Anchor Scope Calculator
Enter water depth, tidal rise, and bow height to get the total rode length to let out at your chosen scope ratio. Accounts for tidal range so the anchor doesn't drag at high water. Nothing uploaded.
Anchorage Details
Rode Length
All-chain rode requires less scope due to catenary action. Mixed chain-and-rope rode requires more scope. In rough conditions or with a rope-only rode, use 7:1 or more.
Learn more: anchor scope, rode length, and chain vs. rope
How much anchor chain should I let out?
The standard recommendation is 5:1 scope for all-chain rode in normal conditions - 5 metres of chain for every 1 metre of total vertical distance (water depth plus tidal rise plus bow height). For rough conditions or mixed rope/chain rode, 7:1 is safer. The total vertical distance must account for the tidal range to high water - the anchor must hold at high tide too.
Why anchor scope must account for tidal range
If you anchor in 3m at low tide and the tide rises 2m, the water depth becomes 5m. At 5:1 scope you need 25m of rode for 5m depth, not the 15m that would be adequate at low tide. Failing to account for tidal range is a common cause of anchors dragging in tidal anchorages. Always base scope calculations on the expected depth at high water to be safe through the full tidal cycle.
Chain vs. rope for anchoring
Chain provides catenary action - it sags in a curve under its own weight, which absorbs shock loads and keeps the pull angle more horizontal at the anchor. This means chain can hold effectively at shorter scope (4:1). Rope is lighter but requires more scope (7:1 or more) and is more susceptible to sudden shock loads and chafe on the seabed. Mixed chain-and-rope rode requires more scope than all-chain.
FAQ
How much anchor chain should I let out?
The standard recommendation is 5:1 scope for all-chain rode in normal conditions - 5 metres of chain for every 1 metre of total vertical distance (water depth plus tidal rise plus bow height). For rough conditions or mixed rope/chain rode, 7:1 is safer.
Why does anchor scope need to account for tidal range?
If you anchor in 3m at low tide and the tide rises 2m, the water depth becomes 5m. At 5:1 scope you need 25m of rode for 5m depth, not the 15m adequate at low tide. Always base calculations on expected depth at high water.
Is chain better than rope for anchoring?
Chain provides catenary action - it sags under its own weight, absorbing shock loads and keeping the pull angle more horizontal at the anchor. This means chain can hold effectively at shorter scope (4:1). Rope requires more scope (7:1 or more) and is more susceptible to shock loads and chafe.