Model Experiments of an Offshore Supply Vessel Running in Astern Waves

Abstract

At the IMO (International Maritime Organization), the second generation intact stability criteria for pure loss of stability was developed in 2020. In its interim guidelines (IMO in “Interim Guidelines on the Second Generation Intact Stability Criteria”, MSC.1/Circ. 1627, 2020 [2]), vessels with extended low weather deck such as offshore supply vessels (OSVs) are exempted from this application, but its background has not yet been explained other than a sample calculation resulting in inconsistencies between different criteria levels. To solve this problem, the authors executed model experiments for a typical OSV in astern waves. The test results demonstrated that the phenomenon assumed by the pure loss of stability criteria is not pertinent to the OSV. Instead, it is the phenomenon which occurs due to trapped water on deck which seems to be of greater relevance for the stability of the OSV in astern seas. The effect of low weather deck length was also investigated by systematically modifying hull forms with the help of CAD software. Further, the on-deck trapped water behaviour was also studied in a separate series of model experiments involving direct measurement of the changing deck water level. The tests confirmed that the trapped water can induce both static and dynamic moments depending on the speed of the vessel and the wave conditions.