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Escaping from politics and inspectors, organized crime found in the sea tanks of ships and the help of professional divers a new method to traffic cocaine abroad.
The year 2026 is not over yet, but the volume of drugs found in these structures, used to cool vessels, in Brazilian ports is already six times that recorded in 2025.
In May, a joint operation between the Federal Revenue, Federal Police and Navy found 341.75 kg of cocaine in the sea chest of the Green K-Max 1, a merchant ship docked in the Port of Santos that was heading to Poland.
The packages were in waterproof packaging, secured with washers used in weight training gyms, preventing the drug from floating out of the compartment.
It was not an isolated episode. Data provided by the Federal Revenue Service to BBC News Brasil shows that, in 2023, a particularly significant contrast occurred: while cocaine seizures in Brazilian port areas fell from 23.7 tons to 14.8 tons, the volume found in sea crates almost tripled, going from 752 kg to 2,272 kg.
Sea chest seizures fluctuated in the following years, falling to 695 kg in 2024 and, again, to 100 kg in 2025. But now they have risen again. In 2026, so far, 630 kg have been seized — more than six times what was recorded in the entire previous year.
The volume includes a recent seizure, in September, when the Federal Police found 140 kg of cocaine in the sea chest of a ship that left the Port of Santos heading to Italy.
According to the Federal Revenue, as supervision improves, criminal organizations are looking for new ways to transport cocaine abroad.
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"A much debated effect on organized crime is the squeeze [something like "squeeze" in English]. When you squeeze a certain sector, there is an overflow to the edges", says frigate captain Igor Alves, commander of the Navy's South-Southeast Naval Patrol Group, based in Santos.
'Parasite' method
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Trafficking methods are not only observed in Brazil. In a report published in January on the diversification of maritime cocaine trafficking, Europol (the European Union's police agency) stated that criminal networks have been multiplying routes and adopting more difficult-to-detect ways to bring the drug to Europe.
These include hiding in sea boxes below the waterline, with professional divers tasked with retrieving packages at destination ports.
The logic of hiding the drug in the submerged part of the ships, hidden in the structure of the vessel itself, is called the "parasitic method".
A 2023 report from the United Nations Office on Drugs and Crime (UNODC) described the evolution of this method, identified since the 1980s.
In early versions, cocaine was placed in cylinders or boxes attached to the outside of the hull. Over time, traffickers also began to exploit structures on the ship itself, such as sea tanks.
Brazil accounted for 63% of the 76 seizures of cocaine hidden in submerged ship structures analyzed in 2023 and 2024, according to a survey by the World Customs Organization. Cases have also been recorded in Colombia and Costa Rica.
The Federal Police were contacted for the report, but did not respond to questions.
The destinies planned by the criminals were even more varied. More than half of the cargo was to be picked up at ports in Western Europe, especially in Spain and Italy. Others went to the Australia and New Zealand region and, in smaller numbers, to China, Türkiye, Mexico and the United States.
In November 2025, this route reached Hong Kong. Local customs found 417 kg of cocaine in a submerged compartment of a ship that had left Brazil — the first seizure of its kind recorded by authorities there.
In the data consulted by BBC News Brasil, cocaine dominates this type of concealment. All seizures in sea tanks reported by the Revenue involved this drug, as well as the 76 cases analyzed by the World Customs Organization.
Other narcotics are also transported by sea, but the sources consulted do not record similar use of sea tanks for these substances.
Illegal cargo can leave clues – but not always
Credit, Disclosure/Brazilian Navy
The choice of this hiding place exploits a structure essential to the functioning of the vessel itself. The sea chest — in English, sea chest — can be compared, in a simplified way, to the refrigeration system of a car.
On ships, the fresh water circulating through the engine needs to be cooled by salt water. So that this heat exchange continues to function even when the vessel is rocking, seawater is captured through openings installed in the lowest part of the hull and accumulated in reservoirs before being pumped through the system.
Large ships may have several sea chests, distributed on both sides of the hull. At the Port of Santos, depending on the size and loading of the vessel, they can be up to 15 meters deep.
On the outside, the openings are protected by metal grilles. To place the drugs in these compartments, the gangs need to use experienced professional divers, capable of removing or manipulating these protections without causing noticeable damage to the ship.
If the intervention causes water to enter or compromise a system, the freighter may need to undergo repairs, and inspection to identify the problem may reveal the packages before departure.
This means that, in practice, a ship can end up transporting drugs between continents without those responsible necessarily knowing that there is a clandestine cargo under the waterline.
But the scheme may leave clues. There are cases in which crew members heard metallic noises coming from the hull or noticed small vessels moving suspiciously nearby and alerted the authorities.
Complaints are one of the ways to trigger an inspection. In other situations, the selection of ships is made based on intelligence information and risk analysis.
The IRS receives information in advance about cargo, containers, vessels and participants in the logistics chain, cross-references commercial and customs data and selects the targets that should be inspected.
Part of the assessment is route analysis, documentary inconsistencies and information shared with Brazilian and foreign authorities.
For operational and security reasons, the IRS does not disclose the specific parameters used to select targets.
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Search for drugs 15 meters deep
When a suspicion involves the submerged part of the ship, the Revenue, Federal Police, Navy and port authorities share information and organize the inspection.
The investigation and repression of trafficking are the responsibility of public security bodies. The Navy assists in these operations, offering specialized personnel, logistical support, intelligence and instruction.
The group commanded by Captain Igor Alves, from the Navy in Santos, is made up of six divers and is responsible for the coasts of São Paulo and Paraná, an area that includes the ports of Santos and Paranaguá — the two largest Brazilian port complexes.
Its military personnel join forces with members of the Federal Police's maritime centers to expand the capacity to carry out these inspections.
Preparation between activating the team and entering the water can take around two hours. Clothing, hoses, cylinders, communication systems and other equipment need to be separated and tested before descent. Each mission requires at least four divers and an armed surface support team.
Before any soldier enters the water, however, one step depends on the vessel itself. The crew needs to report where the sea chests are and turn off the pumps that suck water through the hull openings that will be inspected.
The pumps must be turned off throughout the dive. The suction force is one of the main risks: according to Alves, there are records of divers recruited by criminal organizations who were sucked in and died when trying to access sea tanks.
According to the commander, the crews usually collaborate with this procedure. The companies themselves are interested in discovering any "parasitic" cargo before departure, as a seizure at destination can lead to investigations and penalties.
That doesn't make the job simple. You may need to descend approximately 15 meters to reach the sea chests. Agents also face low visibility, currents, movement of vessels and obstacles on the hull itself.
Underwater robots operated remotely by the PF can reduce some of the work. When current conditions permit, they perform a first inspection of the hull more quickly than a dive team.
But technology doesn't completely replace divers. Stronger currents can prevent the use of the equipment and, if suspected, it is still necessary for a professional to go down to confirm the find and remove the packages.
Why don't inspections reach all ships?
The scale of the Port of Santos helps explain why inspections are not widespread. The number of ships docked at the port complex in 2025 reached 5,708, according to data from the National Waterway Transport Agency.
"There are between 40 and 60 daily entry or exit maneuvers", says Commander Alves. "No country in the world would be able to inspect all of these ships."
Authorities focus on vessels, routes and destinations considered to be at greatest risk. Therefore, the volume seized also depends on which ships are selected and when inspections take place.
When Alves gave the interview, at the beginning of August, Operation Ágata was underway, coordinated by the Ministry of Defense and carried out in partnership with different bodies on the land and sea borders. In the actions carried out in the South-Southeast region, his team had carried out more than 15 dives in two weeks without finding drugs.
For the commander, the result does not necessarily mean that the operation has failed. He argues that the overt presence of agencies and increased inspections could lead criminal groups to delay shipments, change ports or resort to more expensive means.
He calls this effect an "intangible gain": organizations are harmed not because cargo was seized, but because of the interruption and delay of criminal logistics.
The dependence on specialized professionals creates another vulnerability for this type of trafficking. As placing drugs in sea tanks requires experienced divers, in Alves' opinion, the arrest of just one or two professionals co-opted by the gangs could reduce a workforce that is difficult to replace in the short term.
The arrests, he adds, could also discourage other divers in the region from accepting recruitment by criminal organizations.
The race to adapt takes place on both sides. The Revenue states that, in recent years, it has expanded the use of intelligence and risk analysis, reinforced integration with other bodies and improved inspection protocols at ports. He also began to study technologies aimed at inspecting the underwater structures of ships.
The search for cocaine underwater has also gained space in the preparation of divers.
Alves says that the experience accumulated in operations in Santos began to be incorporated into Navy manuals and courses and, today, soldiers from his group are invited to teach how to combat this innovation of cocaine trafficking to teams from other regions of the country.
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