Few feelings beat switching off the engine in a sheltered UK bay, watching the chain run out and knowing the evening is yours. But crowded anchorages are busy on a summer weekend. The difference between a peaceful night and a 3am anchor watch often comes down to a few minutes of thought before you drop the hook.

Read the bay before you choose your spot

Approach slowly and look at the whole bay, not just the first gap. Check the chart, echo sounder and tide table. In many UK bays the tidal range is large: four or five metres on a spring tide is common, and more in the Bristol Channel. A spot that looks generous at high water may be a drying bank at low tide, or leave you too close to a neighbour when everyone swings.

Look at how the boats already there are lying. If they face different directions, some are lying to wind and others to tide. Identify mooring buoys, trots, racing marks, pot lines and fairways. If the bay feels tight, it probably is.

Work out your swinging room

Scope is the length of anchor rode divided by the depth of water. For all-chain, 4:1 is a sensible minimum in settled weather; use 5:1 or 6:1 with rope in the mix or a fresh forecast. In a crowded bay you may not have room for 6:1, so be honest about the conditions.

Measure depth from the bow roller to the seabed, adding the height of tide to the charted depth. With 4:1 scope in 5 metres at low water, you have roughly 20 metres of chain horizontal, plus your boat length: a radius of about 30 metres, or a circle 60 metres across. In 10 metres at low water, the same scope gives a radius nearer 50 metres and a circle 100 metres across. Use low water for depth and swinging room, because that is when the chain is most horizontal and your boat swings widest.

Check fetch, shelter and wind shifts

Fetch is the distance of open water between you and the windward shore. Even a mile of fetch in a fresh south-westerly can build an uncomfortable chop; two miles can make a small bay miserable. Check the forecast for direction, strength and gusts, then look at the chart for shelter. A bay open to the south-west is fine in a northerly, but exposed if the wind backs.

UK weather often brings a sea breeze on a warm afternoon, filling in against the gradient wind. That changes how boats lie and how much fetch you have. Also consider swell wrapping around a headland. Ask: will this spot still be comfortable in six hours, at low water, and if the wind veers 30 degrees? If not, choose another corner.

Respect other vessels and their swinging circles

An anchored boat does not stay in one place. It swings around its anchor, and the size of that circle depends on its length, scope and windage. A boat on a mooring has a smaller circle, but its chain or sinker may still lie on the seabed. Do not anchor on top of a mooring, and do not drop just ahead of another anchored boat where your circles will overlap when the wind shifts.

In a crowded bay, aim for the centre of the largest empty space. A minimum of 30 metres between you and the next anchored boat is a sensible starting point; 50 metres is better if there is room. Avoid fairways, ferry routes, racing marks, trots and areas used by swimmers. If someone anchors too close later, moving early is far easier than fending off at midnight.

Use shore transits to confirm you are holding

Once the anchor is set, pick two pairs of fixed shore objects that line up. A transit is two objects in line: a church tower behind a gap in the trees, a white house behind a rock, a chimney behind a harbour wall. Choose one transit abeam and one astern, ideally at roughly right angles. Write down what you see, or take bearings with a hand bearing compass.

• Abeam transit: if it opens or closes, you are dragging.
• Astern transit: if the objects separate, the anchor is moving.
• Depth check: the echo sounder should match your expectation.
• GPS anchor alarm: a useful backup, but not a substitute for looking.

Give the engine a gentle astern burst to test the hold, then watch the transits for a few minutes. If they move, weigh anchor and try again. In a crowded bay, do not simply let out more chain unless you have room; a longer scope makes your swinging circle bigger.

Settling in and keeping watch

Once you are happy, fit a snubber, note your position and depth, and set an alarm. Keep an eye on the weather and other boats as the tide turns. Boats that were lying comfortably may swing differently as the stream changes. If the wind builds, you may need more scope, but only if there is room. If the bay becomes too crowded or the forecast worsens, move while it is still easy.

A safe anchorage is about room to swing, shelter from fetch, respect for neighbours and a way of checking that nothing has changed. Get those right and you can relax, put the kettle on and enjoy the evening. A few minutes of thought before you drop the anchor is the best insurance you can carry.