2。  Design, regulatory and classification aspects

Presently, ship stability in intact condition is normed by “design oriented” IMO/SOLAS regulations or class rules。 The design approach is typically aimed at verifying specific loading conditions and at determining limitations in terms of acceptable KG values, to guarantee a “sufficient static roll restoring” according to specific requirements。 Fulfilment of such requirements is implicitly assumed to provide a “sufficient level of safety”。

Some general indications are given by regulations regarding the risk involved in having too large static restoring, since this can lead to excessive accelerations (Shigunov et al。, 2011)。 However, such indications do not typically translate into quantitative lim-itations on GM。 Some quantitative indications regarding too large metacentric heights can be applied in the preparation of the cargo securing manual, for those vessels for which this is relevant。

The main weakness of such approach is that the criteria used for the determination of acceptable/unacceptable loading condi-tions are mostly semi-empirical in nature, and do not provide explicit information regarding the specific possibly dangerous phenomena a vessel could be prone to in a specific loading con-dition。 Furthermore, in some cases, existing regulations do not sufficiently or properly cover certain dangerous phenomena, which are typically associated with large amplitude ship motions under the action of wind and waves。

As a result of this situation, it might happen that a vessel may undergo crew injuries or cargo loss or damage in heavy seas despite fulfilling existing regulations。 Conversely, it might happen that a vessel, marginally complying with existing regulations, still has a sufficient level of safety potentially allowing for a further increase of payload and, thus, profitability。 In addition to this, the strongly semi-empirical and statistical nature of present regula-tions does not provide the master with any information regarding the expected behaviour of the vessel at sea。 The lack of informa-tion, in turn, can lead the master to take wrong decisions in case of a dangerous situation (e。g。 selecting unfavourable speed and/or heading in harsh environmental conditions)。 Also, the present regulatory framework is not designed for incorporating active operational measures as a means for providing the required level of safety in certain, potentially dangerous, conditions。

The mentioned limitations in the prevailing regulatory frame-work have recently been tackled, conceptually, in the development of the IMO Second Generation Intact Stability Criteria (SGISC) (Bačkalov et al。, 2015; Peters et al。, 2012)。 Indeed, in the frame-work of SGISC, specific criteria are developed for specific danger-ous stability phenomena in waves。 This allows identifying, at the

Please cite this article as: Bačkalov, I。, et al。, Improvement of ship stability and safety in intact condition through operational measures: challenges and opportunities。 Ocean Eng。 (2016), http://dx。doi。org/10。1016/j。oceaneng。2016。02。011i论文网

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design stage, the type of phenomena the particular vessel is prone to。 The identification of such phenomena becomes clear with the determination of the governing criteria, and associated failure mode, in the definition of acceptable/unacceptable loading con-ditions。 It is worth noting that, because these criteria are based on a dynamic approach, the usual concept of “limiting GM” is, in principle, abandoned, and this can potentially lead to problems on how to treat this situation from an approval (Administration, or Class on behalf of the Administration) perspective。

In addition, the framework of SGISC allows achieving, in prin-ciple, a sufficient level of safety by means of a combination of design requirements and of properly developed ship-specific operational guidance。 Alternatively, it is also possible, in princi-ple, to approve the vessel, in a specific loading condition, subject to the fulfilment of some specific operational limitations。 “Opera-tional limitations” are herein intended as limitations on the overall operability of the vessel in specific loading conditions (e。g。 operations allowed only in certain geographical areas/sheltered waters, or up to a certain significant wave height)。 On the other hand, ship-specific “operational guidance” is intended as a detailed recommendation to the master on how to handle the vessel, in a specific environmental condition, to reduce the like-lihood of inception of “stability failures” to an acceptable level。