Poor underwater visibility cannot always be conquered, but it can usually be tamed to some extent. By doing so the diver not only cuts down the risks, but also increases his productivity and enjoyment.
Visibility, or rather the lack of it, is possibly the greatest and most consistent enemy of the underwater salvor. The
Silent World, as it was called by Jacques Cousteau, is invariably described as one of color and wonder, excitement and silence, with a strange beauty reflecting a frantic sort of calm. The underwater world of the treasure hunter and the marine archeologist often seems vastly different. The seascape is not an endless progression of carnival like colors parading before your eyes. It is, instead, often a pit, dark and somber, cutting out all appreciable light from the outside world. It is a cold clammy world of scrapes and bruises, mashed and bitten fingers. It is inhabited by unseen toadfish, eels, and sharks, which nibble, grab and bite. Tangled lines, cables, trees, overhanging ledges and shifting wreckage are merely dangers that are felt and not seen. Hallucinations loom brighter and are clearer than reality; they mix with the unknown. Fear, whether calm or raging, continually stirs in the recesses of the diver’s mind. The total blackness assumes an identity, a reality of its own. It is there and must not only be fought, it must be conquered. Lack of visibility is probably the biggest factor in turning people against diving or at least diving in certain areas.
THE NOISY SEA
The sea isn’t necessarily quiet. On shallow reefs there is the continual droning of the sea as the waves crash overhead in a muffled roar. Even the fish make noise. Parrot fish grinding away at the coral in a never ending search for food produce a tension building, low range noise that strains the diver as he tries to work in the not so silent darkness. Toadfish, with a mouth full of small but razor sharp teeth and a disposition like a junkyard dog, make a croaking noise. To me, it sounds like they are saying
Gronk!Toadfish seem to love zero visibility waters and hearing their croak only adds to the diver’s natural reluctance to blindly feel along the bottom with his vulnerable hands in search of a prize. Many times, while diving in black water, I have accidentally probed between those ugly creature’s powerful jaws with my fingers. Fortunately their teeth are too short to do any real damage.
This black hell seems to be the natural habitat of anything worth searching for (the wrecks in areas with excellent visibility were more often salvaged at the time of loss) and can be caused or created by any one of the following conditions or situations:
I. Flood waters or heavy runoff from seasonal rains carrying particulate matter eroded from the surrounding countryside may turn waters red in Georgia from the red clay hills; white in the Bahamas from the fine coral sands; and brown in delta areas from alluvial deposits of earth, mud and silt. Some rivers, like the mighty Mississippi, carry large amounts of particulate matter three hundred and sixty-five days a year.
II. Water stained dark by organic matter (such as tannic acid leached from rotting vegetation found in swampy areas, like the Okefenokee, which feeds both the Suwannee River and the St. Marys River).
III. Heavy seasonal concentrations of pollen, plankton or minute organic matter floating, suspended, or swimming in the water.
IV. Breaking surf over the dive site in shallow water with an easily disturbed fine sand, silt or mud bottom.
V. Water too deep for sufficient light penetration, or areas where the light is restricted by overhanging ledges or by vegetation (such as trees along riverbanks or towering kelp on the bottom).
VI. Turbulent water caused by wind driven waves, tidal currents, river currents, etc.
TEMPORARY OR LASTING
Some of these conditions are, by their very nature, temporary and of varying lengths of duration and degrees of severity. Others are relatively constant with only occasional periods of decreased turbidity with the resultant temporary increase in visibility. Those of a temporary nature include seasonal ones caused by periods of heavy rains (see #I), and blossoming flora or fauna (see #II). Whereas, an example of a relative constant state would be #V.
By determining whether or not the poor visibility is of a temporary or lasting nature, the diver can either plan to wait for the increased seasonal visibility
By determining whether or not the poor visibility is of a temporary or lasting nature, the diver can either plan to wait for increased seasonal visibility or he can adapt his diving methods and equipment to suit the particular conditions he will face. Under certain circumstances, the diver might even physically alter his environment.
By far the simplest methods are to wait for improved diving conditions or to dive elsewhere. East Coast divers dive all year around, but they report the time of maximum visibility to be between the last two weeks in November and the end of February. March seems to be the worst time due to high winds accompanied by frequent violent storms. During March the divers simply limit their diving to certain river sites which can be safely worked under all but the worst weather conditions. The period of November through February is the coldest part of the year, but the low temperatures that bring out the dry-suits, are the same ones that kill the uncounted trillions of microscopic flora and fauna, which cloud the visibility during the warmer months. It is also the driest time of the year, so there is less particulate matter from erosion by the rains, which are more prevalent in other times of the year.
The next way to adapt is to change your methods and/or your equipment. This could include such things as using more powerful lights. Unfortunately this is a solution which is helpful only in cases such as #II and #V. The other cases involve situations where there is matter suspended in the water. In these your light would merely reflect back at you causing a blinding situation similar to using a bright light in a fog, and brighter lights would in no way increase your visibility.
If you do use a light, you might consider one of the professional quality, hand mounted or mask mounted lights from
NiteRider. The one I personally recommend is theirBlackwater 3000D Dive Light( http://www.niteriderdive.com/Products.htm ) that sells for $575. Its dimmer switch not only allows you to adjust for conditions, it extends the battery life up to three hours.
Another way to adapt is to use probes. With practice a probe can help the experienced diver differentiate between metal, glass, ceramic or organic objects. The vibrations in sound that the probe (normally made out of a short stainless steel rod with a blunt point and a handle) makes as you strike an object vary. Each type of material gives a unique sound. This difference can be clearly heard and interpreted by a trained diver who uses the probe and his senses together. The probe can also be used to frighten away toadfish and other inquisitive sea life looking to nibble your fingers. A probe can also be used to “look” through the mud and sand without cutting your hands on broken glass while digging in zero visibility.
Digging with your hands into the bottom in zero visibility water can result in nasty cuts when you suddenly find a long sliver of glass. But by using a paddle or by placing your hand in a horizontal position and pumping up and down you can blow a hole in loose sand without touching the bottom. In areas with current, the current carries the agitated sand away leaving the heavier artifacts in the bottom of the hole. In areas with little or no current you need to sweep the paddle or your hand down and across the spot you are digging. Be careful not to touch the sand’s surface, lest you cut yourself on exposed artifacts. Once the hole has been dug you can gently probe for artifacts. After you have dug several hundred holes this way you may begin to notice that your ears can actually pick out the sound of the sand hitting against glass. Sensitive ears may give you an additional tool to use in coping with the darkness.
Communication gear can help to improve safety conditions and coordinate your search in adverse water conditions. The increased communication helps prevent frustrating and/or stressful situations and wasted dive time. It can allow allow you to enjoy added peace of mind and safety by maintaining communication with the surface or with other divers throughout the dive.
There are a number of types of underwater speaker systems offering the diver a wide range of options, but the best equipment allows both diver to diver communication and diver to surface communication. This gear comes both with and without communications cable tying the diver to the surface. Unless I am diving with surface supplied air, I use wireless gear because has no communications cable to get tangled up in the wreckage or other debris on the bottom.
Divelink( http://www.divelink.net/sports.htm ) offers sport, educational, public safety, commercial and military models of communications gear at a wide range of prices.
SURFACE SUPPLIED AIR
Professional divers more often than not, soon learn the advantages of using surface supplied air and find that a properly tended “umbilical” (air hose, communications cable, depth sensor, and safety line mated together) seldom kinks or tangles. It also gives a path that the diver can follow back up to the surface, and more than one diver (myself included) has been hauled back up to the surface by his tender reeling in his “umbilical” when an emergency arose. Helmets used with surfaced supplied air offer added protection to the diver but again are almost prohibitively expensive for the average sport diver, but then, few sport divers care to invade the waters I am writing about anyway so cost versus safety almost becomes a moot point. The best-known maker of surface supplied air units is
Brownie( http://www.browniedive.com/ ).
Divers looking for shipwrecks in clear water are often able to spot the wreckage from an airplane or by towing a diver behind a boat for a visual search. But in black water such methods are useless and towing a diver behind a boat becomes an exercise in futility or if he does find a wreck his dive becomes a suicide mission as he is slammed into the unseen wreckage. Electronic locating instruments such as magnetometers, metal detectors, sonic probes, sub-bottom profilers, and side-scanning sonars can be used to increase the diver’s underwater capability and decrease his exposure to dangerous diving situations.
The proton magnetometer and the cesium magnetometer (or “mags” as they are called) offer the diver a safe more effective way to locate wrecks.
Marine and airborne magnetometers measure variations in the earth’s magnetic field. The cheapest mag worth having runs about $5,000. The best I have owned is a
Geometrics G-882 Marine Magnetometer( http://www.geometrics.com/geometrics-products/geometrics-magnetometers/g-882-marine-magnetometer/ ) and I highly recommend it, but be prepared to spend upwards of $20,000.
You could spend well over $50,000 on a magnetometer but for most projects you would generally be wasting your money, because the extra sensitivity you get for the price is not usually needed for shipwreck exploration. The more expensive equipment is used by the oil industry and is more appropriate for a scientific study of the earth’s crust.
Shipwrecks usually contain large amounts of magnetic interfering material (such as steam engines, boilers, cannons, iron fastenings, and even some of the rock or brick used for ballast) and can be “spotted” by the magnetometer at a considerable distance. Magnetometers have the advantage of not only seeing through muddy waters but can be used to locate wreckage which is entirely buried in the sand. The range for a mag depends largely on the size and configuration of the object being sought and its magnetic potential.
Once a wreck has been located, hand held metal detectors (which have ranges limited from a few inches to a few feet) can be used to search for small artifacts such as coins or jewelry which may be buried in the shifting sands on the wreck. Metal detectors are available with underwater headphones as well as visual gages so they can be used by divers in limited visibility.
Spend as much as you can afford when buying a metal detector as they pay for themselves with added finds. A great place to buy detectors through the mail is
Kellyco( http://www.kellycodetectors.com/Detectorcategories/watersurfdivebeachdetectors.htm). If you can, visit Kellyco’s mega-store in Winter Springs, Florida. They carryCobra,Viper,Minelab,Fisher,Garrett,Whites, DetectorPro,JW Fishersand many other great brands. I definitely trust these people.
Sonic probes (hand held sonars) are useful in mapping underwater topography and reefs quicker or to locate your dive buddy, buoy lines, shipwrecks etc. They can even be used to locate your dive boat after surfacing in swells and waves that make it impossible to see where it is.
Mantasells itsDive Ray( http://www.mantasonar.com/diveray.htm ) for about $300. They definitely serve a useful purpose.
Side-scanning sonars can pick up obstructions sticking out of the ocean floor in almost any visibility and depending on the unit can draw extremely detailed pictures of the wreckage showing amazing detail. Towed units are better than dome mounted or “through the hull” units, as they are less affected by the pitch and roll of the boat. However,
Humminbird( http://store.humminbird.com/products/271398/1197c_SI_Combo ) makes units with transom mounted transducers that sell for under $3,000. They do an absolutely amazing job.
An “inexpensive” towed side-scan, such as that offered by
Seabed Imaging Systems( http://www.starfishsonar.com/store/parts.htm ) will run you about $3,500 while the higher priced models with all of the “bells and whistles” and map making capabilities can cost many times that. Even the low end units can turn out some stunning performances, producing sonographs so detailed that you can recognize something as small as a one inch rope suspended between two fish traps. As good as the machines are, the operator is still the biggest factor in their successful use.
Sub-bottom profilers can be used to locate objects buried in soft mud and some sands, but their prices run into the tens of thousands of dollars and require extremely skilled technicians to operate, maintain and interpret. They are frequently sold as an add on to a side-scan package. To learn more about sub-bottom profiling, check out NOAA’s page on Benthic habit mapping ( http://www.csc.noaa.gov/benthic/mapping/techniques/sensors/subbottom.htm ).
TV’S AND ROV’S
Closed circuit television cameras, whether remotely operated, suspended or diver held, often have the capability of seeing more than the diver’s eye and are excellent tools for searching a wreck with little or no bottom time. Look for wide-angle lens, high-resolution, and low-light requirements.
Sea Viewer Underwater Video Systems( http://www.seaviewer.com/underwater_video_cameras_offshore_complete_system.html ) has a boat dropped color video system complete with monitor that runs about $1200.
Underwater ROVs are remotely operated vehicles that can be fitted with cameras, grabs, sonars, etc. Driving an ROV is similar to operating a video game. ROVs such as those used in the oil industry can cost millions of dollars, but a simple ROV can be built for under $250 ( http://www.engadget.com/2007/09/04/build-your-own-underwater-rov-for-250/).
VideoRay( http://www.videoray.com/products/6-scout ) has professional quality ROV units starting about $6,000.
Many professional divers view the buddy system as an added danger saying that they have enough to worry about just looking after themselves. They may or may not be right. However, divers who do decide to use the buddy system in zero visibility might consider using a six foot aluminum rod between them, as they can signal each other with it and they certainly can’t get tangled in it as they might with a conventional safety line. The rod should have a lanyard or loop on each end for the diver to place over his wrist in case he needs to drop it to use both hands for a minute.
Heavy protective clothing, such as gloves and wetsuits (or drysuits), should be worn to reduce the incidence of cuts and abrasions. Diving in limited visibility takes its toll on diving gear as well as on the diver, as gear is easily damaged or lost in the dark waters. Common overalls can be worn over suits to prolong their life. Thick rubber pads may be added to the knees and elbows of suits when divers expect to be doing a lot of crawling over hard rough bottom.
KNIVES AND SPEARGUNS
Divers need to carry a sharp knife to cut themselves free of entangling lines or nets that they may encounter in zero visibility. Knives should have a serrated edge that is capable of sawing through heavy line. Diving knives always seem to be the first thing you lose on a dive, so a small back up knife is a wise idea.
Under no circumstances should a diver take a spear gun or “bang stick” into zero visibility waters under the mistaken impression that it will protect him from sharks. If you can’t see the shark, you can’t shoot him without a lot of luck, good or bad. Instead you are more likely to injure yourself or another diver. As a rule of thumb I won’t enter low visibility water if other divers are carrying bang sticks. I would rather trust my luck with the sharks.
Another way to overcome visibility problems is to purify the water, or to blanket the work area with clearer water from another source. In 1967, Norman Scott, president of Expeditions Unlimited,” excavated the sacrificial well or cenote at Chichen Itza, Yucatan, Mexico, by treating the entire cenote as though it were a giant swimming pool. Scott, aided by Purex Corporation, purified the water to such an extent that the divers were not only able to see what they were doing, that underwater photographer Mike Freeman was able to get shots that were later used in the
National Geographicmagazine article on the expedition. For more on Scott’s expeditions read: ( http://articles.orlandosentinel.com/1992-08-09/news/9208050974_1_amber-chamber-norman-scott-nazi-gold/2 ).
The same idea was employed in the river at Yorktown, Virginia, by underwater archeologist John Broadwater when he excavated a wreck from the American Revolution ( http://www.jstor.org/pss/25616193). A cofferdam was constructed in the river around the wreck and the water was purified so the work could be carried out in clearer water. Since the water wasn’t being pumped out as you normally do with a cofferdam, the cofferdam didn’t have to be as strong (and therefore as expensive) as a regular cofferdam. The cofferdam had the added benefit of blocking the currents, which would have otherwise plagued the divers. That project also appeared in
Divers in some coastal areas have noticed that the surface waters always seem to be clearer than the water along the ocean floor. They have found that by anchoring their boat at four points, and directing the boat’s propwash straight down, that they can increase the visibility on the wreck sites they are working. In some cases this can mean an immediate increase from absolute visibility to four or five feet of visibility. This is accomplished by attaching a giant pipe elbow to the stern of the salvage vessel. The elbow swings over the propeller and locks into place. The unit is called a “mailbox,” “propwash deflector,” “blaster,” “deflector” or “PDU” and directs the propwash downwards rather than just allowing it to flow behind the boat.
Besides providing the diver with a continuous stream of clearer water, the deflector can be used as a powerful tool for excavating through agitation dredging. When the boat’s engine is run above idle, the propwash exerts enough force to blow the mud and sand away. The boat is positioned by the use of multiple anchors and the taking in and letting out of anchor lines. I once used a boat with four one-ton mooring anchors. Each anchor had a half-mile of wire cable on air powered winches called air tuggers. Depending on how it is controlled a deflector can be the boon or bane of archeologists and salvors. Properly used it can slowly dust off a fraction of an inch of sand at a time, allowing ample time for the careful observation, recording, and recovery of artifacts. Improperly used it will blow artifacts away with the sand. It is often used in areas with heavy sand or mud overburden as even a small propwash unit is capable of digging a five-foot deep hole in twenty feet of water in a matter of minutes.
Depending where you are working, may need a permit to use a PDU for digging. The late Mel Fisher’s treasure-hunting company, Salvors Inc., was fined $589,311. ( http://www.archaeology.org/9711/newsbriefs/florida.html )
Divers using a suction dredge often find they are surrounded by a cloud of muddy silt. This can be reduced or eliminated by using part of the water that powers the dredge as a water jet. The water jet in its simplest form would be a pump on the surface forcing water down to the diver through a hose with an adjustable pressure nozzle. Some water jets are pressure compensated with a back jet to prevent the hose from bucking while the diver is using it. Pressure balanced nozzles allow the diver to use a far larger system. Water jets can be used to cut through hard packed mud, blow sand away, or just to introduce a steady stream of clearer water into the work area. I have used a water jet to pump clearer water into an enclosed area where it would be impossible to use a PDU.
INCREASED SAFETY AND EFFECTIVENESS
Lack of visibility has been repeatedly cited as the chief drawback to underwater archeology (and treasure hunting) in the coastal waters of the United States. An artifact taken from the water tells only part of its story unless the diver recovering it is able to fully examine and record the area surrounding it. In fact it would be best if an overall photo-mosaic could be made of every wreck site. Unfortunately, low visibility usually prevents such conveniences.
At one site the wreckage of two iron ships was so confusing to divers that they were almost unable to discern one wreck from the other in the dark water. Archeology on the site was impractical and salvage limited, until a propwash deflection system was used to increase the visibility. With the increased visibility the archeologists were able to clearly differentiate between the two shipwrecks and begin to understand exactly where to search for cargo. The cargo holds were quickly located, photography was possible, and artifacts were rapidly recovered (without losing provenience). Two extremely rare cannon were found less than one foot from where a line had been tied by the same divers five years earlier. Diving accidents were prevented by the increase in visibility and both archeology and salvage were suddenly possible.
The enemy, poor visibility, cannot always be conquered, but it can usually be tamed to some extent. By doing so the diver not only cuts down the risks, but also increases his productivity and enjoyment.
© 2010 by Edward Lee Spence. This has been revised from my original article that was titled
Black Water Diving.To quote more than a paragraph of this article please contactDr. E. Lee Spenceat HunleyFinder@Yahoo.com