• Proven ISO Compliant Methodologies
  • Provisional and Final Air Gap Criteria


Air Gaps are normally the most critical Metocean related design criteria for fixed offshore structures. Why: because if exceeded, waves will impact the platform deck (deck inundation) and loading levels increase dramatically. Such occurrences are not conceptual nor inconsequential: the majority of platform failures in the Gulf of Mexico have been attributed to Air Gap exceedance. OceanMetriX Ltd has proven capabilities in the specification of Air Gaps world-wide (our work features in the award winning OMAE2009-79466 Structures, Safety and Reliability paper).

Proven, ISO Compliant Methodologies: Metocean parameters which contribute to Air Gap calculations are: extreme storm crest heights, associated storm surge and tide levels. We calculate these as follows: Extreme Storm Crest Heights: Calculated using tried and tested ISO compliant methodologies; Associated Storm Surge levels: Calculated using OceanMetriX’s Conditional Criteria Methodology (CCM); and Tidal levels: Calculated by harmonic analyses of local instrument and global satellite derived datasets. We use ISO specified formulae to combine these parameters to obtain Extreme Water Levels and Air Gaps.

Provisional and Final Air Gap Criteria:


Provisional: intended for concept and sensitivity assessments, they are developed from the wave, surge and tide datasets in OceanMetriX’s archives. Lower Bound: assume surges do not correlate with extreme storm crests, Upper Bound: assume complete dependence.

Final: developed from external, long-period datasets, with association between crest and surge determined by our Conditional Criteria Methodology (CCM). Lower Bound: crest, surge relation specified by the CCM, Upper Bound, specified by the CCM with enforced asymptotic dependence.

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