You are called to the bridge at 0230. The pilot has just disembarked and will not accept the vessel back into the marina until 0600 due to a beam wind exceeding the berth limit. You have a 55-metre yacht drawing 4.2 m, a spring ebb running at 1.8 knots across a narrow, rock-fringed bay. The mate suggests anchoring. You must decide where, on which anchor, how much cable, and what watch state to maintain — and you must get it right first time.
The Tideway Problem
In a tideway the vessel will lie to the stream, not the wind, once the tidal force exceeds windage. This means your swinging circle is governed by the direction of the tidal stream, which may change on the turn. You must know the predicted times of HW/LW and the direction the vessel will swing through each stand and turn of the tide before you commit to a berth. Chart the swinging circle using the full scope deployed — not the minimum you hope to use — and check it clears the seabed hazards, other vessels and the safe-water boundary at every point in the tidal cycle.
In a tideway, both anchors may be required if the swing at the turn of tide would take you into danger. A running moor (both anchors laid in line with the stream, one ahead, one astern) holds the vessel in a fixed position with minimal swing — appropriate where space is tight fore-and-aft. Lay the lee anchor first, veer cable as you drop back, then let go the weather anchor before the cable is taut, equalising cable on both.
Scope in Confined Waters
Scope is the ratio of cable length to depth (water depth plus height of hawse above water). A minimum of 3:1 in very sheltered, firm holding with chain; 5:1 to 6:1 is standard working scope in open anchorages. In confined waters you may have to accept reduced scope — never below 3:1 with chain — and compensate by increasing watch state, shortening the anchor alarm radius, and being ready to weigh immediately. Record the scope deployed and the reasons for any reduction.
Holding Ground and Approach
Identify holding ground from the chart — mud and sand are preferred; rock, kelp and hard sand reduce confidence. Always approach into the tidal stream (not necessarily into the wind). This gives positive control: you can stop the vessel over the chosen spot using astern power and the stream, then lower — not drop — the anchor on to the bottom before veering cable under control.
Anchor Watch and Dragging
In confined waters the watch must be a qualified officer with authority to call the engine room. Set a close GPS anchor alarm immediately. Cross-check by taking two or three visual bearings on charted objects and noting them in the deck log. Check the cable periodically — a taught, vibrating cable indicates dragging. If in doubt, veer more cable; if that fails, use the second anchor or proceed to sea.
Your Immediate Decision in the Vignette
Before letting go: verify depth and swing room on the chart; confirm tide times and stream direction for the next four hours; plot the worst-case swinging circle; brief the mate and engine room; station a lookout on the foredeck. Only then, approaching slowly into the stream, lower the anchor to the bottom and veer to appropriate scope. Log the decision, the position, the scope deployed, and the watch arrangements.