The vessel was in DP operation and carrying out crane
work operations. The crane was on stand-by for the next operation.
It has two hooks, one main hook and one whip-line hook.
On the deck the riggers were working. To prevent uncontrolled movement of the crane the whip line hook is connected to an internal constant tension tugger winch with a constant tension of 4 tons.
During the start up procedure for the crane the pump
for the tugger winch was not started. That means that the whip line did not follow and adjust according to the movement of the crane boom.