Anchor Scope Calculator
Enter your water depth, bow height, scope ratio and any tide rise to find out how much anchor rode to pay out for a secure set.
How to calculate anchor scope
- Enter the water depth at the bow in feet.
- Add the height of your bow roller above the water and any expected tide rise.
- Pick a scope ratio (5:1 for all chain, 7:1 for rope or mixed) and read the rode length.
Examples
20 ft depth, 4 ft bow, 7:1 scope
waterDepthFt = 20, bowHeightFt = 4, scopeRatio = 7
Total height 24 ft, rode length 168 ft
Frequently asked questions
What is anchor scope?
Scope is the ratio of anchor rode let out to the total height from the seabed up to the bow roller. More scope means a flatter pull on the anchor and better holding.
What scope ratio should I use?
A common rule is 5:1 for all-chain rode in calm conditions and 7:1 for rope or mixed rode. In strong wind or a swell, 10:1 gives extra security.
Why add bow height and tide?
Scope is measured from the seabed to the bow roller, not just the water surface. Adding bow height and the expected tide rise keeps the ratio correct at high water.
Does chain weight change the scope I need?
Heavier all-chain rode sags into a catenary curve and pulls more horizontally, so it holds well at lower scope. Lighter rope rode needs more scope for the same effect.
Should I measure depth at low or high tide?
Use the depth when you drop the anchor, then add the further rise you expect. That way the rode is long enough once the tide comes in.
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