Reels, Spools, Guidelines and Line Markers: What They Are For

If one piece of equipment defines cave diving, it is the guideline: a continuous line running from open water through the cave, which the diver can follow out even if lights fail or silt erases visibility. The first of Sheck Exley's ten recommendations for safe cave diving, published by the NSS Cave Diving Section in 1979, is to always use a single, continuous guideline from the cave entrance throughout the dive ^[1]. Nearly four decades later, a review of US cave diving fatalities still found the line rule and the gas-reserve rule to be the two most crucial to survival, and the most common fatal chain to be getting lost, often after silt reduced visibility, and then running out of gas ^[7]. This article explains the hardware behind the guideline and the small markers clipped to it. It does not describe how to lay, follow or repair line; those are hands-on skills taught in cave courses.

Permanent lines, reels and spools

In many frequently dived caves a permanent main line, often carrying permanent arrows, has been installed ^[4][5]. Divers do not simply swim to it from the surface: training standards call for a team to run its own line from open water until it connects to the main line. GUE's entry-level cave course, for example, assesses the use of a penetration reel from open water until the team ties into the main line ^[5].

The kit that carries line comes in a few types:

• A primary reel, carried by the team, holds enough line to reach from open water to the permanent line. The NSS-CDS asks for at least one primary reel per team with at least 75 m of line ^[6]; GUE asks for at least 45 m and a minimalist design whose handle supports a Goodman or hands-free grip ^[5].
• A safety reel or spool is a smaller reserve of line carried by each diver for emergencies. The NSS-CDS asks for two per diver with at least 30 m each ^[6]; GUE asks for one per diver with at least 45 m ^[5].
• A jump or gap spool carries a short length of line used to connect two lines. GUE defines a gap as a place where the main line ends and begins again a short distance later, often where it reaches another entrance, and requires a jump or gap spool with at least 23 m of line at its second cave level ^[5].
• Survey and exploration reels carry longer, often knotted, line; GUE's survey course requires a team exploration reel holding at least 240 m of knotted line ^[5].

The differing numbers show that agencies set their own minimums; they are not interchangeable rules.

What makes a good reel

Exley's 1979 booklet set out design criteria that still read well. The handle should let the diver hold both the reel and a light in one hand, freeing the other; there should be a crank handle and a line guide that stops line spilling off at random; the drum should be large enough for the line but manageable in the water; and the whole reel should be non-corrosive, impact-resistant, jam-free and ideally neutrally or slightly negatively buoyant ^[1]. Exley identified slack line wrapping around the hub as a prime cause of jams ^[1].

The NSS-CDS history credits Forrest Wilson with creating the first jam-proof reel in 1977, and Dana Turner with the L-shaped handle design introduced three years earlier ^[2]. Exley's booklet illustrates a Wilson reel with a Turner handle ^[1].

The line itself

Exley explained the choice of material from experience. Natural fibres rot when wet, and synthetics such as polyethylene and polypropylene float, raising the risk of entanglement; nylon neither rots nor floats ^[1]. NSS divers had found white line the easiest to see in most cave situations ^[1]. Because guidelines tend to part through abrasion against sharp rock rather than lack of strength, braided line was preferred over twisted line for its abrasion resistance ^[1]. Survey work often uses line with knots at fixed intervals so that distance can be counted; DIVER magazine describes knots about 3 m apart and notes that line tension can stretch the spacing ^[8].

How line is placed matters as much as what it is made of. Exley advised keeping wraps and tie-offs to the minimum needed to stop the line drifting into an area too small to swim through, because each wrap slows a diver following the line by touch ^[1]. Placement technique is a core part of cave training and is not described further here.

Line markers: a small vocabulary

Line markers are small plastic devices clipped onto a guideline to convey information by sight and touch. There are three main types ^[4].

Line arrows are directional markers that point toward the nearest exit. In many areas permanent arrows are placed at regular intervals, often around every 30 m, and may carry a number giving the distance to that exit; local practice also uses them to mark side passages and midpoints ^[4]. Because an arrow's shape can be felt, a diver can read its direction even in zero visibility ^[4].

Cookies are non-directional markers that a diver or team uses to mark a particular place: a junction, a route choice, or a point on a jump line that shows who has gone by. They should carry personal identification such as initials, and some divers cut notches or holes so they can recognise their own by touch ^[4]. The essential rule is that a cookie means something only to the person or team who placed it; everyone else ignores it ^[4]. Before cookies, clothespins served this purpose ^[4].

Referencing exit markers (REMs) are a newer, rectangular hybrid. To the diver who placed it, a REM acts like an arrow showing the direction back to that diver's exit; to everyone else it is simply a personal marker. It has space for identification and for short notes such as survey data ^[4]. Other divers should not follow a REM's direction, because an exit that suits one diver's size and configuration may not suit another's ^[4].

Training agencies require divers to carry markers. The NSS-CDS asks for at least two directional and two non-directional markers per diver on its core cave courses ^[6]; GUE asks for at least three of each at its first cave level and six of each on more advanced courses ^[5]. GUE also distinguishes permanent intersections (where no jump spool is visible) from temporary ones, and asks that intersections that appear permanent be marked with non-directional markers ^[5].

A short history of the line arrow

According to the NSS-CDS, Lewis Holtzendorff first used arrow-shaped markers made of duct tape, known as "Dorff markers", after the death of Bill Hurst at Peacock Springs; Forrest Wilson later developed the plastic line arrow that is widely used today ^[2]. A retailer's account adds that the tape arrows slid along the line and were hard to feel in a silt-out, and that Wilson's design came out of a discussion group at an NSS workshop led at Exley's request ^[3].

Trust, etiquette and local practice

Markers work only if they are used consistently. DAN-affiliated researchers reviewing US cave fatalities noted two divers who apparently did not trust line arrows pointing toward the nearest exit and swam further into the cave, while their surviving partners followed the arrows out ^[7]. TDI's guidance stresses that marking conventions differ between regions and teams, that teams should agree before each dive who places and retrieves which markers, that other divers' personal markers are to be ignored rather than used, and that temporary markers must be removed after use so caves are not littered ^[4].

Cutting tools

Because line can entangle a diver, cave standards require cutting tools: the NSS-CDS asks for at least two per diver ^[6] and GUE for at least one ^[5]. They are part of the same system: a guideline that can always be followed, and a diver who can never be trapped by it.