Start hereRules checked 20 October 2026
When a mooring line parts under load, it recoils along and beyond its own line of tension, faster than anyone can move. Mooring is one of the most dangerous routine jobs on deck, and IMO’s own guidance now asks for every mooring area to be treated as a potential snap-back zone.
Lines rarely fail without warning. They wear, chafe, fuse, age in the sun and are overloaded by brakes set too tight or by fittings that are too weak for them. Since 1 January 2024 SOLAS regulation II-1/3-8 requires every ship, new or old, to inspect and maintain its mooring equipment, including the lines, in a suitable condition, with IMO guidelines that describe how.
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In this lesson
- The new mooring lines arrive
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
Try it
The new mooring lines arrive
In plain words
The ship’s fittings (bollards, fairleads, chocks), winches and the steel under them were designed for lines of one particular strength. That number is the ship design minimum breaking load (MBLSD), and it should be on the ship’s towing and mooring arrangements plan.
Mooring line management means three things:
- Know your lines. Every line, tail and joining shackle has an identity, a certificate, a position on the ship and a history.
- Inspect and retire them in time. Lines are inspected regularly as the maker describes, and taken out of service before they fail, not after.
- Replace like with like. A new line should be as strong as the design (100% to 105% of MBLSD), not weaker and not much stronger, and suited to the ship’s fittings and winches.
In detail
The rule and its guidelines
SOLAS regulation II-1/3-8 was rewritten by resolution MSC.474(102). It entered into force on 1 January 2024:
| Paragraph | Applies to | Requirement |
|---|---|---|
| 4 to 6 | Ships constructed on or after 1 January 2007 | Arrangements, equipment and fittings of sufficient SWL, meeting the Administration’s or RO’s requirements, each marked with its limitations |
| 7 | Ships of 3,000 GT and above, contracted on or after 1 January 2024 (or keel laid from 1 July 2024, or delivered from 1 January 2027) | Mooring arrangement designed, and equipment including lines selected, for occupational safety and safe mooring, based on IMO guidelines; ship-specific information kept on board |
| 8 | Same new ships below 3,000 GT | Paragraph 7 as far as reasonably practicable, or national standards |
| 9 | All ships | Mooring equipment, including lines, inspected and maintained in a suitable condition |
The three IMO texts behind it:
- MSC.1/Circ.1175/Rev.1, revised guidance on shipboard towing and mooring equipment: design loads, SWL marking and the towing and mooring arrangements plan.
- MSC.1/Circ.1619, design of mooring arrangements and selection of equipment (new ships).
- MSC.1/Circ.1620, inspection and maintenance of mooring equipment including lines (all ships).
The numbers that link lines and fittings
The fitting and structure figures below come from MSC.1/Circ.1175/Rev.1, which applies to ships constructed on or after 1 January 2024. Ships constructed from 1 January 2007 to the end of 2023 follow the original MSC.1/Circ.1175, so always check your own ship’s towing and mooring arrangements plan.
- The SWL of each mooring fitting, for marking, equals the MBLSD, and is marked in tonnes by weld bead or equivalent. Fittings used for towing also show TOW.
- Hull supporting structure for fittings is designed for 1.15 × MBLSD. For winches it is 1.25 × the maximum brake holding load, where that load is assumed to be at least 80% of MBLSD.
- Lines are selected with an LDBF of 100% to 105% of MBLSD.
- The working load limit (WLL) used in mooring analyses is 55% of MBLSD for steel wire and 50% for synthetic lines.
- Winches should have brake capacity below the MBLSD, or adjustable brake capacity, so the brake renders before the line breaks.
What a line management system contains
Under MSC.1/Circ.1620, the company sets procedures for mooring operations, inspection and maintenance. In practice the documents on board are:
- Identification and control: a record of the number, type and location of lines, tails and attachments, each linked to its records and the maker’s certificate.
- Inspection: periodic inspection of lines, tails and attachments in the planned maintenance system, based on the maker’s criteria, operational experience and environmental exposure. Look for external abrasion, cuts, kinks, heat damage and fusion, and slackening or fraying of eye splices. For jacketed lines, the jacket’s condition does not tell you the condition of the core.
- Retirement: criteria from the maker, so lines are removed before failure. Rotation between drums to even out wear may be part of the maintenance.
- Equipment and fittings: inspected and maintained per the makers, in the maintenance plan, with SWL markings and winch control instructions kept legible.
- Storage: loose lines kept away from UV light, water, chemicals, cargo and extreme temperatures.
- Records: inspection, maintenance and replacement records kept for a period the company sets, but at least until the next annual survey. Original design records kept for the life of the ship.
- Change control: any change of line configuration means updating the towing and mooring arrangements plan.
Selecting replacement lines
Match the designed specification. If that is not possible, consider breaking strength, temperature range, linear density, tenacity, D/d ratios, compression fatigue and stiffness, and update the plan. For stiff lines (wire, high-modulus synthetic), synthetic tails reduce peak loads, but tails change how the line behaves when it fails and can increase snap-back. For wire, consider corrosion protection. Respect the maker’s minimum D/d (bend radius) ratio: lines regularly bent tighter will not reach their rated service life.
Older ships
For ships with a keel laid before 2007 and no design documentation, the owner may establish the MBLSD from the SWL of the existing equipment, or from a strength check of fittings and supporting structure using IACS UR A2 and IACS Recommendation No. 10.
What the rules say
- SOLAS regulation II-1/3-8.9 requires, for all ships, mooring equipment including lines to be inspected and maintained in a suitable condition for its intended purpose. 4
- SOLAS regulation II-1/3-8.7 requires ships of 3,000 GT and above to which it applies to have a mooring arrangement designed, and mooring equipment including lines selected, for occupational safety and safe mooring, based on IMO guidelines, with ship-specific information kept on board. 4
- MSC.1/Circ.1620 paragraphs 3.3.1 and 4.1.1 require procedures to identify and control lines, tails and attachments, and periodic inspection of them in the onboard maintenance plan. 1
- MSC.1/Circ.1620 paragraph 4.1.3 warns that the external jacket of a jacketed synthetic line is not an accurate indicator of the condition of the load-bearing fibre inside. 1
- MSC.1/Circ.1620 paragraph 4.3.1 says in-service lines assessed as no longer suitable should be removed before failure in accordance with the manufacturer’s criteria. 1
- MSC.1/Circ.1620 paragraph 5.2 says any increase in LDBF above 100% to 105% of MBLSD may require a review of the operating parameters and load limits of equipment, fittings and their supporting structure. 1
- MSC.1/Circ.1620 paragraph 6.1 requires inspection, maintenance and replacement records to be kept on board at least until the next annual survey, and paragraph 6.4 requires the towing and mooring arrangements plan to be updated for any change of line configuration. 1
- MSC.1/Circ.1619 paragraphs 5.2.4 and 5.2.8.4 recommend winch brake capacity below the MBLSD, or adjustable, and set the WLL at 55% of MBLSD for steel wire and 50% for synthetic lines. 2
- MSC.1/Circ.1619 paragraph 5.1.10 says mooring areas should be considered potential snap-back zones, with signage to that effect. 2
- MSC.1/Circ.1175/Rev.1, which applies to ships constructed on or after 1 January 2024, paragraph 4.6 sets the marked SWL of mooring fittings equal to the MBLSD, and paragraph 4.3.1 sets the design loads for supporting structure at 1.15 × MBLSD for fittings and 1.25 × the maximum brake holding load for winches. 3
Flag and class notes
- ABS confirms compliance with the all-ships requirements at the first annual safety construction survey after 1 January 2024 (or the renewal survey for passenger ships), checking documented procedures, line identification, the maintenance plan, records, the maker’s retirement criteria, design records and line certificates. 5
- DNV lists typical findings: no mooring procedure or inspection and maintenance plan on board, wrong winch brake settings, and replacement lines with a higher breaking load than designed. DNV offers a voluntary class notation for mooring compliance. 6
- Germany (Safety Bulletin 01-2021) asks crews to report defects in lines, stoppers, winches, brakes and controllers, and not to operate damaged equipment, and shipowners to apply MSC.1/Circ.1620. 7
Key numbers
| What | Value |
|---|---|
| SOLAS II-1/3-8 amendments in force | 1 January 2024 4 |
| Design and selection rule applies to | 3,000 GT and above, new ships 4 |
| LDBF of replacement lines | 100% to 105% of MBLSD 1 |
| WLL, steel wire | 55% of MBLSD 2 |
| WLL, synthetic lines | 50% of MBLSD 2 |
| Marked SWL of mooring fittings | Equal to MBLSD 3 |
| Design load, fitting support structure | 1.15 × MBLSD 3 |
| Assumed brake holding load for winch support design | At least 80% of MBLSD 3 |
| Records kept at least | Until the next annual survey 1 |
What inspectors find
- No mooring line inspection and maintenance procedure or plan on board, or lines not individually identified. 6
- Winch brakes set to hold more than the line can take, or not tested and set to the maker’s instructions. 6
- Replacement lines with a much higher breaking load than the MBLSD, and no update to the towing and mooring arrangements plan. 6
- Older ships where the MBL of lines does not match the equipment number tables, or the marked SWL of fittings is inconsistent with the line MBL. 6
- Line certificates on board but not traceable to the line in use. 5
FAQ
Does a ship built in 2010 need a mooring line management plan?
Yes. Paragraph 9 of SOLAS II-1/3-8 and MSC.1/Circ.1620 apply to all ships. The design paragraphs 7 and 8 only apply to new ships.
Where do I find the MBLSD?
On the towing and mooring arrangements plan. For older ships without one, the owner can establish it from the SWL of the equipment or by a strength check against IACS UR A2 and Recommendation No. 10.
Is OCIMF's Mooring Equipment Guidelines (MEG4) mandatory?
No, but MSC.1/Circ.1620 lists it as a reference, and it is the industry guidance most line management systems are built on, particularly in the tanker and gas trades.
Can we use tails on wire lines?
Yes, and Circ.1620 encourages synthetic tails on high-stiffness lines to reduce peak loads. Follow the maker’s guidance, because tails change the stored energy and snap-back behaviour of the line.
Quiz6 questions
Sources
- 1
IMO MSC.1/Circ.1620, Guidelines for inspection and maintenance of mooring equipment including lines (24 December 2020), Annex, sections 2 to 6. https://wwwcdn.imo.org/localresources/en/Documents/MSC.1-Circ.1620%20-.pdf
- 2
IMO MSC.1/Circ.1619, Guidelines on the design of mooring arrangements and the selection of appropriate mooring equipment and fittings for safe mooring (11 December 2020), Annex, sections 5 and 6. https://wwwcdn.imo.org/localresources/en/Documents/MSC.1-Circ.1619%20-.pdf
- 3
IMO MSC.1/Circ.1175/Rev.1, Revised guidance on shipboard towing and mooring equipment (9 December 2020), Annex, sections 4 and 5. https://wwwcdn.imo.org/localresources/en/Documents/MSC.1-Circ.1175-Rev.1.pdf
- 4
IMO Resolution MSC.474(102), amendments to SOLAS (adopted 11 November 2020, in force 1 January 2024), regulation II-1/3-8. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.474(102).pdf
- 5
ABS Regulatory News, Amendments to SOLAS: safe mooring of ships (December 2022), application and section C, all in-service ships. https://ww2.eagle.org/content/dam/eagle/regulatory-news/2023/Regulatory%20News%20-%20Safe%20mooring%20of%20ships.pdf
- 6
DNV, New SOLAS requirements for safe mooring (2022), typical findings. https://www.dnv.com/news/2022/new-solas-requirements-for-safe-mooring-229703/
- 7
German Flag (BG Verkehr), Safety Bulletin 01-2021, Safe mooring equipment. https://deutsche-flagge.de/de/redaktion/dokumente/ism-rundschreiben/circ2021_2_2_en.pdf/@@download/file/SB_2021-1_Safe%20Mooring%20Equipment.pdf
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
