Scope & Holding

Scope is rode length divided by rise — and the rise is not the charted depth.

It is depth, plus the tidal range you will see before morning, plus the height of your bow roller above the water. Leave out the last term and a small boat in shallow water can overstate its scope by a fifth.

The anchor holds because of the angle the rode makes at the seabed. That angle starts where the rode leaves the boat, not where it enters the water.

Add the tide before you set, not after

A four-foot tidal range means a 7:1 scope at low water becomes something considerably less at high. Anchors drag on a rising tide, in the dark, when the boat you carefully anchored clear of is suddenly much closer than it was.

The standard scopes

5:1 is a minimum for fair weather with someone on watch. 7:1 is the overnight standard. 10:1 is for heavy weather. All-chain rode can hold at somewhat less because the chain's own weight keeps the pull horizontal; rope needs more, because it floats and lifts the shank.

The number nobody calculates: swing radius

More scope holds better and swings wider. In a crowded anchorage the limit is usually not holding power — it is whether the circle you will swing through is clear of other boats, moorings and shoal water.

That radius is not the rode length. It is the horizontal leg of the triangle, and it is worth knowing before you settle in next to someone.

A snubber is not optional on all chain

Chain has no stretch. Every wave shock loads the windlass and the bow fitting directly, and both are designed for static loads. A nylon snubber absorbs that, and it also quiets the boat enough to sleep in.