How Cave Diving Works
Since cave diving is different from other recreational diving activities, many of the techniques people use are also much different. Divers are taught to swim in a prone, or face down, position, with the knees bent and the fins elevated above the plane of the body. This is mainly a precaution against kicking the bottom of a cave and stirring up sediment, but it also offers a good streamline and creates little resistance to the water.
Cave divers move about a cave by using a simple technique called “pull and glide” — using the tips of their fingers, divers look for crevices in rock for a place to hook onto. The rock is usually something hard and porous like limestone, so it should have lots of pockets and places to grab. After grabbing hold, divers pull and release, gliding through the cave with relative ease.
Cave divers learn how to use mostly their feet for directional changes along with short flutter kicks, and, in the case of solid limestone, some can push off a cave ceiling with their feet to propel themselves along.
Divers can also take along battery-powered diver propulsion vehicles (DPVs) to make swimming easier. Although there are many different types, tow-behind DPVs are the most common, which pull divers through caves. DVPs help divers use less oxygen since they’re not exerting themselves as much, and they can significantly increase the length of a dive.
Because there is little to no visibility in caves and cave divers must use their own source of light, guidelines must be placed to ensure people can find their way back to a cave’s entrance.
Most caves already have guidelines in place from past explorers — these are called “gold lines” because of their yellowish color. They consist of braided nylon string and are usually a bit smaller in diameter than regular rope at about an eighth of an inch. These are placed throughout the main tunnels of a cave. Labyrinthine caves also have smaller side tunnels, and these are provided with smaller, white lines. They don’t contact the main line; instead, they usually end within 5 to 10 feet of the main line.
The main line of a cave does not extend to the exit — this prevents open-water divers or untrained or uncertified people from viewing it as an invitation to enter the cave. Therefore, a main guideline typically starts 50 to 100 feet inside a cave.
Still, it’s a cave diver’s responsibility to run a temporary line, or entry line, along a reel from the outside of the cave in order to maintain a continuous guideline from open-water to the main line. This provides direct access to a cave’s exit. To make an entry line, divers make an initial tie-off to something sturdy, like a big rock. A secondary tie-off is also made in case the first one comes loose. The diver must be able to swim along the line with his hand around it, making an “OK” sign, and with his eyes closed make his way out of the cave. The line shouldn’t be run near obstructions in order to avoid snags and keep out of the way of other divers.
Dorf markers, or small, plastic directional arrows, can be tied to lines. These point toward exits, just in case a diver becomes disoriented. Clips, markers that resemble clothespins, are also used at points for notation reasons, including max penetration (the furthest point reached inside the cave) and points of interest for other divers.
The average cave dive will last in excess of one hour, but some can last for as long as 15 hours if the right equipment and gas supply is available. Divers generally use what’s called the “rule of thirds” — when one third of a diver’s air supply is gone, he will stop the dive and begin moving toward the cave’s entrance.