You have it right re: compound pulleys - my mistake, and I'll fix my post above.
Mechanical advantage depends on the number of pulleys, but also their layout, not every four pulley system will give 4:1 advantage. A pretty simple graphic analysis will reveal the ratio. Draw a box around the load and any pulley attached directly to it - the number of ropes leaving the box divided by the number of hoist points gives the ratio.
Deck Rigging Gear
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