Radar-Only Contact in Fog in a Traffic Lane
M/V Skagerrak, 180 m LOA, is eastbound in a traffic lane at 15 kt, steering 090°, in fog at night with visibility 0.6 NM. The X-band radar on 12 NM range shows one contact dead ahead at 6.0 NM on a steady relative bearing, with an ARPA CPA of 0.1 NM and TCPA of 12 minutes. A second contact is on the port quarter at 2.5 NM, overtaking, with a CPA of 0.4 NM. The ship is 0.8 NM south of the lane centreline in a 4 NM wide lane. The sea is calm and the wind light. The master is on the bridge but has left the con to you; there is no VTS reporting requirement and neither vessel has been identified. The engine is on bridge control.
1. Which rules apply and what action do you take? Give timing, magnitude and reasons.
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Rules. Restricted visibility with radar-only detection: Rule 19 governs, with Rules 5, 6, 7, 8 and 10 also in play. There is no stand-on vessel under Rule 19 - both ships must act, but you cannot assume the other ship will.
Assessment. A steady bearing with range falling from 6 NM and a CPA of 0.1 NM is a close-quarters situation. Closing speed is 6 NM in 12 min ≈ 30 kt, so the target is probably near-reciprocal at about 15 kt.
Action - early, substantial, readily apparent (Rule 8):
- A port alteration is prohibited by Rule 19(d)(i), because the target is forward of the beam. So either alter to starboard or reduce speed.
- A 30–40° starboard alteration at 6 NM is large enough to be seen on radar; a 10° alteration is not.
- The ship is only 1.2 NM from the southern lane boundary, so combine the turn with a reduction to about 8 kt (Rule 19(e): reduce to the minimum at which the ship can be kept on her course), and be ready to stop.
- Sound one prolonged blast at intervals of not more than 2 minutes (Rule 35(a)).
- Call the master and keep both targets plotted.
2. How does the overtaking contact on the port quarter affect your plan?
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The overtaking contact. At 2.5 NM on the port quarter with a 0.4 NM CPA she is an overtaking vessel and must keep clear (Rule 13). That does not give you a free hand: under Rule 19 she is not a stand-on vessel either, and your alteration must not create a new risk with her.
- A starboard turn swings the stern to port, toward the overtaking vessel's track. Check the ARPA CPA to her after the planned alteration before committing; if the CPA falls below about 0.5 NM, make the turn smaller and take the separation from speed reduction instead.
- Do not turn to port: that turns toward her and is also prohibited by Rule 19(d)(ii) for a vessel abaft the beam.
- If she is identified and in VHF contact, a short security call helps, but do not rely on it and do not use VHF to negotiate who does what.
- Keep her plotted: at 2.5 NM with a speed advantage she will be past within minutes, after which the head-on contact is again the only constraint.
3. The range closes to 3 NM with the bearing still steady. What now?
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Range 3 NM, bearing still steady. The close-quarters situation is developing and the other ship is not obviously acting:
- Reduce speed further, to the minimum at which the ship can be kept on her course; if the range keeps falling, take all way off (Rule 19(e)). A stopped ship with the engine ready is far safer than a fast ship that cannot turn.
- Once stopped, sound two prolonged blasts with a 2-second interval at intervals of not more than 2 minutes (Rule 35(b)), and keep a forward lookout listening as well as watching.
- Do not make a small last-minute alteration. If a turn is still needed, make it large and in good time (Rule 8).
- Call the master, switch the radar to a shorter range, and use VRM/EBL and the trial manoeuvre to check the effect of any further action.
- Navigate with extreme caution until the danger of collision is over (Rule 19(e)); record times, ranges, bearings and actions in the log, and be ready to report a near miss to the company and the authorities.