Glen H. Egstrom
Diving equipment has evolved dramatically since the 1950s. The increased use of spe-cialized materials has spurred engineering design advances and manufacturing pro-grams. Proliferating full-service dive opera-tions throughout the world are marketing sophisticated products and services to meet the needs of a larger diving population.
Divers in the 21st century have access to a wide range of equipment needed to work effectively in widely differing diving environ-ments (Fig. 3–1). This chapter provides practical insight into some important consi-derations of diving equipment and its effec-tive use. It is important that each diver be comfortable and safe on every dive. It is equally important for divers to be aware of their own limitations when using the wide array of available diving equipment. Ade-quate preparation for safe, effective diving includes proper training in the use of the equipment within the specific requirements of the diving environment. This training, coupled with knowledge of personal limita-tions, minimizes the risk of loss of control, which can lead to injury or death.
MASKS
The purpose of the mask is to provide an air pocket over the eye that permits the eye to focus and thereby allows the diver to see clearly under water. The size of the air pocket can vary from that within a special contact lens to that confined within goggles, masks, and even helmets. Problems with masks are related to visual distortion, a restricted visual field, pressure, volume changes with atten-dant discomfort, and occasional irritation from chemical or bacteriologic sources.
Visual distortion is the result of variations in the distance from the mask lens to the eye.
Air has an index of refraction of 1.0, whereas the index of refraction of water is 1.333. This
difference results in refraction of the light rays at the air–water interface, causing the diver to perceive objects to be closer and larger than they really are. For example, an object 4 ft away appears to be 3 ft away if it is viewed directly forward with the mask lens perpendicular to the line of vision. However, distortion increases as the line of vision devi-ates from the perpendicular to the lens, and the object appears to grow larger. Divers adapt readily to this problem and, with experience, learn to adjust their hand-eye coordination and spatial visual judgments accurately.
Restrictions of the visual field through the mask are annoying and are largely a function of the distance of the lens from the eye, the size of the nose, and the dimensions of the lens and the skirt of the mask. Placing the lens close to the eye widens the visual field.
The size of the nose and the nose pocket found on many masks creates an obstruction in the medial portion of the visual field.
Masks with side lenses at corrected angles are popular, but there is always a distorted area where the planes of the lenses change, which can lead to distorted visual images.
For example, a fish swimming across a diver’s line of vision may be seen out of the side panel, but as it gets closer it may disappear from view or may appear to bend as it comes into view on the front panel. Additionally, some of the newer clear skirts and side windows permit light to come into the mask from the side and reflect off the inside of the lens and back into the diver’s eyes, causing some loss of acuity. Generally, lower-volume masks that place the lens closer to the eye are favored by knowledgeable divers, espe-cially if they enjoy free diving.
Hypoallergenic silicone skirts and straps are more comfortable, cause less irritation of the skin and eyes, and are significantly longer-lasting than natural rubber products.
Periodic cleaning, particularly of the inside of the mask, is especially important in climates 37
where black algae and other organisms can grow easily. Cleaning products for the lenses and skirts should be handled with care. On occasion, some of the cleaning products leave behind a residue that may cause severe eye irritation and potential injury. Thorough rinsing of the mask prior to use is a funda-mental precaution.
The fit of the mask to facial contours is very important and should be considered carefully before purchase because tightening the mask strap on a poorly fitting mask in order to create a seal results in discomfort and potential leaking. Proper placement of mask straps and wider straps minimizes the angle of pull on the mask and reduces the likelihood of a poor seal. Leaky masks usually result from poor fit, trapped hair, or catching of the edge of the hood under the mask skirt. Ensuring smooth contact of the mask with the skin is a much more effective way of making a seal than is tightening the strap excessively. Periodic checks of the mask skirt will reveal any small tears that may cause small leaks.
Contact lens wearers should use care when diving because these can easily be washed out of the eye should the mask flood suddenly. The practice of inserting eye-glasses into the mask cavity does not provide satisfactory vision and is not recom-mended. Lenses with the appropriate correc-tions can be placed in masks quite easily and offer an alternative to contact lenses and eyeglasses.
FINS
Fins (Fig. 3–2) provide a greater resistive surface to improve propulsion. Fins can now meet the needs of almost any diver. The development of long flexible fins for compet-itive fin swimming and the use of new lightweight materials for better thrust and durability have added a new dimension to diving efficiency. The split-fin technology has achieved great popularity, and tests have shown them to be more efficient with less noticeable leg strain. There is a learning curve for the split fins, especially with any kick other than the flutter-type kick, but most users are pleased with the results.
One criterion for evaluating fins involves comfort, both in the foot pocket and in the stress on the leg muscles under diving conditions. Leg length and strength are also important because a diver with weak muscles on long legs may not be able to effectively use an otherwise excellent fin configuration. For example, weak hip rota-tional muscles may permit the hip to rotate during the thrust phase of the kick, resulting in the solid blade fin turning on its edge and slicing through instead of flexing and provid-ing thrust. The split-fin technology does not appear to have this problem because each side of the fin directs water flow out through the slot in the middle of each fin, effectively reducing the torque on the hip joint.
Figure 3–1.Fully dressed scuba diver wearing a wet suit, buoyancy compensator with alternative air source, independent air supply, dive computer integrated with tank pressure gauge, mask, fins, and snorkel. (Photograph courtesy of Mike Steidley.)
Figure 3–2.Several types of diving fins.
Fin studies conducted at the University of California, Los Angeles, and elsewhere have consistently demonstrated that individual variations in the ability to use fins effectively for a particular type of diving dictate which fin may be superior for an individual at a given level of conditioning. In an early UCLA study of nine popular solid-blade fins, nine subjects were asked to use each fin in random order, under three workloads, on two separate occasions in a blind test. The subjects were experienced divers, ranging in height from 5 ft 5 inches to 6 ft 4 inches. The data revealed that the longer, narrower fins tended to be slightly more efficient than the shorter, wider fins and that fins with vents, regardless of their direction, were not supe-rior to those without vents. The longer, less flexible fins required stronger leg muscles and delivered higher levels of thrust, without causing rapid fatigue.
Divers should condition themselves to the fins they intend to use in order to use fins effectively. This may require working with fins of increasing rigidity over time in order to develop the necessary strength and endurance to support the workload imposed by the more rigid fins. Cramping and discom-fort may be the result of poor adaptation to a particular fin. This logic is appropriate for solid-blade fins, but it is clearly not the same issue for the newer split-blade fins. Hardy and associates (personal communication) conducted extensive tests on all currently available diving fins. They demonstrated a 27% advantage of the split-blade over the
solid-blade fins. Their data can be found on the Internet.1 The Hardy studies found that the split fins did require a flutter kick to give the best results. The split-fin technology is superior while the diver swims straight ahead using the shallower flutter kick and results in lower air consumption for experi-enced users. Unique swimming techniques must be mastered to enable the diver to use alternate kick styles such as sculling and maneuvers requiring rapid turns. These alternate propulsive maneuvers are some-what easier to perform with solid-blade fins.
Kicking style is important when evaluating fins because force must be applied in the direction opposite to the intended path. With a drag-dominant kick, in which the fin works primarily as a paddle, the vector of force at 90 degrees of flexion of the knee is primarily to the rear (Fig. 3–3). When the knee is fully extended, the vector of force is perpendicu-lar to the path of travel. A wider, slower kick is more efficient than the rapid, shallow kick often used by novice divers. With a lift-dominant kick, such as a sculling-type kick, the fins respond like propeller blades or wings, directing the resistance to the rear when the leg is nearly straight The power from this type of kick comes from the power-ful rotator muscles of the hip joint; the fins sweep through the water rather than paddle against it. Because these two kicks require the use of different functional muscle groups, it helps to become proficient in both kicking styles in order to prevent fatigue. One of the characteristics of the split-fin design is that Figure 3–3. Diver swimming while monitored by an underwater ergometer. Note the nearly perpendicular angle of the left knee as the diver prepares to execute the power stroke of the kick.
the split blade permits the development of strong lift forces on both sides of the split on both the up and down stroke without a strong feeling of strain on the thigh musculature.
Although the modern, lightweight, durable plastic fins provide excellent thrust charac-teristics and work well with a variety of kick patterns, the buckles and straps are usually large and offer significant drag. Full-foot fins constructed of plastic materials are some-what more efficient. However, they are lost in surf more readily than open-heel fins with neoprene booties. With booties with open-heel fins, the configuration of the foot pocket should be evaluated for comfort with the foot covering (booties) that will be worn.
Many newer booties have thick soles for walking on land, and those attached to or worn with dry suits are often larger than normal. Discomfort from blisters or a tight fit can be avoided with proper fin selection.
Each new pair of fins requires a period of
“breaking in” while the diver is adapting the leg and hip musculature to the new work-load. It is not wise for a diver to use a new, higher-resistance fin on a strenuous dive without preconditioning with the new fin.
Comfort and efficiency with new fins develop with progressive increases in the workload.
SNORKELS
Snorkel tubes, used for easier breathing while swimming on the surface, have evolved from simple tubes that are open at both ends to devices that offer purge valves, swivel mouthpieces, advanced materials, and mouth-pieces of improved design (Fig. 3–4). An adequate snorkel should permit the diver to swim at high workloads on the surface without encountering excessive breathing resistance that would significantly impair the snorkeler’s ability to breathe comfortably.
Longer, smaller-diameter tubes with unnec-essary bends, internal corrugations, and any unnecessary airway obstructions are unde-sirable and may lead to intolerable levels of respiratory distress under moderate to heavy workloads.
Self-draining snorkels have reduced the amount of water the diver must move in order to clear the snorkel. These devices contain an exhaust valve below the waterline that permits water trapped in the tube to drop to the level of the surrounding water. A sharp pulse of exhalation pressure is then
directed against a smaller water column, and water is purged out of the tube with the momentum generated in the water column.
The diver must understand that doubling the flow rate of air through the tube results in the need to overcome the square of the resistance to breathing and that the energy cost of this extra effort greatly increases. The snorkel must be considered an extension of the airway and as such should provide minimal resistance to breathing. If the diver experiences exceptional respiratory dis-tress, he or she should consider swimming on the back with the snorkel removed and, if necessary, also the mask, but only after the buoyancy compensation device has been inflated. Long snorkels increase physiologic dead space and can lead to CO2 retention and hypercarbia. Excessively long snorkels should be avoided.
The snorkel mouthpiece should be able to rotate on the snorkel tube so that the lip flange of the mouthpiece can be placed parallel to the teeth and gums. Blisters of the oral mucosa and temporomandibular joint problems can result from poor align-ment. Some innovative mouthpieces come in several sizes, and care should be taken to obtain a proper fit. Persons who tend to bite through the tabs on the mouthpiece can often be well served with a customized mouthpiece.