Several Russian tankers reportedly turned off their tracking systems 33 times last week, a practice the US says could be used to evade sanctions

• Russian tanker ships turned off their tracking systems 33 times last week, Bloomberg reported.

• The US Treasury has flagged the maritime action as a "deceptive" way to evade sanctions.

• Nine superyachts owned by Russian oligarchs also went dark last week.

Russian tanker ships switched off their tracking systems at least 33 times last week, according to location data provided to Bloomberg by Windward, a maritime risk consultancy. That's double the normal weekly rate, the firm said.

This tactic known as "going dark," or "dark activity" has been flagged by the US Treasury as one of several "deceptive practices used to evade sanctions" in the maritime industry.

The data from Windward also shows that ship-to-ship meetings are taking place that could be long enough to transfer cargo to vessels without sanctions, though the frequency of those meetings is still at a normal level.

Windward also said last week that 22 unique vessels had entered Russian waters for the first time in the weeks since Russia invaded Ukraine.

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The news follows reports that nine superyachts owned by Russian oligarchs and tycoons — several of whom were sanctioned — similarly turned off their tracking signals last week.

All vessels of 300 gross metric tons or more that sail on international voyages must install tracking technology, commonly referred to as an automatic identification system, according to the International Maritime Organization's website.

Certain classes of vessels traveling on international voyages are required by international convention to broadcast their AIS location signal at all times.

In a sanctions advisory last May, the US Treasury warned that "vessels engaged in illicit activities may also intentionally disable their AIS transponders or manipulate the data transmitted in order to mask their movement."

Several countries, including the US and the UK, have barred both Russian oil and Russian vessels from ports following the country's invasion of Ukraine. The sanctions against Russian oligarchs have led to a flurry of highly scrutinized ship movement as superyachts and their owners attempt to escape seizure.

Turning off location data — on commercial or passenger ships — could make it harder for companies to avoid doing business with sanctioned entities or individuals.

"Everyone in yachting is pretty scared. The penalties of directly or indirectly dealing with Russians are just astronomical," Sam Tucker of the market intelligence firm VesselsValue previously told Insider.

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