PROPULSION

WHEN DIVERS CONSIDER TRAINING IN AN overhead environment, many are anxious about reductions in visibility; however, with proper technique, divers can usually control the factors that cause visibility loss. Most sediments mainly accumulate on the floor of a conduit, with a relatively minor collection taking place along the sides. Therefore, as long as a dive team maintains a good feet-up posture and exercises reasonable buoyancy control, they are usually able to maintain good visibility.

Some shipwreck and cave passages are particularly susceptible to diver movement and exhaust bubbles, but most areas can be kept clean with good technique. Errant fin kicks, erratic hand movements, or poor trim can rapidly reduce visibility and are the primary causes of silty conditions; however, a continuous guideline ensures that divers are able to exit safely regardless of visibility.

Proper and modified flutter kick

Open water divers are instructed to use a strong flutter kick, focusing on kicking from the hips with straight knees. While this kick does produce a great deal of power, it also produces significant downward turbulence, as the thrust from this kick is directed from the end of the fins toward the floor. In sediment-filled areas, this turbulence will disturb the bottom and reduce visibility. To avoid this, overhead divers are taught to adjust the style of this kick. A “proper” flutter kick uses a strong leg kick while keeping the legs as horizontal as possible during kicking. This kick has exceptional power and greatly reduces the downward thrust that causes sediment disturbance. The “modified” flutter kick is a similar but less aggressive kick compared to the proper flutter. During these kicks, the legs are bent at the knees. By kicking from the knee, the water can be directed upward, where it is much less likely to disturb any sediment. When executing this kick, a diver’s torso should be flat, in a head-down position, forcing the fins upward. Like most propulsion techniques, this kick can be used with a varying degree of force. In areas that contain easily disturbed sediments, divers should move slowly and kick lightly, being careful to force the water upward. In very silty regions, divers should propel themselves by kicking carefully with their ankles.

Frog and modified frog kick

The frog kick is a particularly effective method of controlling the direction of divers’ thrust. The frog kick resembles the kicking action of a surface breaststroke. Its greatest benefit is that it eliminates the vertical component of a flutter kick cycle. While the modified flutter is generally effective, it maintains a vertical kicking movement and requires that divers exercise greater control over their kicking style. The frog kick can be used as a fairly powerful kick in high-flow conditions or curtailed—”modified”— in low-flow areas with easily disturbed sediments. The frog and modified frog kicks allow greater control of water movement. They direct water up and back rather than down, and they usually create less silt than alternative propulsion methods.

Backward kick

The backward kick is somewhat like a reverse frog kick, allowing divers to back away from a given position. It is also extremely useful during positioning, while filming, and while holding stable against an opposing current. The backward kick requires some practice to reach mastery, but the ability to move backward without any hand or extraneous movement is perhaps one of the more valuable skills divers can learn.

The frog kicks offers a significant advantage over the flutter kick by removing the vertical component of the leg movement during the kick cycle.

The pull-and-glide technique is taken to extreme levels when divers have to squeeze through narrow restrictions.

Helicopter turn

Divers accomplish the helicopter turn by using a frog kick with one leg and a backward kick with the opposing leg. By alternating these kicks, the diver creates a spinning motion and can turn in place.

By executing this maneuver, divers can turn within a small area and do so without disturbing bottom conditions. Helicopter turns are critical for proper positioning and for managing turns within the small confines of some caves or shipwrecks.

Pull-and-glide

Historically, divers in a variety of areas have utilized the pull-and-glide technique. However, as cave diving has increased in popularity, pulland-glide began to produce significant wear and tear in caves. To pull-and-glide, divers pull on a protrusion as they kick, and then glide for a short period. The glide is then followed by another pull and kick. In low-flow areas where gliding is especially unnecessary, swimming or using a diver propulsion vehicle is a better, less destructive option.

In high-flow areas where forward motion is difficult, limited contact with the cave can assist progress. Most high-flow caves have large, stable protrusions, and selective contact with these projections greatly limits the likelihood of damage. However, divers should always strive to limit their contact with the cave and avoid touching fragile or decorated areas.