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Anchor Rode & Swing Radius Calculator

How much rode a chosen scope asks for, and how much room the boat needs to swing around the anchor.

Depth of water under the bow, in metres, at the state of tide you are anchoring in.

Height of the bow roller or anchor attachment above the waterline, in metres. Together with the depth it gives the vertical drop to the seabed.

Rode length divided by that vertical drop, written as a ratio: enter 5 for 5:1. All-chain day stops are commonly 4 to 5, an overnight or mixed rope set-up 6 to 8, and 10 in strong wind.

The rode is the scope multiplied by the vertical drop from the bow roller to the seabed, which is the water depth plus the bow roller height. The swing circle is the horizontal distance the bow reaches from the anchor when the rode is straight and fully taut, √(rode² − drop²); a slack chain hangs in a catenary and reaches less, so treat it as the room the boat can use rather than a guaranteed position. The angle is the rode's angle below horizontal at the bow. Values are refused outside 0.5 to 100 m of depth, 0 to 10 m of bow roller height and a scope of 1.5 to 20, and decimal commas are accepted. This is arithmetic for planning only: it does not judge holding ground, weather, anchor type, chain size or local rules, and it runs entirely in your browser with no storage, uploads or network access.