A dragging anchor is rarely bad luck. It is almost always one of a handful of causes, most of them avoidable. Understand them and you will drag far less often — and catch it early when you do.
Dragging is when the anchor loses its grip on the seabed and the boat starts moving downwind or down-current, dragging the anchor along the bottom rather than being held by it. It can be slow and creeping or sudden and alarming. Here are the seven reasons it happens, in rough order of how often they are to blame.
The seven causes
1 Not enough scope
By far the most common cause. Too little rode makes the pull on the anchor too vertical, so it never buries properly and lifts out when the load comes on. The fix is simple: let out more. Aim for at least 5:1 on chain and 7:1 on rope, and more when it blows.
2 Poor holding ground
Some bottoms simply do not hold well — thick weed, soft mud, loose shingle, hard-packed sand or rock. The anchor skates or sits on top of the weed instead of digging in. Read the chart and pilot notes, and if the anchor will not bite after a couple of tries, move rather than hope.
3 The anchor was never properly set
Dropping the hook and paying out chain is not the same as setting it. If you do not back down under power to dig the anchor in and confirm it is holding, you are trusting an anchor that may only be resting on the surface. Always set it and feel it bite before you relax.
4 The wind or tide increased
An anchor set comfortably in 10 knots can be overwhelmed when it pipes up to 30. Load on ground tackle rises with the square of wind speed, so conditions that felt fine at anchor-down can break the anchor out hours later. Set for the worst you expect, not the calm you arrived in.
5 A wind or tide shift changed the angle of pull
Anchors hold best when pulled steadily in one direction. When the wind veers or the tide turns, the boat swings and the load comes onto the anchor from a new angle, which can trip it out — especially if it was marginally set. Wind-against-tide anchorages, where the boat sails around, are notorious for this.
6 The anchor is undersized or the wrong type
An anchor too small for the boat, or a design that suits a different bottom, will struggle in anything but ideal conditions. Modern designs generally out-hold older patterns, but any anchor asked to do too much will let go.
7 A fouled anchor or obstruction
Sometimes the anchor catches on an object, an old mooring or a rock, feels set, then breaks free when the load shifts. Or it fouls its own chain and cannot dig in. If a set feels odd or the holding seems inconsistent, re-lay it.
Most dragging happens at night, in a wind shift, while everyone is asleep. By the time you feel the motion change, the boat may already be well down on a hazard or a neighbour. This is exactly what an anchor alarm is for.
A prevention checklist
- Choose good holding ground — check the chart and pilot before you drop.
- Let out generous scope, and more as the wind builds.
- Back down under power until you are certain the anchor is dug in.
- Take a transit or note your position so you have a reference.
- Allow room to swing clear of hazards and other boats.
- Set an anchor alarm with a sensible radius before you turn in.
How an anchor alarm changes the odds
You cannot prevent every drag — conditions change, and even a good set can let go. What you can do is make sure that when it happens, you know within seconds rather than after the boat has travelled a hundred metres. A good anchor alarm watches the position you cannot, fires loudly the moment you leave your watch circle, and buys you the time to get on deck and act. Prevention keeps you anchored; the alarm keeps you safe when prevention is not enough.
Catch a drag the moment it starts
HoldFast fires sound, vibration and a notification the instant your boat leaves the circle. Free to download — premium is $4.99/year or $9.99 once for Lifetime.
Download on theApp StoreFrequently asked questions
Insufficient scope is the most common cause. Too little rode leaves the pull on the anchor too vertical, so it never digs in properly or breaks out when the wind increases. Letting out more rode, typically at least 5:1 on chain and 7:1 on rope, prevents most dragging.
Choose good holding ground, let out enough scope, and back down on the anchor under power to set it before you trust it. Then set an anchor alarm so you are warned early if conditions change and it does start to move.
Yes. Even a modern, well-sized anchor will drag if it is set in poor holding such as weed or soft mud, if scope is too short, or if the wind and tide swing the boat and pull it out at a new angle. Good technique matters as much as the anchor itself.