Technique
Governing: RD 191/2026 art. 5.1; Decreto 25/2018 art. 7.3. Builds on: L2.2, L3.1. All example figures are illustrative.
Two circles, not one
When you anchor you create two circles centred on the anchor:
- the seabed footprint: everywhere the chain can lie on or drag across the bottom as the boat swings. This is what the Posidonia rules care about.
- the hull swing circle: everywhere the yacht can be. This is what the boat next to you and the bathing-zone buoys care about.
The method
Let d = charted depth plus tide (negligible in the Balearics) and f = height of the bow roller above the water. Then D = d + f is the vertical drop of the chain. With L metres of chain out:
- Seabed footprint radius (conservative): Rs = √(L² − D²). That is the horizontal reach if the chain were stretched straight; in practice some of it lifts, so the real footprint is a little smaller. Use the conservative figure.
- Hull swing radius: Rh = Rs + LOA.
- Clear sand needed: a circle of radius Rs round the anchor, plus a margin for GPS and mapping error (use at least 5 m).
Worked examples
| Case | LOA | d | f | Scope | L | Rs | Rh |
|---|---|---|---|---|---|---|---|
| A. Sailing yacht | 12 m | 5 m | 1 m | 5:1 on D | 30 m | 29.4 m | 41.4 m |
| B. Motor yacht | 24 m | 10 m | 2 m | 4:1 on D | 48 m | 46.5 m | 70.5 m |
| C. Same, settled weather | 24 m | 10 m | 2 m | 3:1 on D | 36 m | 33.9 m | 57.9 m |
| D. Larger yacht | 40 m | 15 m | 3 m | 3:1 on D | 54 m | 50.9 m | 90.9 m |
Case A in full: D = 5 + 1 = 6 m; L = 5 × 6 = 30 m; Rs = √(900 − 36) = √864 = 29.4 m; Rh = 29.4 + 12 = 41.4 m. The sand patch must be about 59 m across before you add any margin.
Case B to C: dropping from 4:1 to 3:1 cuts Rs from 46.5 m to 33.9 m and shrinks the footprint area from about 6,790 m² to 3,620 m², nearly half. That is a legitimate tool in settled weather, not an excuse to lie to short scope before a blow.
Working backwards from the patch
The app shows a sand pocket with its nearest meadow edge 25 m from where you want to drop. Keep a 5 m margin, so the footprint radius may be at most 20 m. With D = 6 m: L ≤ √(20² + 6²) = √436 = 20.9 m, a scope of about 3.5:1. If the forecast needs more scope than that, this patch is too small. Go somewhere bigger or pick up a buoy.
Doing it on deck
- Approach into the wind over the centre of the patch, not its edge.
- Let go from the bow position, not the antenna position: know the offset on your yacht.
- Pay out as you fall back, then set the anchor gently. A long hard reverse drags chain across the bottom.
- Check the lie visually or with a swimmer. Look at where the chain rises, not only where the anchor is.
- Reassess before every forecast wind shift (L2.2 scenario). Recover slowly, motoring up to the chain so it lifts vertically rather than scraping across the patch.
WARNING — Deep water, bigger circle The formula makes the point for you: the deeper the water and the higher the bow, the more chain, and the wider the circle. Large yachts anchoring in 15 m or more need very large clear sand areas. Often the right answer is a buoy field or a different bay.
TIP — Write it on the whiteboard For your own yacht, work out Rs at 3:1, 4:1 and 5:1 for 5, 10 and 15 m. Crew then compare the number with the patch on the app before the anchor leaves the roller.