Anchor & Rode Sizing

Anchor sizing charts are written for a boat at anchor overnight in ordinary weather. That is a much narrower claim than most people read into them, and the difference matters at three in the morning.

Holding power depends on the anchor type, the bottom it is set in, and the scope you have out — in roughly that order. A well-set anchor in mud holds many times what the same anchor holds in weed or hard sand, and no chart can know which one you are over.

Weight is the least interesting variable

Modern anchor designs — Rocna, Mantus, Spade and their relatives — hold far more per pound than a Danforth or a CQR of the same weight, because the design sets faster and buries deeper. Sizing by weight alone compares products that are not comparable.

What weight does buy is the ability to punch through weed and to reset when the wind shifts.

The storm anchor is a different question

Everything in these tables assumes normal conditions with someone aboard. A boat left unattended, or one riding out a real blow, wants substantially more — the usual guidance is one size up, and a second anchor deployed.

Rode does at least as much work as the anchor

Chain weight creates the catenary that keeps the pull at the anchor horizontal, and horizontal pull is the only kind an anchor resists well. An undersized anchor on all chain with generous scope frequently outperforms a large anchor on rope at short scope.

Set it, and then verify it

Back down at low revs until the boat stops moving with the rode taut. Take a transit on shore and watch it for a few minutes. An anchor that has not been set is a heavy object lying on the bottom, and it will tell you so at the least convenient moment.