Updated IMO Mooring Guidance

Safety4Sea Reports On Updated IMO Mooring Guidance.

New revised guidelines

However, as the revised OCIMF MEG-4 guidelines came into effect July 2018, tankers have to conform with requirements since then (July 2018). It is important to note that construction items (MBL,SWL etc) for ships built prior 1-1-2024, the previous version MSC.1 Circ.1175 remains as the applicable standard. However, these ships should also conform with inspection /maintenance requirements of Circ. 1620.

The revised documents have introduced revised terms and definitions

Most of them are in conformity with those of OCIMF MEG-4.

• Ship Design Minimum Breaking Load (MBLSD) means the minimum breaking load of new, dry, mooring lines for which shipboard fittings and supporting hull structures are designed in order to meet mooring restraint requirements. This is a core value as this item determines the forces of other factors during mooring. For example, Safe Working Load for mooring arrangements should be equal or higher than MBLSD.
• Line Design Break Force (LDBF) means the minimum force that a new, dry, spliced, mooring line will break at. This is for all synthetic cordage materials. This should be maximum up to 105% of MBLSD
• Mooring area refers to the dedicated area on a ship where mooring equipment is installed and line-handling takes place. It also includes areas where there is a risk of personnel injury in event of snap-back or other failure of mooring equipment. There may be multiple mooring areas on a ship.
• Mooring arrangements means the configuration of the mooring equipment and fittings and other design features of the ships related to the mooring operation, i.e. lighting and communication equipment.
• Mooring equipment and fittings means items such as mooring winches, capstans, bollards, bitts, fairleads, rollers, chocks, etc. and also includes mooring lines.
• Mooring lines means ropes, wires and combinations used for mooring operations other than messenger lines but including tails.
• Mooring line configuration means all components of an individual mooring line, including tails, eye splices, etc. Any change or replacement of a component is a change to the line’s configuration, unless a component is replaced by a part having the same specification as in the original configuration.
• Working Load Limit (WLL) means the maximum load that a mooring line should be subjected to in operational service, calculated from the relevant environmental mooring restraint requirement.

There are two (2) main parts for mooring lines that are covered by the new issued circulars. The first is the construction part (including the strength of the lines) and the second is the inspection and maintenance of the all fittings/lines or applicable machinery.

Until now, MSC.1 Circ.1175, provided a list based on calculated Equipment Number (EN) which determined the strength of the lines used on board based on specific environmental conditions, side projecting area. The number of lines was calculated as per IACS Rec.10 based on the side projecting area of the ship. The projecting area for both cases was calculated using heights measured from Summer Load Water line.

The revised MSC1. Circ. 1175 Rev.1, has the following differences:

1. Has incorporated the IACS rec.10 for the number of mooring lines to be used
2. For ships with EN <2000 still determines the strength of mooring lines to be used, however for EN>2000 the calculation of hull side projecting is conducted using the lightest ballast draft.

The calculation formula for the strength of the line is MBLSD = 0.1 *A1 + 350 in kN.

A1 is the side projecting area calculated as per Appendix B of the circular with the differences as mentioned earlier.

As the calculated side projecting area is larger with new guidance the strength of the lines required for a ship will have a higher value. The example below shows the differences in strength values for different standard calculations. In the example we have a 210,000 DWT Tanker and calculations based on different standards. (Table 1)

1. LBP: 295m
2. Depth: 25.20 m
3. Draft (Scantling): 18.48 m
4. The Equipment number is calculated 5800-6100

Table 1: The example shows differences in strength values for different standard calculations

As it is understood, the two latest standards (MEG-4 and MSC 1175. Rev.1) provide higher values for MBL of mooring lines.

Regarding maintenance, circ.1620 has brought to attention the following:.

1. Periodical inspections based on experience and manufacturers guidance. The inspections should be visual (on the length of the line which is used for mooring), technical (using manufacturers instructions or third party guidance).
2. Records of maintenance should be kept.
3. Retirement criteria should be in place for guidance.

All of above items have already introduced with OCIMF MEG-4 (for applicable ships).

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