Typhoon Shelter Anchoring with a Veering Wind
At 1500 you anchor your 15 m displacement motor cruiser in a gazetted typhoon shelter in Tolo Harbour. The Hong Kong Observatory has issued Signal No. 3, with No. 8 expected by 1800; wind is SE 25 knots and forecast to veer SW 45 knots. The shelter is crowded. You choose a gap near the inner breakwater in a charted depth of 4.5 m at chart datum; tide height now is +1.8 m and a small storm surge is forecast. Your ground tackle is a 25 kg anchor with 40 m of all-chain rode, and your engine starts reliably. Other vessels are anchored about 25 m ahead and 20 m astern. The holding ground is soft mud. At 1715 the wind veers, your transit on two shore marks opens, and the anchor chain begins to snub and then slacken.
1. Calculate an appropriate anchor scope and explain how you would set the anchor in this shelter. What limits your choice?
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Depth at the anchor is 4.5 m charted + 1.8 m tide = 6.3 m. With 40 m of chain the maximum scope is 40/6.3 ≈ 6.3:1. In a typhoon shelter, 5–7:1 is a reasonable target; 6.3:1 is acceptable but not generous in soft mud. The limit is the crowded shelter: 25 m ahead and 20 m astern, plus your swinging circle, means you cannot veer all 40 m blindly. Lower the anchor to the seabed, veer slowly while using gentle astern power to set it, then snub and take transits and bearings. Display the anchor ball by day and anchor light at night. Keep the engine ready and fit a snubber to reduce snatch. If the space is too tight for a safe scope, choose another gap rather than anchoring on a short scope in soft mud.
2. At 1715, what is happening, and what immediate actions do you take?
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The opening transit and the chain snubbing then slackening indicate the anchor is not holding or the vessel has sheered and is dragging. Start the engine immediately, engage slow ahead to take the load off the chain, and have a crew member take fresh transits and bearings. If there is room, veer chain to reduce snatch, but do not veer into the vessels ahead or astern. Warn nearby vessels on VHF and by voice; inform the harbour or VTS. If the transit continues to open, weigh anchor and reposition to a clearer spot, or use engine and anchor together to hold position. Do not wait for the anchor to drag into another vessel. If control is lost, call for assistance on VHF 16 and prepare to leave the anchorage.
3. What weather and tide information would you monitor, and what would make you abandon the anchorage?
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Monitor HKO warnings, the expected track and intensity, storm surge, rainfall, wind direction and local observations; keep a barometer and log the trend. Watch the tide height and depth, because surge changes both scope and clearance. Abandon the anchorage if the anchor drags repeatedly, if neighbouring vessels drag down on you, if the shelter becomes exposed after the wind veers, or if you cannot maintain a safe swinging circle. Move early, before the strongest wind, and choose a shelter with good holding ground and room to manoeuvre. Tell the harbour authority and nearby vessels before moving, and keep a VHF 16 and 12 watch.