Anchor Scope, Chain Length & Swing Circle Calculator
Calculate the rode to deploy for safe holding, allowing for tide, freeboard and swing room.
Last reviewed by the myCalculator Editorial Team
Input Parameters
Scope is measured from the bow roller, not the waterline.
Use the rise to high water during your stay, not the full spring range.
Calculation Results
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Formula & How Anchor Scope, Chain Length & Swing Circle Calculator Works
Scope is the ratio of deployed rode to the vertical distance from the bow roller to the seabed, and it is what makes an anchor hold. A flat rode angle keeps the anchor shank horizontal so the flukes stay buried; a steep angle levers the anchor out. The vertical distance must include freeboard to the bow roller and the tide expected to rise during the stay, which is why anchoring at low water without allowing for the flood is a common cause of dragging.
- Enter Water Depth at Anchor (m) (m): Input your target parameter value.
- Enter Bow Roller Height Above Water (m) (m): Input your target parameter value.
- Enter Expected Tidal Rise (m) (m): Input your target parameter value.
- Enter Boat Length Overall (m) (m): Input your target parameter value.
- Enter Expected Conditions: Input your target parameter value.
- Apply Formula: Calculate using
Rode = (Depth + Bow Height + Tidal Rise) × Scope Ratio | Swing Radius = Rode + LOA. - Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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Frequently Asked Questions (FAQs)
How much anchor rode should I let out?
5:1 is the general standard for an overnight anchorage, 7:1 in strong wind and 10:1 in storm conditions. An all-chain rode can use about two ratios less because catenary absorbs shock loading.
Why does scope need to include the tide?
Anchoring at low water on 5:1 scope in 8 m becomes roughly 4:1 once a 2 m tide floods in. The reduced scope steepens the rode angle and is a frequent cause of dragging overnight.
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