A National Oceanic and Atmospheric Administration (NOAA) buoy database of over 2 million wave spectrum measurements from a wide variety of wave climates has been utilized to identify three generalized wave climates, namely Climatic Steep Seas (two variants), Climatic Northern High Latitude Seas and Climatic Long Period Seas. These wave climates are further characterized in the following respects using previously determined long-term climatic wave spectra (CWS):
(a) Trend lines of significant wave height (Hmo) vs modal period (Tp) are determined. These are terminated and then interconnected to form an upper boundary at high values of Hmo
(b) Ochi (3P) wave spectra are determined which closely model the climatic wave spectra over the entire length of each of the modal period trend lines and their upper boundary
(c) Average probability density distributions of Hmo, are determined for each of the generalized wave climates.
The overall Hmo, versus Tp, envelope, and its trend lines defined by (a) is termed the NOAA baseline Operability envelope. A design criterion is recommended which requires that a ship operates within the envelope without experiencing damage or requiring repair or replacement of equipment. The NOAA buoy database is also used to construct a baseline Survivability envelope. In this case, extreme values of Hmo, and associated Tp, lead to a two-segment envelope, namely a segment corresponding to Seaways of Limiting Steepness and one corresponding to Seaways of Extreme Significant Wave Height.
The latter is derived from a database having an effective measurement period of about 10 years. A design criterion is recommended which requires that a ship resist substantial loss of watertight integrity, hull girder failure, capsize, and loss of communication and survivability equipment within the envelope. Modified JONSWAP spectrum approximations applicable to the entire envelope are provided. Based upon a favorable correlation of NOAA buoy and British Maritime Technology's Global Wave Statistics data, the two baseline envelopes are extended to cover Northern and Southern Hemisphere extremes of significant wave height. Comparisons of the Operability envelope and selected seaway criteria currently in use to suggest that the latter correspond mainly to the northern high latitude wave climate identified here. Comparisons of Hogben's independently derived boundaries with corresponding portions of the Survivability and Operability envelopes show remarkable agreement.