The magical beauty of cenotes entices divers from around the world. When divers and snorkelers tour these pristine kingdoms of paradise, they are presented with a wide gallery of environmental factors. These features reward and challenge for a variety of reasons; including conservation, efficiency, enjoyment, safety, silt control and satisfaction.
To preserve these pristine cenotes each visitor should perform to the best of their ability. Knowledge of key skills will not only protect the diver but also a delicate environment. The beauty inside each cenote also provides serious challenges:
1. fragile formations
2. silt on the floors, walls and ceilings
3. delicate rocks and projections
4. restrictions and small passageways
5. low or no visibility
6. dark, light absorbing walls
SWIMMING

To explore these sacred cenotes divers need skill and proper equipment. Snorkelers can get away with fins, mask and snorkel. However, divers experience different degrees of weightlessness. This can be regulated by a buoyancy control device (BCD). Neutral buoyancy is the ultimate skill necessary to be worthy and safe in the cenote environment. Inflating or deflating the BCD means applying the correct force for ascending, descending and negotiating the cave or cavern. Fragile cenotes demand maximum proficiency in buoyancy control. Recognizing when and where to utilize the proper swimming techniques, understanding how to handle the rise in floors and the dips in ceilings, along with brittle conditions are integral aspects of mobility in the cave environment. Efficiency is a goal that must be mastered.
Streamlining and trim are essential. Simply stated: minimize drag, reduce mass and lock down anything that may dangle. It is crucial not to waste energy or reduce efficiency. Being over weighted makes the diver negative and feet-heavy causing the divers fins to stir up silt. Working the BCD properly should minimize this problem. An under weighted diver can experience the opposite effect. When aluminum tanks are depleted and the pressure drops below 1500 psi/102 bar, the buoyant force of the scuba tank increases the chances of damage to the ceiling or stirring particles.
The most efficient use of trim is the horizontal of position. A proper, neutrally buoyant diver pushing through the water wants to carry the least resistance with a profile that exerts the least amount of energy.
Hauling unnecessary weight and non-essential items of equipment increases friction that produces more drag. Disposing the weight and removing the needless gear become imperative. Eliminating danglies such as the submersible pressure gauge, reels, back-up lights, etc. is a diver’s duty. Streamlining is improved, damage to the fragile cave is minimized and line entanglements become less possible.
With appropriate horizontal trim, the diver can execute a variety of fin kicks to avert silting, maximize efficiency while swimming and decrease air consumption. It is extremely important not to move within the water by pushing against the ceiling, walls or any objects of the cave. A diver should never pull himself or herself by touching or grasping formations with the hands. The fragile cave environment does not allow this type of technique to occur. The utmost caution is always advised while using different choices of techniques. Preserving the underwater cavern or cave goes hand in hand with the manner of methods being used in the water.

FLOW OF WATER
A major benefit with diving cavern and cave systems of the Riviera Maya is the minimal flow of water. Many cave systems found throughout the world have high flow which makes diving challenging as the water flow affects a diver’s air consumption and physical stamina. The strong current can also physically harm a diver if buoyancy control is lost and the diver gets bounced around the cave or if the ascent is too rapid with a significant change in depth or the exit out of the cave.
The horizontal water drainage from the inland of the Yucatan slowly meanders toward the Caribbean Sea. The flow of water is not a factor in air consumption, buoyancy control and physical ability. But, with minimal flow of water, stirring up silt is crucial for both conservation and safety reasons. When silt particles are disturbed, the art of good buoyancy control makes it much easier to psychologically handle the predicament.

THE CAVE CONFIGURATION
The variety of different features in the cave systems dictate the choice of technique applied to the particular situation. Skill and experience adds to the success and comfort level of the diver.
Swimming in large cave passages or rooms offer several advantages: It is easier to stay away from the floor, thus, avoiding silting; divers can swim side by side, turn around, communicate with a buddy, and work as a team, rendering buddy assistance when necessary. The only negative problem is disorientation if the cave walls are dark and absorb light. Paying attention to the guideline is strongly advised.
Smaller passageways and restrictions forces the diver closer to the guideline and the floor where silting becomes a factor. The choice of propulsion technique is a major consideration. Buddy assistance, communication, and turning around become more challenging and requires special care.
Silting is an obstacle depending on the cave size and configuration. Percolation from exhaust bubbles can impair visibility, particularly in saltwater passageways, no matter how good the technique. The problem is difficult to avoid unless the cave has seen a lot of diver traffic. Virgin or less traveled areas of the cave demands special awareness to the guideline. If the diver’s experience and/or comfort level is limited, avoiding areas that may produce zero visibility should be the rule.
Depth in the cave systems of the Riviera Maya is usually not a problem. Diving deep minimizes air consumption and prolongs decompression requirements. Excessive exertion must be avoided at depth because of the problems associated with nitrogen narcosis, oxygen toxicity and CO2 buildup which can cause divers to pass out. Only three known places exist in the Riviera Maya and, each one is far enough away, not often encountered by typical recreational cave divers Though the majority of underwater caves found and explored throughout the world offer depth, the luxury of the shallow cave systems in this region makes cavern and cave diving safer and more enjoyable.
Delicate cave formations and limestone projections makes the “art of technique” especially important! It took thousands of years for nature to develop the decorations and formations for cave divers to see and enjoy today. Because of carelessness, lack of experience, poor technique by thoughtless divers, and damage to these natural wonders is gut wrenching. Nothing demands more respect than the awareness of where divers swim, kick, touch and place themselves in the cavern or cave. Once broken or scarred, these formations cannot be repaired or regenerate themselves.

THE BEST TYPES OF PROPULSION TECHNIQUES
The following list of techniques and descriptions is recommended for cavern and cave diving the cenotes of the Riviera Maya.
MODIFIED FLUTTER KICK - the diver is looking straight ahead, swimming horizontally and moving the ankles only in a casual, alternating style, bending the knees and holding firmly in place. This technique is the most common used in cavern and cave diving.
(Illustration)

FROG KICK - the diver is trimmed horizontally, facing down. Though the style will vary amongst different individuals, it basically begins the kick with both legs straight, then stretching out each leg with the knees bent horizontal to the body, then snapping the legs back together straight. The water gust from the fin goes directly behind the diver.
(Illustration)

DOLPHIN KICK - the diver is face down and trimmed horizontally. Legs are held together bent, and whipped like a lobster tail. The entire body move up and down like a roller coaster. It is a strong stroke with an enormous down stroke blast meant for larger passages away from opportunities to disturb silt. A good change of pace type of kick.
(Illustration)

SHUFFLE KICK - using a modified flutter kick, keep the bottom leg stationary below the other leg so that the bottom fin blocks the water blast from the top fin. It is a gentle kick and good for controlling silt.
(Illustration)

TURNING - divers can usually turn easily in larger tunnels and rooms when using the normal modified flutter or frog kick. Kick harder with the fin opposite the direction desired and perhaps using the arms to do a few pulling swimming strokes opposite the direction of turn, or the diver can arch and roll into the turn. All this can be performed without having to slow down.
For small passageways thru a very different approach. The diver must slow down or stop, tuck the legs into a tight ball and then pivot with the hand(s). If it is too small to turn around, continue forward until you reach a space where turning around is possible. If there is too much silt, expect low or no visibility conditions. Backing out is not advised because you cannot see. Getting caught in the guideline or hung up by the equipment is very likely as the tanks becoming wedged from the irregularity in the ceiling or walls.
If the cave passage is so small, it is probably best to consider side mount technique of cave diving. Superb technique, experience and good judgment are paramount in cave diving.
(Illustrations)

HOVERING - for most divers, this is the most difficult skill to achieve and perform in a productive manner. To hover motionless like a hummingbird all depends on the divers trim and buoyancy. Hovering takes practice, but the ability to float mid-water and maintain a parallel appearance is the ultimate goal. Frequently, when divers are performing a task such as using a reel, they unconsciously allow their feet to drop close to the cave floor resulting in unnecessary silting. Divers should never go into a vertical posture because of the possibility for stirring up silt.
(Illustrations)

BAD HABITS
SCULLING - is using the hands in motion to counter balance the equilibrium of the diver’s buoyancy. It occurs when usually negatively buoyant or feet heavy. The movement of hand can stir silt. To stop this poor habit, keep both hands occupied such as holding the light head.
JERKING LIGHTS - unnecessary movement of the light. An annoying penchant that keeps fellow team members checking to see if there is a problem.
VERTICAL DROP - trimmed feet heavy and then going into a vertical position at rest resulting in silt or cave damage. Must stay focused and hover like a helicopter.
All complete, safe cave divers want to eliminate or at least minimize the use of bad habits. Recognizing the weakness, while practicing and becoming proficient lead to a healthy and positive attitude for all safe cave divers.

DILEMMA TECHNIQUES
Unfortunately, unpleasant situations can occur while cavern and cave diving. These undesirable predicaments can result from failing to recognize a present or potential danger. The extent of the hazard or problem all depends on the circumstances and several factors. They include:
awareness
communication
experience level
self sufficiency
prevention
Prevention is the best way to avoid emergencies or problems. Training and practicing techniques will power the odds of these dilemmas occurring. By organizing a good dive plan and using proper procedures potential dilemmas should never become a life threatening emergency.
Important steps to apply in preventing serious problems begin with equipment. Cavern and cave diving as equipment intensive and a dependent activity. Without these tools, it cannot be performed. The entire attitude is based on redundancy; where a contingency back-up piece of gear is available in case of a malfunction or failure. With proper equipment set-up and configuration, swimming in the cavern or cave environment should be safe and comfortable.
Attention to all equipment is a constant responsibility and includes maintenance inspections of the equipment before, during, and after each dive. Two customary procedures are performed before each dive.
MATCHING - members of the dive team compare and check the working function of each piece of their life support system. It includes:
Manifold and/or valves - air/gas turned completely on, placed underwater to check “o” ring seal between valve outlet and regulator first stage.
Regulators - Must check underwater for first stage leaks, second stage breathes properly, no water seepage or free flow.
Inflator system to BCD - working properly along with checking pressure gauge.
Lights - all inspected in the water, no leaks.
Air/gas supply - reviewed, calculated for 2/3’rds exit and compared with team members.
The matching sequence should be an easy and deliberate head to toe inspection of the entire diver’s equipment system. Anything not operating correctly should be replaced, fixed or the dive aborted.
THE SAFETY DRILL - this procedure involves a dive team review and practice of the out-of-air emergency procedure hovering at a shallow depth using text book buoyancy control and trim. The four steps are:
a. communication - the practice of the hand going back and forth in front of the throat indicating “out-of-air”; point to the mouth
b. regulator second stage exchange. Both divers swimming towards each other the diver with air/gas passing the second stage regulator to the ¨öut-of-air¨ diver in an effective and coordinated procedure.
c. Long low pressure hose deployment. The diver with air/gas deploying the long hose in a smooth manner with it not being hung up on any piece of gear.
d. Swimming sharing air. Side by side or single file following a guideline are different options to be familiar with.
e. Valve Management. To be able to close and open both regulator hand wheels to their outpost valves and to close and open the isolator hand wheel valve.

GENERAL PROCEDURES
An emergency usually occurs when you least expect it. The worst time, the wrong place. Right? The typical human reaction is an unprepared, confused state of chaos, no control of the body or the mind. This will get a diver killed or seriously hurt. Not a good situation for safe cavern or cave diving.
There are four life saving points to follow when a diver is caught in a bad situation. It begins with the best word that ever can be applied with anything in life....... (1) STOP! No matter what is going on, if things are about to become unglued, just STOP. Why make it worse? (2) KEEP the dilemma IN CONTROL. Getting in command of the life threatening situation is an absolute priority. An example is a zero visibility condition forcing the diver to follow the guideline by physical touch for hundred’s of feet/meters. Controlling the air consumption would be the first sensible decision, along with maintaining good buoyancy. This is a positive direction rather than a self -destruct, fall apart disaster. By communicating constantly as a dive team the emergency is averted. The third point is (3) THINK. The only way to survive and/or succeed in a bad situation is to assess the predicament. Think it out before reacting. Remember, there are never problems, only solutions. Evaluate all controlling factors. Once thought out and completely satisfied with how to handle the problem then..... (4) ACT. With a decision made, it is important to maintain control and be totally aware of everything around you.
A diver’s ability to handle a stressful quandary in a successful manner will depend on how well the diver can help himself or herself and how his or her dive buddy or team members respond. Solving the dilemma as a team makes the circumstances go smoother no matter how bad it may appear.

POTENTIAL INCONVENIENCES
Not all dilemmas are considered an emergency but rather an inconvenience which does not require ending the dive and exiting. By examining the problem the team can decide if continuing the dive is safe. Anytime an unplanned situation occurs it boils down to a judgment call. How it is handled will depend on the experience and training of the dive team. The following are examples of typical inconveniences that should be easily solved though they do have the potential to evolve into a worse predicament.
GUIDELINE ENTANGLEMENTS - a very common, annoying inconvenience that could possibly turn into an ugly, stressful event. It results from danglies (hanging equipment poorly secured) that will get caught in the permanent guideline, particularly, when forced to get close to the guideline because of restrictions or low passages. If resistance is felt, immediately STOP and gently back up or feel for the guideline to untangle. Once snagged in the guideline the proper procedure is to STOP and signal any team members in front to make them aware of the problem. Make one attempt to fix or untangle the snag, if unsuccessful, have a team member assist in solving the case. DO NOT try to fight or struggle with the snarled guideline, it will only get worse. If the situation is so bad that it requires cutting the guideline be sure you secure the guideline and position yourself, from the cut, on the exit side. The best advice is to avoid cutting a guideline especially in poor visibility.
Poor line management, when using a reel, can create a guideline entanglement. Be careful with slack line and the location of where the guideline is placed to avoid line traps. A loose guideline, hanging from reels attached to the diver, should be fixed and kept in place properly.
Reel jams are caused by poor technique because of inexperience or careless performance. Keeping the guideline taut at all times is a primary goal. While reeling up the guideline be sure to lay the line evenly on the reel preventing the guideline to jump the spool and wrapped around the axle of the reel. Before every dive, examine the reel to ensure that the guideline will spool out the necessary length without causing a jam.
When a reel does jam, STOP, determine if time and air supply are available. If so, make an attempt to fix the reel or wrap the line carefully around the reel and exit. Another solution is to secure the reel and guideline to the floor or wall and retrieve it on another dive.
LIGHT FAILURES - following the fifth rule of “accident analysis”, cavern and cave divers carry a minimum three lights each. A complete loss of lights is highly unlikely within a team. Once a primary light fails the diver should STOP, activate a back-up light, signal the team members and “call” the dive. While exiting a cave, the diver with the back-up light becomes the weakest light and should be placed in the middle or front of the team to be easily seen. Or, everyone in the team should go to their back-up lights so that all lights are equally dim making it easier to see each other.
SILTING - the water in the cenotes of the Riviera Maya are consistently clear year round. Rarely would the natural elements of the cave systems cause poor or zero visibility. Hurricanes or severe storms have been unable to hurt the clarity of the water.
All other causes of silting are created by the diver unavoidable or accidentally. Poor techniques, bubble percolation on the ceiling, or swimming through small, silty passages are typical situations. Once visibility decreases, the diver should get on the guideline and firmly grasp it with one hand using an “OK” hand grip. If visibility is so bad divers can stay together as a team by an emergency procedure called “touch - contact”. This involves one diver holding on to an arm or leg of the diver ahead. Communication is performed with signals by feel. The following are examples:
1. push forward to go ahead
2. pull backward to back up
3. one squeeze to stop
4. two squeezes to go
5. several squeezes to emphasize a problem
When visibility is poor, physical contact with the guideline is the procedure and the use of lights to help maintain buddy location. Exiting slowly and carefully, the teams can keep track of each other without getting too far ahead or further behind.
In high flow caves, the current can usually move the disturbed particles out and re-establish good visibility by waiting and being patient.
Poor equipment maintenance is another cause leading to nuisance inconveniences. Properly servicing and keeping equipment free of mildew and corrosion will prolong the life and prevent problems.

PROBLEMS and EMERGENCIES

BROKEN LINE - nylon string rarely breaks as it is usually very strong and dependable. But, it can happen. The worst case scenario is getting caught in the guideline, becoming stubborn and pulling on the guideline trying to get free. This action snaps the guideline. Because most guidelines are installed with tension having the line recoil and losing sight of it is very possible. Whatever reason a guideline breaks, the diver must assess the predicament before attempting to solve the problem.
The best tool is a safety reel. When the guideline is out of reach or sight, tie-off your safety line. Once secured, carefully search in the general direction where the line has disappeared. When the other end of the permanent guideline is found, tie-in the safety line to it. If time/air is available and the diver is composed enough, repair the break and safely anchor the permanent guideline where it needs to be placed.
Some underwater caves experience changes due to normal weather patterns such as natural flooding from rainy seasons. When these events occur, debris such as logs and other forms of surface intrusion can possibly change the position or break the permanent guidelines. Be prepared for such possibilities.
Some marine underwater caves have natural organic growth on the guidelines. After so much time, the lines will begin to sag and weaken possibly causing a break. A good example is the Sistema Quebrada located on the island of Cozumel. The guidelines of the cave system always have marine growth and must be continually replaced or repaired.
Fortunately, the cenotes and underwater cave systems of the Riviera Maya never experience any flooding or marine growth that could possibly hurt or break the permanent guidelines.

BUOYANCY CONTROL DEVICE FAILURES - the rupture or puncture of the BCD bladders has occurred to divers in underwater caves. Usually it happens because of poor equipment maintenance or ramming into a rock or limestone formation. Because the caves of the Riviera Maya are very shallow, crawling out of the cave system can be performed without much difficulty. One remedy to solve a puncture or hole in the bladder is placing your hand over the area (if reachable) and crimping the BCD bag in order to trap the air. In deeper caves where depth is an obstacle, the use of a redundant BCD system is highly recommended. Today, technical diving equipment manufacturers produce BCD systems with dual bladders for redundancy. Many cave divers prefer to wear two separate BCD back mount wings for redundancy.
Another type of BCD failure is the runaway power inflator. The inflation button becomes stuck or malfunctions because of corrosion or poor maintenance. This problem can cause a rapid ascent to the ceiling causing serious injury and/or major damage to the cave. The only remedy is to orally inflate the BCD. This method should be practiced periodically.
REGULATOR AND VALVE/MANIFOLD FAILURES - poor maintenance can be blamed for most regulator failures. But, even well maintained and serviced regulators can suffer a problem that jeopardizes a dive. That’s why using use of two independent regulators placed on dual orifice valves or manifold is imperative. Valves/manifolds are more rugged and durable but they too can fail or malfunction. Both the regulator - valve/manifold system can be damaged from impact with the cave or cavern walls or ceiling during the dive.
The following is a list of possible malfunctions with regulator breathing systems and valves/manifolds:

Problem Cause Remedy

1. Second stage free flow. Low pressure seat failure. Shut down first stage
High pressure 1st stage Purge button stuck Switch to second regulator
seat failure
2. Second stage breathing water Exhaust valve rotted, debris Switch to second regulator
in exhaust valve in second Flush water to dislodge
debris second stage to dislodge
debris.

3. 1st stage high pressure seat Tank overpressure, worn high Shut down 1st stage.
first stage failure pressure seat Switch to second regulator

4. Inflator hose rupture Abrasion/ impact on ceiling Shut down regulator
or wall Switch to second regulator

5. Inflator sticking/stuck Corrosion, poor maintenance Shut down regulator
Switch to second regulator

6. Ruptured/leaking tank Heat, corrosion, overpressure, Use isolator valve
burst disc metal fatigue to separate tanks if
on double tanks.
If air/gas jeopardized,
share air/gas with buddy.

7. Valve/regulator “o” ring “o” ring fatigue, dry rot, cut, Shut down regulator
failure or worn. Switch to second regulator

8. Tank neck “o” ring rupture Corrosion, “o” ring fatigue Use isolator valve to
separate tanks if
available.
If air/gas supply jeopardized,
share air with buddy.

9. Tank on/off valve leaking air “o” ring failure, corrosion, Shut down valve and switch
and poor maintenance to second regulator.

AIR/GAS VALVE - REGULATOR MANAGEMENT - is a required and/or necessary procedure in training and to be practiced regularly by all divers in overhead environments. All divers should begin with valve(s) opened all the way to insure maximum flow of gas/air and for divers to know there is only one direction to shut down regulators. Regular inspections and maintenance will help minimize these possible problems. Continuous practice in handling these potential air/gas valve problems makes the individual and the team better prepared to handle the potential emergency.

SHARING AIR - Redundant equipment should prevent this but being prepared is always a sacred rule for safe cavern and cave diving. The procedure involves the following:
1. Communication. The out-of-air diver moves flat hand back and forth across throat and pointing to the second stage.
2. Exchange. The most critical part of the out-of-air emergency because of the stress and the element of surprise. Two schools of philosophy of which second stage the diver with air/gas gives.
a. Second stage attached to a quick release device to easily found and deployed. Diver with air does not give up his/her own air. This method considered not practical for safe cave diving.
b. Second stage given from mouth of diver with air. Easy to locate, knows it works, and quickest way to exchange. For cave divers, most preferred method. Either way, the long (7 feet/2.3 meters) or longer of two low pressure hoses should be part of the give away second stage.
3. Exit. Stop - think - exit cavern or cave. With clear water and no obstructions, swim out side by side or single file. No grasp on guideline necessary. If stress, obstructions, and/or poor visibility the out-of-air diver always goes first single file. Diver with air is second who has both visual and/or physical control of the emergency situation. Firm grasp of the guideline by both divers. Touch-contact procedure used if zero visibility or maintaining physical contact as buddy team is involved.
LOST LINE - physical contact with permanent guideline is necessary. Diver loses it because of carelessness or mental/physical problem. Procedure to handle this emergency situation is:
1. Stop.
2. Gain composure/self control, control breathing and THINK!
3. Orient your presence; feel around for an object to tie-off safety reel and line such as a rock, column, stalagmite or whatever can be found. Establish a headquarters or beginning point.
4. Reference tie-off on object, once located, and establishes four points such a,b,c and d or north, east, south and west.
5. Pick a direction. Slowly feel your way across the cave passage floor moving your hand and arm up and down.
6. After so much distance is covered with success in finding the permanent guideline return to initial tie-off point and pick a new direction. (Distance is determined by number of kicks, knots already placed on safety line every 10 feet/3 meters or intuition)
7. Once permanent guideline is located, firmly secure safety line to it. Because of orientation with location in the cave passage or area, choose the best direction for exit and begin to swim out following the guideline. Finding clearer water and/or recognizing a feature of the cave, confirm the correct way out. If wrong, turnaround and swim opposite direction. Other methods include tying-off safety line, lay the line along the floor until reaching the opposite wall, rise off the floor and return back to tie-off point in an effort to “hook” the permanent guideline or tie-off safety line and deploy the line in any chosen direction a certain distance dictated by the cave configuration. Swim in an arch pattern from the tie-off point, as if in a sweeping motion, creating a circle around the tie-off point until locating the permanent guideline.
This is a very rare emergency situation where few divers have ever depended on using the safety reel to find a lost permanent line. For those situations that have occurred, it has always been carelessness and an unusual set of circumstances involved with the problem that resulted in a successful conclusion every time. The best advice is never allowing you to get in such a stressful predicament in the first place.

LOST DIVER - if a buddy team becomes separated it is paramount to re-establish contact with each other or communicate that one or the other has already exited the cave. The following is a review of potential situations:
1. First diver notices buddy(s) is NOT behind him or her.
a. waits and allows buddy(s) to catch up.
b. swim back searching side to side and up on ceiling with
primary light.
c. looks for clues such as silt disturbance or bubbles on
ceiling.
d. if no success locating missing diver (s), leave a message
on slate or clue such as a clothespin and exit the cave.
2. Dive team member(s) lose sight of first diver.
a. establish visual or physical contact with permanent
guideline.
b. leave a clue or signal such a personal directional arrow
marker, clothes pin, back-up light “on” or a slate with
message indicating you have exited the cave.
c. search side to side along cave passages and into side
tunnels as you exit.
The best advice is never jeopardizing your own safety and air/gas supply while looking for a missing diver. The buddy (s) might be anywhere or waiting at the surface outside the cave.
Think positive, maintain solid control of breathing and composure and be aware of all circumstances involved in the emergency. Learn and exchange information and knowledge with other divers about the mistakes made. No matter what the problem, always STOP, get control of yourself, think out the problem and then respond accordingly. Practicing different situations is another way to prepare for possible emergencies. Mentally rehearsing various scenarios is another method. Confidence and believing in your skills and ability always makes a big difference. Knowing your limitations and experience level helps avoid present and potential dangers. Remember, your experience and comfort with the cave environment will make the dive safer and enjoyable.

BIBLIOGRAPHY
Fahning, Mary. 1995 “Emergency Procedures” pp. 113 - 119, The Art of Safe Cave Diving., Saltzman, Dayton. National Association for Cave Diving.
Grey, H.V., 1995. “Swimming Techniques” pp. 67 - 73, The Art of Safe Cave Diving. Saltzman, Dayton. National Association for Cave Diving.