Deepening the wreck of the Assi Euro Link using the trailing suction hopper dredger "Prins der Nederlanden".
Type:
Presented during:
CEDA Dredging Days 2005 - Dredging: The Extremes, Rotterdam
Authors:
Jacobs B.
Abstract: In January 2003 the freight ship Assi Euro Link sank after a collision, 48 nm off the north coast of the Netherlands. As the wreck was located in a busy shipping lane it had to be either removed or lowered below the guaranteed navigable depth of 29 m.
After taking cost and feasibility into consideration Rijkswaterstaat (Dutch Maritime Authorities) decided to have the Assi Euro Link lowered by dredging the existing sea bottom material around the wreck. During the second half of 2003 Rijkswaterstaat and Boskalis developed the dredging option.
The combination of site conditions made the operation a dredging challenge, since it had never been executed before under these conditions. First the location of the wreck was unfavorable for working conditions, due to the open sea environment, very busy shipping and the depth of the sea bottom, which was almost 45 m. These conditions lead to the choice of a modern, versatile and highly manoeuverable trailing suction hopper dredger, being able to dredge up to 80 m. Second the soil properties played an important role, since the material had to flow from underneath the Assi Euro Link after dredging a hole around the wreck’s hull. Third the Assi Euro Link had broken up into two parts and some sections had even collapsed. The risk of damaging or even losing the suction pipe, by uncontrolled movements of wreckage was high. To ensure a safe operation a monitoring system with motion sensors was installed on the wreck, which registered sudden movements and gave a warning.
Since the goal of the project was to lower the wreck below the required navigable depth an effort has been made to continuously monitor the exact location by using an Ultra Short Baseline (USBL) system. As a part of the system several acoustic sensors were fitted on the wreck, prior to dredging operations.Keywords: wreck, deepening, dredging