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Mooring

Structure for securing floating vessels

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The term likely stems from the Dutch verb (af)meren (to 'moor'), 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. They cause lesser damage to the marine environment, and are convenient. Where there is a row of moorings they are termed a tier. They are also occasionally used to hold floating docks in place. There are several kinds of moorings:

Swing moorings

Swing / swinging 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.

Fore & Aft Mooring

This is a mooring type used in sheltered locations to secure boats and prevent them from swinging and colliding. These moorings are used in confined harbours to allow higher density of boats to be moored than if swinging moorings were used. A Fore & Aft Mooring consists of two moorings of similar construction to Swinging Moorings fixed to the seabed a little more than a boat length apart. The two moorings are linked by a “Tracer Line” or “Messenger Line”. A disadvantage of Fore & Aft Moorings is that boats may be held side-on to the wind. This can lead to damage during storms.

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. For example, on the Great Barrier Reef off the Australian coast, a vast number of public moorings are set out in popular areas to prevent damage from so many vessels anchoring in the vulnerable ecosystem.

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. 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.
  • 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.
  • 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.

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