Anchoring Basics

Anchoring, is one of the most basic skills a seaman has to come to grips with. This article covers the basics and the theory, those with experience may wish to skip to other articles on the subject. Anchoring is an art, combined with a bit of science.

In most simple terms anchoring involves attaching your boat to the seabed via an anchor and a chain or rope. The object is that the boat stays put and doesn't go drifting off (within the limits governed by the length of the chain or rope).

All anchors of whichever kind work in the same way... they are lowered to the seabed on their chain, and once they are touching the bottom more and more chain is paid out as the boat drifts backwards either driven by the wind and or tide.

At a certain stage chain is ceased to be paid out and then made fast. The boat is now moving backwards dragging in front of it the chain and the anchor at the bitter end. Because the chain is heavy it tends to drop straight down vertically and then run along the seabed horizontally towards the anchor.

The anchor is designed in such a way that when it is dragged along the seabed horizontally it tries to dig itself in like a spade. Depending on what the bottom consists of it will either dig itself in, often until it is completely and utterly buried, or in the case of a rocky bottom will snag on a rock or crevice.

anchoring your boatAt this stage the boat will stop moving backwards, and the chain (or chain and rope combination) will go taut.... sometimes bar taut. Once the momentum of the boat is halted the chain slackens a bit, and the boat will happily lay to its anchor.

In normal conditions the weight of the chain will ensure that there is always a horizontal pull on the anchor itself, so that the more strain that comes on the more the anchor will tend to dig in.

It is part of the seamans art to know exactly how much chain to pay out, and this can vary depending on the depth, the nature of the seabed, and the weather, tide, and sea conditions in the anchorage.

The object is to make sure that no matter what happens the anchor always has a horizontal, as opposed to a vertical pull on it.

When the tide turns, or the wind pipes up from another direction, the boat tries to drift off in that way. It drags the chain in front of it, and the strain on the anchor changes direction. If it is well dug in it may well stay put, on the other hand it may be dragged out by the change of direction, and then it has to reset in the same manner it was first deployed in... but in a new direction.

Thus whenever an anchor is subject to the strain coming on it from a completely new direction, it is vulnerable to breaking out the seabed, and having to reset itself again.

This means if you secure yourself with only one anchor, caution is warranted at the turn of the tide, or significant wind shift.

If you imagine the anchor as being the central point, and the boat swinging round it 360° on its chain, this is the area the anchor boat can move in and it is called the swinging circle. The length of chain or chain and rope paid out is called the scope, and the chain (or rope/chain combination) paid out is called the anchor rode.

When it is time to weigh anchor, the chain is pulled in (which draws the boat to a point somewhere above the anchor), and the anchor is " broken out". Anchors break out when the direction of pull becomes vertical as opposed to horizontal. The chain and the anchor are got back onboard, and off you go.

This is anchoring explained in its most basic terms, and it's the same whether you are anchoring the dinghy or battleship. A horizontal pull along the seabed digs in the anchor, a vertical pull on the chain dislodges the anchor. A complete change of direction in the pull can dislodge the anchor, and normally it will reset itself... providing the pull on it is horizontal.

The most important thing for beginners to understand is that anchoring is not a the same as mooring, the boat can wander around on its scope within its swinging circle. When the anchor breaks out and resets itself the boat can move off station, the distance depending on how long it takes the anchor to dig in again.

Therefore when choosing a spot to anchor, you will be looking for a place with no big waves, as apart from making things extremely uncomfortable they can jerk out the anchor. You will be looking for a place where the tides are not too fierce, out of the main tidal stream. You will be looking for a place where you have room to swing. And you will be looking for a place with a suitable seabed where your anchor can dig in properly.

You will probably avoid anchoring over rock, as your anchoring then depends on snagging an outcrop. With the turn of tide or wind in the anchor will have to find another outcrop to snag. Finally the anchor can get well and truly trapped in crevices, and you won't be able to raise it.

Mud, providing it's not too gloopy is good, sand is good providing it is free of weed (which can interfere with the anchor digging in).

You will pay out the correct amount of scope to allow a horizontal pull on the anchor... for the moment let's just say 3 to 5 times the depth of the water.. that's a good starting point.

You will watch your anchor dig in, and once it has bitten, you may well use a bit of reverse to dig in some more.

Once you are safely anchored, you will pay particular attention at the turn of the tide or wind shift, as this is when you could start dragging.

Once you've done all this to your satisfaction, watch and see if some idiot doesn't come and anchor right on top of you !

That's it for this primer article, sounds simple but you can spend many, many, years learning more and more about the subject as you go along, and more articles in this series cover other aspects of the art of anchoring.

Many thanks to Steve Bryant for letting us re-produce this article. Please click here to visit his website for more article and harbour information.