FIGURE 9 Example of compilation of wind force and centre of attack
FIGURE 9 Example of compilation of wind force and centre of attack
What should be considered in the stability assessment?
A stable lift is one that remains in a balanced condition, within a safe margin, when subjected to predefined disturbing factors.
Disturbing factors may include wind force, rigging length tolerance, steering line forces, crane movement, CoG shift, vessel motions and friction at the lifting points.
The guidance paper explains several disturbing factors, together with relevant mathematical equations for calculating their impacts. It presents this material in a way that allows these factors to be incorporated into the calculations for rigging stability assessment.
Calculating sliding and effective inclination angles
Example of compilation of wind force and centre of attack
FIGURE 1 Single cr
FIGURE 1 Single cr
Wind profile Bft 4 Wind profile Bft 4
Guidance on stability of lifts
The sliding angle is the inclination angle at which a lifted cargo starts to slide, and it should never be reached during lifting. The angle depends on the friction between the materials in use, and on the shape of the contact surface. For instance, the effective inclination angle of a belly-slung cylindrical object is significantly different to a conical section.
Calculation of sliding and effective inclination angles or uneven cargoes, the effective inclination angle is
The sliding angle is a useful property of a lifting arrangement with friction-dependent lift points (FDLP). It describes, at
which inclination α of the lifted cargo it starts to slide. It depends on the friction factor of the materials in use, but also on the shape of the contact surface. For instance, the effective inclination angle of a belly-slung cylindrical object is significantly different for a conical section.
Calculating sliding and effective inclination angles is useful when assessing lifting arrangements that involve friction-dependent lifting points, which exploit the fact that frictional force resists relative motion between surfaces in contact.
FIGURE 12 Inclination angles for cylindrical and conical objects
Inclination angles for cylindrical and conical objects
Effects of wind attack Wind force to a hanging cargo unit has the following static effects:
Effects of wind attack Wind force to a hanging cargo unit has the following static effects:
� = � – � � = 10 ° – 0 ° � = 10 °
� = � – � � = 10 ° – (–7 °) � = 17 °
When handling a cargo unit with only one ship's crane there will be a slightly inclined pull on the lifting tackle and a negligible increase of the hook-load.
When handling a cargo unit with only one ship's crane there will be a slightly inclined pull on the lifting tackle and a negligible increase of the hook-load.
When handling with two cranes there will be also an inclined pull, but also a re-distribution of hook-loads caused by the component of the wind in the plane through both crane tops.
When handling with two cranes there will be also an inclined pull, but also a re-distribution of hook-loads caused by the component of the wind in the plane through both crane tops.
� = tilt angle � = cone/surface angle � = Effective inclination angle
� = � – � � = 10 ° – 0 ° � = 10 °
When handling with two cranes it may be that the cargo reaches high up between the two crane tops. It may then happen that the point of common wind attack is far above the centre of gravity of the cargo unit or even above the centre of suspension of the rigging arrangement. In such a situation the component of the wind, which is perpen- dicular to the plane through both crane tops, will create an additional tilting of the suspension.
“The guidance includes extensive discussion and formulas to calculate theoretical sliding angles for standard cases. Of course, coefficients indicating degrees of friction can vary significantly, and assumptions should be made conservatively,” Becker comments.
When handling with two cranes it may be that the cargo reaches high up between the two crane tops. It may then happen that the point of common wind attack is far above the centre of gravity of the cargo unit or even above the centre of suspension of the rigging arrangement. In such a situation the component of the wind, which is perpen- dicular to the plane through both crane tops, will create an additional tilting of the suspension.
� = � – � � = 10 ° – 7 ° � = 3 °
The full document is freely available at
https://bit.ly/4f2gBNh. 64 | ISSUE 111 | MAR 2025 | THE REPORT
Figure 12 illustrates how the effective inclination angle δ for a cylindrical cargo is equal to its tilt angle α. For conical
dependent on the tilt angle α but also on the cone/surface angle β. It can also be seen that the effective inclination angle can be significantly higher than the object tilt α – or can even have a different sign to the tilt angle α for certain cone/surface angles β. The following given formulas can be used to calculate theoretical sliding angles for standard
Transverse centre of attack
Transverse centre of attack
cases. It must be kept in mind that friction coefficients can vary significantly; assumptions should be made conservatively.
Transverse view Transverse view
Area Area
Effects The inclin
Effects The inclin
�= arc The force
�= arc The force L = (F
L = (F
Under th the level suspensi
Under th the level suspensi
Exter Exter
or ste One of th lift is lack While du easily co addition the carg lines.
or ste One of th lift is lack While du easily co addition the carg lines.
November 2024
November 2024 November 2024
GUIDANCE ON GUIDANCE ON
STABILITY OF LIFTS Heavy Lift Exchange Forum
Source: Guidance on Stability of Lifts Guidance, Heavy Lift Exchange Forum, 2024
STABILITY OF LIFTS Heavy Lift Exchange Forum
GUIDANCE ON
STABILITY OF LIFTS Heavy Lift Exchange Forum
November 2024 Source: Guidance on Stability of Lifts Guidance, Heavy Lift Exchange Forum, 2024
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148
