Accident caused by dynamic overloading of a ship mooring rope

Abstract

An accident of a passenger ship happened during a docking manoeuvre on a lake in Switzerland. After a regular mooring manoeuvre was completed, the ship was exposed to a wind gust pushing the ship away from the wharf. In that moment the mooring rope ruptured and hit the head of a child. An investigation was commissioned by the federal authority to answer several questions related to the accident.It had to be clarified whether the used rope could fail without being pre-damaged and if the failure could have been prevented by the use of a thicker rope. In addition, the influence of the wind exposure on the loading of the rope should be quantified. The acceleration of the ship by a wind gust was simulated by means of analytical and numerical analyses. Hereby the main goal was to quantify the drag due to water motion. The analysis showed that inertia effects of the water flow around the ship body (motion) have to be taken into account and can be described by an additional hydrodynamic mass which has to be added to the deadweight of the ship.Through the investigation it could be shown that rope failure was possible without a pre-damage of the rope. It was also shown that the use of a thicker rope would have led to a dynamic load condition that is even more critical than for the use of a thinner rope due to its larger stiffness.