The Research On The Intact Stability Of Semi-Submersible Vessels With Transporting And Loading Awkward Cargo

With the rapid development of world’s economy, especially for the offshore oil engineering, transportations of more and more awkward cargoes form docks to designated destinations become problems. However, as ordinary merchant ships are limited to cranes and volumes of ships’holds, they can hardly transport awkward cargoes.For convenience of transportations, semi-submersible vessels are emerged.When semi-submersible vessels are floating-on or floating off, their cargo decks will be temporarily submerged, and due to this particularity of loading mode, it will make evidently changes of ships’hydrostatic parameters and ships’stability during decks are temporarily submerged. If ships’officers do not fully understand these changes, accidents are likely to occur. In addition, while semi-submersible vessels are floating-on or floating-off, they have strict requirements of external environment and ships’officers should also know these constraints.In this paper,50000DWT semi-submersible vessels are taken as the research objects. According to these objects, this paper researches on relevant problems of intact stability and get the conclusion.Firstly, this paper summarizes the variation trend of KM values and GM values when semi-submersible vessels are floating-off by various trim condition without cargo. This paper analyses the variation trend of Ix, KB and V with draft in accordance with the hydrostatic data table, and researches on changings of KM values and GM values based on loading software. At the moment of cargo decks totally submerged, the KM values and GM values drop suddenly and both reach the minimum. If semi-submersible vessels are floating-off by trim, the ratio of declination of KM values and GM values when cargo decks submerged gradually by water are both less than those if semi-submersible vessels are floating-off by even keel. In addition, the minimum KM values and GM values when vessels are floating-off by trim are larger than those when vessels are floating-off by even keel.Secondly, when semi-submersible vessels are floating-off with cargoes by trim, due to the influence of cargoes, the variation trend of KM values are changing from floating-off without cargo by trim. When cargoes begin submerging by water, KM values will increase because of cargoes, and when cargoes are floating on their own, the hydrostatic parameters of ships will happen to drop.Finally, this paper respectively calculates the ability of wind resistant when semi-submersible vessels are navigating and floating-on/floating-off by IMO meteorological criteria and theory of initial stability.