How Far Apart Should Boats Anchor?

The Real Question Is About Circles, Not Distance

A boat at anchor is not parked — it is tethered. As the wind and current turn, it swings around its anchor on the end of its rode, tracing a circle on the water. So “how far apart should boats anchor” is really a geometry question: will your circle and your neighbour's circle overlap? If they can't touch, you are far enough apart. If they can, you are trusting that both boats will always swing in the same direction at the same instant — a bet that comes due on the night the wind shifts and one boat turns before the other.

That is why the boat-to-boat distance you actually need is not a fixed number of metres — it depends on how much rode each boat has out, which depends on the depth and the scope (both are step two of how to anchor a boat). Two boats in a shallow, calm cove can lie surprisingly close; the same two boats in 10 m on 7:1 scope in a blow need a small football pitch between them.

Working Out Your Own Swing Circle

Your swing radius has two parts, and it is deliberately simple:

Swing radius = rode deployed + boat length.

The rode is the depth (add your bow height above the water, plus any tidal rise) multiplied by your scope ratio — 5:1 for settled fair-weather nights, 7:1 as the general overnight standard, more in a blow. Add your boat's length overall, because the boat itself sweeps that extra distance beyond where the anchor rode reaches the bow. Our anchor scope calculator does the whole sum for any depth and boat size, and anchor scope explained covers why the ratio matters.

For two boats not to touch, the gap between their anchors needs to be at least the sum of their two swing radii. When the boats are similar, that's simply double your own radius.

The table is the ideal — full room for everyone. Real anchorages are more crowded than that, and the honest answer is that boats routinely lie closer than the sum of their swing circles and get away with it, because in a steady wind everyone points the same way. The gap in the table is what protects you on the night they don't.

The Unwritten Rules of a Crowded Anchorage

Geometry sets the minimum; etiquette decides who has to honour it. These are the conventions every experienced anchorage runs on — none are formal law, all are near-universal:

• First boat holds the ground. Whoever anchored first sets the pattern. If you arrive later, the room is yours to find, and if a conflict develops it is your job to re-anchor — not theirs.
• Match the boats around you. Anchor with similar scope and rode to your neighbours so you all swing alike. The boat on 3:1 next to boats on 7:1 is the one that ends up in someone else's cockpit.
• Anchor abeam, not on top. Drop level with, or behind, the boats already there — never drop your hook ahead of another boat, over their anchor, so that you settle back onto them.
• Watch before you trust. Sit for a few minutes after you set. Look at how the boats around you are lying and which way they swing before you shut down and go below.
• If in doubt, move. The five minutes it takes to re-anchor with more room is always cheaper than the fibreglass repair, and far cheaper than the 03:00 conversation in your pyjamas.

Why “Same Size” Boats Still Swing Differently

The trap in all of this is assuming the boat next to you will swing when you do. It often won't, because boats respond to wind and current in different proportions:

• Rode type. An all-chain boat lies back on a heavy catenary and swings slowly in a tight arc. A boat on rope-and-chain sits lighter and sails around more widely.
• Wind versus current. A deep-keel monohull is held by the current; a shoal-draft boat or a catamaran is pushed by the wind. In a spot where wind and tide oppose each other, those two boats can point in opposite directions at the same moment.
• Windage. A boat with a big furled genoa, davits and a bimini blows off downwind; a bare-poled boat sits quieter. More windage means a wider, faster swing.

This is why two identical-looking boats can end up bow-to-bow in the same anchorage, and why the spacing that looked generous at sunset feels tight when the sea breeze dies at midnight and the current takes over.

How an Anchor Alarm Fits the Spacing Problem

Spacing protects you from other boats; an anchor alarm protects everyone from your anchor. The two work together, and the key is to set the alarm to your own swing circle — not to the size of the whole anchorage. A boat on 5:1 scope in 5 m of water needs an anchor alarm radius of roughly 40 m — rode plus boat length plus a small GPS margin. Set it that tight, and the alarm stays silent while you swing normally around the anchor, and fires the moment your position leaves the circle — which can only mean the anchor has dragged. Set it too wide “to be safe,” and by the time it goes off you are already in your neighbour's swing circle.

That is the difference between a nuisance and a lifeline. A GPS anchor alarm watches your position all night, even with the phone locked, and wakes you the instant you break out of your own circle — while the boat is still where the geometry says it should be, and before it becomes the boat everyone else is fending off. If you're not sure yours has started to move, here's how to tell if your anchor is dragging.

The Bottom Line

Boats should anchor far enough apart that their swing circles cannot overlap: at least the sum of the two boats' swing radii, where each radius is that boat's rode plus its length. For a typical cruiser that means roughly 75 m between anchors in 5 m of water on 5:1 scope, and more as the water deepens or the scope grows. Real anchorages crowd tighter than that, so honour the etiquette — first boat holds, match your neighbours, anchor abeam — give yourself proper scope, and set an anchor alarm to your own circle so a dragging anchor wakes you before it becomes anyone else's problem.