0027/nd guidelines for Marine Lifting and Lowering Operations

GUIDELINES
 
FOR
 
MARINE
 
LIFTING
 
&
 
LOWERING
 
OPERATIONS 
0027/ND Rev 11 
 
Page 25 of 84 
5.5.7 
If any part of the lifting operation includes lifting or lowering a structure or spool through water, 
analyses shall be submitted, which either: 

Show how the total in-water lifting loads are derived, taking into account weight, buoyancy, 
entrained mass, boom-tip velocities and accelerations, inertia and drag forces, or; 

Calculate the dynamic sling and hook loads to document that slack slings do not occur and 
provide limiting seastate data for the offshore operation. 

Calculate the local and global stresses in the spool; 

Calculate slamming loads on the structure being lifted. 

The dynamic analysis results for a submerged or partially submerged lift may restrict the 
operability of an operation that is subject to the issue of a Certificate of Approval, depending on 
the DAF used for rigging and structure design. 
5.5.8 
As an alternative to the DAFs in Table 5-1, the DAF may be derived from a suitable calculation or 
model test. Where the lift is from or onto a barge or vessel alongside the crane vessel, then the barge 
or vessel motions must be taken into account as well as the crane boom-tip motions. 
5.6 
SKEW LOAD FACTOR (SKL) 
5.6.1 
Skew loads are additional loading caused by rigging fabrication tolerances, fabrication tolerances of 
the lifted structure and other uncertainties with respect to asymmetry and associated force distribution 
in the rigging arrangement. The skew load factor (SKL) is a load distribution factor based on:

rigging length manufacturing tolerances,

sling / grommet measurement tolerances over measuring pins,

rigging arrangement and geometry,

fabrication tolerances for lift points,

sling / grommet elongation,

crane geometry, 
and should be considered for any rigging arrangement and structure (see Sections 11.2 and 11.3) that 
is not 100% determinate. A significantly higher SKL factor may be required for new slings used 
together with existing slings as one sling may exhibit more elongation than the others.
5.6.2 
For rigging configurations involving slings from more than 4 lift points connected to a single hook, skew 
load effects shall be calculated on a case by case basis. 
5.6.3 
When determining the length of a sling or grommet, the effect of the pin used in the measurement of 
the sling / grommet should be considered as the connection points for the sling / grommet may have a 
different diameter to the pin causing the in-use length to be different to the measured length. 
5.6.4 
When determining the rigging lengths and angles, the effect of the hook geometry and hook prong 
diameter should be considered as these will affect the working points for the rigging when determining 
lengths and the hook prong diameter may affect the measured length of the sling / grommet (see 
5.6.3). 
5.6.5 
For determinate lifts (with or without a single spreader bar) the SKL may be taken to be 1.0, provided it 
can be demonstrated that sling length errors do not significantly affect the load attitude or lift system 
geometry. The permitted length tolerance on the slings / grommets for the use of the SKL of 1.0 is 
such that the lengths shall be within 
±
0.5% of their nominal length. Where the tolerance is outside 
this, the effect of the sling length should be considered on the load distribution to the lift points 
incorporating any tilt effects caused by the sling length tolerances. 
5.6.6 
For a lift system using matched pairs of slings and incorporating 2 or more spreader bars, a SKL of 
1.10 is applicable provided the following conditions are achieved: 
a) 
An approximately symmetric rigging geometry is utilised.
b) 
The sling lengths are within 

0.5% of their nominal length.
c) 
The calculated axial load in the spreader bar is at least 15% of the sling load
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