Radar-only avoidance in restricted visibility
MV Alborz (18,000 GT, general cargo) is on passage in the Gulf of Oman, steering 000 degrees at 14 knots, with visibility varying between 0.6 and 1.2 nautical miles in patches of haze. The radar is running. One target is acquired on the starboard bow: range 5.2 miles, bearing 007 degrees relative to heading, CPA 0.4 miles, TCPA 12 minutes; AIS gives the target's true course 185 degrees at 12 knots. A second, weaker echo lies at 2.8 miles on 350 degrees and is not yet tracked. Patchy sea clutter shows to the north-east. The vessel's stopping distance is about 0.55 miles at 14 knots and about 0.25 miles at 8 knots. The second officer is alone on the bridge with a helmsman; the master's night orders require a call in any doubt. The next waypoint is 40 minutes ahead and the traffic lane boundary is 3 miles to port.
1. Which steering and sailing rules govern this encounter, and why are Rules 14, 15 and 16 not applicable? Does a risk of collision exist?
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Which rules apply The vessels are not in sight of one another, so Section II of Part B (Rules 11 to 18) applies, and specifically Rule 19, conduct of vessels in restricted visibility, together with Rules 5, 6, 7 and 8 as far as they are relevant. Rules 14, 15 and 16 presuppose vessels in sight of one another; they identify a give-way and a stand-on vessel and tell the stand-on vessel to keep her course and speed. In restricted visibility there is no give-way or stand-on vessel: each vessel is required to take her own avoiding action under Rule 19, and neither may assume the other will act.
Risk of collision Yes. Under Rule 7, a risk of collision is deemed to exist if the compass bearing of an approaching vessel does not appreciably change. The bearing here is nearly steady, the range is falling from 5.2 miles, and the ARPA predicts a CPA of 0.4 miles with a TCPA of 12 minutes. The courses are nearly reciprocal (000 against 185), so this is a near head-on encounter that will become a close-quarters situation.
Special constraints The target is forward of the beam, so any alteration of course must be to starboard (Rule 19(d)); altering to port is prohibited except for a vessel being overtaken. Rule 19(e) requires reducing to the minimum speed at which the ship can be kept on course, and taking all way off if necessary, if a close-quarters situation cannot be avoided. Rule 35 sound signals apply: one prolonged blast at intervals of not more than two minutes for a power-driven vessel making way.
2. Plan the manoeuvre, with supporting numbers, and explain what you would not do and why.
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Course Make one bold alteration to starboard, of the order of 45 degrees, to about 045 degrees, and check the result on the ARPA.
- Before the alteration the relative track is about 26 knots on roughly 182 degrees, giving the predicted CPA of 0.4 miles.
- A 45 degree alteration changes own velocity to about 9.9 knots east and 9.9 knots north; against the target at 185 degrees, 12 knots, the relative velocity becomes roughly 24 knots on about 207 degrees, and the CPA opens to about 1.7 miles with a TCPA of about 12 minutes.
- A 20 degree alteration would give a CPA of only about 0.55 miles, which is inside the visibility distance and not an effective action. The arithmetic is why one large alteration is correct and a succession of small ones is not; they are confusing to the other vessel and rarely achieve a safe CPA.
Speed Reduce to 8 knots. At 1 mile visibility, half the visible range is 0.5 miles; the stopping distance at 14 knots (0.55 miles) exceeds it, while at 8 knots (0.25 miles) it does not. That is the practical test of Rule 19(b) safe speed and of Rule 19(e).
What not to do
- Do not alter course to port: prohibited by Rule 19(d) for a target forward of the beam, and it would turn toward the other vessel's track.
- Do not alter toward the untracked echo bearing 350 degrees without plotting it first.
- Do not wait for the other vessel to act, and do not assume she has radar or is plotting.
- Do not use VHF to negotiate a passing; VHF-coordinated manoeuvres have repeatedly produced collisions because the agreed intention is misunderstood or not met.
- Do not make a series of small alterations or reduce speed alone: the CPA barely improves.
3. The target's echo is lost in clutter and the ARPA alarms at 2 miles. State your immediate actions, sound signals and reports.
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Assume the worst. A lost echo does not mean the vessel has gone; it means the plot is no longer being updated. Treat the target as continuing on 185 degrees at 12 knots, so a close-quarters situation is developing.
Immediate actions
- Call the master at once, as the night orders require, and state the range, the last bearing and the actions taken.
- Reduce speed to the minimum at which the ship can be kept on course, and be ready to take all way off. If the situation cannot be resolved, stop the engines and take the way off, holding steerage only if needed.
- Sound the fog signal; one prolonged blast at intervals of not more than two minutes while making way, and two prolonged blasts with an interval of about two seconds between them when stopped, with navigation lights on and the engines on stand-by.
- Post a forward lookout with a whistle or gong, and an extra bridge lookout; open the bridge wing doors and use the daylight/vision mode on the radar, changing to a shorter range scale and adjusting the clutter and gain controls to pull the echo out of the clutter.
- Use every available means: the second radar or the AIS, plus a paper plot of the last two or three positions so the last relative track is recorded and the likely CPA from the last plot is known.
- Watch the lane boundary 3 miles to port; do not cross into the opposing lane in a blind manoeuvre, and note that the waypoint is close, which may tempt a premature turn toward danger.
Records and reporting Record the times, ranges, bearings and every helm and engine movement in the bell book and the log. Report to port control or VTS if the area is covered, keep a listening watch on VHF 16 but do not rely on it, and inform the master in writing of the plot when he arrives on the bridge.