Mooring Anchor

Mooring Anchor

A vessel is said to be moored when it is fastened to a fixed object such as a pier, the seabed, or to a floating object such as an anchor buoy. Mooring is often accomplished using thick ropes called mooring lines. 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 by permanent anchor can be accomplished by use of a permanent mooring anchor at the bottom of a waterway with a rode (a line, cable, or chain) running to a float on the surface. This allows a person on the vessel to connect to the anchor.

While many mooring buoys are privately owned, some are available for public use. Always check before tying to any mooring buoy.

Mooring Anchor 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 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. Sailboats generally take 4 to 6 mooring lines.

mooring_anchorMooring 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.

Permanent Mooring Anchor

There are four basic types of permanent mooring anchors; dead weight, mushroom, screw in, and triple anchor. These mooring anchors 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 commonly used to hold dock floats in place.

Example: On the Great Barrier Reef off the Australian coast, a vast number of public mooring anchors 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 in close proximity without mooring anchors.

  • A Dead weight mooring anchor is the simplest kind of mooring 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 such mooring anchors are simple and cheap. A dead weight mooring anchor that drags in a storm still holds well in its new position. Such mooring anchors are better suited to rocky bottoms where other mooring anchor systems do not hold well. The disadvantages are that they are heavy, bulky, and awkward.

  • Mushroom mooring anchors are the most conventional mooring 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 anchor. The disadvantage is that they're more expensive than dead weight mooring anchors, doesn’t hold well on rocky or pebbly substrates and they take time to settle in before reaching full holding capacity.

  • Screw in mooring anchors are a modern method. The screw in mooring anchor is a shaft with wide blades spiraling around it so that it can be screwed into the substrate. The advantages of a screw in mooring anchor are a high holding power to weight ratio. An additional consideration is size. Screw in mooring anchors are so small that they are relatively cheap. The disadvantage is that a diver is usually needed to install, inspect, and maintain these mooring anchors

  • Multiple mooring anchor 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 of a multiple mooring anchor are minimized mass, ease of deployment, high holding power to weight ratio, and ease of access to the required mooring anchor components because temporary style anchors are commonly available.

Mooring Anchor | #1 Mooring Anchors built by Spade Anchor USA


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