Equipment Configurations for Cave Diving: Backmount, Sidemount and Streamlining

Cave divers talk about configuration (how cylinders, regulators, lights and accessories are arranged on the body) far more than most divers. The reason is simple: in an overhead environment a diver cannot swim straight up to solve a problem, so equipment has to keep working, be reachable without looking, avoid snagging the guideline or the cave, and be understood by every member of the team. This article explains the main ideas behind the common configurations. It is not a guide to setting up equipment; that is what training is for.

Redundancy comes first

Sheck Exley's 1979 booklet Basic Cave Diving: A Blueprint for Survival put it directly: the key to cave diving equipment and procedures is redundancy, especially for the breathing system ^[1]. He illustrated the point with a 1973 double fatality at Tarpon Springs, Florida, in which one diver's regulator was found to free-flow uncontrollably after a mechanical fault; his analysis was that a configuration with two independent regulators would probably have prevented the chain of events ^[1]. Exley recommended the dual-valve manifold, which connects two cylinders so that two complete regulators can each draw on the whole gas supply; he noted that an NSS diver had invented the manifold and that it was not yet commercially available at the time of that accident ^[1]. He also explained why experienced cave divers of his era avoided reserve (J) valves, including their tendency to be knocked down by ceiling projections and to snag line behind the head ^[1].

The same logic runs through current standards. The NSS Cave Diving Section (NSS-CDS) requires students on most of its cave courses to use either two sidemount cylinders or a set of manifolded doubles, with two first stages each feeding a second stage, and at least one second stage on a 2.0 m hose ^[2]. Global Underwater Explorers (GUE) lists its own required base configuration in an appendix to its standards ^[3]. Two of Exley's ten recommendations speak to this directly: always carry the safest possible scuba, and always carry the equipment needed to handle emergencies ^[1].

Backmount doubles with an isolator manifold

In the backmount configuration, two cylinders are strapped together on the diver's back and joined by a manifold. GUE's version uses a dual-outlet isolator manifold, which allows two first stages and lets the two sides be separated if one develops a leak ^[3]. One first stage supplies the primary second stage on a long hose (GUE requires 2 m for all cave classes) and the wing inflator; the other supplies a backup second stage worn on a necklace under the chin, an analog pressure gauge and, where used, drysuit inflation ^[3].

The long hose exists for gas sharing. In a narrow passage two divers may need to move in single file while one breathes from the other's supply; a long hose makes that physically possible. Exley already recommended a hose of at least 1.2 to 1.5 m for ease of sharing in 1979 ^[1]; modern cave standards specify about 2 m ^[2][3]. Managing manifold and valve failures is a trained skill set; GUE lists manifold failures among the critical skills its courses practise ^[3].

Sidemount

In sidemount, two independent cylinders are carried along the diver's sides, each with its own first stage and regulator, clipped to a harness with a buoyancy cell on the back. GUE's sidemount configuration, for example, uses independent single-valve cylinders without a manifold, puts one second stage on a 2 m hose, and has both first stages supply a pressure gauge and inflation ^[3]. Because the two cylinders are independent, the diver manages two separate gas supplies rather than one shared one, and sidemount syllabi accordingly include regulator switches, gas monitoring and gas sharing ^[3].

Sidemount is closely associated with confined passages. GUE describes its sidemount cave course as teaching the techniques needed to move safely through confined passageways, together with the advantages and disadvantages of carrying cylinders at the sides ^[3]. The NSS-CDS describes its Advanced Sidemount course as dealing with restrictions small enough that one or both cylinders must be removed, with the "ratchet effect" (being unable to back out of a passage you entered) and with a buddy becoming stuck in a long single-file passage ^[4]. GUE's Sidemount Cave course requires students to pass several sidemount-only restrictions and includes conservation and landowner relations, geology and cave shape, and the advantages and disadvantages of a lateral configuration ^[3].

Neither the NSS-CDS nor GUE treats sidemount as automatically superior. The NSS-CDS accepts either sidemount or manifolded doubles for its core cave courses ^[2], and its advanced sidemount work assumes full cave certification and substantial post-certification experience ^[4].

Minimalism and standardisation: the Hogarthian idea

A strand of cave diving culture emphasises minimal, standardised equipment. The term "Hogarthian" is commonly used for this approach; it is reported to be named after William Hogarth Main, who refined the configuration through trial and error, and the approach was later formalised as "Doing It Right" (DIR) by divers associated with the Woodville Karst Plain Project in Florida in the 1990s ^[5]. Its central ideas are a rigid backplate and simple continuous harness, a long hose, removing anything that serves no clear purpose, and every team member using the same configuration so that gear and procedures are interchangeable ^[5].

GUE states its own philosophy as a standardised, holistic configuration in which each piece functions as part of a system, adapted for sidemount and rebreathers rather than replaced ^[3]. Its base configuration specifies a backplate held by one continuous piece of webbing with a crotch strap and defined D-ring positions, a minimalist wing free of extraneous straps, a wrist-mounted compass, wetnotes, a backup mask and a cutting device ^[3]. Other communities organise their equipment differently; for example, the UK Cave Diving Group has been reported as arguing that a team-based configuration philosophy does not suit British caves ^[5]. These are different responses to different caves, not a single right answer.

Streamlining and why it matters in restrictions

A restriction is any part of a cave too small for comfortable passage, from a low bedding plane to a hole a diver must squeeze through. Restrictions raise the stakes of configuration in several ways. Anything that hangs below the diver can catch the guideline or break formations. Loose hoses or clips can snag. Silt stirred up by fins or contact with the floor can destroy visibility for everyone behind ^[1]. Exley warned in 1979 that large lights catch on rocks in narrow areas ^[1], and that equipment such as backup lights should be kept close to the body when crossing a line ^[1].

Training standards reflect how demanding tight cave is. GUE's entry cave course excludes passages where divers must travel single file for more than about 3 m, leaving such passages for later levels ^[3], and its advanced courses assess the ability to manage equipment through restrictive areas with concern for the environment ^[3].

Rebreathers and stages

Closed-circuit rebreathers and additional cylinders (stages carried for longer dives or decompression) add further layers to configuration. GUE specifies rebreather configurations built on its base kit with one primary and two backup lights, and requires stage cylinders to be clearly marked ^[3]. Rebreathers are covered in a separate article.

What incident data show

In a review of 67 trained cave divers who died in the United States between 1985 and 2015, Potts, Buzzacott and Denoble found that most were diving open-circuit backmount, four in each 15-year period were in sidemount, and rebreather fatalities rose (not statistically significantly) from one to six or seven, the paper's text and table differing slightly ^[6]. The study did not identify configuration itself as the leading problem; the most common chain was getting lost, often after silt reduced visibility, and running out of gas ^[6]. Configuration supports safe diving, but it does not replace the guideline, gas planning and training.