A mooring refers to any permanent structure to which a vessel 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.
The term probably stems from the Dutch verb meren (to moor), which has been used in English since the end of the 15th century.
Permanent anchor mooring
These moorings are used instead of temporary anchors because they have considerably more holding power, cause less damage to the marine environment, and are convenient. They are also occasionally used to hold floating docks in place. There are several kinds of moorings:
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.
Fore and aft moorings
Fore and aft moorings, also known as double moorings or twin moorings, are just a pair of swing moorings with an additional rode between the two primary rodes to remove confusion as to which moorings are paired. A fore and aft mooring may have one or two floats. Fore and aft moorings fix a vessel's position more precisely than a swing mooring, and therefore allow a much greater density of vessels to be moored. They are used in particularly congested harbours, like those of Santa Catalina Island, California.
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.
There are four basic types of permanent anchors used in moorings:
- 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. 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.
- 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
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 fittings on the shore, such as bollards, rings, or cleats, on the other end.
Mooring requires cooperation between people on the pier and on a vessel. For larger vessels, heavy mooring lines are often passed to the people on the shore by use of smaller, weighted heaving lines. Once the mooring line is attached to the bollard, it is pulled tight. On large ships, this tightening can be accomplished with the help of heavy machinery called mooring winches or capstans.
For the heaviest cargo ships, more than a dozen mooring lines can be required. Small vessels generally take 4 to 6 mooring lines.
Mooring lines are usually made out of synthetic materials such as nylon. Nylon is easy to work with and lasts for years, but has a property of very great elasticity. This elasticity has its advantages and disadvantages. The main advantage is that during an event, such as a high wind or the close passing of another ship, excess stress can be spread among several lines On the other hand, if a highly stressed nylon line does break, or part, it causes a very dangerous phenomenon called "snapback" which can cause fatal injuries. Snapback is analogous to stretching a rubber band to its breaking point between the hands, and then suffering a stinging blow from the retracting loose ends of the band - in the case of a heavy mooring line this blow carries much more force and can inflict severe injuries or sever limbs. Mooring lines made from materials such as Dyneema and Kevlar have much less elasticity and therefore much safer to use, but the lines do not float on the water, and tend to sink, are costly, so they are used less frequently. Manila rope is preferred.
Some ships use wire rope for one or more of their mooring lines. Wire rope is hard to handle and maintain. There is also a risk of using wire rope on a ship's stern in the vicinity of its propeller.
Combination mooring lines made of both wire rope and synthetic line can also be used. This results in a hawser. This is more elastic and easier to handle than a wire rope, but not as elastic as a pure synthetic line. Special safety precautions must be followed when constructing a combination mooring line.
The two-headed mooring bitt 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". The Oil Companies International Marine Forum recommend the use of such hooks in oil and gas terminals.
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.
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.
Mooring line materials
- Steel wire
- Polyester (e.g., used for deepsea mooring of offshore platforms)
- High-performance mooring lines
- Anchorage (shipping)
- Mooring mast - a structure designed to hold an airship or blimp securely in the open when it is not in flight.
- Maloney, Elbert S.; Charles Frederic Chapman (1996). Chapman Piloting, Seamanship & Small Boat Handling (62 ed.). Hearst Marine Books. ISBN 9780688148928.
- "About Moorings". The Lake Life.
- Jamestown Distributors. "Mooring Basics - How to Install a Permanent Mooring". How Tos.
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