proceed to the next step. In the worst case, when no suit- able set-up can be found with the initial parameters, then an overall design change of the rigging could be required (red box ‘Revise rigging’).
New guidance on achieving stable lifting operations
FIGURE 1.1 Stable primary suspensions
November 2024
GUIDANCE ON STABILITY OF LIFTS
Heavy Lift Exchange Forum
Abbreviations and Definitions Primary and secondary suspension
Step 3 – Is the CoG above the lifting points? If the CoG is positioned below the lifting points the lift is generally considered stable. The user could then proceed to the next step. But when the CoG is located above the lifting points then the lift can potentially become unstable. This is the case when the CoG is positioned outside the primary suspension and the system cannot find an upright equilibrium state when the lifting operation commences. For more complex configurations with multiple suspensions – i.e. when beams or spreader bars are used – the stability of the arrangement becomes even more complex and requires a careful analysis.
3.1 Assess stability of the lift Various methods are available to assess the stability of a lift arrangement. An overview and comparison of methods that are widely used in the industry is elaborated in the next section. These methods have in common that the stability of a lift is expressed by a metacentric height, analogous to the GM in evaluating stability of ships. This metacentric height is the vertical distance between the (virtual) CoG of the cargo and the suspension point of the lift – typically the crane hook.
The methods presented here are:
• Visual check of virtual CoG • Kaps method • Nikitin method • Numerical computer simulations
arrangement, eventually resulting in a potentially unstable condition. Relevant parameters for the operation could be quantified, with the results documented in the operational procedure.
Guidance on stability of lifts
Guidance on Stability of Lifts has been developed by a sub-working group of the Heavy Lift Exchange Forum, a DNV-initiated round table for heavy-lift shipping companies. Members of the working group are from the companies BBC Chartering, BigLift Shipping, DNV, Heerema, Jumbo Maritime, SAL Engineering and United Heavy Lift.
Possible limits to be set:
What is best practice when it comes to cranes lifting loads onto, off and between ships in port or at sea? New guidance from an industry forum initiated by DNV dives into the key considerations and calculations to help ensure these hazardous operations are performed safely to reduce the risk of loss to life, property and the environment.
• CoG envelope • Tilt limits • Maximum wind speeds • Tugger arrangement and loads • Maximum wave height, period and heading • Crane motions • Temperature and visibility
“The paper Guidance on Stability of Lifts plugs a gap among the many guidance documents available for operations in the maritime sphere,” says Karsten Behrens, Managing Director of SAL Engineering GmbH. “It enables readers to assess the stability of particular lifting arrangements by using the provided methods and data. This puts them in the position to achieve a ‘stable lift’, which is one that remains in a balanced condition, within a safe margin, when subjected to predefined disturbing factors.”
Step 5 – Preparing final rigging plan The rigging plan, complying with the selected criteria, will be finalized and added to the operational procedure.
What is in Guidance on Stability of Lifts?
The paper explains currently available calculation
Where applicable, the stability of the lift must be assessed in both longitudinal and transversal plane, e.g. in a configuration with a lifting beam and 2 spreaders, where 2 triangles are created in perpendicular planes.
Definition of rigging components and geometry (Kaps 2013 ) GUIDANCE
methods, along with relevant explanations, guidance for assumptions on loads and factors, and background information.
Potentially unstable primary/secondary suspension arrangement
Transverse centre of suspension
Virtual centre of gravity
Transverse metacentric height
FIGURE 1.2 Potentially unstable primary/secondary suspension arrangement
Level of centre of gravity (CoG)
Level of lifting points
4.1 Sufficient workable range A final check shall be performed to determine if a suffi- ciently large workable range is obtained for safe execution of the lifting operation. In case the operational range is deemed unsatisfactory, the rigging plan should be revised (red box ‘Revise rigging’).
Ensuring the stability of lifting arrangements is of critical importance to mitigate the risk of damage.
The core of the paper is a flow chart for assessing the lifting stability of a rigging arrangement, which also reflects the common workflows of the participating project partners.
9
Primary suspension
Longitudinal centre of suspension
Secondary suspension
Longitudinal metacentric height
Centre of gravity
“The paper also helps the user to identify important factors for assessing the lifting stability and potentially dangerous combinations of them,” Behrens states.
62 | ISSUE 111 | MAR 2025 | THE REPORT
Following step-by-step guidance
In an easy-to-follow systematic approach, the guidance then works through details clarifying steps from the flow chart...
5
Source: Guidance on Stability of Lifts Guidance, Heavy Lift Exchange Forum, 2024
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