knot to sling a man. As he sits in the slings, one loop supports his back and the remaining two loops support his legs. A notched board that passes through the two loops makes a comfortable seat known as a boatswain's chair discussed previously.
Figure 4-25. Double bowline
e. Two Half Hitches. Two half hitches (Figure 4-26) are used when there is a need for a quick way to tie a rope to a timber. Two half hitches are especially useful for securing the running end of a rope to the standing part. If the two hitches are slid together along the standing part to form a single knot, the knot becomes a clove hitch.
Figure 4-26. Two half hitches
f. Clove Hitch. A clove hitch (Figure 4-27) is one of the most widely used knots. You can use it to fasten a rope to a timber, pipe, or post. You can also use it to make other knots. This knot puts very little strain on the fibers when the rope is put around an object in one continuous direction. You can tie a clove hitch at any point in a rope. If there is not constant tension on the rope, another loop (round of the rope around the object and under the center of the clove hitch) will permit a tightening and slackening motion of the rope.
Figure 4-27. Clove hitch
g. Timber Hitch and Half Hitch. A timber hitch and half hitch (Figure 4-28) are combined to hold heavy timber or poles when they are being lifted or dragged. A timber hitch used alone may become untied when the rope is slack or when a sudden strain is put on it.
Figure 4-28. Timber hitch and half hitch
h. Round Turn and Two Half Hitches. Another hitch used to fasten a rope to a pole, timber, or spar is a round turn and two half hitches (Figure 4-29). For greater security, seize the running end of the rope to the standing part. This hitch does not jam.
Figure 4-29. Round turn and two half hitches
i. Rolling Hitch. The rolling hitch (Figure 4-30) is used to lower a load slowly. The boatswains chair is another important use of the hitch. You can lower yourself by releasing the pull on the fall line and rolling the knot.
Figure 4-30. Rolling hitch
j. Scaffold Hitch. A scaffold hitch (Figure 4-31) is used to support the end of a scaffold planking with a single rope. The hitch prevents the planking from tilting.
Figure 4-31. Scaffold hitch
k. Whipping. The raw, cut end of a rope has a tendency to untwist and should always be knotted or fastened in some manner to prevent this untwisting. Whipping (Figure 4-32) is one method of fastening the rope end to prevent untwisting. The rope is whipped by wrapping the end tightly with a small cord. This method is particularly satisfactory because there is very little increase in the size of the rope. The whipped rope end will still thread through blocks or other openings. Before cutting the rope, place two whippings on the rope 1 to 2 inches apart and make the cut between the whippings. This will prevent the cut ends from untwisting immediately after they are cut.
Figure 4-32. Whipping the end of a rope
Repeated tying of knots causes ropes to wear rapidly. Ropes should be inspected frequently to ensure safety. Check ropes visually for abrasions, broken fibers, cuts, fraying, or deterioration from acids or corrosive substances. Remove from service any defective ropes that are found. When not in use, store ropes in a dry, well-ventilated place.
4-4. Block and Tackle
a. Block and tackle, also referred to as falls, are one type of hoisting equipment used to raise and lower the platform of a swing-stage scaffold. Falls are made in various combinations of single, double, and triple blocks. The number of sheaves (pulleys) used designates the size of the block. As the number of sheaves is increased, the mechanical advantage is increased. To avoid getting dirt into the operating parts of the blocks, reeve a set of blocks by laying the blocks out on a clean and level surface other than the ground. Figure 4-33 shows the reeving and threading of single and double blocks.
Figure 4-33. Reeving single and double blocks
b. When the reeving is completed, the blocks are ready to be fastened. Connect one block securely to the load and the other to a substantial anchor. To move the load, pull on the fall line. When you use a block and tackle for swing-stage scaffolds, the rope must be first-grade Manila that is at least 3/4-inch in diameter.
4-5. Hoisting Machine
This machine (Figure 4-34) is another item used while painting in elevated places. It uses steel cable instead of rope. The hoisting machine has a lock and a brake that are controlled by the painter. Before leaving the machine, you must remove the control handle and lock the brake. Perform daily inspections of all the ropes and cables being used to support the scaffold.
Figure 4-34. Hoisting machine