⚓ Anchor Scope Calculator

Calculate required anchor rode length and scope ratio based on water depth, freeboard, tides, and weather conditions.

Water Depth (m)

Freeboard Height (m)

Tidal Range (m)

Weather / Conditions

Rode Type

Boat Length (m)

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metres of rode required

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Scope ratio

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Swing circle (m radius)

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Total depth (+ freeboard + tide)

Scope Ratios by Condition

Anchor Weight Guide by Boat Length

Boat Length	Working Anchor	Storm Anchor	Recommended Types
Under 6m	3 kg	5 kg	Danforth/Fortress
6–8m	4 kg	7 kg	Delta / Danforth
8–10m	6 kg	10 kg	Delta / Rocna / Bruce
10–12m	10 kg	15 kg	Delta / Rocna / CQR
12–15m	14 kg	20 kg	Rocna / Delta / Spade
15–18m	18 kg	25 kg	Rocna / Spade
18–24m	25 kg	35 kg	Rocna / Spade / Bruce

Anchor Holding Power Comparison

Anchor Type	Sand	Mud	Rock/Weed	Notes
Rocna / Manson Supreme	★★★★★	★★★★★	★★★	Modern scoop design; sets quickly
Delta / Spade	★★★★★	★★★★	★★	Good all-rounder; self-launching
Danforth / Fortress	★★★★★	★★★	★	Excellent in sand/mud; fails in rock/weed
CQR (plough)	★★★★	★★★★	★★	Classic; good but slower to set
Bruce / Claw	★★★	★★★	★★★	Good in varied bottoms; lower holding/kg
Fisherman / Luke	★★	★★	★★★★★	Traditional; best in rock/weed/kelp

⛓️ Chain vs Rope: Chain lies flat on the sea bed, acting as a natural spring and catenary — it requires lower scope ratios (5:1 in calm, 7:1 in rough). All-nylon rode needs more scope (7:1 calm, 10:1+ rough) but provides shock absorption.

🔄 Swing Circle: Your swing circle radius = boat length + rode length. When anchoring near other boats, consider their swing circles too — they may have different rode lengths and set differently.