0027/nd guidelines for Marine Lifting and Lowering Operations

GUIDELINES
 
FOR
 
MARINE
 
LIFTING
 
&
 
LOWERING
 
OPERATIONS 
0027/ND Rev 11 
 
Page 57 of 84 
16 
CLEARANCES 
16.1 
INTRODUCTION 
16.1.1 
The required clearances will depend on the nature of the lift, the proposed limiting weather conditions, 
the size and weight of the lifted object, ability to control the lift, consequence of impact loads and the 
arrangement of bumpers and guides. 
16.1.2 
When evaluating clearances the effect of the maximum motions of the crane vessel associated with 
the environmental design conditions and DP / mooring system capability should be considered. For 
clearances on the transport barge, the motions of the transport barge should also be considered in 
addition to the motions of the crane vessel.
16.1.3 
Subject to the above, for offshore lifts, the following clearances highlighted in sections 16.2, 16.3, 16.4 
and 16.5 should normally be maintained at each stage of the operation. Smaller clearances may be 
acceptable for inshore or onshore lifts. Clearances are based on a level lift (no tilt) of each structure.
Additional clearances may be required for structures with a prescribed tilt. 
16.2 
CLEARANCES AROUND LIFTED OBJECT (FLOATING CRANE) 
16.2.1 
3 metres between any part of the lifted object (including rigging, spreaders and lift points) and the 
crane boom, when the load is suspended. 
16.2.2 
3 metres vertical clearance between the underside of the lifted object and any other previously 
installed structure. For the final stages of the lifting operation when the lifted object is in the immediate 
vicinity of the proposed landing area or installation aid, lowering of the lifted object can commence and 
a 1.5 metre clearance shall be adequate prior to moving the lifted object into its final position above the 
proposed landing area or installation aid. 
16.2.3 
5 metres between the lifted object and other structures on the same transport barge unless bumpers 
and guides are used for lift-off. 
16.2.4 
3 metres horizontal clearance between the lifted object, rigging or crane wire and any other structures, 
including the installation vessel, unless purpose-built guides or bumpers are fitted.
16.2.5 
3 metres remaining travel between travelling block and fixed block at the maximum required load 
elevation with the lift vessel at LAT. “Remaining travel” excludes any travel prevented by system limits 
that cannot be over-ridden for this operation/ 
16.2.6 
Where a structure is securely engaged within a bumper/guide or pin/bucket system, clearance 
between the extremities of the structure and the host structure must be demonstrated to be positive, 
considering the worst possible combinations of tilt. This may require dimensional control surveys to be 
carried out on the host structure and the structure to be installed. 
16.2.7 
Lift arrangement drawings shall clearly show all clearances as defined above. 
16.2.8 
Clearances for lifts by floating crane vessels onto floating structures (e.g. spars, FPSO’s) will need 
special consideration. It is expected that the clearances for this case will need to be larger than those 
stated above. The design clearances will be dependent on the relative motions of the floating structure 
and the lifting vessel and should be agreed with GL Noble Denton. 
16.2.9 
Consideration should be given when lifting and over boarding structures over, or in the vicinity of, a 
subsea asset to provide sufficient horizontal clearance for dropped objects. 
16.2.10 
Clearances less than those stated above may be acceptable, but require special consideration and can 
result in reduced allowable metocean conditions for the lifting operation.