The images of the interception of the M/V Grace in the Caribbean Sea showcase the most visible aspect of a maritime operation. In such cases, authorities can track routes, analyze movements, and cross-reference various signals before deciding to conduct an inspection.
The official video released by the U.S. Coast Guard, which accompanies this report, pertains to the operation carried out in early September against the Grace, when it was sailing towards Cuba carrying fuel. CiberCuba previously reported on the interception of the vessel and the details of the operation coordinated with Mexico.
The Coast Guard stated that the vessel was suspected of using tactics common among the so-called dark fleet or “flota oscura”, a maritime phenomenon that is not limited to Cuba and has been a concern for international organizations for years due to its connection to sanctions evasion, lack of security controls, and pollution risks.
What did they find in the Grace?
After the boarding, the United States escorted the ship to the port of Progreso, Mexico. There, a team from the Mexican Navy confirmed the existence of large quantities of fuel stored in the ballast tanks.
The vessel also carried several containers that, according to the U.S. Coast Guard, are believed to have also contained fuel. Authorities have not disclosed how much fuel there was in total or what type of petroleum product was being transported.
A particularly relevant detail is that the Grace is not an oil tanker. Maritime records classify it as a container ship approximately 100 meters long, built in 2001 and currently registered under the flag of Comoros.
The Mexican Navy reported on September 17 about the seizure in Progreso of a foreign container ship measuring 100.8 meters and flying the Comoros flag due to alleged violations related to the prevention of pollution by hydrocarbons and international marine environmental protection standards.
The Mexican statement did not publicly identify the ship by name, but the disclosed characteristics match those of the Grace.
What exactly is a "dark fleet"?
The expression is not just a journalistic label. The International Maritime Organization (IMO) established a formal definition in the resolution A.1192(33), adopted in December 2023.
The IMO uses the term to refer to ships involved in illegal operations aimed, among other objectives, at evading sanctions, avoiding safety or environmental regulations, reducing insurance costs, or engaging in other illicit activities.
Among the indicators mentioned by the organization are vessels that evade inspections, operate without proper insurance, make it difficult to determine who actually controls them, or take deliberate measures to hinder their tracking.
This may include turning off or manipulating the Automatic Identification System (AIS), concealing the true identity of the ship, or conducting certain cargo transfers between vessels at sea.
These practices do not imply that any ship temporarily turning off its AIS belongs to a dark fleet. There are legitimate security circumstances that may justify signal interruptions. What authorities are looking for is the combination of multiple anomalous signals.
How can a ship attempt to conceal its route?
The AIS functions as a type of electronic identification for the ship. It transmits data such as its name, position, course, and speed, allowing other vessels and maritime authorities to know where it is located.
A joint guide published in 2020 by the U.S. State and Treasury Departments, through the Office of Foreign Assets Control (OFAC), and the Coast Guard identifies deceptive maritime practices such as turning off or manipulating the AIS, physically altering a vessel's identification, falsifying cargo documents, route irregularities, successive flag changes, and opaque business structures.
Another well-known technique is ship-to-ship transfer, referred to in the industry as STS for its English acronym. A shipment can be transferred from one vessel to another at sea without first unloading it in a port.
These operations are legal and commonplace when they comply with regulations, but they can also be used to obscure the true origin or destination of a shipment.
The IMO number: the registration that is much harder to change
The names of the ships may change. Their flags, owners, operators, and managing companies can also change.
For this reason, one of the most important pieces of information for maritime researchers is the IMO number, a permanent identification associated with the vessel. In the case of the Grace, it is IMO 9234422.
Analyzing a ship using that number allows for the reconstruction of its history even when it appears under a different name or registration. Maritime records show that the Grace has previously operated under other names, which precisely illustrates the usefulness of the IMO number as a permanent identifier.
Name or flag changes are legal and common in the maritime industry and, by themselves, do not indicate any illegal activity. They become warning signs when they coincide with other irregularities related to navigation, documentation, ownership, or cargo.
Why finding fuel in the ballast tanks is so important
Ballast tanks serve another purpose. Ships take on water in them to maintain stability, balance, and safe navigation conditions depending on how much weight they are carrying on board.
The International Maritime Organization regulates these operations and the measures aimed at preventing marine pollution.
Using compartments designated for ballast to transport fuel can pose safety, pollution, and regulatory compliance issues that are different from those encountered in transport conducted in spaces specifically designed for hydrocarbons.
In the case of the Grace, the Coast Guard specifically pointed out the environmental risk associated with the fuel found in those compartments, while Mexican authorities initiated proceedings for alleged violations related to regulations aimed at preventing hydrocarbon pollution.
How are these ships detected?
There is no single tool capable of identifying an irregular operation. Authorities can cross-reference AIS signals, port records, cargo documentation, changes of flag, ownership of the vessel, draft of the ship, and previous movements.
The draft —the depth at which the hull is submerged— can provide clues. A ship departing from a port with a deeper draft and subsequently appearing much lighter may indicate that it has loaded and unloaded a significant volume, although this information alone does not allow for a determination of what it was carrying.
When there are sufficient indications, a physical inspection can reveal what databases do not show. In the case of Grace, following the U.S. tracking and boarding, the inspection conducted in Mexico found fuel inside the ballast tanks.
What is still unknown about Grace
Despite the effectiveness of the operation, important questions remain.
The Coast Guard has not publicly disclosed the exact amount or type of fuel transported by the Grace, who the end buyer was, or which entity was supposed to receive the cargo in Cuba.
It has not publicly detailed whether the ship turned off or specifically manipulated its AIS during this journey, conducted boat-to-boat transfers, or forged documentation.
For this reason, it is more accurate to state that U.S. authorities believe that Grace employed common tactics associated with so-called dark fleets, rather than attributing all the practices that international organizations have documented in such networks solely to it.
The Grace is not the first case heading to Cuba
The interception occurs after the detention of the M/V Jaira Provider, another vessel that the U.S. Coast Guard determined was transporting fuel to Cuba.
Official U.S. records show that the Jaira Provider was detained for safety deficiencies during the summer and was carrying approximately 220,000 gallons of diesel. NOAA also reported the presence of a hydrocarbon film around the vessel while it was docked in Mayagüez, Puerto Rico.
The two cases illustrate why monitoring these routes no longer relies solely on locating large oil tankers. A container ship or a support vessel can also transport fuel in ways that are difficult to detect at first glance.
In the case of Grace, the boarding video reveals the visible end of that surveillance. The less obvious part happens beforehand: reconstructing the ship's identity, analyzing its movements, and verifying potential inconsistencies in its cargo or documentation that could turn an apparently commercial route into the subject of an international investigation.
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