What is guideline in diving?

A guideline is a continuous line running from the dive team back to open water, a physical path that guarantees an exit from a cave, wreck, or any other overhead environment. It is laid from a reel or spool, tied off at the entrance and at intervals along the way, and placed so a diver can follow it by touch alone, all the way out.

Why do cave divers need a guideline?

In an overhead environment you cannot simply ascend to the surface. One careless fin kick can stir silt into a cloud that drops visibility to zero in seconds; a light failure does the same. When you can no longer see, the line is the only way out. That is why precise buoyancy control and stable trim are core overhead skills: they keep you off the bottom and the water clear.

What is the difference between a mainline and a primary line?

• Frequently dived caves have a permanent mainline, but it deliberately starts well inside the cave, away from the entrance.
• The team lays its own primary line from open water to the mainline, so the path out is continuous.
• Side passages are connected across jumps and gaps with small spools, and directional markers (line arrows) always point toward the nearest exit.

How do you follow a guideline correctly?

Swim beside the line, within arm's reach, and never carelessly over it — entanglement is a real hazard. In zero visibility you hold the line in a loose OK-hand grip, keep touch contact with your teammate, and read line arrows by feel to confirm the way out.