Calculator
Anchor scope calculator
How much chain should you let out? Enter the depth, your bow height and the tide still to come, and choose the conditions. The calculator gives you the length to let out and the circle your boat will swing in.
- Depth now: 6 m
- Bow roller height above the water: 1 m
- Let out: 35 m
- Swinging radius: 46 m
- Anchor Mate alarm distance: 51 m
Scope used (rules of thumb)
| Calm | Moderate | Strong wind | |
|---|---|---|---|
| All chain | 4:1 | 5:1 | 7:1 |
| Chain and rope | 6:1 | 7:1 | 10:1 |
What scope means
Scope is the length of rode compared with the height from the bow roller to the seabed. More rode makes the pull on the anchor flatter, so it digs in instead of lifting out.
Use the depth at high water
Measure the depth from the bow roller, and add the tide still to come. Scope that's fine at low tide can be too short at high tide.
Leave room around you
Other boats swing too. Boats on rope swing wider and faster than boats on chain, so keep your distance from them.
These are rules of thumb
Holding depends on the anchor, the seabed and how well it's set. Back down on the anchor to set it, and check that you're not moving.
If it drags anyway, Anchor Mate wakes you and every crew phone aboard.
