The images of the interception of the M/V Grace in the Caribbean Sea depict the most visible aspect of a naval operation. In cases like this, authorities can track routes, analyze movements, and cross-reference different signals before deciding on an inspection.
The official video released by the United States Coast Guard that accompanies this report corresponds to the operation carried out in early September against the Grace, while it was heading to 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 employing tactics commonly associated with the so-called dark fleet or "flota oscura", a maritime phenomenon that is not limited to Cuba and has been concerning international organizations for years due to its connection with sanction evasion, the lack of security controls, and the risks of pollution.
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 presence of large quantities of fuel stored in the ballast tanks.
The vessel was also carrying several containers that, according to the U.S. Coast Guard, are believed to have also contained fuel. Authorities have not disclosed how much fuel was onboard 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 in length, 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 registered under the flag of Comoros due to alleged violations related to the prevention of oil pollution and international marine protection regulations.
The Mexican statement did not publicly identify the ship by name, but the disclosed characteristics match those of the Grace.
What is exactly 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 vessels 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 highlighted by the organization are vessels that evade inspections, operate without proper insurance, complicate the identification of their actual controllers, 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 vessel, or conducting certain cargo transfers between ships at sea.
These practices do not imply that any vessel temporarily turning off its AIS belongs to a dark fleet. There are legitimate security circumstances that may justify interruptions in the signal. What authorities are looking for is the combination of multiple anomalous signals.
How can a ship try to hide its route?
The AIS functions as a type of electronic identification for the vessel. It transmits data such as its name, position, course, and speed, allowing other ships and maritime authorities to know its location.
A joint guide published in 2020 by the U.S. Departments of State and Treasury, through the Office of Foreign Assets Control (OFAC), and the Coast Guard identifies among the deceptive maritime practices the turning off or manipulation of the AIS, the physical alteration of the ship's identification, the falsification of cargo documents, route irregularities, successive flag changes, and opaque corporate structures.
Another technique known is ship-to-ship transfer, referred to in the industry as STS by its English acronym. A shipment can be transferred from one vessel to another at sea without first unloading at a port.
These operations are legal and common when they adhere to 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 can 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 registry. Maritime records indicate that the Grace has previously operated under other names, which precisely illustrates the usefulness of the IMO number as a permanent identifier.
Name changes or reflagging are legal and common in the maritime industry and, by themselves, do not indicate any illicit activity. They become warning signs when they coincide with other irregularities related to navigation, documentation, ownership, or cargo.
Why finding fuel in ballast tanks is so significant
Ballast tanks serve another purpose. Ships take in water to maintain stability, balance, and safe navigation conditions depending on how much weight they carry on board.
The International Maritime Organization regulates these operations and the measures aimed at preventing marine pollution.
Using ballast compartments to transport fuel can pose safety, contamination, and regulatory compliance issues that differ from those of transportation carried out 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 launched 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-check AIS signals, port records, cargo documentation, flag changes, ownership of the vessel, the draft of the boat, and previous movements.
The draft —the depth at which the hull is submerged— can provide clues. A ship that leaves a port with a deeper draft and later appears much lighter may indicate that it loaded and unloaded a significant volume, although that information alone does not allow us to determine what it was carrying.
When there are enough indications, a physical inspection can reveal what the 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 thoroughness 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 final 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 voyage, made transfers from ship to ship, or falsified documentation.
Therefore, it is more accurate to state that U.S. authorities believe that Grace was using common tactics associated with so-called dark fleets, rather than attributing all the practices documented by international organizations in this type of networks to it individually.
El Grace is not the first case heading to Cuba
The interception occurred 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 security deficiencies during the summer and was carrying approximately 220,000 gallons of diesel. NOAA also reported the emergence of a hydrocarbon film around the vessel while it was in Mayagüez, Puerto Rico.
The two cases illustrate why tracking these routes no longer relies solely on locating large oil tankers. A container ship or a support vessel can also carry fuel in ways that are difficult to detect at first glance.
In the case of the Grace, the boarding video shows the visible conclusion of that surveillance. The less evident part occurs beforehand: reconstructing the ship’s identity, analyzing its movements, and checking for possible inconsistencies in its cargo or documentation that can turn an apparently commercial route into the subject of an international investigation.
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