This paper addresses collaborative transportation of autonomous surface vehicles (ASVs) operating at a low speed in an open water area to assist in the movement of a ship. A constrained collaborative control method is proposed for ASVs based on a kinematic model. During the collaborative transportation phase, each ASV can converge to the desired position-heading by designing a safety-critical kinematic control law. To achieve the collaborative transportation of ASVs, the collaborative velocity signals are obtained by solving a quadratic programming problem subject to the contact force constraint and the assisted ship constraints such that the safety of ASVs during collaborative transportation can be ensured. By using the proposed constrained collaborative control method, the collaborative transportation of ASVs can be achieved. Simulation results are shown to validate the efficacy of the proposed constrained collaborative control method for collaborative transportation of ASVs.