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Mooring equipment for general cargo vessel

The operation of mooring a vessel has traditionally required the attendance of a large number of deck crew fore and aft. Supervision of the moorings was also necessary to maintain correct tension through changes due to the tides and the loading or unloading of cargo.

The installation of constant tension mooring winches, which maintain tension in ropes through any rise and fall, has removed the need for constant attendance and equipment is available for tying up which is designed for operation by as few as two men.

Large container ships may have four mooring winches on the after deck; each of the self-tensioning type with its own rope drum. Controls are duplicated and are situated at each side of the vessel, giving a clear view of the operation.

Mooring ropes are paid out directly from the drums as they are hauled by the heaving lines from the quay. With the loop in place on the bollard, the capstan is set on auto-tension after slack is taken up and the ship is correctly moored. A common arrangement forward is for two similar winches plus rope drums for auto-tensioning on each windlass.

The introduction of steel hatchcovers not only speeded up the operation of opening and closing the covers but also reduced the number of personnel required for the task. Rolling and folding covers may be operated by a pull wire or hydraulically. Covers for large container ships may be lifted bodily by crane and there are now hatchcoverless container ships in service.

Cargo handling may be by winches and derricks or cranes. Some geared bulk carriers have overhead cranes arranged to travel on rails.

Most deck machinery is idle during much of its life while the ship is at sea. In port, cargo equipment will be in use for one or more days but the machinery for anchoring and mooring is used for a very limited time. Deck machinery with a restricted and intermittent duty may be designed with drives with a rating limited from 30 minutes to one hour. Despite long periods of idleness, often in severe weather conditions, machinery must operate immediately, when required. Cooling vents, open when machinery is working, must be closed for the sea passage.

It is essential that deck machinery should require minimum maintenance. Totally enclosed equipment with oil bath lubrication for gears and bearings is now standard but maintenance cannot be completely eliminated and routine checking and greasing should be carried out on a planned basis.

There are many instances where remote or centralized control is of great advantage, for example, the facility for letting go anchors from the bridge under emergency conditions; the use of shipside controllers with mooring winches; or the central control positions required for the multi-winch slewing derrick system.

The machinery on the deck of an oil tanker is limited to that used for anchor handling and mooring plus pumproomn fans and equipment for handling the gangway and stores. Power was universally provided in the past by steam. Hydraulic equipment is now common, sometimes with air motors for gangway duties. The availability of safe electrical equipment means that electric motor drives can be used where appropriate.

Liquefied gas carriers and product or chemical tankers have similar deck machinery installations but the drive motor for deepwell pumps may be an induction motor of the increased or enhanced (Ex e) safety type. Either electric or hydraulic drives are installed for the deck machinery of dry cargo vessels.

Mooring equipment

Full load duties of warping capstans and mooring winches vary between 3-30 tonnes at 0.3 to 0.6 m/s and twice full load speed is normally provided for recovering slack lines.

The size of wire rope used on mooring winch barrels is governed by the weight of wire manageable by the crew; this is currently accepted as 140mm circumference maximum. The basic problems associated with the use of wire ropes is that they are difficult to handle, do not float and when used in multi-layers, due to inadequate spooling, the top, tensioned layer cuts down into the underlying layers causing damage.

To counteract this problem a divided barrel can be used such that the wire may be stored on one portion and a single layer of wire transferred to the second portion when tensioned. Low density, high breaking strength synthetic ropes (polypropylene, nylon or terylene) offer certain advantages over wire, its main disadvantage being a tendency to fuse if scrubbed against itself or the barrel.

Electrically driven mooring winches with two split drums
Fig :Electrically driven mooring winches with two split drums


Mooring winches provide the facility for tensioning the wire up to the stalling capacity of the winch, usually 1.5 times full load thereafter the load is held by the motor brake, or by the barrel brake when the power is shut off. The winch cannot pay out wire unless the brake is overhauled or recover wire unless manually operated, thus wires may become slack.

Image credit :Wärtsilä Encyclopedia of Ship Technology

Automatic mooring winches provide the manual control previously described but in addition incorporate control features such that, in the automatic setting, the winch may be overhauled and wire is paid off the barrel at a pre-determined maximum tension; also wire is recovered at a lower tension should it tend to become slack. Thus there is a certain range of tension, associated with each step of automatic control, when the wire is stationary. It is not practical to reduce this range to the minimum possible as this results in hunting of the controls.

It should be noted that the principal reason for incorporating automatic controls with the features described is to limit the render value of the winch and avoid broken wires; also to prevent mooring wires becoming slack. Load sensing devices are used with automatic mooring winches, e.g. spring-loaded gearwheels and torsion bars are widely used with steam and electric winches; fluid pressure sensing, either steam or hydraulic oil pressure, is also used where appropriate.

Mooring winches are usually controlled at the local position, i.e. the winch, For vessels of unusually large beam or where docking operations are a frequent occurrence e.g. in ships regularly traversing the St. Lawrence Seaway, remote and shipside controllers are of great advantage.

As mooring techniques vary widely, the position and type of control must be engineered to suit the application. It is considered, especially on vessels where mooring lines may be long and ship position critical, that the greatest asset to the operator is knowledge of the wire tensions existing during the mooring operation coupled with an indication of the amount of wire paid off the barrel. It is quite feasible to record these at a central position and mooring lines would then only have to be adjusted periodically as indicated by the recording instruments.

The majority of automatic mooring winches are spur geared to improve the backward efficiency of the gear train for rendering, the gearing and bearings being totally enclosed and lubricated from the oil sump.

On larger mooring winches were a barrel brake is fitted, it is now common practice to design the brake to withstand the breaking strength of the mooring wire. Worm geared automatic mooring winches are uncommon as the multi-start feature required to improve gear efficiency reduces the main advantage of the worm gear i.e. the high gear ratio.

Summarized below some of the basic operation of deck machinery and maintenance guide :
  1. Powering deck machinery -Systems and components

  2. Pump and motor systems are used for powering deck machinery such as winches and windlasses. Pump and actuating cylinders are normally employed for hatch covers. One or more pumps will be used to supply the volume of fluid at the pressure required to operate one or more motors. ......

  3. Mooring equipment for general cargo vessel

  4. The operation of mooring a vessel has traditionally required the attendance of a large number of deck crew fore and aft. Supervision of the moorings was also necessary to maintain correct tension through changes due to the tides and the loading or unloading of cargo. ......

  5. Hydraulic systems for deck machinery and cargo equipment

  6. The three essential components for a hydraulic circuit, are the hydraulic fluid held in a reservoir tank, a pump to force the liquid through the system and a motor or cylinder actuator to convert the energy of the moving liquid into a working rotary or linear mechanical force. Valves to control liquid flow and pressure are required by some systems. ......

  7. General cargo ship deck machinery electric drives

  8. Electric motors on vulnerable deck areas may be protected against ingress of water by being totally enclosed in a watertight casing. Vents are provided on some winches, which must be opened when the motor is operating in port. ......

  9. Handling deck machinery- Anchor windlasses,Anchor capstan & mooring winches

  10. The windlass cablelifter brakes must be able to control the running anchor and cable when the cablelifter is disconnected from the gearing when letting go'. Average cable speeds vary between 5 and 7 m/s during this operation. ......

  11. General cargo ship deck deck crane

  12. A large number of ships are fitted with deck cranes. These require less time to prepare for working cargo than derricks and have the advantage of being able to accurately place (or spot) cargo in the hold. On container ships using ports without special container handling facilities, cranes with special container handling gear are essential. ......

  13. Mechanically operated steel hatch covers

  14. Hatch cover equipment like the other deck machinery, has to exist in a very hostile environment and the importance of regular maintenance cannot be over-emphasized. Drive boxes and electrical enclosures should be checked regularly for water-tightness. ......

  15. Derricks and cargo winches -Ship cargo handling gears

  16. The duty of a deck winch is to lift and lower a load by means of a fixed rope on a barrel, or by means of whipping the load on the warp ends, to top or luff the derricks, and to warp the ship. ......

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