What Is a Shipwreck? How Archaeologists Study Them Underwater

A shipwreck is what remains of a sunken vessel: a hull, a cargo, the objects on board, everything the sea covered instead of scattering. Not every shipwreck, though, is an archaeological site. Under the UNESCO Convention on the Protection of the Underwater Cultural Heritage, adopted in Paris on 2 November 2001, a shipwreck becomes underwater cultural heritage once it has sat on the seabed for at least 100 years, the threshold set in Article 1 of the Convention.

A wreck younger than that follows its own, separate rules. Once it crosses the 100-year line, it falls under what the Convention protects.

The Convention entered into force on 2 January 2009, as set out in Article 27. Member states commit to working together to protect and manage these sites, and to preserving them for the benefit of humanity. The text explicitly bans commercial exploitation of these sites for trade or speculation: a recognized site isn’t a deposit to mine for pieces to sell.

From the archive to the seabed

A maritime archaeologist does the reading long before the diving starts. According to NOAA, the search for a shipwreck usually starts on paper: an old ship’s log, a wreck account, a period chart. A name, a date, a route noted in an archival document can narrow a stretch of sea down to a manageable search area.

That’s where the instruments take over. Sonar is the most common acoustic tool: it sends out thousands of sound pulses toward the seabed and builds an image of what lies beneath the water’s surface. Where it matters to see past the seabed itself, a sub-bottom profiler uses sound to penetrate sediment layers and produce a two-dimensional image of buried structures. A magnetometer works differently: it picks up shifts in Earth’s magnetic field, which is why it can spot even small iron objects, like cannonballs, through their magnetic signature.

Practical example: a team searching for a wreck noted in an old ship’s log can cross-check the approximate position with a sonar scan of the area, then run a magnetometer over the spots that look promising. An iron signal at that location is the first solid clue that something lies below.

1960, when underwater archaeology became a science

According to NOAA and Texas A&M University’s Institute of Nautical Archaeology, maritime archaeology became a scientific discipline in 1960, when the Turkish government invited George Bass to lead the excavation of the wreck known as Cape Gelidonya. Both sources describe it as the first time an underwater excavation followed the same rigor as a land dig, measurement by measurement. Recovering objects from the sea predated that excavation, but not as systematic, documented work.

Maritime archaeologists dive with scuba gear, document a site with photos and video, and take hand measurements with underwater slates and tape measures. It’s slow work, built to record first and recover second.

Where conditions allow, photogrammetry speeds up the documentation: thousands of overlapping photos, often shot from a remotely operated vehicle, are stitched together into a 3D digital model of the site, one that can be examined far from the water.

Over roughly fifty years of work, archaeologists at the Institute of Nautical Archaeology have followed dozens of wrecks from first survey through to published results.

NOAA runs a similar process at a larger scale: its Maritime Heritage Program oversees 18 national marine sanctuaries across the United States, serving as a reference point for anyone exploring, documenting and protecting these sites. The first of those sanctuaries was established in 1975 around the newly discovered wreck of the USS Monitor, a Civil War-era ironclad.

After the dig: what happens to the artifacts

Among the UNESCO Convention’s principles is in-situ preservation, leaving the wreck where it lies, which is named as the first option to consider, before recovery even enters the picture.

There’s a practical reason behind that choice, too. An object submerged for decades or centuries settles into a new chemical balance with the water around it, and that balance breaks the moment it meets open air: recovered materials need advanced stabilization techniques to avoid deteriorating. Waterlogged wood, for instance, can warp if it’s dried without the right procedures.

When a project wraps up, the work ends with a detailed report and, in some cases, a public display of the recovered artifacts, as NOAA notes for one of the sites its program has followed. The dig isn’t finished the moment the last object reaches shore; it’s finished once the findings are written up and made accessible.

Studying shipwrecks shares more than one tool with other branches of archaeology: reading written sources, documenting systematically, paying close attention to conservation. Anyone curious about how the past gets reconstructed from what’s left behind will find common ground with ancient Egypt, where land excavations follow a similar logic of recording and preserving, or with the Roman Empire, whose Mediterranean trade routes left behind many of the wrecks studied today.