Dark fleet tracking: how analysts read AIS gaps

Every commercial vessel over 300 gross tons is required to broadcast its position over the Automatic Identification System (AIS). That makes the world's merchant fleet one of the most transparent datasets on the planet — until someone flips the switch off. The ships that do this routinely, to move sanctioned oil or evade scrutiny, are what analysts call the dark fleet (or shadow fleet), and reading their behaviour has become a core OSINT skill.

What an AIS gap actually tells you

Turning off a transponder does not make a 250-metre tanker invisible. It creates a gap — and gaps have structure:

• Where the signal dropped. A vessel going dark in the middle of the Indian Ocean reads differently from one going dark twenty miles off a sanctioned export terminal.
• How long it lasted. A 30-minute dropout is usually reception noise. A 72-hour gap that ends with the ship riding lower in the water is a loading event.
• What changed when it returned. Draught, declared destination, even the reported name or MMSI — dark periods are when identities get swapped.

The craft is correlation: pairing the gap with port congestion data, satellite imagery, bunkering records or a sister ship's track. One missing signal means little; a pattern of missing signals along a known smuggling corridor is a finding.

Classic dark-fleet patterns

1. The loading gap. Dark near an export terminal, reappear days later, draught visibly deeper. The cargo "never happened" on paper.
2. Ship-to-ship (STS) transfers. Two vessels go dark in a known STS zone — off Kalamata, in the Laconian Gulf, off Johor — and the cargo changes ownership mid-sea.
3. Spoofing. The transponder stays on but lies: the broadcast track shows a gentle loop in open water while the hull is actually alongside a sanctioned berth. Modern spoofing produces physically impossible tracks — 90-degree turns at 25 knots — that algorithms and trained eyes both catch.
4. Identity laundering. Old tankers acquire new flags, names and paper owners every few months. The hull stays the same; the metadata rotates.

Why traders should care

Dark-fleet activity is not just a compliance story. It is supply data:

• The size and utilisation of the shadow tanker fleet is a real input to freight rates and crude spreads — sanctioned barrels still reach the market, just along longer, costlier routes.
• Sudden growth in dark STS activity around a producer often precedes visible export data by weeks.
• Insurance and sanctions enforcement waves (vessel designations) remove capacity from the shadow fleet overnight, with knock-on effects on mainstream tanker demand.

If your book touches energy, the tanker map is not optional context. It is the physical layer of the trade.

Getting started without a navy

You do not need classified feeds. You need persistent, queryable AIS history, a map that makes gaps visible, and the discipline to correlate before concluding. Public trackers show you where ships say they are; an analyst's tool should also make it easy to see where they stopped saying it.

Veytics renders live vessel positions on the same globe as energy infrastructure, news and market data, so an AIS anomaly can be checked against the refinery it parked near and the spread it might move — in one view. The free tier includes delayed vessel tracking; it is enough to learn the patterns this post describes on real data.