A system for lifting loads from a mobile offshore platform includes a boom pivotally at one longitudinal end mounted to the platform. A boom extension line is coupled at one end to the boom to cause rotational movement thereof about the pivotally mounted end of the boom. Another end of the boom extension line is either (i) coupled to a movable subplatform on the platform or (ii) supported by a device coupled to the movable subplatform. Movement of the subplatform causes change in effective length of the boom extension line so as to move the boom between an extended position and a retracted position.