This paper presents a cooperative consensus control scheme for multiple unmanned dynamic positioning (DP) tugboats to transport an unactuated floating object through cables, aiming to promote the automation and intelligence of marine towing operation. The scheme implements a leader-follower formation strategy among distributed tugboats, maneuvering the object by adjusting the position of the virtual leader in a reasonable manner. To ensure the formation configuration, a cooperative consensus controller is integrated into the feedback controller of each tugboat local DP system. In addition, a customized model parameter-free DP system is proposed to enhance the tracking performance of a single tugboat, addressing the challenges of full unknown model parameters and large cable tension disturbances. The proposed automatic towing control scheme is verified through full-scale nonlinear time domain simulations under variable environmental conditions and formation configurations, demonstrating its effectiveness.