925. You are lifting a 5-ton weight with a single whip rove on a swinging boom set at an angle of 20° to the horizontal. Use the formula for the size of a shackle with a safe working load and determine the minimum size shackle that should be used to secure the head block to the boom.

The shackle securing the head block to the boom must have a safe working load exceeding the 8.2-ton load on the block, calculated from the 5-ton weight lifted with a 20 boom angle. Using the formula SWL = 3d2, where d is the shackle diameter, a 1 3/4 inch shackle provides the minimum adequate safe working load.