All The new movie Open Water wont win diving many converts with its depiction of a couple separated from their dive-boat through a simple head-count muddle. But how realistic is this scenario Steve Warren looks back through case histories and suggests that divers need to take safety into their own hands

Toshiko Nakanishi is dead, along with four of her companions and their dive guide. Toshiko was one of the Palau Six. They were not the victims of shark attack, deep-diving or the bends. They were simply left at sea.
ÂÂÂÂ The group was exploring Peleliu, a part of the Micronesian diving destination renowned for its fierce currents. The divers are thought to have surfaced within sight of Antelope Divings dive boat, which was anchored.
ÂÂÂÂ According to reports, the engine wouldnt start and they couldnt swim to the vessel against the current. There was no safety boat and, apparently, no way in which to summon aid.
ÂÂÂÂ It took an hour to get the motor running. The skipper then reportedly searched for three more hours before going for help. The alarm was not raised until late afternoon.
ÂÂÂÂ The Palauan authorities launched a massive search effort, but by now night had fallen.
ÂÂÂÂ The bodies of three divers were found next day some 10 miles from the dive site. The others were never found.
Those dreadful events in the early 90s might have been expected to send shock waves through the diving industry, yet in the 10 years since the six died, boats have lost divers time and again.
ÂÂÂÂ Divers depend on boats and their crews for access to offshore dive sites, but at times it seems we are willing to entrust our lives to operators whose attitude to safety may not stand up to scrutiny.
ÂÂÂÂ Perhaps it was the distant location, Palau, and the fact that it was Japanese tourists who lost their lives, that kept the Western media at bay in 1994. But four years later an incident off Australias Queensland coast caused a bigger stir.
ÂÂÂÂ Thomas and Eileen Lonergan of Baton Rouge, Louisiana, had been diving from the North Queensland vessel Outer Edge. There were 26 guests on board when the boat headed out to St Crispins Reef, but when she returned to dock, 40 miles from the reef, there were only 24.
ÂÂÂÂ Two pairs of shoes left on the dock might have alerted the five crew-members but the Lonergans were missed only when more of their belongings were found on board days later - 48 hours had passed before a search was mounted.
ÂÂÂÂ Coroner Noel Nunan concluded that the couple had eventually met their deaths by drowning or shark attack, and charged Outer Edges owner Jack Nairn with unlawful killing. When you combine the number of mistakes and the severity of the mistakes, I am satisfied a reasonable jury would find Mr Nairn guilty of manslaughter on criminal evidence, said the coroner.
ÂÂÂÂ The jury did not. Col McKenzie, a Queensland dive industry representative, told me: The prosecution failed to prove that Jack Nairn was criminally negligent in leaving the Lonergans behind - or that they were, in fact, dead.
ÂÂÂÂ The Lonergan incident has been surrounded by speculation, and McKenzie is one of many in the Australian diving industry who give credence to rumours that the Lonergans faked their own disappearance.
ÂÂÂÂ A slate was found with the words: Please help us. Find us soon before we die. So was a fin, marked Eileen L. Dive Queensland, an industry association, alleged that these were planted by the Lonergans. Most marine experts, myself included, feel that the Lonergans are not dead, says Col McKenzie.
ÂÂÂÂ Claims were made that another dive boat returned to base with three extra divers aboard and that a hotel worker and a TV crew saw the Lonergans after they had been reported lost. But the police found no evidence that the couple had fabricated their disappearance or, as was also suggested, committed suicide.

Col McKenzie does not dispute that Outer Edge failed to count all its divers back on board. What happened that day was that there was a communication and systems failure on the Outer Edge, he says. The Lonergans were signed into the water by one divemaster. The divemasters then swapped roles and the Lonergans were signed back on board incorrectly by one of those divemasters. To compound the problem, when the head count was done by the senior instructor on board, he miscounted.
ÂÂÂÂ At the inquiry, confusion over the headcount remained. A dive instructor first claimed not to have made the count, then changed his story. Explaining the miscount, another told jurors: The tourists are constantly moving around you. Theyre on holiday, theyre chatting and drinking, wandering around...
ÂÂÂÂ Barely two years later, a strikingly similar incident occurred in Florida. Aqua Nut 11 is a boat operated from Kellys on the Bay, a motel and PADI dive centre complex on the Key Largo spur, and its problems began when Michael and Lynda Evans were left on John Pennekamp Reef.
ÂÂÂÂ Pennekamp is popular with both American and overseas divers. There were 25 guests aboard when Aqua Nut 11 slipped her moorings on 22 February 2000.
ÂÂÂÂ Captain James Evans (unrelated) and a divemaster oversaw the running of the vessel as she headed for the Elbow dive site, some six miles offshore.
ÂÂÂÂ After their first dive, the Evans surfaced to find that Aqua Nut 11 had departed for the second, and final, scheduled dive and was out of sight.
ÂÂÂÂ Two divers made the second dive, then the boat returned to her berth at Kellys.

It was alleged that neither Captain Evans nor his divemaster conducted a head count. The Evans gear bags remained stowed under a bench seat, apparently unnoticed. Above them two unused cylinders, prepared for the second dive, stood in the racks next to the empty spaces where their used bottles should have been secured.
ÂÂÂÂ Later, when someone at the centre noticed that the couples rented BCs had not been returned, staff responded by leaving a message on their home answerphone requesting their return!
ÂÂÂÂ Back at Pennekamp, the Evans switched to their snorkels and swam for a light tower used to mark the reef - a 130m swim in 1.2m seas. They tied off their BCs and tanks near the base and scrambled onto a small platform to keep clear of the rising swells.
ÂÂÂÂ Lyndas gear eventually broke its lashings and drifted away, to be found by another dive operator who reported it to Kellys. Kellys staff thought it was a set that had been stolen earlier, so still no alarm was raised.
ÂÂÂÂ Fortunately, by this time the Evans were on their way back to the dive centre. They had clung to each other for warmth through the night, with Michael flashing his torch into the darkness at intervals. Daybreak saw the water still rough, with little boat traffic, but a yacht eventually spotted them and alerted the Coast Guard. Twenty-six hours after entering the water, Lynda and Michael Evans were finally safe.
ÂÂÂÂ A prosecution followed, and this time it was successful. Ricardo Investments, which owned Aqua Nut 11, pleaded guilty to endangering human life by the grossly negligent operation of a dive vessel. It was fined $1000, placed on probation for two years, and required to operate Aqua Nut 11 under US Coast Guard supervision, also for two years.
ÂÂÂÂ Judge James Lawrence King also ordered it to set up and operate an effective safe diving program with help from recognised industry experts. The steps it took were to be made available to any interested parties in the Keys.
ÂÂÂÂ As a result Kellys adopted the DAN tagging system, whereby divers must take a tag from a board before entering the water and return it when they come back. It says it now has four separate cross-checks from check-in to the boats return, and that the Coast Guard is satisfied that the requirements of the court order have been fully met.
ÂÂÂÂ The following year, in the Egyptian Red Sea, a press trip again showed how easily things can go wrong. The liveaboard Tiger Lily set sail carrying representatives of the British diving press invited by tour operator Goldenjoy expecting to be suitably impressed by the new addition to the fleet. At Big Brother, freelance writer/photographers Stuart Philpott and Kevin Capon surfaced from an afternoon dive to find that their liveaboard had departed without them.
ÂÂÂÂ Time passed as Tiger Lily cruised off to Little Brother. It was only when the others sat down to supper that it was realised that the pair were not on board.
ÂÂÂÂ Philpott and Capon had hauled ashore onto Big Brother, both being cut by coral in the process. Tiger Lily finally got back to the site after dark but Capon used the safety beacon in his camera strobe to catch its attention.
ÂÂÂÂ In both the Aqua Nut 11 and Tiger Lily incidents, the divers were able to make landfall, but for those lost at sea their survival times are likely to be shorter. Also, as time passes, the area of water that needs searching grows ever greater.

Last August, it happened again. PADI Advanced Open Water divers Olga and Robert Kazarian, both in their 30s, slipped over the side of a speedboat operated by Sandals resort in Cuba to celebrate their 100th dives. The small boat carried about a dozen people, including the captain and two professional instructors.
ÂÂÂÂ The Kazarians followed their guide as briefed, arriving back under the boat after 40 minutes. They had plenty of air left so, with the guides agreement, they decided to surface last. The guide escorted the other four divers in the group towards the surface and signalled to the Kazarians to stay near the anchor line. They watched the others board the vessel and then ascended the anchor line to make their own safety stop.
ÂÂÂÂ Halfway through the stop, the engines started. The boat moved forwards to free its anchor and the couple dived swiftly to 9m to avoid the propeller. Once they felt safe, they surfaced to find the boat gone.
ÂÂÂÂ At first we thought the boat was simply changing position, Olga told me. Then we thought that one of the older passengers might have suffered a heart attack. In reality Olga and Robert had been overlooked. The boat headed back to drop off its passengers, picked up a new set and headed back out for another dive. A holidaying British divemaster, did query the Kazarians whereabouts, but her concerns were dismissed.
ÂÂÂÂ Alone, within sight of land, the couple initially assumed that Sandals would quickly spot their absence and arrange for them to be picked up. They had, after all, left clues - they were using rental tanks, and had left some personal items at the dive centre.
ÂÂÂÂ But in choppy seas they were soon in difficulties. They were using almost all their own equipment but were ill-equipped to help themselves. They had no safety sausages or snorkels, and Roberts mask was swept away when he pushed it onto his forehead.

They struck out for the distant shoreline, but found the currents too strong. At one point Robert thought he saw a shark circle them. He had been swimming on his back and craning his neck and it was bleeding slightly from rubbing against his BC. They were also getting cold.
ÂÂÂÂ A small boat came into view, but when the Kazarians shouted and waved, the people aboard waved back cheerfully and carried on.
ÂÂÂÂ Rescue came after about three hours - in an unlikely guise. As the exhausted couple passed Beaches, another Sandals resort, they crossed the path of a pedalo.
ÂÂÂÂ At one point during their ordeal, Olga and Robert had exchanged goodbyes. The couple go to the gym three times a week and believe they survived in part because of their fitness levels.
ÂÂÂÂ If it seems dramatic to suggest that divers could lose their lives on the surface, such deaths are documented. In June 1999, two divers found themselves on the surface half a mile from their cover boat off the English coast. They were not spotted, though, to his credit, the skipper raised the alarm at once.
ÂÂÂÂ A helicopter, a lifeboat and several other vessels began searching and the two were located within 70 minutes, but one had already been overwhelmed by the sea conditions and was dead.
ÂÂÂÂ Is separation from your dive boat an occupational hazard It shouldnt be acceptable, maintains Olga. There are very simple procedures like a headcount and if this had been done this incident would have been easily avoided.
ÂÂÂÂ Robert concurs: If youre a teacher and you take 20 children somewhere, you always count.
ÂÂÂÂ We were very friendly with the boat captain and all the diving instructors, says Olga. It was halfway through our holiday and we thought people had got used to us. Thats what shocked me.
ÂÂÂÂ But as many of these incidents show, you cant assume youll be missed by either the crew or other guests. Now, we always tell our story on the boat and joke dont forget us! says Robert.

The Lonergan case resulted in DAN (Divers Alert Network) creating a simple and inexpensive tagging system for dive boats to use. However, despite all the publicity that incident created, and the lessons that many boat operators took on board, it seems that progress has been less than uniform across the industry.
ÂÂÂÂ And if boat operators dont get their act together, strict policies may well be enforced from outside the industry.
ÂÂÂÂ Following yet another case, this time off Los Angeles when Dan Carlock was left at sea by Ocean Adventures Dive Company, the US Coast Guard is demanding that PADI implements standardised accounting procedures among its divemasters. And it is hoped that agencies such as PADI, which dominates the international diving market, will act to export higher safety standards overseas as well.
ÂÂÂÂ Though problems can clearly arise with counting divers in and out of the water, in many of the incidents recounted it was the slowness of those on the boat to realise that a separation had occurred that was the defining factor.
ÂÂÂÂ Quick response is vital if missing divers are to be recovered, but too often, even when the problem is identified, skippers have seemed reluctant to raise the alarm at once, resulting in significant delay in the early stages of a developing crisis.
ÂÂÂÂ In 1998, the fishing vessel Sovereign picked up three drifting divers. The divers had not been reported missing by their own dive boat but by those aboard a passenger vessel who had observed the dive boat searching alone in the area of the Longstone Lighthouse.
ÂÂÂÂ Tyne Tees Coastguard then contacted the dive boat to confirm that there was indeed a problem, and launched two lifeboats and a helicopter.
ÂÂÂÂ A recent incident in the Maldives shows the value of fast communication. A seven-strong group entered the water from a boat operated by Sub Aqua from the Hilton Maldives on Rangali Island.
ÂÂÂÂ The group surfaced around 250m from their boat but their safety sausages were not spotted and, overcome by the strong current, they were borne out into open sea. Because the divers were reported missing, a search was able to be organised straight away. Five of them were recovered after four hours adrift by another dive boat and the other two by fishermen. Even with a rapid alert, finding lost divers in areas of strong currents can still be difficult.
ÂÂÂÂ And assuming that it is easier to locate divers in areas of high boat traffic would be dangerous. Phil Smith is a BSAC First Class Diver and National Instructor who serves as Regional Coach for Gibraltar and Southern Spain. Hes a veteran of expeditions to Bikini and Canada, a former diving supervisor for Operation Raleigh and heads a military sport-diving club with an excellent safety record. All its boat-handlers are qualified and the boats carry radios and flares.
ÂÂÂÂ In October 1997 Phil and a buddy were doing a routine dive on Europa Reef, a mile off Gibraltars western coast. We were to spend 25 minutes maximum there, then deploy a DSMB before making our ascent, he said.
ÂÂÂÂ But when the DSMB was deployed the line seemed slack. We reeled in until the bag came back to us. It had split along the entire seam down one side and sunk. No problem, as I had my bag. I attached it to Jacquis reel and gave it a good blast of air. Unfortunately, her reel was fitted with a plastic clip and this parted and let the bag go up alone. We now had two reels and no DSMB.

The pair surfaced normally, pausing to make a brief safety stop. The wind, swell and current had picked up slightly, but we were still fairly close to the cover boat. We shouted, but we were upwind and they couldnt hear us.
ÂÂÂÂ Phil recovered the working DSMB on the surface. However the divers and their boat were now quickly separating. The cover party had acted very quickly when they realised we were overdue. They left the shot to mark the original spot, informed the Coastguard and began a search pattern, said Phil.
ÂÂÂÂ The search was quickly joined by boats from the Gibraltar Squadron RN, Gibraltar Police, Services Police and a visiting diving expedition. Although plenty of small fishing boats and pleasure craft are usually active in the area, nobody spotted Phil and Jacqui.
ÂÂÂÂ We had given up thoughts of rescue and were just slowly swimming towards the nearest landfall when one of the search boats spotted my bag, said Phil. The pair had been at the surface for an hour, and had drifted around the headland, out of the Atlantic and into the Mediterranean.
ÂÂÂÂ I now insist on both divers having a full DSMB system, fitted with metal clips, Phil told me. My whistle is now cable-tied to my BC inflator hose, so its instantly accessible. I now always carry a collapsible flag, signalling mirror and strobe.
ÂÂÂÂ Paul Bew is a Sail, Power and Ocean Yachtmaster Examiner for the RYA and owns Capital Sailing, Londons largest sea school. He has worked as a dive charter skipper in Australia and knows why missing divers are so hard to spot.
ÂÂÂÂ Youre looking for somebodys head, which is the size of a cabbage. Youd be hard pushed to see that on a motorway a third of a mile away, let alone in a seaway. That assumes flat water. In a short chop, say 30cm, you become much harder to spot.
ÂÂÂÂ Ideally both the boat and the lost diver will be on the crest simultaneously. And someone on the boat has to be looking at the right place.
ÂÂÂÂ Its harder still if youre looking into the sun. Your chances of being seen keep reducing.
ÂÂÂÂ The distance over which a boat crew has line of sight is surprisingly short. From a small boat like a RIB, it can be less than three miles. Not only are they looking for a cabbage-sized object but its likely to be disappearing fast.
ÂÂÂÂ A diver caught in a 2 knot current is travelling at more than 2mph. The further from the boat the diver drifts, the greater the search area to be covered, allowing for sideways drift as well.

Even in the UK, well-equipped professional search teams sometimes fail to find missing divers. Three members of Wellington BSAC were cast into the sea off the south coast after their RIB hit a freak wave in 1994. They survived for 16 hours while trying to swim to shore.
ÂÂÂÂ One diver, Nick Chipchase, later criticised the Coastguard, claiming that it had concentrated its search near where the RIB had been found after it ran out of petrol.
ÂÂÂÂ Dive charter skipper John Walker looked over the trios dive plan and planned his own search. All were picked up close to where Walker predicted they would be, two by Walker himself, the third by another fishing boat.
ÂÂÂÂ In 1998 Rob Hadfield, 20, and his 50-year-old buddy dropped towards the wreck of the Moldavia, 25 miles off the Brighton coast. A strong current was running.
ÂÂÂÂ Robs father, Ian, writing an account of his sons death in Diver (September 1999), speculated that his ascent was compromised by the decompression shotline failing to reach the surface and his DSMB becoming entangled in it.
ÂÂÂÂ It is likely that Rob completed his stage decompression stops and surfaced out of sight of his dive boat, Spartacus. He should have been up at around 3.25, Ian estimated, but Spartacus did not raise the alarm until 4.50, according to Coastguard reports.
ÂÂÂÂ Four lifeboats and two helicopters began to comb the area and the hunt was stepped up when the RFA Sir Percival and five merchant ships joined in. The search area now covered 45 square miles with visibility clear and the seas calm. But about 24 hours after the alarm had been raised Solent Coastguard began to wind down its search.
ÂÂÂÂ Ian Hadfield expressed concerns about the way in which the search for his son had been conducted. But assuming that Rob did make it to the surface, the case underscores the point that even the combined resources, expertise and experience of the Coastguard and the Royal Navy failed to find him. What chance then for divers lost in less well-protected locations

Diving often takes place in destinations that are comparatively poor. Big-name hotel chains may open, and dive centres multiply, but this private investment wont necessarily extend even to providing a local recompression chamber. Financing an effective air-sea rescue service may not be a priority and local government may lack the resources or the interest to mount an effective sea and airborne search.
ÂÂÂÂ When a diver sustained a mild bend on a liveaboard near Male, the Maldives capital, the boat could not travel to the chamber safely through the darkness. Despite the tourist dollars divers contribute to the economy, no rescue boats or helicopters were equipped for night work. A lost diver could well be left to drift overnight before an effective search could be mounted.
ÂÂÂÂ A lot depends on the boat crew. When the Brighton-based Sandy Diver realised that two of its divers were missing, it began a search by heading against the tide. We were the second pair in and missed slack water, said Nick Rumble, who was diving with a buddy. Tony and I made our dive with simulated decompression stops.
ÂÂÂÂ I think we had our DSMB up 10 minutes before we surfaced and we came up just off the stern.
ÂÂÂÂ We tried to swim for it and couldnt fight the current. The water was quite choppy and we may have been in a blind spot caused by the sun. That might have made it impossible to see us. The wind drowned out our distress whistles.
ÂÂÂÂ The pair watched as Sandy Diver returned again and again to the shot, but it was only when a passing fishing boat apparently stopped to ask if there was a problem, an hour after the pair had surfaced and begun to drift into the English Channel, that the Coastguard were called.
ÂÂÂÂ Four and a half hours later the divers were winched to safety by a rescue chopper.
ÂÂÂÂ As a skipper, youve got to think that if things go wrong and somebody dies there will be an inquiry and maybe a court case, says Paul Bew.
ÂÂÂÂ Youll have to stand in front of a jury that knows nothing about boats and diving and theyll say to you: You put them in, when did you expect them to come up 11.30. When did you put out the Mayday 12. Why did you delay Well, I thought Id find them.
ÂÂÂÂ It wont wash. Youve also got to think, what would be best for me if I was in the water

Phil Smith concurs. Looking at the timeline of a developing incident, he points out: If you do get lost at sea, your chances of recovery are greater the nearer you are to your dive site, which is when youve just surfaced. If youre marshalling, dont delay in making the call, as this only makes the search more difficult later.
ÂÂÂÂ Before we get too gloomy, some amazing stories illustrate that there is always room for optimism. February 2000 saw Briton Paul Lucas caught in strong currents 250 miles north of Sydney, Australia. Separated from his group, he spent 24 hours in the water, but was lucky enough to make it onto a deserted island, where he took shelter in a cave. He remained on the island for 15 hours until spotted, by chance, from a motor cruiser.
ÂÂÂÂ Senior constable and police diver Ian Morris made a telling point: There was little likelihood that an official search would have located Mr Lucas, as he had surfaced five miles west of where they would have been looking.
ÂÂÂÂ And in 2002 a Boxing Day dive off Negombo, Sri Lanka, went badly wrong for two instructors and three students from Aquatic Adventures after they were swept away. Like many other lost divers, they initially surfaced close to the boat, but werent seen.
ÂÂÂÂ The group tied themselves together with weightbelts to avoid separation. A Navy air and sea search was quickly mounted and after 21 hours at sea the group were rescued by a fishing boat.
ÂÂÂÂ Divers themselves often contribute to the problem by failing to respect briefings or comply with dive plans, or to be suitably equipped should the worst happen.
ÂÂÂÂ Not all divers carry personal location devices, yet it takes little effort to carry suitable devices in a BC pocket.
ÂÂÂÂ Phil Smiths inflated DSMB was seen, but whether his head alone would have been visible is debatable. Had Rob Hadfield been carrying a second DSMB, things might have turned out differently but, as demonstrated in the Sub Aqua and Sandy Diver incidents, even these may not be visible from the boat.
ÂÂÂÂ Toshiko Nakanishi of the Palau Six watched in vain as aircraft overflew and ships passed her by because she had no way of attracting their attention.
ÂÂÂÂ Her testimony to their failure to save her was written on her dive slate. After two days at sea she wrote: Can see a passenger boat and airplane to the right and one to the left. For one minute and two minutes. Quite near but...


When the Lonergans went missing in Australia the well-publicised story had far-reaching implications for dive operators.

Glare on the water can make divers difficult to spot

By day divers can be difficult to spot if the sea is heavy.

If lost at night, carrying some sort of light signal could be a life-saver

A diver making a 15-minute deco stop on a DSMB could cover half a mile in a 2 knot current

Conducting an effective search depends on conditions, time elapsed, the skill of the searchers - and how visible the divers have made themselves

Carry items of equipment that help you to be seen. Low-tech solutions are usually best because they work even after long periods of inattention to maintenance.

A flag on an extending pole in a high-visibility colour (yellow has been proved to be most effective) can be seen over a distance of many miles.

Sausage-shaped surface marker buoys aid detection. Choose one that can be inflated and left inflated [2] rather than the open-ended type.

Consider using a mirror or heliograph. Even a discarded CD secured by a piece of line would make a good reflector in sunny conditions.

Carry a signal-strobe on all dives and replace the batteries regularly. If you are lost at sea you might well be in the water overnight. Rescue helicopters carry image-intensifiers that enable crews to see strobe lights from a distance.

Make sure you have some radar-reflective panels on your hood and upper equipment.

Dont rely on air-horns or whistles.
A boat handler might hear a siren but the problem lies in being able to gauge the direction from which the sound is coming. Compressed-air sirens function for only as long as there is air left in your tank. Whistles are usually too puny to be heard over the sound of a searching boats engine.

Flares have limited use, because you can never be certain that they will work properly - and they rely on someone being there to see them at a certain moment. They dont necessarily pinpoint your position, either.

Dye-markers, which stain the water around you, will aid a search from the air by making the target bigger, but they should be deployed only on sight of a search aircraft.
PLBs (Personal Locator Beacons) are radio devices that function similarly to the EPIRBs (Emergency Position Indicating Radio Beacons) found on lifeboats [4]. They are not powerful enough to send a signal to a satellite and initiate a rescue scenario involving planes and boats, as will a proper EPIRB, but they rely on someone equipped with a suitable tracking device knowing that you are lost.


Be sure that if you are separated from your boat someone will realise that you are lost. See that your dive boat has a foolproof checking system, whether in the form of a roll-call or an effective tagging system.

Stick to the dive plan and dive duration agreed with the crew. This will help avoid the sort of false alarms that make dive supervisors reluctant to call in help if a diver is overdue. Youre more likely to be located if you surface when and where you are expected.

Dont always be the last pair up.

However popular you are, dont assume you will be missed. Agree with other divers to check each others presence aboard after each dive.

If you surface to find no pick-up boat in sight, stick with your buddy. If its a long wait, dump your weights and use the belts or a line from a reel to stay linked.

Keep your BC if you dump the rest of your gear.

Never lose hope. Survival requires willpower.

A welcome sight as you surface.

Sealable safety sausages are worth taking on all dives.

Take steps and you neednt fret about whether the boat has left without you!

There are various tagging systems, like this one from DAN. Tags are taken off the board and clipped onto you during the dive - the boat wont leave until all the tags are back.

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