FIGURE 6 Illustration of a numerical computer simulation in 2D Excerpt from the flow diagram
rigging plan, determine its suitability, and create a frame- work of boundary conditions. It should be noted that
FIGURE 2 Design approach for safe rigging arrangements
2.
FIGURE 6 Illustration of a numerical computer simulation in 2D
YES
dependent lifting points. Also the effect of the asymmetry of the lifting arrangement is visible.
Additional informa- tion about calcula- tion of sliding angles can be found on page 20.
2.1. Determine: • FDLP type • Friction factor • Sliding risk
The assessment of lifting arrangements with this method is time-consuming and requires specialised software tools (e.g. Orcaflex) and specific expertise. Its application is therefore only reasonable for lifting operations that are knowingly critical, and a high engineering effort is justified.
2.2
Sufficient friction? (In-house limit)
NO YES
The assessment of lifting arrangements with this method is time-consuming and requires specialised software tools (e.g. Orcaflex) and specific expertise. Its application is therefore only reasonable for lifting operations that are knowingly critical, and a high engineering effort is justified.
TABLE 1 Comparison of methods
Optional assessment: • In-house tools • Orcaflex • Others
Comparison of methods to assess stability in lifts (extract of table) Complexity
TABLE 1 Comparison of methods
Low Time effort Accuracy Approach
Optional: Monitoring of operational limits
Virtual CoG L w
concept
Low (but for most cases sufficient)
Graphical Range Complexity Time effort Accuracy
Initial stability only
Low Low
External forces Cannot be considered
Lifting points Range
‘fixed’ only
Low (but for most cases sufficient)
Initial stability only
External forces Cannot be considered
Lifting points ‘fixed’ only
Does not con- sider stabilising effect of lifting beam weight as well as sling angles of second- ary suspension.
*analytical assessment based on Kaps method theoretically possible but not developed yet (June 2024).
These methods are the Virtual CoG concept; the Kaps method, which is widely used in the maritime industry; the Nikitin method; and standard and extensive versions of numerical computer simulation methods. The applicability of these methods for various purposes is discussed. For example, Virtual CoG and Kaps allow users to evaluate the initial stability of the lift, Nikitin
Does not con- sider stabilising effect of lifting beam weight as well as sling angles of second- ary suspension.
Gives metacentric height for primary suspension, no info on range of stability. Only consid- ers symmetric arrangement.
Sufficient stability given?
NO Medium
Kaps method
Low YES Medium 5. Prepare final rigging plan Analytical
Excel-based solution available
Initial stability only*
YES Medium Low
Cannot be considered*
Medium ‘fixed’ only
Initial stability only*
Cannot be considered*
‘fixed’ only
Gives metacentric height for primary suspension, no info on range of stability. Only consid- ers symmetric arrangement.
Stability-increasing measures possible?
Medium
4. If applicable: Determine operational limits
Nikitin method
Low High
Analytical Can be automated
4.1
Sufficient workable range?
Medium Low
Cannot be considered
High ‘fixed’ only
Gives initial stability and range of static stability
Only considers symmetric arrangement. Base of primary suspension needs to be identical to top of secondary suspension.
Cannot be considered
‘fixed’ only
Only considers symmetric arrangement. Base of primary suspension needs to be identical to top of secondary suspension.
Gives initial stability and range of static stability
NO
To assist the process, the guidance makes a comprehensive comparison of different methods to assess the stability of lifts. Comparing methods for stability assessments of lifts
Approach Graphical 3.2 Analytical
Excel-based solution available
Analytical Can be automated
YES 3.3 NO High
Numerical computer simulation - Standard
Medium
High (for specific cases and conditions)
Numerical
Simulation software needed
Revise rigging
Stability for defined conditions
High Medium Can be considered
High (for specific cases and conditions)
Stability for defined conditions
Can be considered
Characteristics can be considered
Ultimate failure mechanism not of interest.
*analytical assessment based on Kaps method theoretically possible but not developed yet (June 2024).
provides insight on the stability against the overturning of two-chain suspensions, while numerical computer simulations allow a much more detailed analysis. “The numerical simulations are useful to understand the behaviour of a lift at certain phases of a lifting operation,” explains Sebastian Becker, Team Lead CAD Design, SAL Engineering GmbH.
Efforts for postpro- cessing and documen- tation only as much as needed.
Ultimate failure mechanism not of interest.
High efforts on post- processing to produce GZ-curves and to identify failure mechanisms and points.
Characteristics can be considered
Efforts for postpro- cessing and documen- tation only as much as needed.
High
Numerical computer simulation - Extended
High High Numerical
Simulation software needed
Stability for all angles High
H7igh
Can be considered High
Characteristics can be considered
Stability for all angles Can be considered
High efforts on post- processing to produce GZ-curves and to identify failure mechanisms and points.
Characteristics can be considered
Numerical
Simulation software needed
Revise rigging Numerical
Simulation software needed
Virtual CoG concept
3.1 Assess stability of the Lift
Kaps method
YES 3. 2.3
further clarify the text boxes of the flowchart.
1. Prepare draft rigging plan
Lifting points friction dependent?
2.4 Conduct friction-increas- ing / sliding-suppressing measures
YES
Comparison of methods and recommended areas of application Methods described under 1. (Virtual CoG). and 2. (Kaps) allow the evaluation of the initial stability of the lift only. They do not provide information about the behaviour of the lift when external forces are applied or the CoG is off- set, nor do they allow conclusions about potential failure mechanisms. The Method described under 3 (Nikitin). gives insight on the stability against overturning of two- chain suspensions. It provides the initial stability as well as a range of stability measured by a maximum allowed tilting angle. Nevertheless the Kaps-method is broadly used within the industry. A direct comparison with the also analytical but more complex approach by Nikitin is given in the Appendix. The methods described under 4 and 5 require a numerical simulation.
Friction-increasing / sliding-suppressing measures possible?
dependent lifting points. Also the effect of the asymmetry of the lifting arrangement is visible.
CoG above Lifting Points?
Comparison of methods and recommended areas of application Methods described under 1. (Virtual CoG). and 2. (Kaps) allow the evaluation of the initial stability of the lift only. They do not provide information about the behaviour of the lift when external forces are applied or the CoG is off- set, nor do they allow conclusions about potential failure mechanisms. The Method described under 3 (Nikitin). gives insight on the stability against overturning of two- chain suspensions. It provides the initial stability as well as a range of stability measured by a maximum allowed tilting angle. Nevertheless the Kaps-method is broadly used within the industry. A direct comparison with the also analytical but more complex approach by Nikitin is given in the Appendix. The methods described under 4 and 5 require a numerical simulation.
NO
The below table provides an overview of the introduced methods.
Revise rigging NO NO NO
3.4 Conduct stability- increasing measures
Nikitin method
The below table provides an overview of the introduced methods.
Numerical computer simulation - Standard
Numerical computer simulation - Extended
“Step five is to cre- ate a final rigging plan complying with the selected criteria, which can then be added to the op- erational procedure,” Behrens adds.
Guidance on stability of lifts
Guidance is grouped into five steps. Step one involves preparing a draft rigging plan. Step two is to assess whether the rigging points are friction- dependent. Step three is working out if the centre of gravity (CoG) of the rigging arrangement is above the lifting points. Step four, if applicable, is determining and documenting operational limits.
13
13 THE REPORT | MAR 2025 | ISSUE 111 | 63
Source: Guidance on Stability of Lifts Guidance, Heavy Lift Exchange Forum, 2024
Source: Guidance on Stability of Lifts Guidance, Heavy Lift Exchange Forum, 2024
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