Mooring (watercraft)
From Wikipedia, the free encyclopedia
When used as noun, the word mooring refers to any permanent structure that fixes a vessel's position to the bottom of a waterway without connecting the vessel to shore.
When used as a verb, mooring refers to any means of attaching a vessel to a fixed object such as a bollard, pier, quay or a mooring.
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
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 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 California's Catalina Island.Pile moorings
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.
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 weight, mushroom, screw in, and Multiple anchors.
- Dead weights are the simplest kind 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 for mud and silt substrate. They are shaped like an upside down mushroom which can bury itself in these materials quite readily. The advantage is that it has up to ten times the holding power to weight ratio as compared to a dead weight mooring. The disadvantage is that they're more expensive than dead weight moorings, don't hold well on rocky or pebbly substrates, and they take time to settle in before reaching 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 are a high holding power to weight ratio. An additional consideration is size. Screw in moorings are so small that they are relatively cheap. 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 ease of access to the required anchor components because temporary style anchors are commonly available.
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.
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. Mooring lines made from materials such as Dyneema and Kevlar are 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.
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| Number | Name | Purpose |
|---|---|---|
| 1 | Bow line | Prevent backwards movement |
| 2 | Forward Breast line | Keep close to pier |
| 3 | After Bow Spring line | Prevent from advancing |
| 4 | Forward Quarter Spring line | Prevent from moving back |
| 5 | Quarter Breast line | Keep close to pier |
| 6 | Stern line | Prevent forwards movement |
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.
Mediterranean Mooring
Mediterranean mooring, also known as med mooring and 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
Regular mooring lines- Sisal
- Hemp
- Steel wire
- Polyethylene
- Polypropylene
- Polyester (e.g. used for deepsea mooring of offshore platforms)
- Nylon
- Chain
