A crane for use on an offshore vessel is provided with a boom restrainer, wherein the boom restrainer is a hydro-pneumatic boom restrainer, for reducing upward pivoting of the boom, when the boom is in the top zone, wherein the boom restrainer includes: multiple hydraulic cylinders, each having a hydraulic circuit and a cylinder rod with a cylinder head, wherein the cylinders are mounted on the crane structure with the cylinder heads directed towards the boom of the crane, preferably are mounted on a stay of the crane structure, a catcher for each hydraulic cylinder, wherein each catcher is mounted on the boom and is configured for receiving the cylinder head of the corresponding hydraulic cylinder, and to lock the cylinder head, preferably pivotable locks the cylinder head, relative to the boom, when the boom pivots upwards in the top zone; a gas buffer for each hydraulic cylinder, wherein each gas buffer is mounted to the corresponding hydraulic cylinder, and is connected to the hydraulic circuit of the corresponding hydraulic cylinder via a medium separator, wherein the gas buffer forces the hydraulic cylinder in an extended position, and wherein the volume ratio between the hydraulic cylinder and the gas buffer is such that the hydraulic cylinder acts as a progressive spring, e.g. the gas buffers each have a size in the range of 1000-1400 litre, for example 1200 litre and the hydraulic cylinders each have a size in the range of 800-1000 litre, for example 900 litre, and preferably the ratio between the volume of the gas buffer and the volume of the associated hydraulic cylinder is 4:3.

A backstop to prevent contact between a spacer and a peripheral member includes a rear jib backstop for a crane, having an outer cylinder, an inner cylinder, a spacer, a spacer holder and a lock mechanism. The spacer holder supports the spacer pivotally and swingably about an axis thereof and allows the spacer to fit on the inner cylinder, to keep the rear jib backstop from contracting in accordance with a change in a posture of the rear jib backstop when a boom rises. The lock mechanism enables locking of the spacer in such a manner as to keep the spacer from swinging about a swing central axis in a state where the spacer is located away from an outer surface of the inner cylinder.

A backstop to prevent contact between a spacer and a peripheral member includes a rear jib backstop for a crane, having an outer cylinder, an inner cylinder, a spacer, a spacer holder and a lock mechanism. The spacer holder supports the spacer pivotally and swingably about an axis thereof and allows the spacer to fit on the inner cylinder, to keep the rear jib backstop from contracting in accordance with a change in a posture of the rear jib backstop when a boom rises. The lock mechanism enables locking of the spacer in such a manner as to keep the spacer from swinging about a swing central axis in a state where the spacer is located away from an outer surface of the inner cylinder.