Buoyancy, Trim, Propulsion – The fine art of diving
Good diving technique is important in any diving environment and at any level of diving ranging from the openwater diver to the technical diver, rebreather diver or cave diver. Skills necessary and accumulated in one environment don’t necessary translate into another environment and could be potential hazardous. The very essentials of every divers set of skills are propulsion, gas management, buoyancy control, equipment management and awareness towards the environment, dive partner and dive team. Essential skills vary between levels of training and diving, a openwater diver has a different level of skills then for example a technical diver but the essentials, and the basic skills are the same in either one of them.
Good diving techniques such as perfect trim and buoyancy let the diver swim with relative ease to enjoy the marvelous of the environment visiting while taking care of not destroying the environment dived in. It avoids silting and makes dives more enjoyable, rewards a diver with better gas consumption, reduces fatigue and stress. While diving we have to be at all times neutral buoyant in a horizontal position in order to avoid contact with the floor, bottom or ceiling while changes in buoyancy control will also affect gas consumption. Events like silting and changes in current flow and direction will modify the swim pace and alterations to swim posture can increase drag.
Superb mask clearing skills are essential and will enable the diver to clear the mask at any time, any position and any situation without much second thought and the knowledge the mask will be clear. Safe and efficient diving demands superb technique. Always practice, practice your diving techniques. You must be willing to continue with your diving training and practice what you have learned during training throughout your diving life.
Propulsion
A wide array of propulsion techniques can be used to propel a diver through the water. Depending on environments such as caves or wreck with changes in strength of water currents a dive can choose between propulsion techniques that best suit his or her environment or situation. Various propulsion techniques do use different muscle groups in our legs and during strenuous or long distance swims we can alternate and change from one muscle group to the next while the group not being used can rest and relax for a while.
Cave divers have developed and use an assortment of swimming kicks that have one characteristic in common, that is the legs and fins are always up and not coming close to the floor or bottom, and are not usually employed by open water divers but they work excellent in all environments and are essential to a divers tool chest of diving skills. The kicks you can learn to use include a variety of frog kicks, modified flutter kicks, shuffle and dolphin kicks. Many environments need and involve precision swimming where the full range of propulsion techniques can be used on every dive. Hand movements are very seldom used in tight wreck or cave passages, uncontrolled hand movements are not part of a controlled dive.
Modified Flutter Kick
In open water diving the flutter kick is the standard kick used with a strong downward motion of the stretched leg. In sediment filled caves, wrecks or close to a fragile coral reef this might lead to destruction or visibility reduction due to sediment agitation. The modified flutter starts off not using straight but upward bent knees. While kicking from the knee the water is directed back and downward. When the leg is coming into the horizontal position the kick is terminated and the leg brought upward for the next kick. Modified flutter kicks are frequently used in cave and wreck diving. The basic flutter kick involves a gentle up-down (vertical scissors) leg motion and is executed while swimming horizontally with your body parallel to the floor or bottom. When using this kick make sure your downward thrust does not extend below your body axis. To execute a modified flutter kick, a diver extends his legs and uses a vertical scissors motion to propel himself forward. To avoid silting, the sweep should not extend lower than your horizontal axis and a minimum distance between the diver and bottom is needed. If this minimum distance is to small silting or contact with the bottom will occur and the frog kick must be used.
Frog Kick
The frog kick originates in the upward bent legs with the knees bend, and then the legs are pushed back reassembling a surface breaststroke. Before the end of the stroke the fins are tilted slightly into a V in order to deflect the water upward and away from the silty floor or coral reef. Frog kicks can be used in various environments and a wide array of current. A wide frog kick is accomplished with your body in a horizontal posture. First the fins slide gracefully without power outward to a full extension. Usually the legs are slightly elevated to maintain maximum distance from the floor or bottom. The fins are then cupped by twisting the ankles and the power stroke is on the inward travel portion of the kick. It will place demands on your leg muscles as you deliver the kick in powerful, continuous strokes. The same kick can be used while not extending the legs out to the side completely but sculling out of your knees or ankles. The frog kick enables the diver to control the water flow to a greater extends and flushes the water up and back rather than down in other propulsion techniques.
Dolphin Kick
The modified dolphin kick is a very powerful fin technique and kick originating in the bend knee upward position when both legs and stroking downward until the horizontal position utilizing both legs at the same time for maximum propulsion.
Shuffle Kick
The shuffle kick or ankle kick is used in small areas or for horizontal turns. The knees are bend and the legs in the upward position and if moving then our ankles we can propel ourselves slowly by moving your ankles up and down. This motion effectively controls silting.
The one-legged shuffle kick was developed for use when leg cramps occur. It also works well in silty areas. This kick uses full range of motion similar to the modified flutter. The difference is one leg is a kicking leg and the other a resting leg. The “ kicking ” leg travels downward until it rests on the diver’s other leg, which is extended, but not moved. The extended leg serves as a shield to minimize fin turbulence on the down stroke.
Backing up and Turning around
Equally important as to propel oneself through the water efficiently is the essential skill of backing up without using the hands and turning around while maintaining buoyancy and a horizontal position. Backing up is archived through a reversing frog kick and enables the diver to back up from reefs, walls or marine life without the use and disturbance of hands, even preventing injury from contact to parts of a wreck or a coral reef. When diving in a horizontal position and the need arises to turn around either to check on a dive partner or to leave a wreck or cave it is essential not to go into a vertical position but to maintain the horizontal and turn on the spot without using the hands for sculling.
Hand use and Propulsion
When swimming and diving underwater with fins a diver’s hands are normally kept close to the body to maximize streamlining and minimized drag and water resistance in order to glide through the water. Waving (or sculling) your hands to maintain buoyancy or orientation in the water column must be avoided. The turbulence caused by sculling may result in substantial silting in caves and wrecks and could cause injury while getting in contact with parts of a wreck, cave or coral reef.
Trim
Body posture and the divers position in regards to being horizontal or vertical in the water column are extremely important and ideally the diver should have a horizontal position in the water to minimize drag and maximizes efficiency and streamlining. Proper trim enables the diver to move with less effort through the water column and minimize silting in silty areas encountered inside wrecks or caves.
Traditional Bcd’s do only to a certain extend allow the diver to have a proper horizontal trim since their upward lift is on the upper part of the body and the forward lift or force of the weight belt is on the lower part of the body pivoting the diver into a vertical position which will increase drag while being less streamlined and in silty areas create silt.
The wing style bcd with a harness and backplate or soft pack are a much better solution for proper trim since the upward lift and downward force are centered in the same area giving the diver the advantage of coming into a horizontal trim much easier.
Drag and Streamlining
To picture this posture, imagine yourself as an axis. Your body is the pivot point. While swimming in a horizontal posture no kick will extend more than 10 degrees below your midline. Your head must be held up to see where you’re going. At first this may result in some sore neck and lower back muscle ache. A properly trimmed diver will stay horizontally in the water even without any forward movement. The combination of wing style type buoyancy compensators with a harness system and single or double tank configuration provides the diver with a stable platform. Fine-tuning can be archived by moving tank bands, harness systems or BCD’s slightly and can be enhanced by placing weights onto or between (V – weight) the tanks.
Buoyancy
Buoyancy control is one of the most crucial and essential diving skills in all diving environments and is one of the hardest one to learn. It provides the diver with a stable position, to be submerged weightless in the water column, to effortless glide over reefs, wrecks or into caves, run lines and work with reel’s or interact with marine life in an non-impact way.
When diving, your buoyancy needs to be so precise that you can become totally relaxed when hanging in a fixed position. Upon inhalation your body will rise ever so slightly. The reverse is true upon exhalation. In some situations you will be required to be either negatively or positively buoyant. But, most of the time you will be neutrally buoyant. It is imperative that you re-establish your buoyancy at each “ change point ” in the dive. Change points occur when you ascend to a deeper part of the dive or ascent to a shallower portion of the dive, add or remove stage bottles, enter a cave system or wreck , add or remove reels or other equipment, deplete a significant portion of your gas supply or encounter silting surfaces. Good buoyancy techniques are a must for cave, wreck and coral reef conservation.
Neutral buoyancy in a horizontal trim position with the legs pointing up provides the diver with a streamlined and balanced profile while that particular position does protect the diving environment. What looks to us solid may be fragile or soft silt that can be agitated or broken with one uncontrolled touch of the hand or fin. Divers must be able to turn in a horizontal position, maintaining the horizontal position and depth without touching anything. It requires practice to become a comfortable diver, it requires dedication for environmental preservation.
Greetings
Matt