Anchor correctly

A bay in the Kornati islands off the Croatian coast. Crystal-clear water, pleasant temperatures and cosy restaurant terraces on the shore of the anchorage attract one yacht crew after another. At sunset, around 15 boats are moored downwind of a wooded, somewhat incised slope. An hour later it suddenly bristles, and the wind picks up. Soon the first boat breaks loose and drifts through the field with a slipping anchor. In the course of the night, about half of the yachts drift, but it is impossible to see exactly how many in the dark.

The observers are in the middle of it, but they’re safe. Why? It's hard to say why one yacht broke away and the other didn't, but the crew in question took three things to heart: firstly, they informed themselves about the area and expected that the calm weather could change during the course of the evening. Secondly, they deployed a riding weight in order to be able to lie safely despite the relatively short chain in the crowded bay. And third, a crew member went snorkelling to be sure the anchor had dug in.

Still, the night was restless because no one could be sure that the slipping anchor of another boat wouldn't rip out their own anchor. But thanks to an anchor bearing and a shiftily organised anchor watch, even such a case would not have come as a surprise. In essence, anchoring properly means being well prepared. Whole books have been written on how to prepare for anchor manoeuvres well. We cannot and do not want to reproduce them here. But we can draw on our experience and that of our clients.

Anchor type and anchor ground

In the experience of the Pantaenius claims department, slipping anchors are one of the most frequent causes of damage associated with anchor manoeuvres. Several causes are conceivable. One possible cause is that the anchor has not been able to dig in properly. The anchor must be suitable the anchor ground. A plate anchor, for example, cannot dig in well in seaweed. In sand, on the other hand, it can hold well. Seagrass is a difficult anchoring ground anyway, but if anything, you can anchor properly there with a stirrup anchor.

Some anchor types have to be adapted to the respective anchoring ground before use - by adjusting the angle between the flukes and the shank, for example, and this must always be taken into account.

Weight and size of the secondary anchor

It is advisable to have different anchors on board for different anchoring grounds. Each of these anchors must be able to hold the boat on its own in terms of weight. Manufacturers' tables provide information on the size required. Sometimes these state that a secondary anchor can be smaller or lighter than the main anchor, but this is not recommended.

A smaller stern anchor, such as is used in an archipelago to keep the stern in position, is not meant for this. In these cases, the boats are secured with shorelines against the wind direction. The stern anchor only supports.

A full-fledged second anchor harness is not only used as a substitute in case of damage or loss of the main anchor. It can also limit the sloop circle on narrow and busy anchorages by deploying it in a V-shape as a second bow anchor. A second bow anchor is also a useful safety measure in strong winds. Finally, a second anchor harness can be deployed with the current in tidal areas, so that no new anchor manoeuvre is necessary when the tide turns. In all these cases, the second anchor must be able to hold the boat on its own, at least for a short time.

Anchor chain slowly freeing

Another conceivable reason for the anchor slipping, is that the chain may have hindered the anchor from digging in. This can happen, for example, if the chain breaks out uncontrollably, perhaps because someone has simply released the brake on the windlass. Then it can happen that the anchor has not yet turned properly, while the chain is already coming to rest on the flukes. In the worst case, the boat pulls the whole pile of chains over the bottom before the fluke has had a chance to dig in.

Instead, it is best to sail the anchorage once before the anchoring manoeuvre and determine the anchorage ground and the water depth before you make the actual manoeuvre. Then you know how many metres of chain are needed to reach the bottom. This length of chain is lowered in a controlled manner when the boat is no longer moving. When the anchor is at the bottom, the boat slowly moves backwards, while the chain is guided along in a controlled manner. This ensures that the anchor can turn freely on the bottom and dig in.

Anchor manoeuvre and anchor gear

The next cause that comes into question for slipping anchors, is that the anchor has not been retracted. The anchor should always be actively pulled into the ground with support, i.e., it should be retracted. Admittedly, the wind pressure acting on the boat can also dig the anchor in. But especially in a calm water, the impression that the anchor is holding can be deceptive. It can happen that the anchor holds superficially but slips when the wind comes up. If you want to anchor properly, you should be prepared for this and retract the anchor.

When the required length of chain has been weighed, the chain is loaded and the boat is stopped. Ideally, the chain will slowly stiffen and the bow will align itself in the direction of the anchor. This is already a good sign. If the bow does not turn in, something is wrong. In addition, you should give a little gas and put a hand on the chain below the ship's side. A slipping anchor can be felt by vibrations in the chain. If the chain is stiff, the anchor will hold. An anchor bearing does not make sense here because the boat is still moving.

Digging in the anchor correctly

Even if you perform the anchor manoeuvre under sail, you can still bring the anchor in. The foresail should be recovered in time to have space on the foredeck, but the mainsail can be left standing. Initially, during the push up, with the sheet tied, but when the anchor chain is occupied, it can be held back to put tension on the chain. If there is the slightest doubt as to whether the anchor will hold, repeat the manoeuvre. It is better to sail to the same anchorage three times than to drift away in the middle of the night and perhaps in the rain.

If possible, check to see if the anchor has dug in. If the boat is at snorkelling depth, you can easily pull yourself down to the anchor on the chain to a depth of five metres. You are lucky if you anchor in clear water - then you can sometimes see the anchor from the surface. If you are sailing in cool water, it is a good idea to carry a wetsuit. A controlled anchor offers a safe feeling. This is especially true if you plan to leave the boat in the meantime. 

Fastening the anchor properly to the chain

Even if the anchor holds at first, it can break out later. Even the boat's buoyancy around the anchor can, in extreme cases, cause the anchor to break free. Especially with boats that tend to sway, the effect should be limited as much as possible. This can be done with a second anchor, or with a riding weight that is lowered to just above the bottom. Wind shifts or gusts of wind can have a similar effect: The anchor is suddenly loaded across the wind direction.   

The anchor harness can mitigate some of this risk. If possible, the chain should not be shackled directly to the anchor, because then the movements of the chain are transmitted directly to the anchor. A swivel shackle can be used on the anchor to allow the anchor to rotate around its longitudinal axis. A curved chain shackle can be attached to this, which gives the last chain link room to move so that the chain can turn around the anchor without the anchor itself immediately starting to move.

If the anchor is driven over a bow roller, the shackles can hinder handling. In this case, an alternative is an anchor swivel, which has two joints and is curved so that the anchor automatically turns in the right direction by gravity when hoisted. Under all circumstances, when hoisting or in the event of sudden wind changes, you must remember that the anchor will only hold securely as long as the pull is acting horizontally on the bottom. As soon as the pull acts upwards, there is a danger that the anchor will break free.

Chain length and anchor buoy

How much anchor chain has to be put in so that it engages horizontally with the anchor shaft is usually calculated by rule of thumb. The literature contains a wide range of information, from four times the water depth for chain to ten times the water depth for line. These rules of thumb are as old as they are controversial. They do not take into account that the anchor chain is sagging, i.e. it describes a curve and is not a straight line. This is taken into account by the formula of Pantaenius customer Matthias Wagner. It reads as follows:

 L=√Y(Y+2a)

Y is the anchor depth and a is a parameter that depends on the boat and wind strength and must be determined. This results in a chain length of L. The detailed derivation can be found on Wagner's website. It can be made somewhat easier with the app Anchor Chain Calculator, which Wagner developed. The app only requires the input of some boat and weather data and then throws out a chain length at which the angle of attack at the anchor is zero. If the chain length is limited, on the other hand, the app displays the angle of attack and the expected load.

For an overview of the length of the deployed chain, it is useful to mark the chain at intervals. For example, marking every five metres could be useful. Sometimes the anchor chain is marked with spray paint. However, this has to be repeated relatively often because of abrasion. Alternatively, coloured plastic plates are available that are pressed into the chain links. However, these can also get lost over time, especially when working with a windlass. In any case, it makes sense to mark them.

Anchoring properly with riding weight

On a spacious anchorage alone, it is relatively easy to put as much chain as necessary. Provided the boat has enough storage space, can take the weight and you carry enough chain. The situation is different on small boats, for example, which cannot stow long anchor chains, or on narrow or crowded anchorages. In such cases, it is advisable to use a riding weight in order to be able to anchor relatively safely despite the limited chain length.

A riding weight is dropped on the anchor chain or anchor line with the help of a second line until just above the bottom. It helps to keep the chain on the bottom and reduce the angle of pull on the anchor. On the market there are ready-made riding weights made of lead with a cast-in wire and pulley. But in a pinch, a riding weight can also be improvised. For example, you can carefully fatten a bucket with stones or use a small collapsible dragline tied together on a large shackle. The main thing is to get weight down that does not interfere with the chain. 

Set the anchor buoy correctly

Even with the best preparation and flawless anchor manoeuvre, danger can loom: other anchors can break out your own anchor. This can happen if neighbouring anchor berths go on drift or break out your own anchor on the chain when you are retrieving the anchor. This cannot be completely avoided, but with an anchor buoy you can at least prevent it somewhat. An anchor buoy on your own anchor shows your position and ideally encourages your neighbours to keep a sufficient distance.

Practical side effect: a sufficiently strong line on the anchor buoy can also serve as a trip line and help to recover the anchor. Attached to the opposite end of the chain, a trip line allows a different angle of pull on the anchor. If the anchor can no longer be broken out conventionally - for example, because it has tilted - there is at least a chance of pulling it up vertically on the trip line. In addition, the anchor is marked with the trip line in case it has to be recovered by a diver.

The right material for anchoring

When choosing an anchor harness, it pays to go for quality. Not all steel is the same. Even if anchor chains and shackles look the same at first glance in the catalogue or on the reel: the devil is in the detail. For all parts used, pay attention to the breaking load, which should be stated in the technical data. Guidelines can be found, for example, at classification societies and often directly in the catalogues. It is no coincidence that the proverb says, ‘the chain breaks at its weakest link’. Many cases of damage are due to material fatigue, for example in anchor swivels. That is why the entire harness should be checked regularly and replaced from time to time.

Finally: Anchoring is something you learn first and foremost while anchoring. And as with all skills that are newly acquired, sometimes something will go wrong with anchoring, despite all the preparation. That alone is not a bad thing, but part of the learning process. It's just a matter of minimising the risks and perhaps not anchoring at night in a storm upwind of a busy shipping lane. It is also worth exchanging experiences with other skippers and sharing knowledge. To be on the safe side, you can find the right insurance for your boat at Pantaenius.