When does risk of collision definitely exist at night?

The presence of both sidelights of another vessel being visible at night is a clear sign that a risk of collision exists. This scenario indicates that the observer is likely approaching another vessel head-on or in a crossing situation, as the sidelights are positioned on either side of the vessel. In such cases, the orientation of the lights conveys that both vessels are on converging courses, escalating the potential for collision.

Sidelights are part of the navigation rules designed to ensure vessels can determine each other's relative positions and movements during nighttime or low visibility conditions. When both sidelights are visible, it signals that the other vessel is not just nearby but on an intersecting track. This situation demands immediate attention to navigation and course correction to avert a collision.

Other scenarios, such as seeing only one light or relying solely on radar signals, do not provide enough definitive information about the relative position and direction of other vessels to assess an imminent risk of collision. Thus, the presence of both sidelights accurately indicates an increased risk and necessitates prudent seamanship to avoid an accident.