How to Track Dark Vessels When AIS Goes Silent

2,157 cargo ships and tankers over 10,000 DWT went dark in Q2 2026, nearly five times the 449 recorded in Q1. Prolonged dark events, three days or longer, rose sevenfold to 3,137. Russia alone recorded roughly 4,000 dark activity events in the quarter.

The Gap Is Now the Norm

2,157 cargo ships and tankers over 10,000 DWT went dark in Q2 2026, nearly five times the 449 recorded in Q1. Prolonged dark events, three days or longer, rose sevenfold to 3,137. Russia alone recorded roughly 4,000 dark activity events in the quarter.

The Strait of Hormuz shows what that looks like at chokepoint scale. AIS-visible transits fell 83% from the pre-conflict baseline after February 28, 2026, from roughly 3,750 a month to 450. Ships did not stop moving. They stopped reporting.

AIS is a cooperative signal. It tells you where a vessel says it is, when the vessel chooses to say so. Any operator, compliance team, or analyst whose picture depends on it alone has a picture with holes in it, and the holes are where the risk sits.

Why Vessels Go Dark

Not every AIS gap is deliberate. Coverage drops in congested waters, and GPS interference has become routine: more than 24,000 vessels experienced jamming between Q1 and Q3 2025 per Windward multi-sensor data, with position jumps averaging 6,300 km. The first analytical step is separating a vessel that cannot transmit from one that will not.

The deliberate cases cluster around a short list of purposes. A tanker switches off before a ship-to-ship transfer so the cargo’s origin cannot be tied to a sanctioned loading port. A vessel goes dark on approach to a port it should not be calling at, then reappears on the far side with a clean-looking track. A ship transiting a contested chokepoint drops off to avoid being targeted, or to avoid being seen using a corridor it is not supposed to use.

The common thread is that the gap itself is the signal. Where it starts, how long it lasts, and where the vessel reappears say more than the transmissions on either side of it. Some vessels skip the gap entirely and broadcast a false position instead. That calls for a different check, covered below.

How to Track a Dark Vessel

Tracking a vessel with no AIS is a sequence, not a single lookup. Each step narrows the area the next one has to cover.

Start From Behavior, Not From the Sensor

The last transmission fixes a position, heading, and speed. Draft, cargo type, declared destination, and the vessel’s own route history bound where it can plausibly be after a given number of hours. Windward’s Maritime AI™ assesses each gap against that vessel’s activity baselines, not a generic model. A tanker that goes dark near a known transfer area and a bulk carrier that drops off in a jamming corridor produce different search areas and different priorities.

Confirm Physical Presence With SAR

Synthetic aperture radar detects hulls regardless of cloud cover, darkness, or whether the transponder is on. SAR scenes also typically cover a larger area than EO, which makes SAR a natural first sensor for initial detection. Within the behavioral search box, SAR answers the first question: is there a vessel here that is not transmitting AIS? Windward correlates every radar detection against AIS so that reported vessels can be filtered out and only unreported contacts remain. A cluster of large, unreported hulls at a known transfer location is a lead.

SAR also ties a dark voyage back to where it began. On March 8, 2026, a sanctioned VLCC left the Kooh Mobarak terminal east of Hormuz carrying approximately 1.77 million barrels of Iranian Heavy Crude bound for Dalian, China. It then stayed dark on AIS for more than 15 days. Windward’s Remote Sensing Intelligence had already placed a VLCC-class hull at the terminal on March 7. Two things tie that hull to this ship: the vessel’s last recorded voyage ended at Kooh Mobarak, and the hull in the SAR image is VLCC-sized.

Read the RF Picture, Including the Silence

RF does the same job as SAR from a different direction. SAR finds hulls. RF finds emitters, geolocating the navigation radar and communications equipment a vessel keeps running after it switches off AIS. Like SAR, it confirms that something is there without saying which ship it is.

RF also depends on the vessel emitting. On May 8, 2026, Windward detected 521 RF transmissions across the Strait of Hormuz area, and only 84 matched an AIS broadcast. The northern corridor and the commercial lane showed no RF emissions at all during the observation window, which suggests commercial transits there were running under strict emissions control. Yet EO imagery collected at 13:21 UTC the same day identified five inbound vessels transiting the Strait.

Identify With EO

SAR and RF tell an analyst that a vessel is there. EO shows which vessel it is. Windward’s high-resolution EO resolves down to 30 centimeters, fine enough to pick out the distinguishing features that separate one ship from another.

In August 2026, two subsea cables off Perth, Indigo West and Indigo Central, were damaged inside Australia’s Submarine Cable Protection Zone. A vessel had entered Australia’s EEZ on July 28, anchored off Perth, and stayed in the area for nearly two weeks. Its ETA was set to January 1, 2027, a placeholder value typical of vessels with no real port call planned. On August 3, at 02:12 UTC, EO imagery captured the vessel roughly 11 kilometers west of Perth, off Marmion Marine Park, and confirmed it was where its AIS record said it was. On August 8, at 21:42 UTC, SAR imagery placed the same vessel directly on the cable route. No vessel has been publicly named or formally attributed by the Australian government.

On August 8, 2026 at 21:42 UTC, synthetic aperture radar (SAR) imagery placed the vessel directly on the cable route.

When AIS Lies Instead of Going Quiet

JIN LI (IMO 9855525), an OFAC-sanctioned 228-meter tanker previously known as OCEAN KOI, was seized by Iranian naval forces in the Gulf of Oman on May 8, 2026. The first sign of location manipulation came from Windward’s Maritime AI™, whose models are trained to recognize AIS patterns that indicate spoofing. Windward then procured SAR imagery. It showed the vessel was not at its transmitted position, and showed where it actually was. JIN LI has a long record of Iran-linked trading, ownership changes, and suspected fraudulent registration.

What This Means for Operators

Every AIS gap gets the same treatment. Check it against the vessel’s own baseline, put SAR and RF on the area where it could be, confirm with EO, and log the track. That log is what enforcement and compliance decisions stand on: a record of what the vessel did while it was off AIS.

Windward’s All-Source Operational Intelligence fuses AIS, SAR, EO, and RF into one operational picture, so a vessel stays tracked whether it transmits or not. See it in action.

Written by Ziv Gidron, Director of Content, Windward. Reviewed by Noam Rabinovich, Director of Product Marketing, Windward