Anchor Chain & Rode Size Calculator (ABYC Design Loads, Chain Grade, Nylon Snubber, Windlass)

How it works

design load: ABYC table by LOA (e.g. 40 ft: 300 / 1,200 / 2,400 / 4,800 lb at 15 / 30 / 42 / 60 kt), interpolated and scaled for windage (load ∝ wind²) · chain: smallest size whose WLL ≥ load (G30 1/4″ 1,300 lb … 1/2″ 4,500; G43 1/4″ 2,600 … 1/2″ 9,200) · nylon rode: breaking strength ÷ 4 ≥ load; snubber ÷ 5 · windlass pull ≥ 3 × (chain + anchor weight)

How hard a boat pulls on its anchor depends on its windage and the wind squared — a 42-knot gust loads the rode with roughly eight times what 15 knots does. The ABYC design-load table (used by chandlers and anchor makers) gives that pull for a typical boat of each length; scale it for a flybridge or a catamaran, choose the condition you want to survive, and everything else in the ground-tackle chain follows: chain sized to its working load limit, nylon rode and snubber sized with a stretch-friendly factor, oversized shackles, and a windlass that can lift the weight you carry. The anchor itself is chosen from the maker's table for the same boat length and the bottom you expect.

Worked example

A 38 ft sailboat sees about 2,160 lb at 42 knots; with a 1.25 safety factor the tackle is sized for 2,700 lb. G43 high-test chain of 5/16″ (WLL 3,900 lb, 1.4× the design load) handles it — 200 ft weighs about 220 lb — where G30 proof coil would need 7/16″. The nylon rode should be 5/8″ (break 12,200 lb at 4:1) and the snubber 3/4″ × about 19 ft; with a 45 lb anchor the windlass should pull at least 795 lb.

Frequently asked questions