When is a ship ‘not under command’?

A situation in the Gulf of Oman highlighted how the colloquial language of the sea can be misconstrued by landlubbers

MarineTraffic Live Map showing active vessels reporting their navigational status as “ Not Under Command” through AIS in a 24-hour period (20 August)

A one-week period in late June and early August was an uneasy time for ships in the Gulf of Oman when two attacks took place on vessels in the Middle East waters. At the end of July product tanker Mercer Street was hit by a drone carrying explosives, which sadly resulted in the death of two of those onboard – a British security guard and the vessel’s Romanian captain.

Just a few days later in early August and bulk cargo ship Asphalt Princess was hijacked. The 9,700 DWT vessel was also sailing in the Gulf of Oman when the scenario unfolded. According to news reports the crew managed to thwart the hijackers and no one was harmed in the incident. 

Around the same time it was noticed that the AIS (Automatic Identification System) signals of a few vessels in the Gulf were reporting as ‘not under command’ (NUC). It unsurprisingly prompted fears that attacks were unfolding on these vessels too, with possible cyber attacks being mooted.

According to IMO’s COLREGs (Convention on the International Regulations for Preventing Collisions at Sea) the term, ‘not under command’ is reserved for use when a vessel, “through some exceptional circumstance is unable to manoeuvre as required by these rules and is therefore unable to keep out of the way of another vessel”.  Such scenarios would include steering gear failure, engine failure, electrical supply system failure, fire, flooding, uncontrollable cargo shifting and stability issues. It is not supposed to be used in any other circumstances. 

In the case of the ships in the Gulf of Oman, they were intentionally drifting.

However, seafaring tradition dictates that NUC is regularly used when a ship is intentionally drifting and apparently it’s a scenario accepted by those who plough the waves.

According to MarineTraffic data there were 446 ships signalling that they were NUC in a 24-hour period between 16-17 August. Whilst it was not the same period as the hijacking and drone attack, it does highlight how regularly the signal is used – it’s fair to presume that it’s unlikely that so many vessels are experiencing engine failure, fire, flooding or any other ‘exceptional circumstances’. Indeed, it is likely that these vessels were intentionally drifting too.

Of the overall figure 13 vessels were located in the Gulf of Oman, and 22 in the Persian Gulf. The area with the largest number of vessels displaying NUC was the South China where 30 vessels were likely to be intentionally drifting. 

The misunderstanding in the Gulf of Aden was eloquently explained by journalist Jonathan Boonzaier in a TradeWinds article.

Boonzaier, who had a brief seagoing career, writes that he was always asked to display the NUC signal when the ship was intentionally drifting. He explains the rationale: “In the days before AIS, there was no distinction for why a ship was drifting. If a vessel was at sea with its engines idle while its anchors were still firmly housed in hawse pipes, it was considered as being not under command.”

Today ships’ positions are transmitted through the AIS so that other ships are aware of their positions. AIS information is also used to power ship tracking platforms such as MarineTraffic. 

Related: Vessel details that can be changed in AIS transponders

Ships are required to report their navigational status and as well as NUC ships can announce that they are underway by engines, moored, constrained by draft or use one of several other signals available to them. This MarineTraffic article explains the terms.

According to Global Fishing Watch, there are more than 400,000 AIS devices across the globe broadcasting vessel location, identity, course and speed information.

It’s good to know that there are people out there looking at AIS data and spotting trends. As the next time it may be the real thing.

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