Anchoring manoeuvres

This post is also available in: Italiano (Italian)

Any boat, of all kinds and dimensions, is provided with a range of anchoring, mooring and capstan equipment. Quantity and complexity of the equipment depend on the boat length and the effort to resist. The external environment i.e. waves, currents and winds affects the anchored boat by means of forces that tend to move it from its anchor point and that have to be opposed by the anchoring system (anchor and chain).

Among the different types of mooring, anchoring is no doubt the most difficult to perform perfectly and safely mainly because the boat usually is in only partially sheltered waters and therefore exposed to winds, coastal storms and currents. And it is also the most common issue discussed at the Sailor bar!

An anchoring system is essentially formed by a chain (or chain and line) connected to one extremity of the bow and, on the other side, to the anchor lying at the bottom of the sea. The weight of the anchor, or better, its penetration capacity, must be such that it resists the forces that try to move the boat and drag the anchor from its initial position.

When the boat departs again, both the anchor and the chain have to be retrieved and stowed aboard so that they do not hinder anchoring manoeuvres, do not move and are at hand for the next mooring.

It is good practice to have a spare anchor available aboard in case that in use cannot be weighed because it got stranded on the sea bottom or in wrecks.

A spare anchor is also required to support mooring operations in bad weather conditions (not yet kedged i.e. attached to the main anchor) or to be used as a second anchor at an angle or as a stern anchor to be used to moor without swivelling or when the bow is towards the dock.

During anchoring it is important to let the chain and/or the line slide overboard and prevent them from tangling and get stuck in obstacles that may be found on deck or bow roller. It is also necessary to fix securely the other cable or chain end to the boat, if possible by a piece of line, so that it can be quickly cut in case of need i.e. if the anchor cannot be weighed. Of course when the anchor is weighed, the chain and/or the line must freely slide in the opposite direction. The chain, in particular, must automatically coil in the anchor peak avoiding dangerous manual operations.

Smaller boats (up to 6-7 meter length) aren’t normally provided with retrieve equipment. This is why anchor dropping and recovery are manually carried out and both the anchor and the cable and the chain, if any, are always manually stowed in the peaks.

Bigger boats, where carrying the weight of anchor and chain requires heavy labour, are provided with a windlass placed in the boat forward area. This is a motor having a horizontal or vertical axis of rotation usually installed above the chain locker. Mostly the motor is board battery-operated while in some cases it is operated by a hydraulic circuit. Only some motors have a manual rotation system for emergency use.

The main components of a windlass are:

• Gypsy (windlass wheel) generally made of cast iron to increase wear-resistance, coupled through gears to the motor that pays out (and hauls in) the chain and pairs the chain links with the gears. This is achieved only if the chain links are the same and have defined dimensions (calibrated chains).

• Support bearing, middle axis, gears, speed reducers, casing etc. according to the project design.

• Capstan always on axis with the main motor. Used essentially as a winch for lazy lines. Specifically shaped to hold the cable in the minimum radius area with anti-slip surface. The capstan extremity is provided with a cap to prevent cable removal.

The windlasses provided by some manufacturers have a fiberglass base instead of a metal one (usually light alloy), which makes the equipment lighter but equally sturdy.

Last-generation windlasses count the number of gypsy laps by means of a sensor and display the meters of chain paid out (scope). But note that these new windlasses are quite delicate.

Table 1 here below shows 12V-windlasses main data and relevant boat dimensions:

KINDS OF CHAIN

There are 3 kinds of chain generally used in the marine sector:

• BBB

• Grade 30

• Grade 43 HT

• SS 316 L

• Grade 70

The number indicated shows 1/10 of the load necessary to break a chain link. Load is given in N/mm². It is therefore necessary to calculate the diameter of each link.

A feature common to all chains is the standards (NACM, DIN, ISO, ASTM and ASME) but the most immediate reading system is the grade.

Chains are made of different grades of steel, then hot galvanized. Stainless steel is a valid alternative in case of frequent moorings, provided appropriate knowledge exists of its alloy and characteristics.

The links of BBB chains are shorter than usual and have grade 30, their identification wording is 3B. It is typical of the Anglo-Saxon countries.

A chain grade 43 HT or G43 (or G4) has a high proportion of carbon, which makes it 25% stronger than stainless steel 316 and 40% stronger than a chain grade 30 or G3.

CONNECTORS

Often neglected, I often see ridiculously tiny shackles matched to big chains or big anchors. This is the weak link…..the focus of accelerations, rotations, impacts and which often doesn’t let the anchor swivel correctly, once weighed.

Many are available on the market, but the cheap ones are not recommended.

Those that, due to their crooked shape, have the advantage of straightening the anchor on the bow roller are very good.

However a chain can also be jointed, but as the breaking load of a connecting link is not the same as a common link, joint it only if it is strictly necessary, or try to use a coil to pay out the chain.

ANCHORS

Although there are many types of anchors, they are divided into two categories depending on how they grip to the bottom of the sea. The former category includes all the anchors that hook to the sea bottom and are therefore especially suitable for rocky seabeds and coral reefs (hard seabeds). To the latter category belong anchors designed for muddy or sandy seabeds or made of shells (soft seabeds) into which they completely sink. The anchors of the former category are called weight-effect anchors while the latter are called shape-effect anchors. However the hold of an anchor upon a ground depends on the angle between the anchor and the seabed (angle of pull). The smaller the angle, the better the hold. It is obvious that to have reduced angles of pull, the length of the cable to be paid out together with the anchor has to be increased. The amount of cable or line paid out with the anchor is called scope, whose length depends on the seabed depth. In order to have a good anchoring power, the length of the cable paid out may vary, to get an at least general approximation, from 5 to 10 times the seabed depending on the type of anchor. Weight-effect anchors need a shorter scope to hold to rocky seabeds compared to that required in muddy seabeds by shape-effect anchors.

Unlike the chain, the cable, when in water, is very light and so the anchoring efficacy is only due to the anchor strength and the traction transmitted by the cable itself. In order to form an adequate angle of pull the cable has to position so that the scope is at least 3-4 times the seabed under normal weather conditions. The more the intensity of the forces acting on the boat increase, the longer the scope has to be, up to 6-7 times the seabed.

The length of the scope depends also on the kind of anchor and of the seabed. In case of heavy anchors and rocky seabeds the grip is good also when the cable is inclined a lot (the scope shall be twice the seabed) while in case of shape anchors and muddy seabeds the cable shall be low on the horizon (the scope shall be 7-8 times the seabed). In the event of a storm the length of the cable to be paid out shall be higher than 10 times the seabed. Moreover in areas with wide ranges of tide it is good practise to increase the length of the scope to avoid the cable places vertically when the tide rises and the anchor is aweigh.

This improves considerably when not only a line but also a short piece of chain is linked to the anchor as the increased weight of the anchor helps to get the chain taut at a smaller angle.

It’s even better if only a chain is available as, in this case, due to the weight of the chain itself, the angle of pull is practically equal to zero and to the weight of the anchor that of the chain lying on the seabed has to be added. As a consequence anchoring efficacy highly increases.

In small boats the anchor is connected to the boat by means of a nylon rope as the anchor is not heavy. In this case retrieve equipment is not required, with considerable weight and room-savings on deck. Anyway it is advisable to use a piece of chain next to the anchor to reduce wear caused by dragging on the seabed. Moreover the increased weight of the chain will add weight to the anchoring while reducing the angle of pull and highly improving the penetration capacity of the whole system.

When an anchor gets to the seabed, it acts in two steps: first it lays on it and then it slowly sinks depending on the solidity of the seafloor and on the weight and shape of the anchor. It is clear that the more sharpened the shape of the anchor, the higher the pressure exerted on the seafloor and the penetration into the soil. When the anchor is tightened the flukes widen and distribute the force exerted by the anchor tightening on a wider block of soil. If the soil resistance cannot oppose that of the anchor, the block of soil is stripped and the anchor comes loose.

The function of any anchor is to cling to the seabed so as to react with its hold/grip to the forces that try to move the boat from its anchorage point. This maybe achieved if the anchor has specific characteristics.

Admiralty or fixed arms anchors are provided with a movable stock consisting in a rod postioned orthogonally to the arms plane. When the anchor rests on the seabed, the movable stock lays horizontally on the seafloor forcing the arms to position perpendicularly so as one of the flukes clings to the soil. If the chain is properly taut, the fluke sinks and holds to the soil with the whole arm. The movable stock slides in the anchor head and then lies along the shank in rest position. When a boat has to be anchored, slide the stock until it finds the shank, then lock it. This anchor has the advantage of being very sturdy. It works well in every seafloor. An anchor with narrow flukes has a good grip in rocky seabeds or seabeds having compact sand. An anchor with wide flukes has a better grip in muddy or soft seabeds.

The most widespread anchors are provided with flukes or articulated arms. There are a lot of anchors of this type, of which Hall is the oldest model. Both the arms and the flukes are hinged at the base of the shank by means of a transversal pin and swing around it from +40° to about  40°, resting on a dedicated plate when inclined. During anchoring a Hall anchor rests on the bedfloor with its flukes parallel to the shank. When the chain is tightened, the shank moves and the flukes hold to the bedfloor and make anchoring particularly effective. When the seafloor is particularly hard or covered with dead algae that hinder or prevent the penetration of the flukes into the soil, so that chain tightening drags the chain without this being able to grip to the soil, we say the anchor is coming loose. It must be noticed that anchors with a fixed-arm movable stock have only one fluke that penetrates the soil while articulated-arm anchors have a higher anchoring power as two flukes penetrate the seabed. Hall anchors have quite a stocky shape that makes it difficult to penetrate soft seafloors. The two anchors described above owe their penetration capacity to their weight and therefore they are called weight-effect anchors.

However some anchors owe their penetration capacity not to their weight but to their shape and fluke area. They are called shape-effect anchors or anchors with a high anchoring power. The plow anchor (or CQR) is so called as its shape reminds that of a plow. It consists of a shank with a pin in its basis where a single plowshare-shaped fluke is hinged. This anchor particularly suits poor grip seafloors such as sandy or muddy seabeds. Moreover the articulated shank allows the anchor to keep its position no matter the intensity or the direction of chain tightening due to the motion of the boat caused by winds and currents. Delta anchors are similar to CQR anchors in the shape but they are jointless. Also Bruce anchors are based on the same concepts but as they are shell-shaped they dig a soil portion to use its weight in addition to that of the anchor and the chain.   

Danforth anchors have a rectangular-section shank whose arms are made by a straight rod hinged at the shank basis and by flat, trapeze-shaped flukes having a wide surface area. In this case arms are much wider than flukes and works like a movable stock that is they keep the flukes horizontal so they both cling to the seafloor.

Their very sharp flukes penetrate easily the hardest seabeds and their wide surface make the anchor grip firmly also in muddy or sandy seabeds. The flukes swinging is limited by a plate inside the arms. Placing the articulated movable stock at the same level as the flukes, a Danforth anchor can be stowed flat thus saving a lot of space. The same anchor made in a special light alloy and totally disassembled is called Fortress. In my opinion it has a very good grip especially in the sand but not in hart mud or seaweeds as it is very light. SBM anchors are very similar to Danforth anchors but it is more sturdy and therefore they are much heavier, given the same dimensions.

Northill anchors are modular. Their movable stock is sliding in the crown. It is easily stowed onboard by removing the movable stock or folding it against the shank. The flukes shape ensure a good grip in muddy seabeds, where the anchor sinks up to shank thus increasing its grip capacity.

Grapnel anchors have four or five fixed curved arms symmetrically placed around the crown and the circular cross-section shank. It is the most efficient anchor but it is also very cumbersome and heavy. It is widespread among fish vessels as it rapidly grips to rocky and uneven seabottoms. It is advisable to have one as a sheet anchor or to kedge before the main anchor.

Grapnel anchors have a circular cross-section shank and four articulated flukes hinged on four pins placed on the crown. When the flukes are in rest position they are bent towards the shank and kept tight by a ring sliding along the shank itself. The same ring is used to keep the flukes open when the anchor lies on the seafloor. This kind of anchor has a good grip on rocky seabeds or covered with seaweeds but it is less good on sandy or muddy seabottoms. User-friendly for small or medium-sized boats or dinghies.

The recently developed Spade and Ultra anchors are both very good and, in my view, they outperforms Delta or Bruce anchors, with the advantage of being light.

The anchors of the latest generations are very efficient: Rocna, Mason, Mantus.

This generation of anchors is really very effective, maybe not so easy on the eye but they are the future. They are not very widespread ….

ANCHORING

In my opinion two good anchors should be ready for onboard use. We all can moor on double anchors or kedge an anchor. I prefer the latter anchoring as weighing is easier and I use it when the wind speed is more than 25 knots and increasing.

Mooring on double anchors is difficult if you think you can shift the anchor outboard using a dinghy. It is also difficult to make it grip firmly and it is to be hoped that the wind doesn’t change. This kind of mooring is a good one if your boat is provided with two bow anchors and so you can manoeuvering via engine. First drop one anchor with a long chain and then, after having changed your position, the other anchor and then retrieve the first anchor. It is good for big and heavy boats.

To kedge an anchor is difficult if you don’t know the technique for dropping the second anchor, which has to be dropped beside the bow, generally with 5m-chain, on 3-4m seafloor and dropping the second anchor at sea level. While in reverse mode, drop the first anchor with determination, release it, then drop the second one and after 30m you are firmly anchored. Dive with a mask to check.

A technique you must know is the use of the signalling buoy, i.e. a small fender placed on a floating rope intended to help retrieve the anchor in case it tangles, as it is pulled out from the front, trying to overturn it (it’s easier said than done, but worth trying). You can do it from the dinghy, but a person has to stay at bow to counterbalance your weight and that of the anchor.

A maneuvre few are able to do is anchoring tiying up ashore. If your crew is small or if you are no more agile than before, I suggest you this technique that I have developed over time. Two people are required.

The captain (that is generally the person who criticizes someone elses’s work) singles out a place to anchor (usually the wind blows from the coast, i.e. from the stern). He will drop the dinghy with about 30m-line and a fender, then he will leave the steering of the boat to a member of his crew. While the boat is keeping its position or sailing roadstead, the captain gets off the boat and fix an extremity of the line to a rock or a tree and then will move towards the boat. The line will lay on the seafloor and the fender will stay in the wind, far enough from the shore not to impact the steering, thanks to the wind.

Once back onboard the anchoring will be performed by aligning to our stern signalling buoy, The line lying on the seabed will be retrieved by means of a mooring hook and used to tie up the stern ashore.

While the captain was offboard, he had checked the seafloor. Do try it. This is a safe technique, not to be found on manuals.

BUOY GRIP

It can be an operation easy or difficult. All depends on how you reach the buoy, on the shape of your boat (boat edge), if you lift the buoy and pull it onboard or if you have to put a line through the buoy. We cannot always know what we can expect but, once the boat is anchored, go and check: rusty chains, worn lines, small shackles or undersized concrete blocks are the most common causes for the loss of a boat.

You should make a survey or assess how the other boats are moored and decide what to do accordingly. If the fixed mooring has to be retrieved, sail the boat beyond the buoy, generally for a third of its length, not more. Raise the fixed mooring and, at the same time, stop the boat, reverse gear to the minimum, head to the wind. Securely tie the line to the cleat and wait until the boat stop swinging before adjusting the mooring. It can happen you sail beyong or through the fix mooring … do not insist, leave it and try the maneuver again or you’ll risk to fall into the water or break the mooring hook.

Should you have to insert a line but you cannot from the bow, get near to the stern and, if you have a platform or an equipped upper stern, you’ll see that maneuvering will be easier. Then follow the boat movements with a very long bow line, helping you with motor and steering. The tiller shall stay in the middle position once maneuvering has come to an end otherwise our boat will be moving towards the next ones.

Always moor your boat near boats having the same length.

HOW TO BEHAVE IN HARBOURS

1. Read the harbour book.
2. Check wind direction and how many boats are present.
3. If possible, try to position among the last arrived boats, near boats having the same length and, probably, the same scope.
4. If the direction of the wind changes, ask your boat neighbours where their anchors are positioned and, if every position is different, sail a little away before dropping yours, that is keep a wide safety margin. In this case wait even 20 min to see how the other boats are steering. (For example a long keel boats moves more slowly than a regatta boat).
5. Drop the anchor to a 4-5m deep bottom while keeping the head to the wind. Make sure there are no shallows, cliffs and that you can pay out further chain.
6. Once the anchor has reached the seafloor pay out 4-5m chain and start moving in reverse gear or at about 1200 rpm. to make the anchor grip. Min. scope 3 times the seabottom, then 5 scopes more.
7. Stop the chain and when the anchor holds firmly to the bottom, test the grip for 3 minutes at 1800-2000 rpm in reverse gear.
8. Release the gipsy tightening by means of a line to hook to the chain and tie the line to a cleat.
9. If the bay is crowded, position the fenders.
10. Operate your GPS or Eco alert or keep watch in case of strong wind. Monitor your boat neighbours and keep a horn at hand.

FINAL REMARKS

Anchoring is one of the most important maneuvering to perform. It doesn’t depend only on the skipper but on the anchor, the boat, the seafloor and the depth. Many people know the good rule is to pay out a chain whose length (scope) is at least 5 times the depth of the seafloor but this is just a suggestion. If your boat swings or hauls a lot, this length will not be enough and an even heavier one will be required. As harbours have less and less room I suggest to have an even bigger anchor so to spare some metres of chain.

Chains are made of galvanized steel or stainless steel. The latter is generally weaker but of course oxedation-free. Never forget to check your connector and secure the chain to the cleats by means of a line, thus releasing the windlass. Remember also to use a line to firmly fix the anchor to the pulpit during sailing, when waves can remove it from the roller. I give you my word as a sailor.