International audienceCurrently, second generation intact stability criteria are being developed and evaluated by the International Maritime Organization (IMO). In this paper, we briefly present levels 1 and 2 assessment methods for the criteria of pure loss of stability and parametric roll failure modes. Subsequently, we show the KGmax curves associated with these criteria. We compute these curves for five different types of ships and compare them with the curves embodied in the current regulations. The results show that the safety margin ensured by the first level-1 method of calculation for both pure loss of stability and parametric roll seems to be excessive in many cases. They also show that the KGmax given by the second level-1 method and by the level-2 method may be very similar. In some cases, the level-2 method can be more conservative than the second level-1 method, which is unanticipated by the future regulation. The KGmax curves associated with parametric roll confirm that the C11 container ship is vulnerable to this failure mode. The computation of the second check coefficient of parametric roll level 2 (C2) for all possible values of KG reveals the existence of both authorized and restricted areas on the surface formed by both the draft and KG, which may replace the classical KGmax curves. In consequence, it is not sufficient to check that C2 is lower than the maximum authorized value (RPR0) for a fixed ship’s loading condition
International audienceParametric roll is an amplification of the roll motion due to the periodic variation of the restoring moment in waves. This phenomenon is mostly observed in head and following seas and is the cause of several accidents occurred on container vessels during recent decades. One of the second generation intact stability criteria, currently under finalization and validation by the IMO, requires computing the maximum roll angle with regard to parametric roll. Both proposed methods are relatively complex to implement and require tools that naval architects are not accustomed to. In this paper, we propose an easier alternative method providing the amplitude of parametric roll for any loading condition at any speed, based on energy considerations and assuming a linear GZ. The implementation of this easy method in the corresponding second generation intact stability criterion provides almost the same value of KG(max) than the on-degree-of-freedom time simulation proposed by the future regulation
_ The International Maritime Organization (IMO) provides criteria to assess the vulnerability of ships toward the phenomenon of parametric roll. Such long-term vulnerability assessments permit to qualify statistically the ships vulnerability regarding parametric roll. However, it does not permit to assess the risk of parametric roll in real time. Thus, researchers and private company have developed methods and software to evaluate this risk using the real-time ship motions provided by the onboard inertial unit. Those methods detect parametric roll events when it appears and warn the officer of the watch of the immediate danger. This paper presents an innovative real-time detection method and its validation. The detection method considers physical conditions required for parametric roll to appear. Especially, it considers the coupling between the roll and pitch motions. The method and its associated parametric roll alarm are entirely described. The results show that the method correctly identifies parametric roll in regular longitudinal waves and do not lead to false detection in regular beam waves. A statistical study in irregular waves based on simulated data presents very promising results with a parametric roll detection rate in head seas above 80% when heavy roll motions appear and a false detection rate in beam seas below 4%. Finally, a 2.5-day full-scale validation on a container ship provides promising results. Introduction The container ships, with typical hull shape presenting flat stern and pronounced bow flare, are especially subject to parametric roll. Operationally, several accidents which have led to the loss of containers at sea may be imputed to this phenomenon (France et al. 2003; Carmel 2006; MAIB 2020; DMAIB 2022). Following the accidents of the C11-class container ship (France et al. 2003) and of the Maersk Carolina (Carmel 2006), both due to parametric roll, insurers asked the shipowners to take measures to avoid such failure to appear (Dølhie 2006). Two solutions are rapidly developed to answer this request. The first one is developed by SeaSense and named SeaSense Monitoring (Nielsen et al. 2006).
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