Anchoring: choosing an anchorage, anchoring safely and keeping an anchor watch

Anchoring safely means choosing a bay that is sheltered from wind and swell all night, on sand or mud with enough room to swing, letting out three to five times the depth in chain depending on the wind, setting the anchor by motoring astern and running an anchor watch with a GPS alarm that also notices a night-time wind shift.

How do I recognise a good anchorage?

By four things: shelter from wind and swell, good holding ground, suitable depth and enough room to swing. The shelter has to last the whole night, not just for the wind when you arrive.

Swell wraps around headlands into the bay even when the wind is kept off: a spot can be calm in the wind and still roll. The chart shows the type of bottom with abbreviations such as S (sand), M (mud), R (rock) and Wd (weed). In the Mediterranean, seagrass meadows (Posidonia) are protected in many places, and anchoring on them is prohibited there. Never anchor over cables and pipelines marked on the chart.

How much anchor chain should I let out?

As a rule of thumb, with chain three to five times the depth of water, more in strong winds and swell. With an anchor rode of rope you need considerably more length.

Measure the depth from the bow roller: depth of water at high tide plus the height of the bow above the water. More chain lies flat on the bottom, pulls the anchor horizontally and dampens snatching.

Where other boats lie close together, let out roughly as much as they have, so that everyone swings in a similar way.

How do I set the anchor properly?

Approach slowly head to wind, lower the anchor to the bottom, pay out chain as you drift back and set the anchor by motoring astern.

1. Motor slowly head to wind to the spot where the anchor should lie, and stop the boat.
2. Lower the anchor briskly to the bottom, then pay out the chain gradually as you drift back, not in a heap.
3. Make fast at the planned length and wait until the boat swings head to wind and the chain comes taut.
4. Set the anchor by motoring astern with slowly increasing power and check with two bearings or a transit ashore that the boat is holding. If the chain judders under your hand, the anchor is dragging.
5. Rig a chain hook with a line (snubber) so the load is not on the windlass.
6. By day show the black anchor ball, at night the white all-round light (COLREGs Rule 30).

How does an anchor watch work?

An anchor watch checks whether the boat stays inside its swinging circle: in the past with bearings and someone on watch on deck, today with a GPS alarm. The circle belongs around the anchor, not around the spot where the boat happens to be when you switch it on.

Its radius is roughly chain length plus boat length, with a reserve for GPS inaccuracy. Too small, and every wind shift wakes you; too large, and the watch notices dragging too late. At night, add a look at the wind, the neighbours and the shore, a charged phone and a torch within reach.

Why do I need to check the night's wind?

Because an anchorage only gives shelter from certain directions. If the wind shifts to the open side at night, the boat is on a lee shore, often in the darkest hour.

Common reasons: the sea breeze dies in the evening and the land breeze or gradient wind takes over, a front shifts the wind, thunderstorms bring gusts from any direction, and local winds such as the Bora set in suddenly. Read the marine forecast before anchoring, memorise the way out in daylight and decide in advance at what wind strength you will move. More on sudden gusts in the guide Gusts and thunderstorms, on swell under Sea state and waves.

How does Sailseer help with anchoring?

The info page of a harbour on the map lists the nearby anchorages with their shelter for each wind direction, calculated in 30-degree sectors from the distance to the coast. The night check lays the wind of the next 14 hours from the consensus of the weather models over each anchorage and names the critical hour in local time, for example “exposed from 03:00: wind W 18 kn, gusts 27 kn, swell in the bay”. That way you can see in the afternoon whether the bay will still give shelter at three in the morning, for example in the western Baltic, in Ireland, in the Caribbean, in the Maldives or on inland lakes.

The anchor watch runs in the browser, with no account and no app: “Anchor dropped here” stores the position, the radius comes from chain plus boat length plus 5 m or can be entered directly, and the circle can be moved. If the boat is outside three times in a row or the GPS goes silent for 90 seconds, the alarm goes off with sound, vibration and a notification; imprecise positions with more than 60 m of error do not trigger a false alarm. When started, the watch fetches the night's wind for the anchorage and keeps an eye on it with its own thunderstorm watch. The track is shown on the map, and a boat GPS connected via the boat instruments can replace the phone.

Sailseer is a planning aid and not for navigation. A look outside, the official chart and the marine forecast take precedence.