Wreck search or, more precisely, the investigation of underwater obstructions, is a special application of hydrographic surveying. Its goal is primarily the determination of the location and shallowest depth of objects on the seabed. These data are normally shown on nautical charts to ensure the safety of shipping. Not only ship wrecks are surveyed but all sorts of obstructions including
boulders, containers, old ammunition, among others. But also wrecks that do not pose any hazards to shipping are of importance, for example with regard to fisheries.
Echosounder record of a rock in the Flensburger Förde.
The top edge of rock is about 4,5 meters above sea bottom. You can easily see the continuation of rock under the mud layer.
Different survey methods are used to search for wrecks. Sonars (side-looking sonar or object search sonar) are used to identify the shape and position of objects. Depth measurements are made using echosounding equipment. As a rule, a diver is deployed additionally who examines the obstruction in more detail and precisely measures the shallowest depth. 200 objects are surveyed annually, including 40 newly discovered wrecks. The other surveys cover the positions of known obstructions. The position of wrecks on the seabed is not stable. Wrecks may change their position due to scouring, and also the depth above a wreck is subject to change. For that reason, many wreck positions are routinely re-surveyed. The BSH is keeping a database of all underwater obstructions which comprises about 2,500 positions. All underwater obstructions constitute potential hazards to navigation and should be given a wide berth. Information about wrecks that is of importance to navigation is published in the official nautical charts.
Wreck positions in the North and Baltic Seas
Modern wreck search methods
Historical wreck search methods
Why wrecks are surveyed repeatedly