The Vessel Traffic Service (VTS) provides support to marine traffic in congested waters to ensure safe and smooth vessel movement in the waters under its purview. The VTS operators monitor the traffic with the decision support system at hand and talk to the ships on the Very High Frequency (VHF) radio. Safe channel navigation is proactively achieved by interaction and communication on the radio. Thus traffic management within the VTS domain is a complex joint activity, in which diverse stakeholders (bridge teams, VTS operators, pilots etc.) adopt one or more available communicative roles within technologically-mediated interactions to achieve safe and fluent traffic movement. This paper argues that the communicative achievement of channel navigation is a complex joint activity requiring the building up and active sustenance of common ground to promote teamwork and contribute to safe and efficient vessel movements. Monitoring common ground is integral to monitoring oceangoing traffic. This paper draws upon data from the audio recordings of the working channel of the VTS in a major South Asian world port. The authors argue that the proactive, real-time dynamic management of common ground contributes to enhanced situational awareness and sustains safe channel navigation.