Navigation General · Radar Plotting & CPA
A vessel observes a target on radar with a bearing that is NOT changing and a range that is decreasing. This situation indicates:
- AThe target will pass ahead at a safe CPA
- BThe target will pass astern at a safe CPA
- CThe two vessels are on a collision course✓ Correct
- DThe target is crossing from port to starboard
Explanation
A steady bearing with decreasing range is the classical radar indication of a collision course. COLREGS Rule 7 specifically cites 'a compass bearing which does not appreciably change' as sufficient to assume a risk of collision. Action must be taken well in advance per Rule 8.
Authority: Radar Navigation Manual (Pub. 1310), Ch. 4
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