James Trelawney
Start with the seabed, not the chandlery
Most anchoring trouble in British harbours begins on the seabed, not at the bow roller. Before you worry about which pattern of anchor looks most convincing in the chandlery, work out what lies beneath you. Mud, sand, shingle and weed each demand a different compromise, and a harbour that looks uniform from the cockpit is often a patchwork of all four.
Local knowledge is worth more than any specification sheet. The harbourmaster, a neighbouring berth holder or the sailing club bar will tell you whether the holding is soft ooze, firm sand over clay, or a thin skin of sand on rock. Ask where boats dragged last winter. That is the ground you need to plan for.
Matching the anchor to the ground
Holding power comes from fluke area and how deeply that fluke buries, so the shape of the ground dictates the shape of the anchor.
- Mud and soft ooze: the anchor must penetrate before it can hold. Deep flukes with plenty of surface area work best; flat flukes tend to skim across the top and clog. An anchor that sits on the surface in mud will drag in the lightest breeze.
- Sand: the most forgiving ground, provided penetration is good. Sharp-toed scoop and plough patterns bury quickly and stay buried. Flat-fluked anchors set well in sand but can break out and foul their own chain when the tide swings the boat through 180 degrees.
- Weed and eelgrass: the enemy of flat flukes, which simply lie on the fronds. A plough pattern with a narrow, angled fluke cuts through to the sand beneath. Where weed sits over rock, a traditional fisherman's anchor with a stock and long arms can hook into crevices where nothing else will.
- Shingle and gravel: anchors bite well when well set, but small stones can jam between the flukes and the shank and stop them digging. Heavy chain helps here, keeping the shank low.
Most of us carry one main anchor. If that is your case, choose the pattern that suits the worst ground in your usual cruising area, not the best.
Holding power, weight and the chain that does half the work
An anchor that is one or two sizes above the recommendation for your boat is a sound investment in tidal waters, but weight alone is not holding power. A heavy, blunt anchor on weed will drag while a lighter, well-designed one of the right pattern digs in and stays put.
The rode matters just as much. All-chain gives abrasion resistance and catenary, that graceful curve of chain that absorbs snatch loads and keeps the pull on the anchor horizontal. For a boat of around nine to ten metres, eight millimetre chain is a sensible minimum, with twenty-five to forty metres of it before you even think about rope. Where you do use rope, a nylon snubber or a rope rode adds stretch and takes the violence out of a gust.
The angle of pull is everything. A horizontal pull lets the fluke dig deeper; an upward pull levers it out. Chain lying along the seabed is doing quiet, unglamorous work all night.
Scope, tide and the turn of the stream
In a harbour with a four or five metre tidal range, the water will move a great deal while you sleep. The anchor must survive not just the load but the reversal. On the ebb the boat swings one way, on the flood the other, and the anchor is asked to reset twice a day.
As a working rule, lay at least three times the depth in calm conditions and five times or more where tide and wind are in play. Measure from the bow roller to the seabed, and remember that a rising tide slackens the rode while a falling tide tightens it. Anchor on a falling tide if you can, so you are not left bar-tight and short-scoped as the water disappears.
Slack water is the kindest moment to anchor. Drop the anchor, pay out chain steadily as the boat falls back, then set it properly by motoring gently astern against the tide until you feel the chain come up hard and the boat stop. Take transits on two fixed objects ashore and note them. If the transits move, so have you.
Anchoring in a crowded harbour
Tight anchorages reward forethought.
- Plan your swinging circle before you drop, allowing for the full tidal range and the different behaviour of yachts, motorboats and moored craft.
- Avoid anchoring on a slope or on the edge of a channel, where you will swing into deeper water or into someone's line at low tide.
- Check what is already on the bottom. Old mooring blocks, chain and lost anchors are common in popular harbours and can foul your own gear.
- If the ground is foul or rocky, buoy the anchor with a tripping line so you can recover it without losing it.
- Keep an anchor watch, electronic or human. A quiet alarm at two in the morning is far better than a knock on the hull.
Where space is genuinely tight, accept that you may only manage a three-to-one scope, and choose the anchor with the best holding power at that angle. More chain is often the cheapest improvement you can make.
A workable compromise for British waters
For most cruising grounds around our coast, a modern scoop or plough pattern of generous size, backed by a good length of chain and a snubber, will handle mud, sand and weed with reasonable confidence. Add a fisherman's anchor for rocky, weedy anchorages and a flat-fluked anchor for pure sand if your locker allows.
Whatever you carry, practise with it in daylight and in clear water. Know how it feels when it sets, how it feels when it drags, and how much scope you need before the chain lifts off the seabed. That knowledge, more than any specification, is what keeps you secure through a night of turning tides.
