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10.13 ESTIMATING HELIDECK DOWNTIME DUE TO WAVES
Estimates of the likely helideck downtime can be made by combining the information about the helideck motion characteristics (RAOs) (see Section 10.11) with the expected operating wave climate in the scatter table (see Section 10.12), and the helideck motion limits (see Section 10.12.1).
The process is similar to that described for wind in Section 10.9.6, but is more complex because it involves the three parameters (wave height, wave period and wave direction). The helideck wave motions in each of the seastates defined in the scatter table are estimated, and the sea state probability summed if the motions exceed the limiting operating criteria. This sum is the total probability that the conditions will be unacceptable. The analysis should take due account of vessel heading, which might be fixed, or may vary with changing wave directions. The process should be performed by a competent naval architect using the appropriate specialised software.
Once the helideck downtime has been estimated, the vessel operator can decide whether it is at an acceptable level or not. Helideck downtime will lead to disruption of the vessel operations, and these will have a cost. Relocating the helideck to a vessel location with lesser motions and thus lower downtime may be appropriate, but it should be borne in mind that for smaller ships the limiting motion criteria vary depending on the helideck location on the vessel. Lesser motions are permitted for bow mounted helidecks, owing to the poorer visual cues available to the pilot.
11. HELIDECK SYSTEMS
11.1 INTRODUCTION
The items that make up the whole helideck facilities package cover a wide range of individual systems and components. Each system and its components contribute to the overall serviceability of a helideck, which is a Safety Critical Element (SCE).
Several discipline engineers, as part of their discipline responsibilities, will often manage the work associated with the helideck systems and components. However, there is a pressing need to ensure this work is properly co-ordinated to ensure that the final product is ‘a fully certified helideck’ ready for flight operations, preferably with no operating restrictions.
The following sections deal with the various systems and components in detail, to provide designers with practical guidance for optimising designs and operation.
11.1.1 Hazardous Area Classification and Equipment Selection
The helideck should be positioned at a safe location on an installation or group of installations, and under normal platform operating conditions be free from any potentially explosive atmospheres created by the platform drilling and production processes. In this respect the helideck should be located in, and classified as a non-hazardous area.
However, in the event of a process upset condition and where potentially explosive atmospheres (e.g. gas release) may occur, the effects of these events on the safety of helicopters and helideck operations should be fully taken into account in the installation safety case. Helideck safety systems such as automatically activated status lights or, where appropriate, equivalent 'manual' alerting systems should be in place, along with adequate platform emergency and communications procedures.
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离岸直升机起落甲板设计指南 OFFSHORE HELIDECK DESIGN GUIDELINES 2(33)
