Anchor Swing Radius Calculator

Geometry: 120 ft of rode in 20 ft of effective depth reaches only √(120²−20²) ≈ 118 ft horizontally — the depth 'uses up' hypotenuse. Shallower anchorages convert more rode into swing; deeper ones less. Add your LOA because the stern, not the bow, hits the neighbor: a 36-footer's true claim here is ~154 ft of radius.

Slightly outside the computed swing radius, measured from the ANCHOR (drop a pin at the drop), not from where the boat settles — the classic setup error that makes alarms cry wolf or sleep through a drag. The 15% pad in this tool absorbs GPS scatter and rode stretch. Radius set from the boat's settled position must be nearly double, defeating the purpose.

Enough that circles don't overlap at full swing UNLESS you'll swing in unison: boats on similar rode and windage swing together like a corps de ballet, letting harbors pack tighter than pure geometry allows. The dangerous mismatches: all-chain heavy displacement next to nylon-rode lightweights, deep keels in current versus shallow hulls in wind, and anyone on a mooring (tiny circle) inside an anchoring fleet.

The boat traverses it: a 180° shift sweeps the stern across the full diameter — over 300 ft for this example — which is why the spot that looked roomy at arrival gets tested at the wind shift, and why the holding-ground question ('will the anchor reset when pulled backwards?') is part of swing planning. Modern roll-bar anchors reset reliably; older designs may trip and drag across the diameter.