“Mighty Whale” is an offshore floating type wave power device based on the oscillating water column (OWC) principle. The prototype of Mighty Whale was installed at the test location, the mouth of Gokasho bay in Mie Prefecture, on July 1998. The open sea tests were started on Sep. 1998, and we are keeping on measuring many data to show the safety and economic features of the device.
Generally, it is important to decide environmental design conditions, wind speed, wave height and so on, when we design offshore structures. Therefore, these design methods are showed by many papers and rules. However, there are few cases to verify whether design methods for actual installed offshore structures are right.
In this paper, we verify design methods by using measurement data on Mighty Whale, and have some concluded points as follows. 1) It is necessary to consider long return year (over 50 years) even if actual year is short (4 or 5 years). 2) In case of using adjacent site conditions data, it is important to consider geographical features. 3) It is practical to cut off extreme data if we decide return years by short-term data. 4) It is better to consider swell conditions by typhoon on the coasts of the Pacific.