Oil tanker mooring at jetty berth

Effective ship mooring management requires a sound knowledge of mooring principles, information about the mooring equipment installed on the ship, proper maintenance of this equipment and regular tending of mooring lines.

The safety of the vessel and hence its proper mooring is the prime responsibility of the master. However, the terminal has local knowledge of the operating environment at the site and knows the capabilities of shore equipment, and should therefore be in the best position to advise the master regarding mooring line layout and operating limitations.

Type and quality of mooring lines
The mooring lines used to secure the tanker should preferably all be of the same material and construction. Ropes with low elastic elongation properties are recommended for larger tankers as they limit the tankers movement at the berth. High modulus synthetic fibre ropes are a viable replacement for winch stowed steel wire ropes for the mooring of large tankers to terminals, other than single point moorings, provided that the recommendations contained in the OCIMF publication Guidelines on the Use of High Modulus Synthetic Fibre Ropes as Primary Mooring Lines on Large Tankers are followed.

Moorings composed entirely of high elasticity ropes are not recommended as they can allow excessive movement from strong wind or current forces, or through interaction from passing ships. Within a given mooring pattern, ropes of different elasticity should never be used together in the same direction.

It should be realised that mooring conditions and regulations may differ from port to port. Where dynamic (shock) loading on moorings can be caused by swell conditions or the close passing of ships, fibre tails on the ends of mooring wires and high-modulus synthetic fibre mooring ropes can provide sufficient elasticity to prevent failure of the mooring and other components in the mooring system. Such tails, whose length should not exceed one third of the distance between the ships fairlead and the shore mooring bollard, may be provided by the tanker or the terminal.

Because fibre tails will deteriorate more rapidly than the wires or high modulus synthetic fibre ropes to which they are attached, they should be at least 25% stronger than the line to which they are attached. They should be inspected frequently, particularly in way of their connection to the wire, and be replaced at regular intervals.

Management of moorings at alongside berths

Tending of Moorings
Ships personnel are responsible for the frequent monitoring and careful tending of the tankers moorings, but suitably qualified shore personnel should check the moorings periodically to satisfy themselves that they are being properly tended.

When tending moorings which have become slack or too taut, an overall view of the mooring system should be taken so that the tightening or slackening of individual lines does not allow the tanker to move or place undue loads on other lines. The tanker should maintain contact with the fenders and moorings should not be slackened if the tanker is lying off the fenders.

Use of Standby Tugs
The possibility of using tugs to maintain position should be considered whenever the following conditions exist or are expected:
  1. Significant increase in wind speed or change in wind direction, particularly if the tanker has substantial freeboard.
  2. Excessive swell.
  3. Periods of maximum tidal flow.
  4. Limited under keel clearance (UKC).
  5. The close passing of other ships.

Tension Winches
Self tensioning winches fitted with automatic rendering and hauling capability should not be used in the automatic mode while the vessel is moored. In automatic mode, such winches, by definition, will render under load and will allow the vessel to move out of position, with consequent risk to cargo arms or hoses.

Self Stowing Mooring Winches
Because their weight and size make manual handling difficult, mooring wires used by tankers are normally stored on self-stowing mooring winches which may be either single drum or split drum.

A number of features of these winches need to be clearly understood by ships personnel in order to avoid vessels breaking adrift from berths as the result of slipping winch brakes. The holding power of the brake depends on several factors, the first being its designed holding capacity. This may either have been specified by the shipowner or be the standard design of the winch manufacturer. Some winches have brakes which are designed to slip or render under loads which are less than 60% of the breaking load of the mooring line (MBL) handled. Every ships officer should be aware of the designed brake holding capacity of the self-stowing mooring winches installed on the vessel.

In addition, deterioration of the brake holding capacity will be caused by wear down of the brake linings or blocks, and it should therefore be tested at regular intervals, not exceeding twelve months. A record, both of regular maintenance and inspections and tests, should be kept on the vessel. If the deterioration is significant, particularly if the initial designed holding capacity was low in relation to the breaking load of the mooring, the linings or blocks must be renewed.

Some of the newer self-stowing mooring winches are fitted with disc brakes, which are less affected by wear. Kits are available for testing winch brake holding capacity which can be placed on board for use by the crew. There are also a number of operational procedures that can seriously reduce the holding capacity of winch brakes if they are not correctly carried out. These include:

The number of layers of wire on the drum.
The holding capacity of a winch brake is in inverse proportion to the number of layers of the mooring wire or rope on the drum. The designed holding capacity is usually calculated with reference to the first layer and there is a reduction in the holding capacity for each additional layer. This can be substantial - as much as an 11% reduction for the second layer.

If the rated brake holding capacity of a split drum winch is not to be reduced, only one layer should be permitted on the working drum.

The direction of reeling on the winch drum.
On both undivided and split drum winches, the holding power of the brake is decreased substantially if the mooring line is reeled on the winch drum in the wrong direction. Before arrival at the berth, it is important to confirm that the mooring line is reeled so that its pull will be against the fixed end of the brake strap, rather than the pinned end. Reeling in the contrary direction can seriously reduce the brake holding capacity, in some cases by as much as 50%. The correct reeling direction to assist the brake should be permanently marked on the drum to avoid misunderstanding.

Winches fitted with disc brakes are not subject to this limitation.

The condition of brake linings and drum.
Oil, moisture or heavy rust on the brake linings or drum can seriously reduce the brake holding capacity. Moisture may be removed by running the winch with the brake applied lightly, but care must be taken not to cause excessive wear. Oil impregnation cannot be removed, so contaminated linings will need to be renewed.

The application of the brake
Brakes must be adequately tightened to achieve the designed holding capacity. The use of hydraulic brake applicators or a torque wrench showing the degree of torque applied is desirable. If brakes are applied manually, they should be checked for tightness.

Shore Moorings
At some terminals, shore moorings are used to supplement the tankers moorings. Where shore personnel handle shore moorings, they must be fully aware of the hazards of the operation and should adopt accepted safe working practices.

If the adjustable ends of the shore mooring are on board the tanker, the moorings should be tended by the tankers personnel in conjunction with its own moorings. If shore based wires with winches are provided, agreement should be reached over the responsibility for tending. If shore based pulleys are provided, the tanker should tend the mooring since both ends of the line are on board. For the avoidance of doubt, there should be clear agreement between the responsible officer and the terminal representative with regard to who will take responsibility for tending any moorings provided by the terminal.

Whilst moored alongside, anchors not in use should be properly secured by brake and guillotine, but otherwise be available for immediate use.

Related information on safe practice by oil tankers:

Offshore moorings safe practice

Oil tanker mooring at jetty berth

Oil tanker mooring at bouy

Related precautions during cargo work:

Precautions for external openings in superstructures

Management of central air conditioning and ventilation systems

Precautions for openings in cargo tanks during cargo works

Procedure for inspection of oil tankers cargo tanks prior loading

Ship and shore cargo connection for oil tankers cargo operation

How to prevent accidental spillage of oil cargo

Oil tankers precautions at berth

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