Anchor Holding Power & Wind Load Calculator

Manufacturer and independent pull tests: the anchor set at proper scope in a defined bottom (usually firm sand), pulled by an instrumented boat or winch until it drags. Modern roll-bar designs (35 lb class) commonly test at 2,000–5,000 lb in good sand — order-of-magnitude above the old fisherman/Danforth-era assumption that anchors held their weight times ten. The fine print is the bottom: the same anchor in soupy mud holds half or less.

It's the ABYC-lineage planning approximation for steady wind on a boat lying head-to-wind — good within ±25%, which is plenty for sizing. What it deliberately excludes: yawing (sailing at anchor can double peak loads — bridles and riding sails help), current (add its drag), and wave surge (transient multiples that the snubber's elasticity must eat). Storm planning takes the steady answer and adds margin for all three.

Chart abbreviations and the anchor's behavior on set: hard sand (S) is the 1.0 reference; soft mud (M) 0.5–0.7 with slow deep setting (let it soak); grass/weed (Wd) 0.3–0.5 and modern sharp-tip anchors strongly preferred; rock is binary (snag = bombproof until it isn't; no snag = nothing). When the set 'skips' or comes up with a salad, the factor — and the night's plan — should drop accordingly.

Because the margin buys the EXCEPTIONS: the unforecast 40 that was supposed to be 25 (load ratio 2.6×), the mediocre mud you didn't choose, the yawing surge at 3 a.m. The square-root law means you can't buy unlimited safety with size — but one size up converts 'marginal at forecast' into 'asleep at forecast plus ten,' which is the actual product being purchased.