You are lifting a 5-ton weight with a single whip rove on a swinging boom set at an angle of 60° 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?

Correct Answer: Option D — 1 7/8 inch

Applying standard USCG cargo gear formulas for a 5-ton lift on a swinging boom at 60 degrees, the elevated load factor and dynamic stress require sizing up the shackle. Using the standard sizing formula yields a minimum shackle size of 1 7/8 inches.