Moving tools on offshore structures with a walking carriage

A remotely-operated subsea carriage arranged to walk along an elongate member of an offshore structure while carrying a payload, the carriage comprising:

• individually-operable upper and lower clamps that are spaced axially along a common longitudinal axis around which the clamps can be closed;
• an axially-extensible frame connecting the clamps;
• and
• a walk drive comprising an actuator acting on the frame, operable to extend and retract the frame in a direction parallel to the longitudinal axis to vary an axial distance between the clamps;
• wherein at least one of the clamps is attached to the frame via a rotationally-displaceable coupling for relative angular movement between the associated clamp and the frame about the longitudinal axis, the rotationally-displaceable coupling comprising at least one arcuate slot providing a path curved about the longitudinal axis, and at least one pin engaging with and being movable relative to the at least one slot;
• wherein the carriage further comprises a rotational drive comprising an actuator which when actuated is configured to drive relative movement of the at least one pin along the curved path provided by the at least one slot so as to drive movement of the coupling, and the associated clamp, circumferentially about the longitudinal axis.