Anchors & How They Work

This lightweight anchor shows the typical parts of a modern cruising anchor. Anchors dig into the bottom rather than holding by immovable weight. To do this they have flukes to dig into softer bottoms or to find a crevice in hard bottoms. The anchor at left excels at digging into sand or softer mud but may drag relentlessly in harder bottoms. Since there is no one anchor good for all bottoms most boats will carry at least two different anchors with one as the primary.

In the adjacent photo we can see a lightweight anchor on the bow of a small powerboat. The assembly at the bow holding the anchor is called the bow roller. The bail on top keeps the anchor from jostling about and coming free in heavy waves. This boater has chosen to use an all line anchor rode which is not recommended. This will make the anchor hard to set without the needed weight of anchor chain to hold the anchor on the bottom. The line has an eye splice which is much stronger than a knot. Inside the eye splice is a metal thimble which prevents chafe on the line. This is attached to the anchor with a shackle which should be seized with stainless steel wire to prevent it from coming loose.

Let's take a look at some anchors that not only work in soft bottoms but are also good for hard mud, weeds, and rocky bottoms. One of the most popular anchors on cruising boats, that will be anchoring in many different types of bottom conditions, is the plow style. So named because it resembles a farmers plow. Of these, the brand CQR holds a venerable reputation shown to the left. Note the pivot at the crown allowing the shank to swing side to side as the boat moves around in the wind.

Another variation of the plow style, brand name Delta, has become quite popular with boaters. Here we see it on the bow of a sailboat. The Delta does not have the same pivot at the crown as the CQR above. Simple, one piece design makes it popular. Another variation of the plow style, brand name Delta, has become quite popular with boaters. Here we see it on the bow of a sailboat. The Delta does not have the same pivot at the crown as the CQR above. Simple, one piece design makes it popular.Another variation of the plow style, brand name Delta, has become quite popular with boaters. Here we see it on the bow of a sailboat. The Delta does not have the same pivot at the crown as the CQR above. Simple, one piece design makes it popular.

The last type of anchor we'll talk about is the claw style. Rather than the sharp point of the plow it uses a scooping action to grab the bottom. The most popular of these is the Bruce brand.  In the photo to the left we see one on the bow of a sailboat.The Bruce anchor was invented to anchor oil rigs in the North Sea but seems to do well in a wide variety of conditions. Do you see the small hole in the crown of the anchor? This is where you can attach a trip line which we'll talk about later.

Which one of these anchors is best? Well, that depends on what type of bottom condition you're anchoring in. If it's usually sand to soft mud you might go for the lightweight. If there are times when you anchor in hard bottoms then you'll choose one of the later anchors.

Not only can you choose from one of the above anchors but there is now a new generation from which you may pick. There's the Super Max, Rocna, and XYZ along with many others. Some claim great results. As in so many other things in life; educate yourself, look at the possibilities, then make a decision.

Along with the anchor other important considerations are the weight of the anchor and the anchor rode. The heavier the anchor, for any given type, the better it will set and hold. When choosing an anchor you might very well wish to go with heavier than recommended to give yourself a margin of safety and confidence.

The anchor rode is what we use to attach the anchor to the boat when anchoring. It can be all line, part line and part chain, or all chain. The chain acts as weight to hold the shank down on the bottom to provide an easier set. Without any chain it is difficult to get a shallow enough angle of pull on the anchor to allow it to set.

Most boats longer than 30' will have an electric windlass to raise the anchor. If the rode is part chain and part line then, at some point in raising the anchor, you will have to switch from line to chain. This is not such an easy transition because the line is attached to the chain with an eye splice and shackle arrangement that we saw above. The line being taken in by the drum of the windlass has to be let go and the chain then coiled around the chain gypsy of the windlass. So, a real advantage of all chain rode is that it stays continuously on the chain gypsy of the windlass making raising and lowering that much easier.

How an anchor works:

Scope is the ratio of the depth of the bottom from the bow to the horizontal distance the bow is from the anchor. The depth can be conveniently measured by the depth sounder then add the height of the bow above the water. In areas of large tidal range what is adequate scope at low tide may not be sufficient at high tide. Generally speaking, 7 to 1 scope is considered adequate for overnight anchoring. The more scope, the better the anchor will hold. There are many factors that come into play but, if you have the room, why not throw out more rode creating more scope? After all, it's free.

Another way to increase holding power is to drop the anchor on an up slope. This might be a sand bar or an area where the depth gets more shallow from a deeper area. You can also use a sentinel and kellet to increase holding power, this is a weight clipped onto the rode and lowered part way down, along the rode. The weight acts the same as more scope would because it decreases the angle of the rode to the bottom.

There are anchor kellets made that will slip down over an all chain rode. If you have a combination of chain and line the eye splice and shackle at the transition would not allow for passage beyond that point. Understand, if high winds come up there is a real possibility the anchor line will straighten out and any effect provided by the kellet will disappear.

Snubbers are used to cushion the load, acting as a shock absorber, on an all chain anchor rode . A snubber will also move the load from the bow roller to a bow cleat which can help with any chain noise in the forward cabin. After the anchor has been deployed and set tie a length of nylon line onto the chain with a rolling hitch, let out more chain, then tie the snubber onto a bow cleat. Now, let out even more chain so that the entire load, from the anchor, goes through the snubber and to the cleat. Use nylon line because it stretches; and, 3 strand stretches more than braided. Just be sure to prevent any chafe which might occur.

A variation of the basic snubber would be to have a dedicated bridle with a chain hook in the middle. This could be tied off to both bow cleats thus distributing the load. See next paragraph for a description of a bridle.

We use a bridle arrangement when anchoring a catamaran. Usually, you will have a pre-made anchor bridle all set to go when you anchor. This is made from two lengths of 3 strand nylon line with a chain hook joining them together. The two free ends attach to bow cleats after the anchor is set.

Alternatively, you can make up the bridle by attaching two nylon lines to the anchor rode using rolling hitches so they won't slip.

The bridle arrangement can also be used on a monohull vessel with good results.

Dropping and setting the anchor.

With a basic understanding of how the anchor attaches itself to the bottom and some anchoring techniques we'll now look at the procedure of dropping, then setting the anchor. Once a spot is chosen to drop anchor approach slowly from downwind or down current, whichever is stronger. When you arrive at the spot you want to drop, having made adequate accounting for scope and swing, come to a complete stop, lower the anchor. Now you want to get the boat going backwards so the falling chain doesn't foul the anchor. You might slowly engage reverse then go back to neutral; just enough to get the boat headed backwards. She won't go straight back because the wind wants to blow the bow off first. Be patient as one or more of the crew lets out the anchor rode. When you have let out enough cleat the line or the chain. The boat will now align itself with the anchor rode as it takes out all the slack.

Set the anchor by backing down on it. Engage reverse; first at idle speed and watch for any movement. The easiest way to do this is to set up a range with two non-moving objects (not other boats) and watch to see if they come out of alignment.

It really doesn't matter which two non-moving objects you use. Could be a point of land with a tree beyond. Or, a navigational marker and a tree beyond. You get the picture. The slightest movement of the boat will show up when looking at the range you have set up. If the anchor holds at idle speed reverse, then increase to 1500 rpm (or one half the full cruising rpm). If the anchor holds now then increase to 2500 rpm (or full cruising rpm). Keep the engine in reverse for several seconds to see what happens. If no movement, slowly lower the rpm, shut the engine down, and relax.

What if there is no land around or no available range to be found? In this situation do the same as above in terms of backing down on the anchor at various engine speeds but, without the range, put your hand on the rode and you will be able to feel a vibration if the anchor is skipping along the bottom. Really works, try it.

What if the anchor fails to hold while backing down on it? Increase scope by letting out more rode is the first solution. What if you've already let out most of your rode? If the anchor is dragging then stop the motion of the boat. Take the engine out of reverse and come to a stop. Then, slowly start again from idle speed reverse on up through. Often times, the anchor will grab once you have stopped the reverse movement. Take it slowly and be patient. If you just can't get it to set then pick it up and drop in another spot. You'll have to start all over again but once you get the anchor properly set you'll be much more confident about it holding overnight.

Use the same range to check on any suspected anchor dragging later on. Even the smallest amount will show up. At night it's usually a good idea to find a couple of lights that are in, or near, alignment to use as a check. You can set an anchor watch on your ship's GPS but, with wind and waves, will you hear the alarm when it goes off?

Retrieving an anchor. Getting the anchor back onboard should be an easy matter with today's electric anchor windlasses. Start by powering the boat toward the anchor using the engine, not the windlass. We save the windlass to bring the anchor up once we are over it. Many times the anchor simply breaks itself free as we motor up to it and tension the chain.

If it doesn't break loose right away then, when you are directly over the anchor, cleat the rode and power forward. This should easily break it out. But, what if it's still stuck? First, you might try pulling in different directions with greater and greater force. If you had thought about this ahead of time you could have set a trip line when you anchored. If the flukes of the anchor get caught under a rock or obstruction the trip line will allow you to pull the anchor out the way it came in. Just motor around to the back side of the anchor, being careful to keep out of the way of the rode, pick up the trip line and pull the anchor free.  In order for this to work you must rig the trip line and buoy ahead of time. What if you didn't think to do that?

While you can hook up a trip line in advance on any anchor there are some anchors that have a special slot in the shank allowing the anchor rode to slide down to the crown when pulled from the opposite direction.

What if you don't have one of those special anchors? If the water is not too deep and it's clear you could free dive and attach a line to the crown. Another trick you can try is to place a large diameter metal eye, or ring, on the anchor rode at the bow. It will need to be large enough to slide all the way down your anchor shank. You will have to disconnect the bitter end of the anchor line to get the eye onto the rode. Now, tie a line onto this eye and slide it down the anchor rode. By keeping the anchor rode taught you will be able to drop this eye all the way down the rode, over the shackle, then down the shank to the crown where you can now use it just like a trip line.