The search and rescue of missing persons always represents a challenge for the rescue specialists deployed, regardless of the environment in which they work.

But the teams searching for the missing people on board the Bayesian yacht, which sank off the coast of Sicily and claimed several lives, faced particularly difficult conditions. Although the boat is in relatively shallow water of 50 meters, underwater operations are influenced by numerous factors that make them some of the most complex search and rescue operations.

Best practice shows that search operations should be coordinated, with areas to be searched expanding outward from the last known location. This makes the most efficient use of available teams and equipment, selected according to the targets and environments to be searched, while updating and refining the operation as new information becomes available.

Land-based searches can be easier because the recovery team can usually walk or move more easily. Searches in water are more challenging, whether in rivers, lakes or the open sea.

Searches on inland waterways such as rivers, canals and lakes are more limited in scope due to surface area and depth than on the sea and open ocean.

Searchers use a variety of techniques, such as trained search dogs to recover victims, sonar devices to reflect sound waves off target objects, underwater radar devices that can detect objects under sediment, and remotely operated underwater vehicles (ROVs). The combination of techniques used depends on the environment and scenario.

Sea searches, on the other hand, can be more difficult as they typically cover much larger areas both spatially and in terms of water depth. Other factors to consider include salinity, temperature and strong currents, as well as the fact that the seabed can be rugged, which could harm divers, sonar equipment and ROVs.

Drowning was the third leading cause of death from “accidental injuries” worldwide, claiming around 360,000 victims in 2021, revealing a globally increasing trend in the cause of death.

And for every drowned person recovered, there are many more who remain missing. Recent Danish research has shown that only 45% of people missing in the water are successfully found and recovered within 12 months of their disappearance.

Searches at sea cover a wide range of disasters, from tsunami victims such as the 2004 Boxing Day tsunami, to fishermen on sinking trawlers and migrants on unseaworthy boats. Then there are issues related to mechanical problems, such as the Argentine submarine San Juan in 2017, and plane crashes such as the still-missing Malaysian Airlines flight MH370 in 2013.

Finally, there is the search for missing divers or underwater vehicles such as the submersible Titan, which imploded in 2023 during a dive to the wreck site of the Titanic in the Atlantic Ocean.

Be careful when diving

The search for the missing sunken Bayes yacht – the cause of which is currently unclear – should have been relatively straightforward. Helicopters, presumably equipped with thermal imaging equipment, and rescue boats were quickly deployed to search for survivors, although the body of cook Recaldo Thomas was found floating on the surface.

Five victims were recovered from inside the yacht, which was discovered close to shore in relatively shallow water (50 m) and had a good knowledge of local ocean currents. Had they been washed out to sea, ocean currents, the decomposition process, scavengers and other factors could have made this forensic search even more problematic.

However, it is challenging for divers to work at depths of 40 metres or more. One reason for this is the risk of nitrogen narcosis. The deeper divers go, the higher the pressure becomes.

At higher pressures, the gases divers breathe from their tanks cause symptoms such as drowsiness and impaired judgment, which is an obvious danger underwater. Another problem is decompression sickness, which occurs when divers ascend too quickly and is often referred to as “divers’ sickness,” meaning divers can only spend ten minutes on the wreck itself.

In the case of the Bayesian, underwater ROVs were deployed, likely with live audio, lighting equipment and sonar to assist with navigation and tracking and to minimise risk to divers in this difficult environment. The 56m yacht was turned on its side, had 1.3cm thick glass windows that were difficult to break, and was full of debris that made recovery of the missing people difficult.

The chances of finding the missing people alive decreased rapidly the longer the underwater search lasted. However, in rare cases, people were found even after several days, clinging to debris or floating objects or stuck in air pockets on sunken ships.

Harrison Okene, a fisherman on a trawler that sank in 30 meters of water 30 kilometers off the Nigerian coast in 2013, was found alive by divers after being trapped in an air bubble in the capsized boat for 60 hours. He later published a book about his rare survival story. There are also several famous seafaring stories of people being rescued by rafts after drifting at sea for weeks or even months.

Although the initial search and rescue operation tragically turned into a recovery mission, the rapid deployment of search teams, including specialized divers, helicopters, rescue boats and ROVs, resulted in a rapid “successful” operation.

This is of utmost importance when it comes to identifying victims and determining the cause of death. Unfortunately, this is not always the case in such rescue operations, for example in the case of undocumented migrants lost at sea.

The lack of resources to salvage sunken ships in relatively shallow waters to determine the cause of their sinking would help prevent future shipwrecks and the tragic loss of life that all too often accompanies them.

This article is republished from The Conversation under a Creative Commons license. Read the original article.