Anchoring - Scope, Swing Circles & Beaching

Scope

Adequate Scope is necessary if your boat is to be anchored safely.

Scope is the ratio of the length of the anchor line to the distance from the bow chocks to the bottom. Satisfactory scope is generally considered to be a ratio of 5 or 7 to 1. If you anchor in 10 feet of water, you should pay out 50 to 70 ft of rope.

The holding power of an anchor increases with a longer scope. A scope of 3 to 1 is the minimum that should be used under calm conditions when anchoring for a few hours during the day. Overnight anchoring requires a scope of at least 5 to 1, and if it's going be windy, this should be increased to 7 to 1. A scope of 10 to 1 is not too much when anchoring in stormy conditions.

A crowded anchorage can have an influence on the amount of scope people use. A long scope will produce a wide swing circle for a boat at anchor. Ideally, the swing circles of various boats in an anchorage should not overlap with each other. As a result, in a crowded anchorage, many people will attempt to use minimum scope possible. The draw back of a shorter scope is the increased potential for your anchor to drag and the boat to drift.

People on a short scope will generally let out more rode if the weather changes and the wind picks up. The potential for overlapping swing circles has also increased, along with the possibility of boats bumping into each other in a crowded anchorage.

Remember also that a rising tide will change the scope. If the distance becomes 15 ft to the bottom (from an initial 10 ft), you should pay out another 25 - 35 ft of rope.

Swing Circles

In an ideal world, all boats in the anchorage would swing in unison in response to the same wind, current, and waves, and thus eliminate the problem of boats bumping into one another when they have overlapping swing circles.

In reality, boats come in assorted sizes, keel configurations, and above water profiles.

They react differently to the wind, waves, and current, and in varying degrees, swing out of unison. The occasional and minor overlaps in swing circles will probably not result in two boats to make contact with each other, but it can happen.

Therefore, good judgement is needed in determining how much anchor rode is out when anchoring, so as to ensure such accidents don't happen.

Beaching

When coming in for the landing, drop and anchor over the stern 50 to 75 ft away from the shore, and as your boat proceeds slowly toward the shore, set the anchor by placing tension on it until it holds.

This stern anchor not only keeps the stern away from the beach, but when hauling in the anchor line as you get underway, the boat will automatically be pulled away from shore. Just as the boat reaches shore, a bow anchor can be set ashore or the bow line tied to a sturdy handy object.

For obvious reasons, you never should drive your boat up on the beach.