The story
Apparently a corruption of raddling by folk-etymological reanalysis as rat + line.
First known use, by meaning
- from 14th c. The rope or similar material used to make cross-ropes on a ship.
- from 17th c. Any of the cross ropes between the shrouds, which form a net-like ropework, allowing sailors to climb up towards the top of the mast.
Etymology from Wiktionary, CC BY-SA 4.0.