Seeing a sunken hulk materialize out of the blue is a thrill I never tire of. It doesn’t matter if it’s a ship, plane, or automobile, the siren song to come and explore rings loud and clear, beckoning me closer. Beyond the romantic lure of priceless treasure waiting somewhere deep within its hold, there are other treasures associated with almost all wreckage under the sea. Bountiful marine life is a thrilling visual treat, but even more alluring is the history and mystery contained within the wreckage. Our minds wander back in time as we cruise the decks, peer into a porthole, or gaze into an empty cockpit. Even artificial reefs, purposely sunk, often have a colorful past with which we can connect. However, the romance surrounding these sunken gems can make visiting them a potentially hazardous affair. Whether it’s a submerged Chevy in a Kansas quarry or a WWII battleship off Bikini Atoll, sunken objects pose potential risks for divers that can shift an open-water dive into the technical realm of the “overhead environment.”
A typical recreational scuba dive involves a descent, a bit of underwater exploration, and an unimpeded ascent to the surface when planned bottom time and/or air supply dictate. A “safety stop” at around 15 feet (5 m) for several minutes is the norm, performed as an extra measure of safety against decompression sickness. This “down and up” type of dive differs greatly from one in which a “ceiling” — a barrier that prevents a diver from making a direct ascent — is present. Ceilings can be real, impenetrable objects such as a shipwreck or cave, or virtual, as in a required decompression stop. Diving in overhead environments requires additional training, equipment and preparation. It also requires that divers be mindful of the risks involved.
The Challenges Overhead
The very nature of wreckage almost guarantees there will be entanglement hazards, sharp edges, and confined spaces. Ships and other objects placed as artificial reefs have usually been made “diver friendly” through the removal of potentially hazardous materials. Numerous exit holes are cut into bulkheads, and some areas of the ship are sealed off. However, even “clean” wrecks pose potential hazards. Somewhere at the top of the list is a seemingly benign natural threat: silt and sediment.
Whether it’s the bottom of a muddy lake or the sandy seafloor, silt and sediment can quickly accumulate inside a sunken wreck. The vessels themselves contribute rust and other debris to the mix. Careless fin kicks can stir up a cloud of silt. Exhaust bubbles may cause rust to rain down from overhead surfaces. A diver who minutes earlier was in clear water may find himself inside the equivalent of a snow globe, a blizzard of fine silt obliterating his view.
Trying to navigate inside a shipwreck in poor or zero visibility is challenging even when the vessel is sitting upright on the bottom. Disorientation can be compounded if the wreck is resting on its side, fun-house style, or if it’s at nitrogen narcosis-inducing depths.
Not all wrecks are triple-digits deep. In fact, many intentionally sunken wrecks and artificial reefs are placed in areas shallow enough that divers of all experience levels may cruise their exteriors safely. However, some popular wreck sites are at deep depths that present a multitude of challenges: the technical concerns of penetration, rapidly depleting gas supply, limited no-deco times, and the mind-altering effects of nitrogen narcosis.
Perhaps the most daunting physical challenge of diving in overhead environments is that the path to the surface isn’t straight up. In the case of wreck or cave diving, it’s often sideways, meaning that a diver has some horizontal swimming to do before making a vertical ascent to the world of the unlimited air supply. When decompression diving (whether the dive was planned in advance as a deco-required dive or the deco stop is as a result of accidentally staying down too long) it’s straight up, but with one or more deco stops along the way. Either scenario becomes complicated — and potentially dangerous — if a diver’s air supply is limited and may not last the time it takes to break the surface.
Packing Enough Air
Every entry-level diver learns the importance of managing his or her air supply. This becomes more important when a direct ascent to the surface isn’t available. As a general rule, a diver should monitor his air gauge closely so that he knows his remaining air supply at all times. Estimating how long a supply of air will last at a particular depth is a useful tool, especially when planning penetration dives. (For more information, see “Why You Use So Much Air … and What to Do About It,” Dive Training, July 2005). While most sport divers use a single tank, and a lot of caves and wrecks are safe to dive with a single tank, the use of dual cylinders is common for those who frequent overhead environments. The addition of an extra tank requires equipment modifications and usage procedures that are taught in specialty courses such as Wreck Diver, Cave Diver or Extended Range Diver.
Wreck and cave divers often employ the rule of thirds when penetrating an overhead environment. This allows the use of one-third of the air supply for penetration, one-third for return, and the final third for contingencies and to allow a safe ascent. The technique works well for planned decompression diving, too. Obviously, for this to work, strict discipline has to be maintained throughout the dive plan. It is also very common for divers to carry a redundant air supply.
A completely redundant air source consists of a separate cylinder with its own regulator system. Everything from a 1.7-cubic-foot Spare Air® that fits in a holster or buoyancy compensator (BC) pocket to another cylinder equal in size to the diver’s primary tank counts as a redundant backup system. The size that would be most effective depends on the type of diving, depth, and ease of maneuverability, among other factors. For limited wreck penetration that’s at moderate-to-deep depths (80-100 feet [24-30 m]) a 13- to 19-cubic-foot pony bottle is a good choice. Pony bottles are available for rent at many popular technical diving destinations. Divers planning air travel with scuba cylinders as checked or carry-on luggage should consult the Transportation Security Administration (TSA) Web site (www.TSATravelTips.us) for instructions on how to prepare cylinders for travel.
Some dive operators provide extra redundancy on wreck diving outings by stationing a spare tank and regulator at a designated location on the wreck, to be used only in the event of a low-air emergency. This may be in addition to a “hang tank” found hanging from a line off the stern of the dive boat at a depth of about 15 feet (5 m). It is intended for use by divers who might run low on air during a safety stop.
Accessorizing for Overhead
The accessorizing doesn’t end with the addition of more air. Several accessory items should be added to (and at least one item removed from) the gear bags of those who enter the technical realm. With the addition of each item comes the need to know how and where to secure it, how to deploy it and use it correctly, and how to stow it after use. It’s important for divers to practice these skills in a pool or open-water environment before placing a ceiling overhead.
Safe entry into and return from overhead environments often involves the use of a guideline and reel, which marks the divers’ route and exit path. Each diver should have his or her own line/reel.
Entanglement is a concern when penetration diving, so a good dive knife — one with a serrated edge for cutting monofilament line — is a must. When it comes to knife selection, bigger isn’t always better. There are a variety of multipurpose dive knives available in an array of sizes and styles. Some divers also carry a pair of shears for backup.
Each diver should be outfitted with a minimum of two good dive lights (one large primary light and one or more smaller lights that can fit into a BC pocket as backup) when entering wrecks or caves. Lanyards should be attached to each light for easy use and to prevent loss.
Gloves, though frowned upon on reef dives, are a good idea due to the potential of sharp metal and other hazardous material likely found on a sunken ship.
A compass, while useful for navigating a beautiful stretch of reef, may be of little use while wreck diving, as compasses tend to be unreliable around large masses of metal.
One item useful to sport divers that should be scratched from the accessory list while penetration diving is the snorkel. Inside a wreck or cave, the snorkel can easily snag in confined areas. If a snorkel will be needed later for the surface, a foldable model that can be tucked into a BC pocket is a good choice.
Divers who penetrate into planned decompression dives usually carry with them at least two dive computers and a timing device, either a dive watch or bottom timer. Using one wrist-style computer and one console-mounted style makes it easy to track both units simultaneously. If decompression data varies from one computer model to the next, depending upon the algorithm, it’s best to plan the dive using the more conservative model.
Sport divers know the importance of keeping gauge consoles, alternate second stages, and other danglies well secured and close to the body. This goes double for divers who’ll be finning their way down submerged stairwells or through narrow tunnels.
Sport divers also know the mantra, “plan your dive and dive your plan” but nobody knows it like tech divers. While a typical recreational predive briefing might not involve more than a few squiggles scrawled on a dry erase board, wreck and cave divers go to great lengths when preparing for and planning their dives. They often study detailed maps and drawings, committing key features to memory so that they may feel more familiar with the area when diving it. Many tech divers use visualization techniques on “dry dives” that help them prepare for the psychological challenges associated with tech diving. This type of advanced predive preparation goes a long way toward creating a safer, more enjoyable experience.
Putting it All Together
Just as certain equipment modifications are made for exploring overhead environments, a few basic adjustments to standard diving techniques are tweaked for tech diving, too. Cave divers have developed several kicking styles used to avoid stirring up silt.
One technique is called the “modified flutter kick.” The feet are held slightly up with the knees bent at 90-degree angles to the diver’s body. Motion is accomplished with very small movements of the ankles or calves only. The thighs remain stationary.
Another kick is called the “shuffle kick,” which has the legs placed like the modified shuffle kick; the calves are shuffled a few inches back and forth. Hand motion is minimal, and if contact has to be made with a ship’s hull or cave wall, a single finger can be extended to arrest movement or regain balance.
These techniques will only work with sufficient space and excellent buoyancy control. If a diver is overweighted and struggling to stay off the bottom, it won’t matter what type of fin kick is used.
Proper weighting, control of breathing and anticipating buoyancy changes are very important when diving in confining spaces. The key to proper weighting is to use only the amount of weight necessary to overcome surface buoyancy and to maintain a safety stop at the end of the dive, but efficient weighting involves more than just adding weights to a weight belt or quick-release BC weight pockets. Rather than placing all of it around the waist, many experienced divers transfer some weight where it would help maintain horizontal trim. For instance, a diver whose feet are buoyant might benefit from wearing ankle weights. Some BCs are equipped with nonditchable “trim” weight pockets on the back of the BC to allow for better horizontal trim. Proper weighting and trim takes a little experimentation, but makes for more enjoyable diving and can be important in overhead environments.
Breath control is a way for a diver to fine-tune his buoyancy control. For example, if he were swimming down a corridor and needed to descend slightly to bypass an obstruction, he could exaggerate his next exhalation, which would make him a little less buoyant. The change isn’t instantaneous; there is a short lag time between when air is added or expelled and the expected result occurs. Conversely, to rise above an obstacle, a diver might inhale slightly deeper than normal. Of course, this type of subtle buoyancy control isn’t possible if the diver is overweighted or not breathing in a controlled manner.
Precise buoyancy control is particularly important for those who engage in planned decompression dives. When “deco diving” it is necessary to halt the ascent at specific depths and hover at that depth for several minutes before proceeding to a shallower depth. Here again, breath control is important. The subtleties of buoyancy and breath control can be mastered with continued practice.
Overhead penetration diving is popular with large segments of the diving population, even though any dive that does not allow for a direct vertical ascent to the surface carries increased risk. Does this mean divers who engage in these activities are foolhardy risk-takers? No. There’s a big difference between managed risk and foolhardiness. Those who manage and minimize the risks by getting proper training, using the appropriate equipment, practicing their skills and recognizing their physical and mental limitations can explore the inner chambers of cave or cruise the decks of a submerged shipwreck more safely.
Divers who wish to transition into the world of overhead diving environments should start by perfecting basic skills such as buoyancy control and swimming techniques. Once the basics are second nature, enrolling in advanced and specialty courses is the best way to get the information and skills necessary to tackle more challenging environments. Then you’ll be ready to explore the world of overhead environments and ensure that the experience is not only an enjoyable one, but a safe one, too.
Easing Into Overhead Environments
Not all overhead environments require that divers gear up in dual cylinders with redundant air supplies and other tech accessories. In fact, many intentionally sunk wrecks placed as artificial reefs serve as great “starter kits” for Open Water divers who think they might enjoy the more technical realm of wreck penetration. These ships typically have several large openings cut into them which allow the diver to swim in one side and out the other, with plenty of ambient light penetrating the wreck and an exit point always nearby. Some wrecks even have “you are here” signs permanently affixed to them, with arrows pointing to the closest exit. Others may have permanent guidelines installed as navigation aides.
Cavern diving also serves as a great intro to penetration diving. Cavern diving is limited to the “light zone” — the area at the entrance to a cave where natural light is visible. Introductory cavern tours are offered at many popular dive destinations such as the Florida springs and Mexico’s Yucatan Peninsula.
Other overhead opportunities can be found in lakes and quarries across North America, where divers can swim though interesting “wreckage” such as sunken school buses and airplanes.