GUIDELINES
FOR
MARINE
LIFTING
&
LOWERING
OPERATIONS
0027/ND Rev 11
Page 72 of 84
19.5.2
Allowable maximum set-down velocity can be determined based on impact analysis.. It may be
necessary to use a heave compensator to ensure that the actual set-down
velocity is less than or
equal to the maximum allowable set-down velocity.
19.5.3
The possible magnification of heave motions due to resonance should be taken into account while
deciding allowable heave motion during landing.
19.5.4
The possibility of snap loading in the lifting wire when the object is
set on the seabed should be
considered.
19.5.5
Effect of additional dynamic forces due to impact on equipment and structural elements should be
evaluated. This effect is most relevant when installing an object on a hard surface.
19.5.6
Surface guide-wires can be used to control the position and orientation of the lifted equipment as it is
lowered into position. The guide-wires can either be secured to the installation vessel or be attached
to sub-surface buoyancy elements. Surface buoys can be used but their interference with other down
lines and umbilicals shall be considered
in their design, deployment and operation.
19.5.7
Visual (ROV) monitoring of the touchdown of the lifted equipment onto the seabed or the host structure
is required. ROVs can also be used to control position / orientation / landing of light structures subject
to the ROV capacity on location.
19.5.8
Subsea guide-wires attached to subsea buoyancy can be used in deep water and are connected by
the ROV after over-boarding of the lifted equipment.
19.5.9
Subsea rigging release systems shall be designed so that the
crane vessel can quickly be
disconnected from the lifted equipment. There should also be contingency systems in place to re-
connect the rigging if retrieval is required. Hydraulic shackles and ROV
release systems shall be
certified and function tested.
19.5.10
The seabed condition should be considered if wet parking is planned. The consideration shall include
bearing capacity and seabed inclination. It is possible that seabed preparation can be needed.
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