Which relative motion scenario is inconsistent with a definite risk of collision?

Which relative motion scenario is inconsistent with a definite risk of collision?

• A. Decreasing range and constant bearing
• B. Increasing range
• C. Decreasing range and changing bearing
• D. Head-on approach

Answer: (B)

Think about how danger arises from relative motion: a definite risk of collision shows up when the distance between vessels is closing. If the distance (range) is getting smaller, you’re on a converging path and collision is plausible, especially if the other vessel’s bearing isn’t moving away in a way that would prevent a meeting. If the range is increasing, the two vessels are separating, so there isn’t a definite collision risk. That’s why the scenario with increasing range is inconsistent with a definite risk of collision. The other situations—decreasing range with constant bearing (you’d see a steady line of sight as you close in), decreasing range with changing bearing (path still converging but not at a fixed bearing), and head-on approach (two ships on opposite courses toward a common point)—all indicate some form of collision risk.

Think about how danger arises from relative motion: a definite risk of collision shows up when the distance between vessels is closing. If the distance (range) is getting smaller, you’re on a converging path and collision is plausible, especially if the other vessel’s bearing isn’t moving away in a way that would prevent a meeting.

If the range is increasing, the two vessels are separating, so there isn’t a definite collision risk. That’s why the scenario with increasing range is inconsistent with a definite risk of collision. The other situations—decreasing range with constant bearing (you’d see a steady line of sight as you close in), decreasing range with changing bearing (path still converging but not at a fixed bearing), and head-on approach (two ships on opposite courses toward a common point)—all indicate some form of collision risk.