New SOLAS regulations for mooring equipment

New mooring regulations -SOLAS, Chapter II-1/3-8

(Effective 01/01/2024)

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INTRODUCTION

Navigating the intricate web of SOLAS regulations concerning mooring equipment can be daunting for those unaccustomed to legal texts. In this article, we endeavor to present and review the new regulations on mooring equipment and arrangements that came into effect on 1 January 2024.

At the heart of this regulatory framework lies SOLAS regulation II-1/3-8. Supporting this regulation are resolutions issued by the Maritime Safety Committee and circulars providing guidance and standards on aspects such as design, inspection, maintenance, and interpretation of the regulations. Table 1 below offers a concise overview of the evolution of SOLAS regulations for mooring equipment, providing historical context along with a basic description of the relevant publications.

Following Table 1, the remainder of the SOLAS Regulations Section in this article is dedicated to presenting and commenting on the important aspects of each resolution and circular.  Links to the full MSC documents are provided in this article that will open the Circular or Resolution in a separate window.

Additionally, we will review the Unified Requirement UR A2 and Recommendation 10 by IACS, which reflect Classification Society rules on the matter.

Finally, we will compare the new SOLAS regulations to the (MEG4) Guidelines issued by OCIMF, which have traditionally served as the primary reference for mooring matters.

Through this review, our aim is to provide a “map” of the regulatory landscape for easy reference while outlining the main points of each regulation.

SOLAS REGULATIONS FOR MOORING EQUIPMENT

SOLAS Mooring Regulations Overview (Table 1) 

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Table 1 below outlines key Resolutions and Circulars issued by the Maritime Safety Committee (MSC) since 2005. While Resolutions establish regulatory frameworks, they often lack detailed specifications, necessitating supplementary guidance Circulars and, eventually, a Unified Interpretation document. To navigate this complex regulatory landscape effectively, it’s important to understand the different purposes behind these documents.

On one hand, Resolution MSC.194(80) primarily addresses the necessary strength requirements for mooring equipment. Conversely, Resolution MSC.474(102) introduces additional stipulations for the selection, inspection, and maintenance of mooring arrangements and equipment.

Similarly, the various guidance Circulars listed in the table focus on distinct aspects of mooring equipment. For example, MSC.1/Circ.1175 and its revised edition MSC.1/Circ.1175/Rev.1 primarily address design and construction issues relevant mainly to shipyards. Meanwhile, MSC.1/Circ.1619 and MSC.1/Circ.1620 emphasize the design of arrangements, equipment selection, and inspection and maintenance requirements.

We trust that the table below will aid in maintaining clarity amidst the regulatory complexity.

Table 1 – SOLAS Resolutions and Guidance publications on mooring equipment.

In the remainder oif this Section, we will present and comment the mooring-related aspects of the Resolutions and Circulars in the table above  (There are other subjects covered by the reviewed regulations, but we are only considering here mooring equipment and related matters.)

Resolution MSC.194 (80), adopted on 20 May 2005

(Amendments for the International Convention for the Safety of Life at Sea)

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This is a Resolution that introduced amendments to SOLAS Chapter II-1 in 2005. The section regarding mooring and towing equipment came into effect on January 1, 2007. Click here for the full Resolution content in a separate window.

Regarding mooring equipment, the Resolution contains the following self-explanatory text:

Regulation 3-8

Towing and mooring equipment

1 This regulation applies to ships constructed on or after 1 January 2007, but does not apply to emergency towing arrangements provided in accordance with regulation 3-4.

2 Ships shall be provided with arrangements, equipment and fittings of sufficient safe working load to enable the safe conduct of all towing and mooring operations associated with the normal operation of the ship.

3 Arrangements, equipment and fittings provided in accordance with paragraph 2 shall meet the appropriate requirements of the Administration or an organization recognized by the Administration under regulation I/6*

4 Each fitting or item of equipment provided under this regulation shall be clearly marked with any restrictions associated with its safe operation, taking into account the strength of its attachment to the ship’s structure.

∗ Refer to MSC/Circ.1175 on Guidance on shipboard towing and mooring equipment.

Circular MSC.1/Circ.1175 of 24 May 2005

(Guidance on Shipboard Towing and Mooring Equipment)

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which The Resolution MSC.194 mentioned above lacks specificity in some areas. Circular MSC.1/Circ. 1175 serves as a more detailed guidance on Shipboard Towing and Mooring Equipment. Click here for the full Circular content in a separate window.

It aims to establish standards for the design and construction of shipboard fittings and supporting hull structures associated with towing and mooring, which Administrations are recommended to adopt. The provisions of this guidance do not mandate standards for tow lines or mooring lines onboard the ship.

This Circular remains applicable to vessels built between January 1, 2007, and January 1, 2024. For ships built on or after January 1, 2024, there is a revised version (as detailed in the relevant paragraph below).

Section 4 of the Circular outlines the design load values for supporting hull structure and shipboard fittings, which are defined as bollards, bitts, fairleads, stand rollers, and chocks used for the normal mooring of the ship, as well as similar components used for the normal towing of the ship. (A similar Section 3 addresses towing systems in the Circular, but this article focuses on the mooring aspect, with a similar approach taken regarding towing equipment.)

Some important points in the Circular:

Shipboard fittings for mooring should be located on longitudinals, beams and/or girders, which are part of the deck construction so as to facilitate efficient distribution of the mooring load. Other equivalent arrangements may be accepted (for Panama chocks, etc.).

Regarding load considerations:

The design load applied to shipboard fittings and supporting hull structures should be 1.25 times the breaking strength of the mooring line provided in accordance with Table 1 in the Appendix, which is based on the equipment number (EN). This design load should be applied through the mooring line according to the arrangement shown on the towing and mooring arrangements plan.

The breaking strength is defined in the Appendix of the Circular. The same figure of 1.25 times also applies to supporting hull structure for winches and capstans, being in this case 1.25 times the maximum hauling-in force.

The method of application of the design load to the fittings and supporting hull structure should be considered so that the total load does not exceed twice the specified design load (1.25 times the line breaking strength). This means that the design load of, for example, a bollard, should be based on no more than a single mooring line with one 180º turn around it.

There is an interesting concept here that might lead to confusion if the sentence in blue above is taken literally. When the mooring rope acts in a single direction (i.e., no change of direction around the fitting), the design load applied on the hull fitting is – for design purposes – 1.25 times the mooring rope strength. However, if a mooring rope is arranged around the fitting, the acting force on the fitting can be as much as twice the tension on the mooring rope. This means that designing the fitting and its supporting hull structure for just 1.25 times the breaking force of the mooring strength is not safe enough. In other words, the resultant of the forces in the two directions is to be calculated based on 1.25 times the mooring rope breaking strength. It is also confusing, in my opinion, that the value of the SWL marked on the fitting is the same as the breaking strength of the rope. In practice, the load acting on the fitting may be larger, depending on the angle taken by the rope.

The selection of shipboard fittings should be made by the shipyard in accordance with industry standards (e.g., ISO 3913:1977 Shipbuilding-Welded steel bollards) accepted by the Administration. When the shipboard fitting is not selected from an accepted industry standard, the fittings should be equivalent to a recognized industry standard in compliance with the design load as per 4.3

Regarding allowable stresses:

Allowable bending stress: 100% of the specified yield point for the material used; allowable shearing stress: 60% of the specified yield point for the material used; no stress concentration factors being taken into account.

Safe working load (SWL)

The SWL of a shipboard fitting should not exceed 80% of the design load determined above. (Meaning that the SWL should not exceed the breaking strength of the mooring line).

The SWL of each shipboard fitting should be marked (by weld bead or equivalent) on the deck fittings used for mooring. The above provisions on SWL apply for a single post basis (no more than one turn of one line).

Towing and mooring arrangements plan

The SWL for the intended use for each shipboard fitting should be noted in the towing and mooring arrangements plan available on board. Information provided on the plan should include in respect of each shipboard fitting: 1) location on the ship, 2) fitting type, 3) SWL, 4) Purpose (mooring/harbour towing/escort towing), and .5) Method of applying load of towing or mooring line including limiting fleet angles.

Table to determine breaking strength (kN)

Table 1 in the Circular (not in this article) can be used to determine the breaking strength (kN) of the mooring lines and tow lines to be used onboard. The breaking strength will depend on the Equipment Number (EN), which is defined in the Appendix.

Note: it is not necessary to keep a tow line onboard, however, the table above provides the breaking strength that such a line should have. This value is important as is the reference value from which the load on the hull supporting structure and fittings is calculated.

Equipment Number (EN)

The Equipment Number (EN) should be calculated as follows: EN = ∆2/3 + 2.0hB + A /10

where: ∆ = moulded displacement, in tonnes, to the Summer Load Waterline

B = moulded breadth, in metres

h = effective height, in metres, from the Summer Load Waterline to the top of the uppermost house. (The Circular provides clarification on how exactly h should be measured that we do not include here).

A = area, in square metres, in profile view, of the hull, superstructures and houses above the Summer Load Waterline which are within the equipment length of the ship and also have a breadth greater than B/4

As can be seen, the EN depends solely on the geometry of the ship.

SUMMARY for Circular MSC.1/Circ.1175:

The provisions of this guidance do not require tow lines nor mandate standards for mooring lines onboard the ship.

Basically, this Guidance establishes the design criteria for shipboard equipment. This Circular is still applicable to vessels built between 1 Jan 2007 and 1 Jan 2024.

Summary of design criteria for shipboard equipment:

  • Calculate EN using the given formula.
  • From the EN value, the breaking strength of the mooring lines is determined (Table 1 of the Circular).
  • From the breaking strength, the design load on the hull supporting structure and shipboard fittings is calculated, typically by multiplying x 1.25.
  • The SWL to be marked on the equipment by welding seams is 80% of above or equal to the mooring line breaking strength.
  • Adjustment to above load are made based on the mooring plan and the angle on the mooring rope.
  • Once the loads are known, the supporting structures should be calculated as to withstand such load. Particularly, the maximum bending stress on fittings is taken as 100% of the yield stress. The maximum shear stress is taken as 60% of the yield stress.

Resolution MSC.474 (102) of 11 Nov 2020

(Amendments to SOLAS Chapter II-1)

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This is a Resolution of the Maritime Safety Committee whereby some amendments are made to SOLAS Chapter II-1

Below are the most significant points of the resolution when it comes to mooring arrangements. Otherwise, click here for the full Resolution content in a separate window.

4    Ships shall be provided with arrangements, equipment and fittings of sufficient safe working load to enable the safe conduct of all towing and mooring operations associated with the normal operation of the ship.

5    Arrangements, equipment and fittings provided in accordance with paragraph 4 above shall meet the appropriate requirements of the Administration or an organization recognized by the Administration under regulation I/6.

6   Each fitting or item of equipment provided under this regulation shall be clearly marked with any limitations associated with its safe operation, taking into account the strength of the supporting ship’s structure and its attachment to it.

Above paragraphs 4 to 6 apply to ships constructed on or after 1 January 2007.

Paragraphs 7 and 8 below only apply to ships for which a building contract is dated on or after 1 January 2024, or -if no contract- to ships with keel laying date on or after 1 July 2024, or to ships delivered on or after 1 January 2027.

7    For ships of 3,000 gross tonnage and above, the mooring arrangement shall be designed, and the mooring equipment including lines shall be selected, in order to ensure occupational safety and safe mooring of the ship, based on the guidelines developed by the Organization. Ship-specific information shall be provided and kept on board.

8    Ships of less than 3,000 gross tonnage should comply with the requirement in paragraph 7 above as far as reasonably practicable, or with applicable national standards of the Administration.

Lastly, para 9 below applies to all ships:

9    For all ships, mooring equipment, including lines, shall be inspected and maintained in a suitable condition for their intended purposes.

So, basically, the previous Resolution 194 was aiming to establish safe standards regarding the equipment working load. The new Resolution MSC.474 adds considerations regarding the design and equipment selections aspects of the mooring arrangement based on guidelines by the Organization and / or national standards as applicable. It also puts an emphasis on onboard records and inspection and maintenance requirements for all vessels.

Circular MSC.1/Circ.1619 of 11 Nov 2020

(Revised Guidance on Shipboard Towing and Mooring Equipment)

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Below is the summarized content of the Circular. Click here for the full content.

SECTION 1 is an Introduction and summarizes the most important aspects in broad terms:

On ships of 3,000 gross tonnage and above constructed on or after 1 January 2024, the mooring arrangement shall be designed, and the mooring equipment including lines shall be selected, in order to ensure occupational safety and safe mooring of the ship.

Ships of less than 3,000 gross tonnage constructed on or after 1 January 2024 should comply with these requirements as far as reasonably practicable, or with applicable national standards of the Administration.

SECTION 2 provides some definitions used in the Guidelines:

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.

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.

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.

Towing and mooring arrangements plan means the plan as described in section 5 of the annex to the Revised guidance on shipboard towing and mooring equipment (MSC.1/Circ.1175/Rev.1). This plan presents specific information regarding the towing and mooring fittings aboard the vessel, the mooring lines, as well as the arrangement of mooring lines and the acceptable environmental conditions for mooring.

SECTIONS 3, 4 and 5:

These define that the goal of the Circular is the safety o operations and describe functional objectives such as minimizing obstructions and exposure of personnel to risks. Comprehensive design recommendations for an appropriate mooring arrangement are given in Paragraph 5. These are predominantly of a practical nature and relate to ship construction phase when the mooring system is designed. Please use the link to the full version of the Circular for the details.

Despite the generic approach of many of the points, there are a few clear references:

All components of a ship’s mooring system, within defined tolerances, should be selected based on MBLSD.

When selecting mooring lines, the Line Design Break Force (LDBF) should be 100% to 105% of the MBLSD;

SECTION 6 (Documentation on deviation) is important as it establishes:

A supplement to the “Towing and mooring arrangements plan” should record the deviations if any, in relation to the following paragraphs:

  • .1 5.1.2 (where a straight lead is not possible);
  • .2 5.1.4 (unobstructed views);
  • .3 5.1.5 (protection of winch operators);
  • .4 5.1.8 (access to mooring equipment and fitting);
  • .5 5.1.9 (exposure of the shipboard personnel to lines under tension); and
  • .6 5.1.11 (minimize the need for manual handling of towing and mooring lines)

The documentation should include justification for such deviations and suitable safety measures, if any.

A reference to the supplement should be included in the towing and mooring arrangement plan so as to make the shipboard personnel aware of the safety measures which need to be considered during mooring operations.

Circular MSC.1/Circ.1175/Rev.1 of 9 December 2020

(Guidelines for inspection and maintenance of mooring equipment including lines)

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The Circular provides standards for the design and construction of shipboard fittings and supporting hull structures associated with normal towing and mooring operations in harbours or sheltered waters, which Administrations are recommended to implement. This circular also contains design guidance for fittings of ships that are further intended to be towed by another ship or tug, e.g. in an emergency.

This circular does not require tow lines nor mandate standards for mooring lines on board the ship; and is not applicable for services such as: Escort Towing, Canal Transit Towing, and Emergency Towing for Tankers.

IMPORTANT: This revised guidance is applicable to ships constructed on or after 1 January 2024 and does not supersede the Guidance on shipboard towing and mooring equipment (MSC.1/Circ.1175) which remains applicable to ships constructed on or after 1 January 2007 but before 1 January 2024.

Below is some significant information extracted from the Circular. While the Circular applies to both Towing and Mooring equipment, in this presentation, we have focused on mooring equipment. The intention of our work is to assist the reader in navigating the various Resolutions and Circulars, understanding the main purpose of each document, and grasping the relevant points included within.

Please follow this link for access the the full content of MSC.1/Circ.1175/Rev.1.

DEFINITIONS:

  • Normal towing means towing necessary for normal ship manoeuvring.
  • Other towing means towing by another ship or tug, e.g. in case of emergency.
  • Shipboard fittings mean bollards and bitts, fairleads, pedestal rollers and chocks used for mooring of the ship and similar components used for normal or other towing of the ship.
  • Industry standard means international or national standards which are recognized in the country where the ship is built, subject to the approval of the Administration.
  • Safe working load (SWL) means the safe load limit of shipboard fittings used for mooring operations in harbours or similar sheltered waters.
  • Safe towing load (TOW) means the safe load limit of shipboard fittings used for normal and other towing.
  • 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.

Please note that the previous Guidance MSC.1/Circ.1175 of 2005 used the term ‘breaking strength of the mooring line.’ The current Guidance employs the term ‘Ship Design Minimum Breaking Load,’ which is also recommended by the MEG4 Guidelines.

MOORING

Load considerations:

The minimum design load applied to supporting hull structures should be:

  • For shipboard fittings: 1.15 times the ship design minimum breaking load of the mooring line provided in accordance with appendix A. (Note that it used to be 1.25 times the mooring line breaking strength in the previous Guidance).
  • For winches: 1.25 times the intended maximum brake holding load, where the maximum brake holding load should be assumed not less than 80% of the MBLSD of the mooring line according to Appendix A
  • For capstans: 1.25 times the maximum hauling-in force.

The design load applied to the fitting, should consider all possible directions in accordance with the towing and mooring plan.  When the acting force is a combination of two forces in different directions (e.g. a line turning around a bollard) the resultant force is to be considered, however, the design load applied to the fitting need not be more than twice the load calculated for a single line.

Shipboard fittings may be selected from industry standards accepted by the Administration and based, at least, on the ship design minimum breaking load of the mooring line.

Below sentence is highlighted as we understand it may lead to confusion:

The SWL, for the purpose of marking, should be equal to the ship minimum breaking load of the mooring line.

The SWL, in tonnes, of each shipboard fitting should be marked (by weld bead or equivalent) on the fittings intended for mooring. For fittings intended to be used for both mooring and towing, TOW, in tonnes, according to 3.6, should be marked in addition to SWL.

The above provisions on SWL apply for the use of no more than one mooring line.

Towing and mooring arrangements plan

The SWL and TOW for the intended use for each shipboard fitting should be noted in the towing and mooring arrangements plan available on board for the guidance of the master. It should be noted that TOW is the load limit for towing purposes and SWL is the load limit for mooring purposes.

Information provided in the plan should include, in respect of each shipboard fitting:

  • Location on the ship
  • Fitting type
  • SWL/TOW
  • Purpose (mooring, normal towing or other towing)
  • Method of applying load of towing or mooring line including limiting fleet angle, i.e. angle of change in direction of a line at the fitting.

Furthermore, information provided on the plan is to include:

  • The arrangement of mooring lines showing number of lines (N)
  • The ship design minimum breaking load of each mooring line (MBLSD)
  • The length of each mooring line
  • Restrictions or limitations on the type (including material and construction), stiffness, and diameter of mooring lines that are compatible with the mooring equipment and fittings
  • The acceptable environmental conditions as given in appendix A, Section 3, for the recommended ship design minimum breaking load of mooring lines for ships with Equipment Number EN > 2000.

Note: When the applied design environmental criteria exceed the above given criteria, information provided in the plan should include the design environmental criteria, similar to the parameters in appendix A.

  • Wind speed and direction
  • Current speed and direction

The next Section in the Circular is the Appendix A mentioned above.

At this point, let us provide a brief summary of the philosophy behind the current guidelines and their main points:

The approach to determining the design parameters of mooring equipment is still similar to the used in the previous Guidance MSC.1/Circ.1175 but there are some changes and additions that are supposed to improve the methodology.

Table 1 in the Appendix of the Circular, which provides the Ship Design Minimum Breaking Load (MBLSD), now includes a new column which shows the number of mooring lines. As indicated above, the new term “Ship Design Minimum Breaking Load” is now used. Said Table 1 applies to ships with EN <=2000.

For vessels with EN > 2000 a more detailed procedure is given, which is based on the typical arrangement of head line, two breast lines, two spring lines, and a stern line. The number of lines used, and their strength is based on the side-projected area of the ship. Detailed Instructions are provided on how to determine such area depending on the type of ship, presence of cargo on deck and other criteria.

Once the side-projected area A1 is determined, the value is entered in below formula to calculate the MBLSD in kN:

MBLSD = 0.1 A1 +350

However, above formula is valid for certain assumptions on maximum current speed (1 m/s) and maximum wind speed (variable values depending on type of ships and their side-projected area).

So, the way the Ship Design Minimum Breaking Load is calculated is different than the procedure used in the MEG4 guidelines. In fact, not only the approach (based on the Equipment Number and/or the side-projected area in this Circular is different, also the current and wind speed assumptions are different.

Furthermore, The Circular specifically mentions that:

Additional loads caused by, for example, higher wind or current speeds, cross currents, additional wave loads or reduced shielding from non-solid piers may need to be particularly considered. Furthermore, it should be observed that unbeneficial mooring layouts can considerably increase the loads on single mooring lines.

The Circular also states that the ship design minimum breaking load may be limited to 1,275 kN (130 t). However, in this case the moorings are to be considered as not sufficient for the assumed environmental conditions. Accordingly, a formula is provided to calculate the acceptable wind speed if such MBLSD is used.

Note: in no case should a MBLSD be adopted that would correspond to less than 21 m/s.

Then, a procedure is given to calculate the total number of head, breast and stern lines based on  the side-projected area.

For a spring lines, the minimum number is based on the Equipment Number: two lines where EN < 5,000 and four lines where EN ≥ 5,000.

In either case, the number of lines can be adjusted depending on the selected value for MBLSD.

In Appendix B, the formula to calculate the equipment Number is provided:

EN = ∆2/3 + 2.0 h B + A/10

  • ∆ = Moulded displacement in tonnes measured at the Summer Load Line.
  • B = Moulded breath in meters.
  • h = Effective height, in metres, from the Summer Load Waterline to the top of the uppermost house
  • a = vertical distance in meters from Summer Load Line to upperdeck
  • S = Side projected area.

Note: For a detailed definition of above parameters, please refer to the full Circular.

Circular MSC.1/Circ.1620 of 24 Dec 2020

(Guidelines for Inspection and Maintenance of Mooring equipment, including lines)

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The guidelines outlined in this Circular offer recommendations and guidance for the maintenance and in-service inspections of mooring equipment, including lines and tails, along with criteria for identifying worn-out components for removal from service and the selection of suitable replacements.

Below is a summary of the main points. Click here for the full content of the Circular

General:

These guidelines apply universally to all ships, with specific provisions intended for shipboard personnel and others for Company personnel responsible for procuring replacement mooring lines.

Definitions:

Key definitions include Bend radius (D/d ratio), Line Design Break Force (LDBF), Mooring arrangement, Mooring boat, Mooring equipment and fittings, Mooring line configuration, and Ship Design Minimum Breaking Load (MBLSD).

Safe use of mooring equipment:

Emphasizes the need for maintaining and operating mooring equipment according to its original design concept, including proper procedures for mooring operations, inspection, and maintenance. Practices for protecting and storing mooring lines are outlined, along with procedures for controlling mooring lines and reporting defects.

Inspection and maintenance of mooring lines:

Details the requirements for periodic inspection of mooring lines, mooring line tails, and associated attachments to prevent deterioration. Maintenance procedures should specify replacement of in-service mooring lines and include criteria for condemning worn-out mooring lines.

Inspection and maintenance of equipment and fittings:

Highlights the importance of properly inspecting and maintaining mooring equipment and fittings based on manufacturer recommendations, with records of inspection and maintenance being kept on board.

Selection of replacement mooring lines:

Stresses the importance of selecting replacement mooring lines compatible with onboard mooring equipment and fittings, considering factors such as breaking strength, environmental conditions, and D/d ratios. Any increase in Line Design Break Force (LDBF) above specified limits may require a review of operating parameters and load limits.

Updating of ship documents and record-keeping:

Underlines the need to retain records of inspection and maintenance of mooring equipment, inspection, and replacement of mooring lines on board, along with considerations for controlling and certifying mooring lines, wires, tails, and associated attachments.

By adhering to these guidelines, ship operators can ensure the safe and efficient use of mooring equipment while maintaining compliance with regulatory requirements.

Circular MSC.1/Circ.1362/Rev.2 of 14 July 2023

(UNIFIED INTERPRETATION)

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This Circular revokes MSC.1/Circ.1362/Rev.1 and includes clarification related to the documentation which is necessary to support an Administration or a recognized organization (RO) in verifying compliance with SOLAS regulation II-1/3-8.

Click here for the full version of the MSC.1/Circ.1362/Rev.2

Below is a summary of the most significant points in the Circular:

Owners and designers should comply with:

– MSC.1/Circ.1175/Rev.1
– MSC.1/Circ.1619
– MSC.1/Circ.1620

For ships of less than 3000 GT:

It is recommended that the Towing Arrangement Plan is provided for reference with information on the winch brake holding capacities in addition to the information required as per annex to MSC.1/Circ.1175/Rev.1.

A technical specification document of the mooring lines supplied with the ship should be provided which should include the manufacturers’ recommended minimum diameter D of each fitting and the Line Design Break Force (LDBF) of the mooring lines.

The properties of mooring lines related to LDBF and bend radius (D/d ratio) should be submitted to the Administration or the RO. A warning should be provided that the wear rate of lines may be higher for lower diameter (paragraph 5.6 of MSC.1/Circ.1620).

At delivery of the ship, the Administration or the RO should confirm that the towing and mooring arrangements plan is provided on board.

For ships of 3,000 gross tonnage and above, the following is recommended in addition to those above:

The designer to supply a supplement to the towing and mooring arrangements plan, confirming that MSC.1/Circ.1619 has been considered and that the deviations incurred, if any, were unavoidable.

Deviations should be recorded. Justification and suitable safety measures should be provided in the supplement to the towing and mooring arrangements plan. A reference to the supplement should be included in the towing and mooring arrangements plan.

If deviations are not found necessary, and the supplement is not needed, then this should be mentioned explicitly in the towing and mooring arrangements plan.

The mooring winchesʹ brake holding capacities should be less than 100% of the MBLSD. The winches should be fitted with brakes that allow for rendering at a safe load.

At delivery of the ship, the Administration or the RO should confirm that the towing and mooring arrangements plan and the supplement describing deviations and suitable safety measures is provided on board.

Interpretation

1    The expression “all ships” in SOLAS regulation II-1/3-8.9 means ships constructed before, on, or after 1 January 2009 in accordance with SOLAS regulation II-1/1.3.3II-1/1.1.3.2.

2    Irrespective of the scope of review by the Administration or a recognized organization (RO), as clarified below, for ships covered by the application provisions described in SOLAS regulations II-1/3-8.1 and II-1/3-8.2, as amended by resolution MSC.474(102), owners and designers should comply with the:

2.1 Revised guidance on shipboard towing and mooring equipment (MSC.1/Circ.1175/Rev.1);

2.2 Guidelines on the design of mooring arrangements and the selection of appropriate mooring equipment and fittings for safe mooring (MSC.1/Circ.1619); and

2.3 Guidelines for inspection and maintenance of mooring equipment including lines (MSC.1/Circ.1620), footnoted in SOLAS regulation II-1/3-8, in its entirety, and ensure that appropriate measures are taken to mitigate any occupational risks arising from deviations.

3    While applying the requirements of SOLAS regulation II-1/3-8.4 to regulation II-1/3-8.6 and SOLAS regulation II-1/3-8.8, for ships of less than 3,000 gross tonnage, the following is recommended:

3.1 The “Towing and mooring arrangements plan” should be provided for information, where the winch brake holding capacities should be included in addition to the information provided in section 5 (Towing and mooring arrangements plan) of the annex to MSC.1/Circ.1175/Rev.1. A technical specification document of the mooring lines supplied with the ship should be provided for information. The manufacturers’ recommended minimum diameter D of each fitting in contact with the mooring lines and the Line Design Break Force (LDBF) of the mooring lines should be included in the document.

3.2 For confirmation of the appropriate selection of mooring line, the properties of mooring lines related to LDBF and bend radius (D/d ratio) should be submitted to the Administration or the RO. A warning should be provided that the wear rate of lines may be higher for lower diameter (paragraph 5.6 of MSC.1/Circ.1620); and

3.3 At delivery of the ship, the Administration or the RO should confirm that the towing and mooring arrangements plan is provided on board.

4    While applying the requirements of SOLAS regulation II-1/3-8.4 to regulation II-1/3-8.6 and the SOLAS regulation II-1/3-8.7, for ships of 3,000 gross tonnage and above, the following is recommended in addition to those specified under paragraph 3 of this interpretation:

4.1 A document should be provided by the designer for information and as a supplement to the towing and mooring arrangements plan, confirming that MSC.1/Circ.1619 has been considered. The document should explicitly state that the deviations, if any, were unavoidable;

4.2 Deviations should be recorded (paragraph 6.1 of MSC.1/Circ.1619), justification and suitable safety measures should be provided (paragraph 6.2 of MSC.1/Circ.1619) in the supplement to the towing and mooring arrangements plan. A reference to the supplement should be included in the towing and mooring arrangements plan (paragraph 6.3 of MSC.1/Circ.1619);

4.3 If deviations are not found necessary, and the supplement is not needed, then this should be mentioned explicitly in the towing and mooring arrangements plan;

4.4 The mooring winchesʹ brake holding capacities should be less than 100% of the Ship Design Minimum Breaking Load (MBLSD) (paragraphs 5.2.3.3 and 5.2.4 of MSC.1/Circ.1619). The winches should be fitted with brakes that allow for the reliable setting of the brake rendering load; and

4.5 At delivery of the ship, the Administration or the RO should confirm that the towing and mooring arrangements plan and the supplement describing deviations and suitable safety measures is provided on board.

5    While applying the requirements of SOLAS regulation II-1/3-8.9, the following should be complied with, and compliance should be confirmed by the surveyor at the initial survey for new ships or at the first annual survey for the issuance of the Cargo Ship Safety Construction Certificate or renewal survey for the issuance of the Passenger Ship Safety Certificate after 1 January 2024 for existing ships:

5.1 Procedures for mooring operations, inspection and maintenance of mooring equipment, including mooring lines, should be established and available on board (paragraph 3.1 of MSC.1/Circ.1620), taking into account industry practices (section 7 of MSC.1/Circ.1620);

5.2 Procedures to allow the identification and control of mooring lines, tails and associated attachments should be established and available on board (paragraph 3.3 of MSC.1/Circ.1620); MSC.1/Circ.1362/Rev.2 Annex, page 4

5.3 The periodic inspection of mooring lines, mooring line tails and associated attachments should be included in the onboard maintenance plan or equivalent maintenance management system (paragraph 4.1.1 of MSC.1/Circ.1620);

5.4 Manufacturersʹ criteria for replacement of mooring lines should be available (paragraph 4.3.1 of MSC.1/Circ.1620);

5.5 Records of the original design concept, equipment, arrangements and specifications should be available on board (paragraph 4.4.4 of MSC.1/Circ.1620). For ships the keels of which were laid before 1 January 2007 and without appropriate documentation, owners may establish the MBLSD for mooring based on the safe working load of mooring equipment provided on board. If no safe working load is specified, then owners are advised to check strength of mooring equipment and their supporting hull structure based on MSC.1/Circ.1175/Rev.1 and determine MBLSD based on actual capacity of the equipment and their supporting hull structure on board. Manufacturers’ test certificates for mooring lines, joining shackles and synthetic tails should be kept on board and properly linked back to the equipment, if available (paragraph 6.2 of MSC.1/Circ.1620); and

5.6 A document should be provided on board for gathering the information above and describe how the information listed above is filed and collected.

6    While applying the requirements of SOLAS regulation II-1/3-8.9, the following should be complied with, and the compliance should be confirmed by the surveyor at the periodical survey for endorsement/issue of the Cargo Ship Safety Construction Certificate or the renewal survey for the Passenger Ship Safety Certificate after 1 January 2024 for existing ships:

6.1 The records of inspection and maintenance of mooring equipment and inspection and replacement of mooring lines, since the last periodical survey, should be kept updated and available on board (paragraphs 4.4.3 and 6.1 of MSC.1/Circ.1620).

MOORING REQUIREMENTS OVERVIEW TABLE

Below table is based on the UNIFIED INTERPRETATION outlined in MSC.1/Circ.1362/Rev.2.

Owners and designers should comply with the Guidance MSC Circulars in blue (3rd Column) in its entirety and ensure that appropriate measures are taken to mitigate any occupational risks arising from deviations.

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Unified Resolution UR A2 Rev.2 actually applies to ships contracted for construction from 1 January 2007. There are further revisions that apply to different years of construction. Please check with your Class.

Always double check with your Class Society on exact application dates of the regulations as the date may be based on keel laying, contract date or other milestones in the shipbuilding process. It is not the scope of this document to address this aspect.

CLASS REQUIREMENTS

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The green entries in the table above come from the IACS (International Association of Classification Societies). So, let us briefly describe what Unified Requirement and Unified Interpretations are:

IACS Unified Requirements

IACS Unified Requirements are the minimum class requirements shared among all IACS Member Societies. Unless an application date is specified, Unified Requirements are to be incorporated in the Rules and practices of each IACS Member Society within one year of their adoption by IACS.

IACS Unified Interpretations

IACS Unified Interpretations were created with a view to the uniform implementation of IMO conventions among all IACS Member Societies and provide interpretations of IMO Conventions which are vaguely worded or have been left to the satisfaction of each Administration.

The UR A2 deals with Shipboard fittings and supporting hull structures associated with towing and mooring on conventional ships.

The latest edition of the relevant UR for mooring equipment can be read using this link: UR A2 Rev.5.

Here is a short summary of URA2 using MSC.1/Circ.1175/Rev.1 as a reference for comparison:

The UR A2 covers aspects such as strength and arrangements of shipboard fittings, load considerations, fitting selection, supporting hull structure, SWL, and towing and mooring arrangement plan, which are similar to those points in MSC.1/Circ.1175/Rev.1.

In particular, below paragraphs are included in both documents with very similar wording:

“The minimum design load applied to supporting hull structures should be 1.15 times the ship design minimum breaking load of the mooring line.”

“The design load should be applied to fittings in all directions that may occur by taking into account the arrangement shown on the towing and mooring arrangements plan. Where the mooring line takes a turn at a fitting, the total design load applied to the fitting is equal to the resultant of the design loads acting on the line. However, in no case does the design load need to be more than twice the design load on the line.”

From above two paragraphs, we understand that there is a minimum design load for a shipboard fitting as 1.15 x the MBL the design load, although such design load could be higher depending on the geometry of the mooring line around or through the fitting and the value of the resultant force, up to a maximum of twice the design load on the line (which we understand is 1.15 x MBL).

The paragraph above refers to the “design load on the line” which, as far as we can see, has not been defined. There is a definition in the industry for Line Design Break Force (LDBF), but we do not think this is the intended meaning here. We understand that by “design load on the line”, they mean 1.15 x  MBLSD, which is the basic design load to be considered on the fitting when there is no combination of forces due to the angle of the mooring rope around the fitting.

So, what about the SWL? This is where things get even more confusing. Now we have different wording when we compare the Circular 1175. Rev.1 to the UR A2.

In the circular, we can read:

“The SWL, for the purpose of marking, should be equal to the ship design minimum breaking load of the mooring line according to appendix A.”

This means SWL for marking purposes = MBLSD. We understand, that for operational purposes, the SWL will depend on the actual design load for the fitting. In any case, it is very confusing. In the first pace the whole concept of SWL is adulterated. The figure that should be marked on the fitting does not really apply to the fitting…

Perhaps because of the potential confusion, the UR A2, in Section A2.2.3 introduces some additional text that cannot be found in the Circular:

“When a safe working load SWL greater than that determined according to A2.2.6 is requested by the applicant, then the design load is to be increased in accordance with the appropriate SWL/design load relationship given by A2.2.3 and A2.2.6.”

The relevant paragraph in section A2.2.6 reads:

“Unless a greater SWL is requested by the applicant according to A2.2.3 3), the SWL is not to exceed the ship design minimum breaking load …”

We understand that this new text was added as to enable a more realistic SWL marking on the fitting in those cases where the mooring rope angle causes a force on the fitting that is greater than the stress on the line. However, the wording is not clear enough in our humble opinion. Has there been a change in the approach? If so, it should be clearly stated.

In the SWL Section of UR A2, they define the SWL for the fitting as follows:

“The Safe Working Load (SWL) is the safe load limit of shipboard fittings used for mooring purpose.”

And next paragraph reads:

“Unless a greater SWL is requested by the applicant according to A2.2.3 3), the SWL is not to exceed the ship design minimum breaking load…”

So, above we see a definition of SWL that refers to the physical limits of the fitting and drops the phrase “for marking purposes”. We understand that the correct SWL (meaning a SWL that applies to the fitting based on the resultant forces applied on it and considering a safety margin) can now be marked if the applicant requests to use a SWL value greater than the MBLSD.

There are other differences between the Circular and the UR A2:

  • When dealing with the design criteria for shipboard mooring fittings, The UR A2 includes subsections for Corrosion addition, Wear allowance, and Survey after Construction, which certainly are meaningful, especially for professionals involved in the design and construction of the ship.
  • The UR A2 does not include the info and table in the Appendix A for determination of the number of mooring lines, the guidance on mooring layout, calculation of MBLSD nor the method to calculate the Equipment Number in Appendix B of the MSC.1/Circ.1175/Rev.1
  • However, the UR A2 includes references to IACS Recommendation No. 10 “Anchoring, Mooring and Towing Equipment”. In Section 2, Recommendation 10 includes guidance as in MSC.1/Circ.1175/Rev.1 which was missing in the UR R2.
  • The criteria for establishing the MBLSD and the minimum recommended number of mooring lines for ships with EN (Equipment Number) <= 2000 is the same in both documents. Having said that, the Recommendation 10 includes info on the minimum length of the mooring lines that cannot be found in the MSC.1/Circ.1175/Rev.1.
  • The criteria for establishing the MBLSD and the minimum recommended number of mooring lines for ships with EN (Equipment Number) > 2000 uses the same formulas in either case, however, the parameter A1, is defined in a slightly different way. The A1 parameter is used to calculate the MBLSD and the maximum wind speed assumed. For oil tankers, chemical tankers, bulk carriers and ore carriers, the ballast draft is used to calculate A1, in both documents, however, for other type of vessels the definition of A1 is different.

COMPARISON TO MEG4

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The Maritime Guidelines on Mooring Equipment issued by OCIMF are aimed primarily at tankers, gas carriers and oil and gas terminals. In any case, they have traditionally been a widely recognized industry standard. The latest edition of these guidelines, issued in July 2018, is number 4, hence the name MEG4.

The Aim of MEG4 is to minimise the risk of failure of mooring lines and all other mooring components and their recommendations were intended as additional to the minimum requirements set forth by the IACS, in a sector going through changes in the design of terminals, ships and mooring lines, with increasing safety concerns related to mooring operations.

MEG4 is applicable to ships built after its publication. For other vessels, the OCIMF advises as follows:

“If new build ships under construction or existing ships are unable to follow the recommendation of this publication, they should, as a minimum, develop a Mooring System Management Plan (MSMP) and a Line Management Plan (LMP) that will:

  • Remain on the ship throughout its life as part of the management of change records.
  • Identify a timeline and measures needed to follow the recommendations of this publication.
  • Detail interim measures taken to address the recommendations in this publication, with reasons given for why the changes have not been implemented yet.

Additionally, Section 3.3 and 3.4 provide guidance on factors to be considered for calculating Ship Design MBL with a simple process flow diagram in figure 3.2 (page 54).”

Once the IMO issued new regulations, those who were adhering to MEG4 might wonder what the differences are between MEG4 and the new rules.

In its 4th edition, MEG had already addressed some new areas as compared to previous editions:

  • Update in terminology
  • Improved guidance on management of mooring lines, from purchasing to retirement
  • Improved guidance on documentation for mooring equipment
  • New chapter on human factor
  • New chapter on Jetty design
  • New chapter on Ship-Shore interface
  • New Chapter on alternative technologies
  • Mooring System Management Plan (MSMP).
  • Line Management Plan (LMP).
  • Some technical design aspects such as updated wind and drag coefficients.

Regarding terminology, MEG4 clarifies the Minimum Breaking Load concept and its acronym MBL, which was being used in an inconsistent way at times, and recommends the term Ship Design Minimum Breaking Load (MBLSD) instead.

Definitions and important parameters.

Ship Design Minimum Breaking Load (MBLSD) is defined as

Line Design Breaking Force (LDBF) is defined in MEG4 as the minimum force that a new, dry, spliced mooring line will break at when tested according to the specified standards. For nylon ropes, which are tested wet, the manufacturer states the LDBF on the mooring rope certificate.

Working Load Limit (WLL) of a mooring line is defined as the maximum load that the mooring line should be subjected to during regular operations.

MEG4 highlights the importance of the MBLSD as the reference value from which others important parameters are determined. For example:

LDBF is to be in the range 100% – 105%                         of Ship Design MBL
Brake design load of a winch is to be 80%                     of Ship Design MBL
WLL for cordage ropes is to be 50%                                of Ship Design MBL
WLL for steel wire ropes is to be 55%                             of Ship Design MBL
Brake release adjustment is to be 60%                          of Ship Design MBL
Winch pulling force:  22% -33%                                        of Ship Design MBL

Some important requirements included with MEG4

When it comes to implementation of OCIMF MEG4 onboard, ship operators must comply with the following requirements:

  • The manufacturer certificates for mooring lines, shackles, and synthetic tails must be kept on board the vessel. Additionally, there should be a clear indication specifying which components have been installed on each piece of equipment.
  • A Mooring Ship Management Plan (MSMP) should be used and kept on board each ship, which should address the risks associated with the mooring operation. The MSMP can be made specific to each ship or applicable to the ships under a Company management and integrated in the SMS.
    The MSMP will consist of:
    • Part A    General ship particulars;
    • Part B    Mooring equipment design philosophy;
    • Part C    Detailed list of mooring equipment;
    • Part D    Inspection, maintenance and retirement strategies;
    • Part E    Risk and change management, safety or personnel and human factors;
    • Part F    Records and documentation;
    • Part G   Mooring System Management Plan Register (MSMPR)
    • MEG4 also recommends that onboard mooring equipment and fittings, including mooring lines, are identified as critical equipment or systems.
    • A Line Management Plan (LMP) should be implemented on each ship with procedures for line maintenance, inspection, and retirement based on manufacturer’s guidance and operational experience. The LMP can be a separate plan or may be integrated into existing safety or maintenance management systems; in any case, it should be a controlled document, subject to change management procedures. The LMP is specific to an operator, ship type, and should address each specific line onboard (e.g. should include mooring hours, test reports, and inspection records for each mooring line or tail). It should also be updatable and accessible for use, consultation, or ship inspection purposes.

Comparison considerations

When comparing MEG4 and the new IMO regulations, there are no significant discrepancies when it comes to documentation and operational requirements. All the requirements by IMO that came into effect on 01 Jan 2024 are met by just following MEG4, with perhaps some minor adjustments in the MSMP or LMP.

When comparing construction and design requirements, however, we observe a more distinct approach which relates to the way the Ship Design Minimum Breaking Load (MBLSD) is determined.

While, as we have seen above, IMO regulations determine the MBLSD from the so-called EN, which, in turn, depends on the ship side projected area and other geometrical factors. Classification Societies and their umbrella organization IACS use also the EN as the base parameter from whchi they calculate MBLSD.

On the other hand, OCIMF advises that MEG4 guidelines, which are to be considered as additional to minimum requirements by IACS, use a different approach based on dynamic analysis of the forces acting on the ship under the so-called OCIMF Environmental Criteria for mooring restraint requirements.

While it is not the scope of this article to get into the details of the procedure to determine the MBLSD as per MEG4, we can comment that a first step is to determine the forces acting on a vessel at a terminal or mooring location. MEG4, call it calculating the mooring restraint requirements. As an example, the wind speed assumed under the OCIMF Environmental Criteria is 60 knots. There are assumptions regarding the angle of the wind force, the current speed, etc. Clearly, the environmental criteria assumed by OCIMF is different than the described in the IMO regulations, so is the procedure itself.

Summarizing, irrespective of the details of the calculation procedures, the relevant point is that there are two different standards to determine an important reference parameter on which the whole mooring system is designed. Probably, the values obtained by using the two different methods do not vary significantly, however, there is an inconvenient redundancy in that professionals involved in the design of a mooring system will probably have to try both methods and then choose to apply the one demanding a greater MBLSD. Otherwise, the shipbuilder might be questioned as to why they do not comply with the minimum MBLSD value of the method they have not used.

  • Continued efforts persist in improving the safety of mooring operations (and maritime shipping in general) through new and updated requirements and regulations set forth by OCIMF, IMO, and IACS (Classification Societies), which are commendable and necessary.
  • The new SOLAS regulations that took effect on 1 January 2024 necessitate greater efforts for ship managers regarding the documented management of mooring equipment. For instance, they must establish documented procedures for mooring operations, inspection, and maintenance of mooring equipment, including mooring lines, as well as procedures for the identification and control of mooring lines.
  • In offering constructive feedback on the clarity with which certain concepts are addressed, we have identified an area of ambiguity concerning SWL markings on mooring fittings.
  • In our view, the multitude of regulations, guidance Circulars, and recommendations do not enhance the clarity of the subject matter. The abundance of references, sometimes with cross-references, renders the texts challenging to comprehend for individuals not accustomed to legal language.
  • An important parameter such as the MBLSD has two different calculation methods in the industry, prompting questions regarding whether this discrepancy is inevitable or if the relevant industry organizations can take additional steps – perhaps by improving collaboration among themselves – to ensure consistency and clarity

Meet the Author

Hello all, my name is Pablo, a former Chief Engineer at Sea, with extensive experience ashore as well, including roles like Superintendent Engineer and Technical Manager.

In my free time, I enjoy crafting posts for this Blogs section. Your comments and thoughts on the topics discussed, or even on the puzzles, are greatly appreciated.

I'm married and a proud father to a little daughter. She keeps me grounded and reminds me of life's true treasures.

Join me as we delve into the depths of maritime expertise. Smooth sailing ahead!