What is "to underrun a tackle"

Underrun \Un`der*run"\, v. t. To run or pass under; especially (Naut.), to pass along and under, as a cable, for the purpose of taking it in, or of examining it.

Note: The cable passes over the bows and stern of the boat used, while the men haul the boat along by pulling upon the cable.
--Totten.

To underrun a hose (Naut.), to lift it up at one end, then walk along shifting one hand after another so that the water will run out.

To underrun a tackle (Naut.), to separate its parts and put them in order.