7.11
TWIST FACTOR
TW
7.11.1
If the risk of twisting a fibre lifting rope exists, a twist factor
tw
shall be applied.
7.11.2
The twist factor γ
tw
shall be determined by testing and the corresponding permissible number of turns
established.
11
GUIDELINES
FOR
MARINE
LIFTING
&
LOWERING
OPERATIONS
0027/ND Rev 11
Page 35 of 84
8
SHACKLE DESIGN
8.1
INTRODUCTION
8.1.1
The following section covers the design of shackles using the loads derived in Section 5. The various
factors and their application are illustrated in Figure 5-1 which is for guidance only, and is not intended
to cover every case. In case of any conflict between the flowchart and the text, the text shall govern.
8.2
DESIGN CONSIDERATIONS
8.2.1
The working load limit (WLL) is generally used as reference for the strength of shackles. The WLL is
normally determined by the shackle manufacturer or a Certifying Body.
8.2.2
Shackles shall be loaded according to the manufacturer’s recommendations.
8.2.3
Shackle dimensions should be selected with due regard to bending radii of slings and grommets (see
Section 7.8) and to suit the geometric details for the lift points (see Section 12).
8.2.4
The shackle WLL should not be less than the static sling load.
8.2.5
The shackle safety factor should be included on the shackle certificate or otherwise documented and
the minimum breaking load (MBL) is determined by the WLL x the safety factor.
8.2.6
In addition to Section 8.2.1, the shackle dynamic load is to be less than the minimum of the following
values:
a) Shackle WLL x DAF
b) Shackle MBL / 3.0
c) Documented proof load value for shackle (see Section 15.3.11)
8.2.7
Wide body shackles should not be connected bow-to-bow unless specifically allowed by the
manufacturer.
8.2.8
Shackles are designed and rated to withstand loading in line with the plane of the shackle bow and
perpendicular to the shackle pin. Other load conditions should normally be avoided.
8.2.9
Eccentric loading on shackles may be acceptable if the shackle capacity is de-rated according to
original manufacturer guidelines and/or calculations. The total pad eye thickness at the hole shall not
be less than the requirements of 12.5.4.
8.2.10
Where the shackle is at the lower end of the rigging, the weight of the rigging components above the
shackle, (including effects of the DAF and taking account of sling angle) may be deducted from the
shackle load.
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