Mooring (watercraft) - Mooring To A Shore Fixture

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 highlystressed 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.

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.