Cable-Driven Parallel Robots have several advantages over both conventional serial and parallel robots, notably in terms of scalable workspace. These robots could provide an alternative to mobile and gantry crane systems, increasing payload stability, allowing higher accelerations and reducing cost. However, in order to provide such capabilities, the base attachment points must be located outside the workspace boundaries, meaning that the cables form straight lines running through the workspace to the mobile platform. Consequently, such systems can only feasibly operate in unencumbered locations, or alternatively, be configured with a specific task in mind thus severely limiting their functionality. One potential solution to this problem is a composite mechanism that docks then deploy a sub-mechanism. In this paper, a methodology is proposed to obtain the Wrench-Feasible-Workspace of a composite Cable-Driven Parallel Robot by determining its Available Wrench Set. We define three operation modes of such system and show that the Available Wrench Set in each operation mode depends on the static equilibrium of the dual-platform and contact conditions. The Available Wrench Set is constructed by the Hyperplane Shifting Method and is validated in simulation.