On the maiden voyage of a vessel it encountered heavy weather on the North Atlantic. In the heavy waves and ship motions the retractable thruster in the bow were moving up and down with vibrations and noise and cracks were found in their locking mechanisms. The cause of the motion and the cracks had to be found and solved.

A measurement setup was designed and installed on board of a sistership which sailed with it for several days. After analysing the data it was confirmed that after waves exceeded a certain height the thruster was moving up and down. High stress due to this motion was also registered.

Wave height(hor) versus locking device gap (vert)

Together with the supplier a new locking device design was conceived which prevents the motion and has significantly improved fatigue strength. These devices were installed on all of the sister ships and the problems are solved.

New design locking device