Motion compensating crane for use on an offshore vessel

Abstract

A motion compensating crane for use on an offshore vessel having a hull with a design waterline, wherein the crane includes a revolving superstructure, a main boom mounted to the revolving superstructure and pivotally connected at an inner end thereof about a substantially horizontal boom pivot axis to the revolving superstructure, the main boom having a tip end remote from the inner end, a main boom luffing assembly adapted to set an angle of the main boom relative to the superstructure within a main boom working angle range, a rigid jib frame pivotally connected to the tip end of the main boom about a substantially horizontal jib frame pivot axis, and a level setting assembly adapted to set the rigid jib frame in a levelled position whilst the main boom has an angle within the main boom working angle range. The rigid jib frame is provided with a set of parallel X-direction tracks which are substantially horizontal in the levelled position of the rigid jib frame. The crane further has a mobile carrier supported by the X-direction tracks and movable by a motor powered X-motion displacement actuator assembly. The mobile carrier is provided with one or multiple parallel Y-direction tracks and a mobile jib hoist cable suspension member is supported by the one or more Y-direction tracks and movable relative thereto.