Mooring

Structure for securing floating vessels

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A passenger ship mooring onto a harbour in Limone sul Garda, Italy. A dockworker places a mooring line on a bollard.

A mooring is any permanent structure to which a seaborne vessel (such as a boat, ship, or amphibious aircraft) may be secured. Examples include quays, wharfs, jetties, piers, anchor buoys, and mooring buoys. A ship is secured to a mooring to forestall free movement of the ship on the water. An anchor mooring fixes a vessel's position relative to a point on the bottom of a waterway without connecting the vessel to shore. As a verb, mooring refers to the act of attaching a vessel to a mooring.[1]

The term likely stems from the Dutch verb meren (to moor), used in English since the end of the 15th century.

Permanent anchor mooring

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Mooring line of Polish ship Fryderyk Chopin.

These moorings are used instead of temporary anchors because they have considerably more holding power. They cause lesser damage to the marine environment, and are convenient. Where there is a row of moorings they are termed a tier.[2] They are also occasionally used to hold floating docks in place. There are several kinds of moorings:

Swing moorings

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Swing moorings also known as simple or single-point moorings, are the simplest and most common kind of mooring. A swing mooring consists of a single anchor at the bottom of a waterway with a rode (a rope, cable, or chain) running to a float on the surface. The float allows a vessel to find the rode and connect to the anchor. These anchors are known as swing moorings because a vessel attached to this kind of mooring swings in a circle when the direction of wind or tide changes.

For a small boat (e.g. 22' / 6.7 m sailing yacht), this might consist of a heavy weight on the seabed, a 12 mm or 14 mm rising chain attached to the "anchor", and a bridle made from 20 mm nylon rope, steel cable, or a 16 mm combination steel wire material. The heavy weight (anchor) should be a dense material. Old rail wagon wheels are used in some places (e.g. Clontarf, Dublin, Ireland) for this purpose. In some harbours (e.g. Dun Laoghaire, Ireland), very heavy chain (e.g. old ship anchor chain) may be placed in a grid pattern on the sea bed to ensure orderly positioning of moorings. Ropes (particularly for marker buoys and messenger lines) should be "non floating" to reduce likelihood of a boat's propeller being fouled by one.

Pile moorings

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Pile moorings are poles driven into the bottom of the waterway with their tops above the water. Vessels then tie mooring lines to two or four piles to fix their position between those piles. Pile moorings are common in New Zealand but rare elsewhere.

While many mooring buoys are privately owned, some are available for public use. For example, on the Great Barrier Reef off the Australian coast, a vast number of public moorings are set out in popular areas where boats can moor. This is to avoid the massive damage that would be caused by many vessels anchoring.

Twenty foot diameter sheet pile cell mooring structure and five steel pipe pile tripods

Pile cluster and another sheet pile cell mooring structure

Mooring dolphins with solar panels and LED lights

There are four basic types of permanent anchors used in moorings:[3]

Dor-Mor pyramid-shaped anchors used in mooring

• Dead weights are the simplest type of anchor. They are generally made as a large concrete block with a rode attached which resists movement with sheer weight; and, to a small degree, by settling into the substrate. In New Zealand old railway wheels are sometimes used. The advantages are that they are simple and cheap. A dead weight mooring that drags in a storm still holds well in its new position. Such moorings are better suited to rocky bottoms where other mooring systems do not hold well. The disadvantages are that they are heavy, bulky, and awkward.
• Mushroom anchors are the most common anchors and work best for softer seabeds such as mud, sand, or silt. They are shaped like an upside-down mushroom which can be easily buried in mud or silt. The advantage is that it has up to ten times the holding-power-to-weight ratio compared to a dead weight mooring; disadvantages include high cost, limited success on rocky or pebbly substrates, and the long time it takes to reach full holding capacity.[4]
• Pyramid anchors are pyramid-shaped anchors, also known as Dor-Mor anchors. They work in the upside-down position with the apex pointing down at the bottom such that when they are deployed, the weight of wider base pushes the pyramid down digging into the floor. Lateral pulls cause the side edges or corners of the pyramids to dig deeper under the floor, making them more stable.[5][6]
• Screw-in moorings are a modern method. The anchor in a screw-in mooring is a shaft with wide blades spiraling around it so that it can be screwed into the substrate. The advantages include high holding-power-to-weight ratio and small size (and thus relative cheapness). The disadvantage is that a diver is usually needed to install, inspect, and maintain these moorings.
• Multiple anchor mooring systems use two or more (often three) light weight temporary-style anchors set in an equilateral arrangement and all chained to a common center from which a conventional rode extends to a mooring buoy. The advantages are minimized mass, ease of deployment, high holding-power-to-weight ratio, and availability of temporary-style anchors.

Mooring to a shore fixture

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Crew of Hong Kong's Star Ferry using a billhook to catch a hemp mooring rope.

A vessel can be made fast to any variety of shore fixtures from trees and rocks to specially constructed areas such as piers and quays. The word pier is used in the following explanation in a generic sense.

Mooring is often accomplished using thick ropes called mooring lines or hawsers. The lines are fixed to deck fittings on the vessel at one end and to fittings such as bollards, rings, and cleats on the other end.

Mooring requires cooperation between people on a pier and on a vessel. Heavy mooring lines are often passed from larger vessels to people on a mooring by smaller, weighted heaving lines. Once a mooring line is attached to a bollard, it is pulled tight. Large ships generally tighten their mooring lines using heavy machinery called mooring winches or capstans.

A sailor tosses a heaving line to pass a mooring line to a handler on shore.

The heaviest cargo ships may require more than a dozen mooring lines. Small vessels can generally be moored by four to six mooring lines.

Mooring lines are usually made from manila rope or a synthetic material such as nylon. Nylon is easy to work with and lasts for years, but it is highly elastic. This elasticity has advantages and disadvantages. The main advantage is that during an event, such as a high wind or the close passing of another ship, stress can be spread across several lines. However, should a highly stressed nylon line break, it may part catastrophically, causing snapback, which can fatally injure bystanders. The effect of snapback is analogous to stretching a rubber band to its breaking point between your hands and then suffering a stinging blow from its suddenly flexing broken ends. Such a blow from a heavy mooring line carries much more force and can inflict severe injuries or even sever limbs. Mooring lines made from materials such as Dyneema and Kevlar have much less elasticity and are therefore much safer to use. However, such lines do not float on water and they do tend to sink. In addition, they are relatively more expensive than other sorts of line.

Some ships use wire rope for one or more of their mooring lines. Wire rope is hard to handle and maintain. There is also risk associated with using wire rope on a ship's stern in the vicinity of its propeller.

Mooring lines and hawsers may also be made by combining wire rope and synthetic line.[clarification needed] Such lines are more elastic and easier to handle than wire rope, but they are not as elastic as pure synthetic line. Special safety precautions must be followed when constructing a combination mooring line.

A typical mooring scheme Number Name Purpose 1 Head line Keep forward part of the ship against the dock 2 Forward breast line Keep close to pier 3 Forward or head spring[7] Prevent forward movement 4 Back or aft spring[7] Prevent backward movement 5 Aft breast line Keep close to pier 6 Stern line Prevent forwards movement

The two-headed mooring bitts is a fitting often-used in mooring. The rope is hauled over the bitt, pulling the vessel toward the bitt. In the second step, the rope is tied to the bitt, as shown. This tie can be put and released very quickly. In quiet conditions, such as on a lake, one person can moor a 260-tonne ship in just a few minutes.

Quick release mooring hooks provide an alternative method of securing the rope to the quay: such a system "greatly reduces the need for port staff to handle heavy mooring ropes &#; means staff have to spend less time on exposed areas of the dock, and [reduces] the risk of back injuries from heavy lifting".[8] The Oil Companies International Marine Forum recommend the use of such hooks in oil and gas terminals.[9]

The basic rode system is a line, cable, or chain several times longer than the depth of the water running from the anchor to the mooring buoy, the longer the rode is the shallower the angle of force on the anchor (it has more scope). A shallower scope means more of the force is pulling horizontally so that ploughing into the substrate adds holding power but also increases the swinging circle of each mooring, so lowering the density of any given mooring field. By adding weight to the bottom of the rode, such as the use of a length of heavy chain, the angle of force can be dropped further. Unfortunately, this scrapes up the substrate in a circular area around the anchor. A buoy can be added along the lower portion of rode to hold it off the bottom and avoid this issue.

Other types

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Non-line mooring ("hands-free") is used where pier time is highly valuable, and includes suction cups[10][11][12] or magnets.[13][14] It can also be used between ships.[15]

Mediterranean mooring

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Mediterranean mooring, also known as "med mooring" or "Tahitian mooring", is a technique for mooring a vessel to pier. In a Mediterranean mooring the vessel sets a temporary anchor off the pier and then approaches the pier at a perpendicular angle. The vessel then runs two lines to the pier. Alternatively, simple moorings may be placed off the pier and vessels may tie to these instead of setting a temporary anchor. The advantage of Mediterranean mooring is that many more vessels can be connected to a fixed length of pier as they occupy only their width of pier rather than their length. The disadvantages of Mediterranean mooring are that it is more likely to result in collisions and that it is not practical in deep water or in regions with large tides.

Travelling/running mooring

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A mooring used to secure a small boat (capable of being beached) at sea so that it is accessible at all tides. Making a Travelling Mooring involves (1) the sinking of a heavy weight to which a block (pulley wheel) is attached at a place where the sea is sufficiently deep at low tide, (2) fitting a block / pulley wheel to a rock or secure point above the high tide mark, and (3) running a heavy rope with marker buoy between these blocks.

Mooring involves (a) beaching the boat, (b) drawing in the mooring point on the line (where the marker buoy is located), (c) attaching to the mooring line to the boat, and (d) then pulling the boat out and away from the beach so that it can be accessed at all tides.

Canal mooring

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A wooden mooring bollard

A mooring used to secure a narrowboat (capable of traversing narrow UK canals and narrow locks) overnight, during off boat excursions or prolonged queuing for canal lock access. Water height with minimal exceptions, remain constant (not-tidal); there is water height variance in close proximity to locks.[16]

Types of canal moorings:

Mooring pin (boat operator supplied) driven into the ground between the edge of the canal and the towpath with a mooring-line rope to the boat.[17]

Mooring hook (boat operator supplied) placed on the (permanent) canal-side rail with either (boat operator supplied) rope or chain-and-rope to the boat.[17]

Mooring ring (permanent) affixed between the edge of the canal and the tow path, with (boat operator supplied) rope to the boat.[17]

Mooring bollard (permanent) affixed canal-side on lock-approaches for the short-term mooring of advancing boats and lock-side to assist in ascent and descent.[17]

Mooring line materials

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High-performance mooring lines

See also

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• Anchor &#; Device used to secure a vessel to the bed of a body of water to prevent the craft from drifting
• Anchorage (shipping) &#; Designated location at sea for ships to drop anchor

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• Berth (moorings) &#; Designated location in a port or harbour used for mooring vesselss
• Mooring mast &#; Structure designed to allow for the docking of an airship
• Sailing &#; Propulsion of a vehicle by wind power

References

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Each vessel has been designed with mooring arrangements such that ropes and wires of recommended strength can help it moor safely alongside a berth, floating platform, buoy or jetty. Fundamentally a vessel has to be positioned alongside a jetty or a berth, between mooring buoys, to a mooring buoy, to another ship or barge and then made fast using her own anchors, mooring lines or shorelines.

Some very common methods of mooring are Mediterranean mooring, Baltic mooring, Running mooring, Standing mooring, Spider mooring buoys, Single-point or single buoy mooring, Conventional or multi buoy mooring, Ship to Ship Mooring

While Moored alongside a fixed or floating jetty or a sea berth there are various forces acting on the vessel such as wind, current, tide, wave action, swell, surging induced due to passing ships and trim of the vessel.

The spring, breast and head lines prevent the vessel&#;s movement against the action of these forces. The directional effect of these need not be unidirectional. It can be multi-directional or at various angles to the vessel.

The resultant direction of these forces often changes with changes in direction of onshore/offshore winds or tidal streams, currents upriver and down streams. Thus a combination of breast ropes, head ropes and spring ropes is the best method to counter these forces and keep the vessel safely alongside.

Often mixed moorings are observed as some terminals based on local conditions and experiences require vessels to use more lines than they are designed for. Thus the method in which wires in conjunction with soft ropes with different SWL and construction are used as well is termed Mixed mooring.

The simplified resultant of these forces would tend to move a vessel in the transverse or longitudinal direction with respect to the jetty. Thus spring lines prevent the longitudinal motion and the breast lines check the transverse motion.

It is always preferred to avoid mixed moorings due to variable loads and elasticity of various kinds of ropes and wires which lead to different strains or weights on the lines. This can result in excessive loads on some lines than others and eventually part them putting the vessel in danger. However,  for safety reasons or in a desperate situation shipmasters or pilots may have to resort to mixed moorings.

Vessels sometimes also use the seaward anchor in conjunction with mooring lines to haul the vessel out of the jetty while casting off or while making fast the vessel alongside use the seaward anchor to assist the control of the rate of lateral movement towards the berth. This manoeuvre can be carried out with or without the assistance of tugs.

Ship to Ship transfer operation involves mooring alongside two different or same sized ships for cargo transfer. During this operation, either one of the ships is at anchor or both are underway.

The mooring arrangement depends on the size of the ships. A vessel either at anchor or stopped and maintaining a constant heading is approached by the manoeuvring ship at an angle of approach as smaller as practicable. The region of approach is usually abaft the beam of the constant heading ship.

During the approach as the manoeuvring ship comes closer, it steers a course parallel to the heading or course of the other ship and reduces the horizontal distance between ships to less than 100 metres. Once this state is achieved the manoeuvring ship uses engine and rudder movements and reduces this distance further until the fenders touch each other.

The two ships thus then make parallel contact and the lines are passed respectively as per the mooring plan. As a common practice during the approach, the wind and sea are preferred to be from ahead or at very small angles to the bow.

Single buoy or single point mooring: Often larger ships that cannot approach ports and terminals are berthed outside the port limits or in sheltered anchorages and the cargo transfer carried out with the help of Single-point or single buoy moorings.

The basic principle of the buoy is to keep the position of the vessel with respect to the buoy steady and at the same time allowing vessels to swing to wind and sea..

Often a tug is provided at the aft to keep the ship at a fixed angle and distance from the buoy. The buoy is fixed by positioning it in the centre of four anchors connected to it. The ship is made fast to the buoy with the help of a single chain or two which is secured onboard to the bow stopper.

In general, while approaching Single point or single buoy moorings weather is a major criteria in determining whether to berth the vessel or not. Calm seas with low swell and wind force below 15kts are considered favourable to make an approach. Presence of strong tidal current limits the interval for berthing and unberthing.

The headway approach has to be slow often less than while at the same time approaching at a smaller angle to the buoy and then gradually hauling in the buoy messenger rope and pulling the vessel slowly towards the buoy using engine kicks at short intervals to control and maintain headway along with mooring winches to haul in the vessel when she nears about 150-200 meters from the buoy.

For unberthing the chain is released from the bow stopper and a short kick on the engines going astern swings the bow to starboard for right-handed propellers thus clearing the vessel of the buoy. Tug&#;s assistance can also be sued to pull the vessel astern and clear it of the buoy. Know more about single point mooring here. 

Conventional buoy or multi buoy mooring: In this method, the bow of the ship is secured using both her anchors whereas the stern is secured to buoy around it. In the approach firstly vessel approaches the final berthing position from forward at an angle of 90 degrees to her final direction of berthing.

The starboard anchor is then let go first at a pre-decided spot while the ship is making headway. The required amount of cable is paid and the astern propulsion too operated simultaneously to stop the vessel. Once the vessel is stopped in the water port anchor is let go and thus vessel positions her stern along the centerline bifurcating the buoys.

For aligning the vessel along this centerline port cable is paid out and starboard cable heaved in with astern propulsion. The helm and engines are to be carefully used during this manoeuvre to ensure the stern is swinging clear of any of the buoys.

During unberthing, the anchor cables are heaved in to move the vessel forward and the weight is taken on windward lines while casting off other lines to prevent swinging of the stern into the other buoys. This manoeuvre requires skill and efficient operation of the ship&#;s crew as well as of the mooring equipment as often weight of the lines can be immense.

Read on baltic mooring here.

Mediterranean mooring: For this type of mooring, a pre-calculated position is determined and approached using engine movements. The bow initially is made to cant towards the berth and the starboard anchor is let go in that position.

After this, the engines are run astern and the port anchor is let go at the designated spot. The vessel falls astern and swings to starboard. Thus vessel is held by both the anchors as it approaches the quay. Stern lines are then passed. Moorings are kept tight by using the anchor cables.

The positioning of the vessel is such that mooring is completed with around four shackles on each anchor. Often tide is used to control the drift of the vessel towards the quay while positioning it by heaving or paying out on one of the anchors. Read more on mediterranean mooring here.

Running Mooring: This manoeuvre takes a relatively short duration compared to the Mediterranean mooring and offers more control of the vessel. The vessel&#;s starboard anchor is let go at a position approximately four to five shackles from the final position of the bow and around 9 shackles paid out while moving ahead on engines.

Then as she falls astern with the tide the port anchor is let go and the starboard anchor is heaved onto five shackles. This method restricts the swinging room and reduces the load on the windlass.

Standing Mooring: This is practised during crosswinds. As the vessel is stopped the port anchor is let go and with the tide around 9 shackles are paid out. The starboard anchor is let go and simultaneously port anchor heaved on.

Thus the port anchor is kept on 4 shackles being generally the flood anchor and starboard on five as it is the ebb anchor. This vessel takes longer duration and provides less control over the vessel. The load on the windlass is more as compared to running moor.

Over to you..

Do you know any other important mooring methods that can be added to this list?

Let&#;s know in the comments below.

About Author

Abhishek Bhanawat is a chief officer who has worked on various types of tankers. He specializes in Crude Oil and Product Tankers. He is highly passionate about his work and loves to sail.

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The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.

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