Fog patches off Lutry: four light configurations and a signal from the starboard bow
You are motoring back to Lutry on Lake Geneva at 22:40 in a 6.5 m open motorboat at 8 kn, heading 240°. The air is clear but fog patches are forming over the water, and within 20 minutes visibility drops from 1 km to about 150 m. Between patches you make out four light configurations ahead and to starboard: (a) two all-round red lights in a vertical line, low and stationary about 400 m away; (b) red-white-red in a vertical line, moving slowly; (c) green above white, moving at about 4 kn; (d) a single white light, lower than your own, not moving, close to the shore. You have a hand-bearing compass, a foghorn, a GPS and a VHF on channel 16. Your GPS track shows you 300 m to the right of the leading line into the harbour. From your starboard bow you hear one prolonged blast about every 90 seconds.
1. Identify each of the four configurations, say what the vessel is doing, and give your action for each.
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(a) Two all-round red lights, vertical - a vessel not under command. She cannot manoeuvre as required, so she is effectively a moving (or here, stationary) obstruction. Treat her as give-way to everyone: reduce to steerage way, keep well clear, be ready to stop, and do not assume she will hold her position if she is drifting.
(b) Red-white-red, vertical - restricted in her ability to manoeuvre: dredging, survey, cable work, a tow with a long scope. She can only manoeuvre with difficulty, so again you keep clear and pass at a distance that allows for her gear and her unpredictable movement. Her slow speed tells you nothing about her ability to turn.
(c) Green over white - a vessel engaged in trawling. The green-over-white stack is fishing, not a pilot or a ferry. She is slow, her gear trails astern and can be hundreds of metres long: never cross her stern close aboard and never pass between her and her gear. Pass ahead of her at a safe distance, or well around.
(d) A single low white light, close to the shore, not moving - an anchored or moored small craft, a mooring buoy with a light, or a shore light. Because you cannot tell which, treat it as a fixed obstruction and do not pass between it and the shore; the depth there is unknown and the light may sit over a shoal.
General rule. An unidentified light is assumed to be the more dangerous of the possibilities until you have resolved it. At 8 kn you cover 150 m in 36 seconds.
2. What sound signal must you make, what does the single prolonged blast from the starboard bow tell you, and what should you do about it?
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What you must sound. A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than two minutes. If you stop and are still under way but not making way, two prolonged blasts with a gap. You are entitled to sound it, and obliged to - silence is not an option in fog.
Your speed is wrong for the conditions. Rule 19 requires you to proceed at a safe speed, which in practice means a speed at which you can stop within half the visible distance. At 150 m visibility that is about 75 m of stopping distance - you need to be down at 3–4 kn or less, not 8 kn.
What the blast means. One prolonged blast every 90 seconds is a power-driven vessel making way. From your starboard bow with a steady bearing, that is a crossing or converging situation in which neither of you can see the other. She may not have heard you, and you have no idea of her speed.
Action. Reduce to minimum steerage way, sound your own signal, and stop the engine briefly to listen - you will hear the bearing far better than you see it. Take a compass bearing and repeat it after 30 seconds. If it is steady and closing, alter course to starboard: Rule 19 forbids turning to port for a vessel forward of your beam, and forbids turning toward a vessel abeam or abaft. If the bearing draws forward or aft, hold your course and pass.
Five short rapid blasts means doubt or danger, usually 'I do not understand your intentions'. If it is meant for you, answer it and state your intention plainly on the VHF rather than resolving it by guesswork.
3. You see the same vessels again at 14:00 the next day. What shapes should each show, and what do you do if a light or shape does not match what the chart and your expectation suggest?
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Day shapes. Vessel not under command: two black balls in a vertical line, where they can best be seen. Restricted in ability to manoeuvre: ball, diamond, ball. Trawling: two black cones, apexes together, one above the other - the point-to-point pair is the trawling signature and is easy to confuse with the ball-diamond-ball at a distance. A vessel at anchor by day: one black ball forward.
Shapes only work if you look for them. At 400 m a 0.6 m ball is a dot. Use the glasses, and cross-check with the aspect: a vessel showing two balls but clearly making way is either drifting or has not set her shapes, and you should assume the worse case - she may not be able to keep out of your way.
When something does not fit. A steady white light exactly on your leading line at night is more likely a fixed leading light than a vessel; check the chart for sector boundaries before you alter. A light that changes colour as your bearing changes is a sector light and the colour is telling you about depth, not about traffic. A light that is fixed (steady) where the chart shows a flash is either a different light or not a light at all.
Procedure when unsure. Slow down, take a bearing, sound the appropriate signal, identify by angle and by aspect, check the chart for charted lights and marks in that sector, and give the object a wide berth until it is positively identified. Passing close to something you have misidentified is how groundings and collisions both happen.