.
Materials of construction
.
Helicopter fuelling
.
Firefighting.
Parameters for the design of MODU helidecks that are specific to Floating Production Systems, and should be considered by the designer, are set out in the following sections.
(Photograph courtesy of Kerr McGee plc)
7.3.4 Marine Operating Environment
7.3.4.1 Semi-submersibles
The marine operating environment of a semi-submersible is similar to a fixed installation insofar as the helideck heading is generally fixed as a result of the anchoring system. However, it differs from a fixed installation in that the helideck has a dynamic movement in roll and pitch axes, heave, surge and sway due to the vessel’s dynamic characteristics.
In addition to wind speed and direction, the normal helideck movement (velocity and accelerations) induced by the floating structure must be fully accounted for during both helideck and system design and helicopter operations. See Section
10.
7.3.4.2 Vessels
Taking advantage of the ‘natural weathervaning’ characteristics of a turret moored vessel can help helicopter operations by keeping windflows at favourable angles over the helideck. This may not be the case for all wind, wave and current combinations.
However, advantages with wind speed and direction across the helideck should normally be obtainable as a result of the ‘natural weathervaning’ that usually holds the vessel heading within a few degrees either side of the vessel’s mean position centreline. This feature should be fully exploited by the designer during design, when optimising helideck location and orientation, so as to achieve the best available landing and take-off sectors.
Additionally, where sufficient thruster power is available to move the vessel off head, the ship’s crew may be able to further improve helideck orientation into the most favourable winds for given approach and take-off sectors. This situation only applies where it can be clearly demonstrated that moving the vessel off head does not induce excessive adverse helideck motions (roll, pitch and heave), or compromise vessel stability. Such capability may also be useful in minimising potential hazards due to emissions and turbulence generators.
As in the case of semi-submersibles, normal helideck movement (velocity and accelerations) induced by the floating structure must be fully accounted for during both helideck and system design and helicopter operations. See Section 10.
7.3.5 Vessel / Helideck Classification / Verification Process
The unique nature of an FPSO as a marine structure, which is classed as both vessel and an offshore installation, will invariably require close attention to be paid to the helideck classification and verification processes.
Often the vessel or semi–submersible will retain its ship classification, therefore the hull and marine systems will be designed and built to ships’ or MODU rules.
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