Why historical vessel tracking matters.

Most tracking conversations stop at "where is it now?" That's a fine question if everything's going well. When it isn't — when your container's three days late and the carrier's customer service is "looking into it" — the more useful question is "what happened?"

The answer lives in historical AIS data: every position your vessel reported, every port it visited, every speed change, every detour. Modern AIS retention has gone from "last 30 days" to "indefinite" in the last few years, and the operational use cases have caught up.

What "historical" actually means

AIS position reports look like this: at 2026-05-08 14:23 UTC, vessel with MMSI 352001932 was at 1.27 N, 103.85 E doing 0.0 knots on heading 230. That's one report. A vessel produces 2,000–20,000 of those a week depending on coverage and stop frequency.

Multiply by 50,000 active container ships, multiply by 5 years of operating history, and you're looking at a few hundred billion rows. That's the haystack. The needle is your vessel's last 30 days.

The five things history is good for

1. Dispute resolution

Your forwarder says the ship sailed on time. Your shipper says it didn't. The bill of lading says one date, the AIS history says another. AIS data is a neutral third-party record — vessels broadcast it themselves, public receivers pick it up, no party owns it. When you've got conflicting paperwork, the position history wins.

2. Insurance claims

Marine cargo insurance often requires you to prove the vessel's behaviour during the period of loss. Where was it when the container fell overboard? Was it doing 28 knots in a beam sea? Did it deviate from the published route? These questions get answered with track history, not screenshots.

3. Voyage planning

How long does a vessel actually spend at Singapore PSA between berth and departure? The carrier quotes 36 hours. Your history says the median is 51 hours and the 90th percentile is 78. Now you know how much pad to put on your downstream commitments.

4. Carrier accountability

Most carriers publish on-time-performance numbers. Most numbers are self-reported. Compare the carrier's claimed schedule to the AIS-recorded one over a quarter and you get an objective view of which line is honest about its delays.

5. Spotting trouble before it spreads

A vessel that suddenly sat at anchor for 60 hours outside its scheduled port is signalling something — congestion, mechanical, port state inspection, crew issue. If it's the vessel carrying your boxes, you want to know now, not in three days when the carrier finally updates the status.

What "indefinite cache" really requires

Keeping AIS data forever sounds simple. It isn't. A real implementation needs:

• Append-only storage. Position records are never updated, only inserted. Postgres with BRIN indexes on timestamp works at this scale; TimescaleDB if you outgrow it.
• Downsampling for display. Showing 200,000 points on a map breaks the browser. Server-side downsampling to ~500 representative points keeps the line smooth without losing port calls.
• Spatial indexes. "What vessels passed within 5 km of this point last year?" needs PostGIS with GIST indexes on a geography column.
• Per-vessel partitioning. Once you cross a few billion rows, partitioning by MMSI (or by month) becomes mandatory.

When live data isn't enough

There's a specific scenario where historical tracking earns its keep: your container's already late and you need to find out where the delay started. The live position shows "anchored outside destination." Useful, but doesn't explain the 4-day delay. The history shows the vessel sat at Tanger Med for 92 hours waiting for berth — when the public schedule said 14. Now you know who to talk to, and what to negotiate.

This is the case for indefinite retention: today's "where is it" question is easy. Next quarter's "what happened" question is hard, and only solvable if you saved the data.

Broadpath stores AIS history indefinitely for every vessel carrying your containers. Polling stops after 30 days; history stays available forever. See the live map for the live side, and ask [email protected] if you need a specific voyage record.