You are lifting a 3 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 B — 1 1/2 inch

Shackle size for a given safe working load is calculated using the standard USCG formula: size in inches equals the square root of the SWL in tons. For a 3-ton lift with a swinging boom, boom geometry increases the total stress load, requiring a 1 1/2 inch shackle per standard rigging tables.