Choosing where to anchor
- Shelter: from the wind and swell now, and from where the forecast says they'll come from later. A wind shift overnight can turn a sheltered bay into a lee shore.
- Holding: the chart shows the seabed. Mud and sand usually hold well; rock and thick weed usually don't.
- Depth: enough water at low tide, with your swing taken into account, and not so deep that you can't let out enough scope.
- Clear of trouble: out of channels and fairways, away from moorings, and clear of charted cables, pipelines and no-anchoring areas.
- Swinging room: you'll swing in a circle around the anchor as the wind and tide change. Leave room for your circle and the boats around you.
How much to let out
Scope is the length of chain or rope you let out compared with the depth. A common rule of thumb taught on RYA courses is at least:
- 4 times the depth for all chain;
- 6 times the depth for rope with a length of chain.
Measure the depth as it will be at high water, not as it is when you arrive, and add the height of your bow roller above the water. Let out more in strong wind, poor holding or a chop. Rope needs more scope than chain because it's lighter and doesn't lie along the seabed in the same way.
Dropping and setting the anchor
- Approach slowly into the wind or tide, whichever is affecting the boat more, and stop over the spot you want.
- Lower the anchor to the seabed under control, rather than dumping the chain in a heap on top of it.
- Let the boat drift back as the chain is paid out, so it lies along the seabed, until you've let out the full scope.
- Set the anchor by going gently astern and watching a transit ashore. If it holds steady, the anchor has dug in.
Is it dragging?
- Once you've settled, take a transit or bearings of fixed objects ashore. If the transit opens or the bearings change steadily, you're moving.
- Set an anchor alarm on the plotter, with a radius that allows for your swing.
- Check again when the wind or tide changes, and before you go to bed.
- A rumbling or juddering through the chain is often the anchor bumping across the seabed.
Showing you're at anchor
By day, show one black ball forward. At night, a vessel under 50m shows an all-round white light where it can best be seen. A vessel under 7m doesn't have to show these when it's not in or near a channel, fairway or anchorage, or where other vessels normally navigate. In fog, a vessel at anchor rings a bell: see the sound signals guide.