What is the mechanical advantage, neglecting friction, of tackle number 4 as shown in illustration D029DG below?

Correct Answer: Option D — 4

A two-fold purchase consists of two double blocks. With four parts of the line supporting the moving block, the theoretical mechanical advantage is 4. This calculation assumes no friction. In practical application, friction significantly reduces this efficiency, but for theoretical USCG exam purposes, the count of supporting parts suffices.