The
phrase "Swinging the lead" is used to describe someone who is 'taking it easy' or is
lazy and not doing their job properly.
As with many English idioms, this expression has a nautical origin: Before the advent of depth sounders, sailors used to measure the depth of shallow waters beneath their vessel using a marked rope with a lead weight attached to the end. Swinging the weighted rope out and calling out the depth indicated was regarded as an easy job compared to the other tasks a crew member might be called upon to perform and sailors looking for a rest would stretch out the time they "swung the lead".
"Swinging the lead" quickly became synonymous with laziness and passed into everyday use.