What is scope?
Scope is the ratio of rode let out to the vertical distance from the bow roller to the seabed. More scope pulls the anchor more horizontally so it digs in. Measure depth at high tide and include the bow height above the water.
Vertical = Depth + Tide rise + Bow height
Rode = Vertical × Scope
Swing r = √(Rode² − Vertical²) + Boat length
Example
15 ft of water, 3 ft of tide and a 4 ft bow: 22 ft vertical. At 7:1, let out 154 ft. Your swing radius is about 182 ft, so keep that much clearance from other boats and hazards.
Choosing a scope
- 5:1: all-chain rode in settled weather
- 7:1: standard for rope/chain combinations
- 10:1: storms and strong wind
Frequently asked questions
How much anchor chain do I need?
Enough for 5:1 scope in the deepest water you plan to anchor in, including bow height and tide.
Why add bow height to depth?
Scope is measured from where the rode leaves the boat, not the waterline.
What if there isn't room for 7:1?
Use more chain and less rope, add a kellet, or find a different spot.