Why Did a Ship Disappear From Tracking?
You were following a ship, and now it's gone — or frozen in place with a timestamp hours old. Before you worry: this is the single most common question in ship tracking, and the answer is almost always boring.
The short answer: nobody's listening there
AIS is VHF radio, and VHF is line-of-sight. A shore receiver hears ships out to roughly 40–60 nautical miles. Between coasts — on an Atlantic crossing, a Pacific run, the long empty middle of any ocean — there may simply be no receiver in range. The ship keeps broadcasting; nobody hears it. Satellites fill some of the gap, but their coverage passes are intermittent, so mid-ocean positions arrive in bursts rather than a steady stream.
The usual suspects, ranked
- Ocean-crossing coverage gap — by far the most common. Quiet for hours or days, then the ship pops back up near land, exactly on schedule.
- Congested-water signal collisions — in packed anchorages (Singapore, the Bosphorus) thousands of transponders compete for airtime, and some transmissions get lost. Gaps here last minutes.
- Position aged out — VesselFlow removes dots older than 24 hours rather than showing a ship where it isn't. The vessel is still searchable; it just has no trustworthy live position.
- Transponder off or malfunctioning — rare for commercial ships (it's required equipment), though naval vessels legitimately go dark, and equipment does occasionally fail.
Rule of thumb: match the gap against the route. A ship mid-ocean going quiet is expected; the same ship silent while sailing a busy coastline would be unusual. Real emergencies activate dedicated rescue systems (EPIRB beacons, DSC distress calls) that have nothing to do with tracking apps — a missing dot is not a distress signal.
How VesselFlow handles gaps honestly
- Freshness on every vessel: an “updated X ago” stamp tells you whether a fix is 40 seconds or 14 hours old — markers tint green when it's under 30 minutes.
- No zombie dots: positions expire off the map after 24 hours instead of lingering for days like on some trackers.
- Freshness filter: restrict the map to ships heard in the last 30 minutes, hour or six hours when you only want live traffic.
- Watchlist patience: a starred ship stays in your list through a gap — when it's heard again, its position simply resumes.
When the ship comes back
Reappearance is usually as sudden as the disappearance: the vessel closes within range of a coastal receiver and the map catches up. With VesselFlow Pro, the recent-track view then shows the route it sailed, and the voyage view re-anchors the ETA — often the moment you learn the crossing went exactly as planned.
Track ships with honest freshness
Every position stamped with its age — no zombie dots. Free on iPhone & iPad.
FAQ
How long do AIS coverage gaps usually last?
Minutes near coasts; hours to a few days on ocean crossings. Ships reappear as they near shore receivers.
Does a ship disappearing mean something happened to it?
Almost never — gaps are reception, not events. Real emergencies use separate rescue systems entirely.
Why does VesselFlow hide ships with old positions?
A day-old dot can be 360 nautical miles wrong. Positions age off after 24 hours, and every fix shows its timestamp.