Risk of collision exists when an approaching vessel has a(n) __________.

The situation described by a generally steady bearing and decreasing range indicates that the two vessels are on a collision course. When one vessel maintains a constant bearing relative to another while the distance between them is decreasing, it signals that they are likely to intersect each other's paths. This conceptual understanding is crucial in maritime navigation because it highlights the need for one or both vessels to take action to avoid a collision.

In contrast, other scenarios like an increasing range and fluctuating bearing suggest that vessels are moving apart or not on a collision course, while a steady range and changing course implies that the relative positions are not static, which typically does not indicate an immediate risk of collision. Fluctuating speed and bearing can create an unpredictable situation, but it does not inherently indicate a risk of collision if the overall trajectory remains safe. Understanding these factors is essential for safe navigation and avoiding potential incidents at sea.