Travel Articles

There really isn’t much to anchoring safely but what has to be done, has to be done carefully and thoroughly. Four major factors come to mind – the nature of the sea bottom, the range of tide for the time you’ll be at anchor, the scope that you’ll use and the swinging circle that will have to be allowed for.

1. Nature of the sea bottom  

You’ll get this from your chart or plotter but the properly equipped navigator should have a printed copy of the symbols used on charts for the relevant area.  

Most people would know that you should not anchor over rocky terrain. Most suitable anchors either will not dig in or will dig in so well that you can’t dig them out. Similarly, weedy bottoms can prevent the anchor digging in.  

What you really should look for is mud or preferably sand. For either of these bottoms you need the sort of anchor, like a plough or CQR or Bruce, which will dig in and hold.  

2. Range of tide  

Tidal ranges are marked on charts and can vary enormously. In some cases the range may never be much more than two metres (six feet). In others it can be more than ten metres (33 feet). So, in the nearly six hours between high and low water, you could go from a comfortable depth to being aground.  

Also, as you’ll see when we get to talk about the swinging circle, the range of tide can affect the size of that circle.  

3. The scope  

This is the amount of chain or warp that you will let out before securing the anchor. It is the amount between the anchor and the bow of the boat. Generally speaking, this is allowed at three to five times the depth of water. If, however, you’re going to be anchored for one complete cycle of the tide, you will have to allow for the range for that day.  

The best way to handle this, once you have calculated the scope, is to lay the anchor on the foredeck ready to drop and take the warp along the deck to the stern. Because you know the length of your boat you then know what proportion of the scope that first length is. The next section of warp should go from the stern to the bow. Keep doing that until you have the length of scope you need lying along the deck, free to run.  

Then, when you anchor, you stop at the spot you’ve selected and let the anchor down to the sea bed as you very gently reverse the boat. This will prevent the anchor chain or warp from fouling the anchor itself. The warp can be tied off when the calculated amount has been let out.  

4. Swinging circle  

To understand this properly you really must plot it on a paper chart. Set your dividers or compass to the scale of the chart and use the length of scope as the radius of the circle you’re going to draw. Using the anchoring spot as the centre, describe the circle.  

Whichever way the wind should change, you will go to the full extent of the scope in the direction opposite to the direction of the wind. You have to be certain that there are no dangers within that circle.  

Remember that if you have a large tidal range, the actual swinging circle will change, getting bigger as the tide drops and smaller as it rises. That will have to be taken into account as well.  

There, we’ve got you safely anchored. Staying safely anchored is another matter.

Copyright 2009 Bevanda Pty Ltd

After 60 years of cruising and racing on yachts, both inshore and off, Jim Murrant shares many of his experiences with you.

Get your Free Introduction to The Boating Bible Manaul of Seamanship from: http://www.theboatingbible.com/Introduction1.htm It includes sample animations, interactive quizzes and other content from 6 CDs making up The Boating Bible Manual of Seamanship.

Learn more about sailing in The Manual: http://www.theboatingbible.com/Product.htm

Follow the blog, read free articles and sign up for a weekly newsletter – earlier copies still available.

It’s all about Sailing!