Distance line

A distance line, penetration line or guide line is an item of diving equipment used by scuba divers as a means of returning to a safe starting point in conditions of low visibility, water currents or where pilotage is difficult. They are often used in cave diving and wreck diving where the diver must return to open water after a penetration when it may be difficult to discern the return route. Guidelines are also useful in the event of silt out.

Distance lines are wound on to a spool or a reel. The length of the distance line used is dependent on the plan for the dive. An open water diver using the distance line only for a surface marker buoy may only need 50 metres / 165 feet, whereas a cave diver may use multiple reels of lengths from 50 ft (15 m) to 1000+ ft (300 m).

Reels for distance lines may have a locking mechanism, ratchet or adjustable drag to control deployment of the line and a winding handle to help keep slack line under control and rewind line. Lines are used in open water to deploy surface marker buoys and decompression buoys and link the buoy on the surface to the submerged diver, or may be used to allow easy return navigation to a point such as a shotline or boat anchor.