Methodology
Where this data comes from
This record is built from AIS transmissions — the safety broadcasts vessels make continuously at sea — collected around the clock, filtered to yachts of 30 m and over, and distilled into arrivals, departures and stays. The result is a ledger of port calls: not where a yacht is this second, but where it has actually been, for how long, and where it went next.
Where does the data come from?
Every entry is derived from AIS (Automatic Identification System) transmissions — the positional broadcasts large vessels make continuously for safety reasons, received via terrestrial receiver networks. We collect these signals around the clock, filter them to yachts of 30 m and over, and derive port calls from the positions. Nothing is scraped from other tracking sites and no private sources are used.
How are arrivals and departures decided?
Each harbour, anchorage and shipyard in the record has a hand-drawn boundary. A yacht whose positions sit inside a boundary continuously for at least twenty minutes is recorded as arrived; twenty sustained minutes outside closes the call and records a departure. The buffer prevents a vessel manoeuvring at a harbour mouth from producing a flurry of false entries.
Why are positions vague?
By design. Published coordinates are rounded to roughly 100 m — enough to say a yacht is in Port Hercule, deliberately not enough to say which berth. The map shows last recorded positions as periodic snapshots, refreshed with the record at most hourly; it is a record of where yachts have been, not a live surveillance feed.
Why is a yacht missing, or its history patchy?
Coverage is regional and grows over time: the record currently watches the Côte d’Azur, from Saint-Tropez to Monaco, plus the La Ciotat yards. A yacht that sails beyond the monitored area goes dark in the record until it returns — such gaps are shown honestly as time outside the monitored area rather than guessed at. Yachts also occasionally switch their AIS transmitters off.
What does “probable refit” mean?
A stay of more than seven days inside a shipyard’s boundary. It is an inference from time spent, not confirmed knowledge of work being done — hence “probable”.
How fresh is the record?
Pages are rebuilt through the day as movements come in, typically within the hour. Every page carries an “as of” timestamp in the masthead stating exactly when its figures were generated.
Can I use the data?
The movements feed is published as RSS for personal use, and short excerpts with attribution are welcome. The record is compiled from safety broadcasts and is provided for general interest — it is not suitable for navigation or operational decisions.
Corrections are part of any honest record. If an entry looks wrong, see the privacy & takedown page for how to reach us.