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Scope is the ratio of anchor rode deployed to the depth of water plus the height of your bow above the waterline. Getting scope right is the single most important factor in whether your anchor holds.
Minimum scope. For an all-chain rode in calm conditions, 3:1 to 4:1 is the minimum. For a chain-and-rope rode, 5:1 is the minimum. In strong winds or when overnight anchoring, use 7:1 to 10:1 for chain, 7:1 to 8:1 for mixed rode. More scope means a lower angle of pull on the anchor, which dramatically increases holding power.
Example. You are in 4 metres of water. Your bow is 1.5 metres above the waterline. Total depth from bow cleat to seabed: 5.5 metres. For a 7:1 scope with chain: deploy 5.5 × 7 = 38.5 metres of chain. Round up to 40 metres.
d3kOS anchor watch. d3kOS includes an Anchor Watch feature that sets a geofenced alarm radius around your anchored position. If the boat drifts outside the radius — meaning the anchor has dragged — the alarm sounds and Skipper Don announces the situation verbally. The default radius is 25 metres, adjustable in the Anchor Watch settings. Available on all tiers.
Tidal change. If the tide rises significantly while you are anchored, your effective depth increases and your scope ratio decreases. In tidal areas, calculate scope based on the high-water depth, not the depth when you anchored.
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