(Photo courtesy of Shell Aircraft Limited)
The locations for aviation fuel storage tanks, pumping and dispensing equipment should be selected to ensure that ingress of sea water into the aviation fuel system does not occur. Also, the system components (e.g. Tote Tanks) should be well secured to prevent damage in heavy seas.
7.2.3.9 Air Gap on MODUs
Too large an air gap under the helidecks of a MODU can be critical to vessel stability. This is due to the potential for airflows under a helideck to generate forces that may significantly increase the overturning moment of the structure for certain wind and ballast conditions. Therefore, when determining the optimum air gap for a MODU, the likely effect on vessel stability must be fully taken into account. Refer to Section 10.
(Photo courtesy of Transocean Inc)
7.3 FLOATING PRODUCTION SYSTEMS
7.3.1 Introduction
Floating Production Systems (FPS), which include Floating Production, and Storage and Offloading (FPSO) vessels, are classed, when on location in UK waters, as offshore installations.
A FPS featuring a vessel hull (e.g. VLCC tanker) will be typically moored using a permanent, widely spread anchor system that is fixed to a turret arrangement situated forward of amidships. This arrangement tends to allow the vessel heading to ‘weathervane naturally’ into the prevailing wind, wave and current conditions. (See Figure 7.5)
A FPS based on a semi-submersible hull is moored using traditional anchor winches and chains located at each corner of the hull. The unit is generally held at the location on a fixed heading within the anchor pattern. (See Figure 7.6)
7.3.2 Main References
Lloyds Register of Shipping – Rules for the Design, Construction and Classification of Floating Production Systems. [Ref: 72]
(Photograph courtesy of BP plc)
7.3.3 Specific Features to Consider in FPSO Helideck Design
The following sections cover specific topics that are relevant to FPSO structures (but differ from fixed installations) and require specific consideration during the design of such FPSO structures. The requirements set out below are in addition to those applied to fixed installation helidecks and should be read in conjunction with the sections of these guidelines that deal with structures, equipment, etc.
Features to consider in design are broadly the same as MODUs (covered in Section 7.2). These include:
.
Operating environment
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Anchoring
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Dynamic positioning
.
Drainage
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Helideck size, location and obstacle environment
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