Guidelines for safe mooring
Mooring operations have always been associated with significant risks, and accidents in this area can have severe consequences. This was the key driver behind the new SOLAS II-1/3–8 requirements related to mooring issued by the IMO. These guidelines aim to provide comprehensive recommendations and guidance for the maintenance and inspection of mooring equipment, encompassing both mooring lines and tails.
In addition, OCIMF MEG4 introduces even more detailed and in parts stricter recommendations, particularly for tankers and terminals in the hydrocarbon and chemical sector. As a result, operators are often faced with the question: which guidelines apply to my vessel – and what does that actually mean for the design and operation of my mooring system?
They advocate for a holistic approach, outlining criteria for identifying worn-out lines and tails that should be removed from service before any potential failure occurs. Additionally, they offer criteria for selecting replacement mooring lines and tails, ensuring a thorough and effective approach to maintaining safety and functionality. In the following pages, we summarise the key points and show how they translate into practical dimensioning of MBL, D/d ratio and other essential parameters.
Overview about guidelines
| Ship relevant details | Relevant Circulars | |
| Ships built on/after January 2007 | Regarding construction | MSC.1/1175 Rev.1 Guidelines on shipboard towing and mooring equipment |
| Ships built on/after January 2024 | Regarding construction | MSC.1/1175 Rev.1 and MSC.1/1619 Guidelines on the design of mooring arrangements and the selection of appropriate mooring equipment and fittings for safe mooring |
| All vessels in operation after January 2024 | Regarding inspection and maintenance | MSC.1/1620 Guidelines for inspection and maintenance of mooring equipment including lines |
| All oil and gas tankers and terminals | Regarding design of terminals and ships, design of mooring line and equipment technology | OCIMF Mooring Equipment Guidelines (MEG4), 4th Edition The mooring equipment guideline focuses on the safety of terminal and ship personnel |
Certificates
Gleistein mooring solutions meet the highest safety standards and are supplied with all required certificates.
- Work Certificate 2.2* confirms that the ropes comply with the order specifications; the technical data provided is based on measured values of the respective constructions.
- Acceptance test certificate 3.1* additionally confirms the strength performance of the production batch by means of specific breaking load tests.
- Acceptance test certificate 3.2* requires the involvement of an independent inspection body to witness and confirm the specific breaking load tests.
- MEG4: In the safety-critical oil and gas sector, the most stringent requirements have been established. MEG4- certified mooring lines have passed extensive testing and verification.
* according to DIN EN 10204
Mooring system break load
Why a stronger main line can be beneficial
The mooring system break load is a ship-specific design value used to dimension the mooring system. It defines the window within which the line design break force (LDBF) of the ropes must lie: it should not be undershot and, according to OCIMF MEG4, should not be exceeded by more than a small margin. Within this overall system, the rope arrangement of main line, tail and connecting lashing forms one component with its own system breaking load.
In FLX-type mooring arrangements, MEG4 recommends that the tail be designed significantly stronger than the main line. This compensates for higher abrasion on the tail, but it also means that, in an overload situation, the long-life main line is likely to fail first – the most expensive part of the system, and the one that is hardest to replace. For vessels that are not required to comply with MEG4, there is no requirement for the tail to be stronger than the main line. As SOLAS does not define which rope component should be stronger or weaker, Gleistein recommends deliberately making the tail the weakest element in the rope system.
This configuration offers several advantages: in a failure scenario, the break is more likely to occur close to the quay edge, reducing the risk of uncontrolled snapback in the mooring station and on shore; tails can be replaced quickly and cost-effectively; and the stronger main line benefits from lower utilisation and thus an extended service life. Because all elements are connected in series, the rope system cannot transmit higher loads than the tail can withstand – the system breaking load remains within the prescribed range, while the main line gains robustness and longevity. As additional guidance, Gleistein recommends that the safe working load should not exceed 50% of LDBF and that the typical operational range of mooring lines should remain within 20–25% of their MBL. For detailed background information and test data, please refer to the technical statement accessible via the QR code.
Gleistein recommendations
- SWL ropes: 50% of LDBFSD
- Operational range of mooring lines for long service life should not exceed 20–25 % of MBLSD2
1 Norm: MSC.1/Circ 1619; 2 Gleistein reccomendations
D/d ratio
Realistic guidance based on testing
OCIMF MEG4 recommends a D/d ratio of at least 15 for HM mooring lines. In practice, however, this is almost never achievable across all fairleads, rollers and bitts on board – simply because the space required for such large bending radii is not available on existing vessels. SOLAS MSC.1/Circ. 1619 therefore does not specify a fixed D/d value, but requires that the D/d ratio be taken into account when selecting mooring lines in order to limit bending-related strength losses.
To understand what this means in real applications, Gleistein has carried out Angled Break Force (ABF) and Angled Endurance (AE) tests on representative FlexTwin and X-Twin main lines at D/d ratios of 5 and 10, based on the MEG4 test requirements. The results show that, for these rope designs, increasing the D/d ratio beyond 5 does not lead to a relevant improvement in residual strength under the tested conditions – the performance at D/d 5 is essentially comparable to that at D/d 10.
In other words: for these lines, a D/d ratio of 5 already provides the performance needed for safe use within the specified operating range. For detailed background information and test data, please refer to the technical statement accessible via the QR code.
Gleistein recommendations
- Please try to select the D/d ratio as large as possible for your rope.
- If this is not feasible, let us review the options together and choose the most suitable rope.
Exclusiv für Gleistein-Kunden
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