Marine knuckle boom crane

A marine knuckle boom crane comprising:

• a stationary pedestal to be mounted to or formed integral with a vessel;
• a crane housing having an upper portion, a central portion and a lower portion, the crane housing being rotational relative to the pedestal about a vertical rotation axis;
• and
• a knuckle boom assembly attached to the crane housing, the knuckle boom assembly comprising:
• a main boom comprising an inner end, a central area and an outer end, the inner end of the main boom being connected pivotably about a first horizontal pivot axis to a lower portion of the crane housing;
• a jib comprising an inner end, a central area and a tip opposite the inner end of the jib, the inner end of the jib being connected pivotably about a second horizontal pivot axis to the outer end of the main boom, wherein the jib is pivotable at least between an extended position in which the tip extends mainly forward from the main boom, and a folded position in which the jib is folded back, with the tip of the jib being brought to be close to a middle portion of the main boom;
• a tensioning member and a curved extension guide, for positioning the jib with respect to the main boom, the tensioning member extending between the crane housing and the curved extension guide,
• wherein the tensioning member comprises:
• a first portion comprising at least two articulated interconnected elongated rods;
• and
• a second portion comprising sheaves and a cable, a length of the cable being variable, one of the at least two articulated interconnected elongated rods being connected to the second portion via a first pivot point, the at least two articulated interconnected elongated rods being interconnected via a second pivot point,
• wherein a distal sheave of the second portion is directly connected to the one of the at least two articulated interconnected elongated rods, and
• wherein the curved extension guide is mounted to the jib, pivotable together with the jib about the second pivot axis, and comprises:
• three spokes including a first spoke, a second spoke and a third spoke, each having a distal end;
• a connecting beam extending from a third spoke to the tip of the jib, wherein the tensioning member is connected to the third spoke, and wherein the first and second pivot points of the tensioning member are adapted to coincide with the distal ends of the first and second spokes of the curved extension guide, respectively and wherein:
• when the jib is in the folded position, the first portion of the tensioning member is guided by the curved extension guide, and the first and second pivot points of the tensioning member coincide with the distal ends of the first and second spokes of the curved extension guide, respectively,
• when the jib is in the extended position, the first pivot point is spaced apart from the distal end of the first spoke by a distance, with the distal end of the first spoke being a free end, and the second pivot point is spaced apart from the distal end of the second spoke by a distance, with the distal end of the second spoke being a free end, and
• when the jib is in an intermediate position between the folded position and the extended position, the first pivot point is spaced apart from the distal end of the first spoke by a distance, with the distal end of the first spoke being a free end, and the second pivot point coincides with the distal end of the second spoke;
• a tensioning winch configured to vary the length of the cable of the tensioning member and thus to position the jib;
• a luffing cable for positioning the main boom, extending between the outer end of the main boom and the upper portion of the crane housing;
• and
• a luffing winch configured to vary the length of the luffing cable and thus to position the main boom.