How can you determine that you are overtaking another vessel?

When you can see only the stern light of another vessel, it indicates that you are overtaking that vessel. According to navigation rules, when you are behind another vessel and can only see its stern light, it means you are positioned to pass it from behind. In this scenario, the overtaking vessel is required to give way to the vessel being overtaken, ensuring safe navigation and adherence to maritime protocols.

In contrast, if you were approaching head-on or from the bow, you would be in a crossing situation rather than an overtaking one. Being at dock does not pertain to overtaking dynamics at sea and would not apply in this context. Thus, recognizing that only the vessel's stern light is visible is a clear indication that you are overtaking it.