Marine knuckle boom crane comprising: - a stationary pedestal to be mounted to or formed integral with a vessel; and - a crane housing having an upper portion, a central portion and a lower portion, which is rotational relative to the pedestal about a vertical rotation axis; - 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 which is connected pivotably about a first horizontal pivot axis to a lower portion of the crane housing; and ∘ a jib comprising an inner end, a central area and a tip opposite the inner end of the jib, the inner end of which is 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, essentially parallel along the main boom; characterized in that - in order to position the jib with respect to the main boom, a tensioning member (11a, 11 b) and a curved extension guide are provided, the tensioning member extending between the crane housing and the curved extension guide, and the curved extension guide being connected to the jib and being pivotable together with the jib about the second pivot axis, and guiding a portion of the tensioning member, wherein a second winch allows to vary the length of the tensioning member and thus to position the jib; - in order to position the main boom, a luffing cable (12; 112) is provided, extending between the outer end of the main boom and the upper portion of the crane housing, and wherein a third winch allows to vary the length of the luffing cable and thus to position the main boom. - a stationary pedestal to be mounted to or formed integral with a vessel; and - a crane housing having an upper portion, a central portion and a lower portion, which is rotational relative to the pedestal about a vertical rotation axis; - 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 which is connected pivotably about a first horizontal pivot axis to a lower portion of the crane housing; and ∘ a jib comprising an inner end, a central area and a tip opposite the inner end of the jib, the inner end of which is 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, essentially parallel along the main boom; ∘ a main boom comprising an inner end, a central area and an outer end, the inner end of which is connected pivotably about a first horizontal pivot axis to a lower portion of the crane housing; and ∘ a jib comprising an inner end, a central area and a tip opposite the inner end of the jib, the inner end of which is 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, essentially parallel along the main boom; - in order to position the jib with respect to the main boom, a tensioning member (11a, 11 b) and a curved extension guide are provided, the tensioning member extending between the crane housing and the curved extension guide, and the curved extension guide being connected to the jib and being pivotable together with the jib about the second pivot axis, and guiding a portion of the tensioning member, wherein a second winch allows to vary the length of the tensioning member and thus to position the jib; - in order to position the main boom, a luffing cable (12; 112) is provided, extending between the outer end of the main boom and the upper portion of the crane housing, and wherein a third winch allows to vary the length of the luffing cable and thus to position the main boom.