“How deep does an anchor penetrate the seafloor?”. This question has been explored by a team of scientists and technicians as well as the crews of three involved ships in the German Bight. One HHP AC 14 and one Hall type anchor have been dropped and dragged in a series of 18 trials following an exact specified procedure. The behaviour of the anchor, especially the impact on the seafloor and the maxiumum penetration depth have been documented and surveyed before, during and after the anchor trials. For this different hydroacoustic methods like Sediment Echosounder (SES) and Sonarsystems (MBES, SSS), video-documentation and the measurement of pressure and pulling forces have been implemented.
Motivation for this large scale fieldwork is the shore connection of wind-energy parks by sea cables in the German Bight. The actual regulations prescribe a burial depth of 3m for sea cables in shipping channels. The reason for these increased requirements is the risk potential which is seen by anchor manouvres in emergency cases and disasters. On the other hand the realization of a burial depth of 3m is very ambitious from a technical point of view as well as very cost intensive.
Therefore the approving authority (Generaldirektion Wasserstraßen und Schifffahrt, GDWS) and the transmission system operator Tennet Offshore GmbH agreed upon this investigations to determine the real penetration depths of anchors into the seafloor. The results of the tests potentially shall support the improvement of the regulations for the burial depth of sea cables in shipping channels.
Next to Tennet the Federal Maritime Hydrographic Agency (BSH) the Dutch research institute Deltares and the Federal Waterways Engineering and Research Institute (BAW) have been involved in the field work, the documentation and the scientific evaluation of the results.