Plotter failure on a night crossing of the East Lamma Channel
You are coxswain of a 12 m GRP motor cruiser with twin 250 hp outboards, carrying six guests and one deckhand, on passage from Sok Kwu Wan, Lamma Island to a mooring off Causeway Bay. At 2115, ten minutes after clearing the Lamma ferry pier, the chart plotter and its internal GPS freeze and will not reboot. The night is clear with about 4 nm visibility, wind easterly force 3, slight sea. On board you have the paper chart for the area, a hand-bearing compass, an echo sounder, radar and one hand-held VHF. Traffic is normal for a Saturday night: fast ferries on the Central–Lamma run, an inbound container ship shaping up for the East Lamma Channel, and a scatter of small craft. Two guests are drinking on the aft bench and a third wants to sit on the foredeck while you are underway.
1. How do you fix and then monitor your position for the rest of the passage without GPS? Set out the steps and the cross-checks that tell you the fix is right.
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Make the boat safe for the work first: come off the plane to displacement speed, keep all guests seated aft of the helmsman, and put the deckhand forward as a lookout with the hand-held VHF so you are not single-handed while head-down over the chart.
Fix by bearings. Choose three charted, lit objects that are identifiable at night and spread 60° to 120° apart - for example a lit navigation mark on Lamma, the loom of a lighthouse, and a radar-conspicuous headland. Take the bearings quickly in sequence, plot all three, and treat the centre of the cocked hat as the position. A large cocked hat means you misidentified a mark or mistimed a bearing; re-take them rather than averaging your error into the plot.
Confirm with an independent source. Compare the echo sounder reading and its trend against the charted contour along your intended track, and take a radar range and bearing on a headland to check the bearing plot. Identify every lit mark by its charted light characteristic - colour, rhythm and period - before you rely on it; at night two similar lights a mile apart are easy to swap.
Then run a dead-reckoning plot: log speed, course and time between fixes, and re-fix at least every ten minutes, after every alteration, and before closing any shoal water or the channel edge.
2. Describe how you cross the East Lamma Channel and what you would transmit on VHF. What are your obligations towards the inbound container ship?
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Plan the crossing where and when you can see the whole width of the channel and the traffic in it, rather than creeping along the edge of the lane where you cannot see what is coming and ships cannot see you early. Cross on a steady course at, or as near as practicable to, right angles to the direction of traffic flow: your aspect is then unambiguous and you spend the minimum time in the channel.
Rule 9(b) puts the onus on you. A vessel of less than 20 m, or a sailing vessel, must not impede the passage of a vessel that can safely navigate only within a narrow channel or fairway. An inbound container ship in the channel is committed to the deep-water route and cannot stop or turn for a 12 m cruiser. Treat the fast ferries the same way in practice: their closing speed is deceptive and at 25 to 30 knots you have very little time to correct a bad decision.
On VHF, call the ship by name if you can read it from AIS or her hull, or call Hong Kong Vessel Traffic Centre on its published working channel, and state your position, course, speed and intention. Wait for an acknowledgement before you act on it. Never assume a VHF call transfers responsibility - the Collision Regulations still apply and a bridge team may not have heard you.
3. A rain squall reduces visibility to under 200 m. What do you do?
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Reduce to a safe speed - in practice slow enough to stop within half the distance you can see - and do not try to keep planing through it. Check that the all-round navigation lights are on and working, start and tune the radar, post the deckhand where he can both see and hear best, and keep the guests quiet and seated so you can listen.
Sound the restricted-visibility signal: one prolonged blast at intervals of not more than two minutes for a power-driven vessel making way (Rule 35). Listen for the fog signals of ferries and ships, and for your own echo off the land.
Navigate from the plot: dead reckoning from the last good fix, radar ranges on headlands, and the echo sounder to keep you off the shoals. If you cannot fix your position with confidence, or the squall looks set in, the safe option is to turn back or to anchor clear of the channel and the ferry routes - never in the fairway - and to tell Vessel Traffic Centre and any nearby traffic where you are and what you intend. A dinner booking is not a reason to press on.