How Much Anchor Chain to Let Out: Scope Explained

Let out at least four times the maximum depth of water for all-chain, and around six times for a chain-and-rope rode. Measure depth at high water, not the depth when you arrive, and add the height of the bow roller above the water. So in 5 m at high water with a 1 m bow, let out at least 24 m of chain. In strong wind or poor holding, increase the scope to 6:1 or more if swinging room allows.

An anchor stowed on a yacht's bow roller — Scope is measured from the bow roller. Photo: Andy Mitchell from Glasgow, UK, CC BY-SA 2.0.

What scope means

Scope is the ratio of the length of rode let out to the vertical distance from the bow roller to the seabed. A longer scope pulls on the anchor more horizontally, which is what makes it dig in and hold. A short scope lifts the shank and can break the anchor out.

A yacht at anchor in 5 m of water with a 1 m high bow roller, showing 4 times 6 m gives 24 m of chain, plus scope ratios for chain, rope and strong wind — Chain = 4 × (depth at high water + bow height).

A yacht at anchor showing depth, freeboard and the length of chain needed to give a 4:1 scope — Scope is measured from the bow roller to the seabed, at high water.

The calculation

Find the depth now from the echo sounder, and check the tide table for how much more water there will be at the next high water.
Add the height of the bow roller above the water (freeboard).
Multiply by the scope ratio: 4 for all-chain, 6 for chain and rope.

Example: 3 m now, rising 2 m by high water, 1 m freeboard. Maximum distance is 6 m. All-chain at 4:1 is 24 m; rope rode at 6:1 is 36 m. The rule of twelfths helps if you need the height at a time between tides.

Typical scope ratios
Conditions	All chain	Chain and rope
Settled, good holding, lunch stop	4:1	6:1
Overnight, moderate breeze	5:1	7:1
Strong wind or poor holding	6:1 or more	8:1 or more

Things that change the answer

Swinging room: more chain means a bigger circle. Check the boat will clear other boats, rocks and shallows at low water.
Holding ground: sand and mud hold well; weed and rock less so.
Wind forecast: if it is going to blow, let out more before it does.
Marking chain: paint or tag the chain every 5 or 10 m so you know what is out.

The how to anchor a yacht guide covers the full process, and the anchoring lesson works through examples.

Related guides

Frequently asked questions

What is a good anchor scope?

At least 4:1 for all-chain and 6:1 for chain and rope, measured from bow roller to seabed at high water. Increase it in strong winds.

Do you measure anchor depth at high or low water?

Use the depth at high water for scope, so you have enough chain when the tide is in. Check depth at low water to make sure you will not ground.

Can you let out too much anchor chain?

Only if it puts you out of swinging room or too close to hazards. More scope generally holds better, so the limit is space, not the anchor.

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