Stranded while drift diving

Conditions on the first dive of the day included a fairly swift current and excellent visibility.

This was a scheduled series of dives between a charter boat and a dive boat.
Five divers between the ages of 30 and 70 went on a drift dive for the second dive of the day in the late afternoon. The plan for the drift dive included the dive boat taking the divers to the dive site and the charter boat remaining stationary.

The captain of the dive boat accompanied the divers as divemaster, and a designated crew member remained aboard the dive boat to monitor and retrieve the divers after they surfaced. Post-dive the dive boat was expected to return the divers to the charter boat. Unfortunately, the dive boat experienced complications when the crew member fouled the prop in the line floating off the rear of the boat and was therefore unable to follow the divers while they drifted. It took a significant amount of time to cut the line and free the prop, so the crew member was unable to simultaneously monitor the divers. By the time the dive boat was mobile again, he could not locate the divers, and he had not let the charter boat captain know about the delayed status of the dive boat.

Meanwhile, the divers surfaced with no boat in sight. It is estimated the divers had drifted a few miles from their entry point. One diver had an inflatable signalling sausage, but the crew member on the dive boat did not see it. The dive group decided to swim for 45 minutes until they reached the shore of a deserted island. They had no means of communicating to any boats or calling for help. Having had no communication from the dive boat, the charter captain felt the divers were long overdue so using a smaller console boat he began searching for them and he eventually found and retrieved the entire dive party approximately one hour after they had reached the shore. Other than exhaustion, the divers experienced no injuries

DAN comments

Thorough pre-dive planning for a worst-case scenario may seem excessive. However, this case shows the benefit of critically discussing and reviewing dive operation plans. Details disregarded as minor may be crucial in an emergency situation. Diver monitoring, communication protocols and diver preparedness are three areas in which this dive operation plan could have been improved.
Drift diving from a boat is when divers ride the current through a dive site and, instead of swimming to the boat upon surfacing, are followed and picked up at the conclusion of the dive. Following divers’ bubbles can be an effective monitoring plan; a more dependable way is to utilise a float line. This requires a diver to tow a line and a surface marker, usually consisting of a float with an attached diver-down flag. The surface marker provides a more noticeable reference of the diver's location than bubbles, especially in rough waters.

‘Ideal’ conditions

The divers reported ideal diving conditions; even so, a surface marker could have provided a better reference point than bubbles alone, especially as the dive boat crew member was distracted by freeing the boat prop. It is unknown if there were any other crewmembers or "bubble watchers" aboard the dive boat but it is helpful to have more than one person observing from topside to ensure the location of the divers is known

Communication failure

An important detail in this incident is the failure of communication between the two boats. Had the charter boat been notified of the mishap with the dive boat's prop, the charter boat captain could have provided assistance sooner, potentially preventing the divers from becoming stranded. Just as dive buddies need to ensure effective communication via hand signals, dive boat operators should also maintain effective communication devices and protocols when dive planning.
The preparedness of the divers should also be considered. The diver reported a safety sausage was deployed once the divers realised the boat was nowhere in sight. Unfortunately, the safety sausage went unnoticed, and the divers had no other signalling devices available. Visual signalling devices should be large enough and brightly coloured to be noticed from afar. To be prepared for various scenarios, it is recommended to have a variety of signalling devices available while diving.

Being stranded at sea is psychologically taxing as well as physically demanding. Hazardous marine life encounters, dehydration, exhaustion and hypothermia are all possible life-threatening scenarios. This case serves as a reminder that thorough dive operations planning and thoughtful consideration to details can have a big impact on dive safety.

References:

1. Doolette DJ, Gerth WA, Gault KA. Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives. Technical Report. Panama City (FL): Navy Experimental Diving Unit; 2011 Jul. Report No.: 11-06.2. Spisni E, Marabotti C, De Fazio L, Valerii MC, Cavazza E, Brambilla S, Hoxha K, L'Abbate A, Longobardi P. A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco. Diving Hyperb Med. 2017;47:9-16.
3. Blatteau J-E, Hugon M, Gardette B, Sainty J-M, Galland F-M. Bubble incidence after staged decompression from 50 or 60 msw: effect of adding deep stops. Aviat Space Environ Med. 2005;76:490-2.
4. Ljubkovic M, Marinovic J, Obad A, Breskovic T, Gaustad SE, Dujic Z. High incidence of venous and arterial gas emboli at rest after trimix diving without protocol violations. J Appl Physiol. 2010;109:1670-4

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