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Assessment of the Realistic Range of Variation of Ship Equivalent Metacentric Height Governing Synchronous Roll Frequency
Published in Adam Weintrit, Tomasz Neumann, Safety of Sea Transportation, 2017
In the contrast to the buoyancy, the ship stability is a more complex matter and it has to be considered both at the design stage and during the routine operation. The main potential threat is related to excessive roll motion and the large amplitudes of roll. Although the large amplitudes of ship roll are highly unlikely during cargo handling in a port (Krata et al. 2013), the dangerous excessive rolling may happen at seaway (Kobylinski & Kastner 2003), thus then proper stability assessment should be applied as a routine part of ship management. Historically, the first approach towards ship stability evaluation was based on an experiment only. Till the time of boat launching one could not be sure the design correctness so the design process had to be based on architect’s and seamen’s experience and on the earlier projects similitude. Since the mid-eighteenth century the development of researches in the field of ship stability is noticed. The studies of numerous scientists laid the groundwork for deeper understanding of the stability notion and characteristics. Primarily, the works of Bouguer from 1746, Euler from 1749, Bernoulli from 1757 and Attwood from 1796 are recognized as the foundations of the scientific approach towards ship stability related issues. Bouguer introduced the metacentric height notion which remains the only measure utilized to assess ship stability till the end of the nineteenth century (Kobylinski & Kastner 2003). In the mid-nineteenth century the righting arm curve was already known and thanks to Moseley’s publication from 1850 also the concept of dynamical stability was introduced. Although, those theoretical achievements were not fully applied in practice and none stability standards were elaborated at that time (Kobylinski & Kastner 2003).
The viability of retro-fitting a re-liquefaction plant onboard a 150,000m3 DFDE LNG carrier
Published in Journal of Marine Engineering & Technology, 2023
Kenneth Gordon Montgomery, John Chudley
The critical factors for re-liquefaction plant selection differ between onshore and onboard. Whereas the thermodynamic efficiency of liquefaction plants onshore is the most critical criterion, other aspects are more critical in onboard re-liquefaction projects. The space available to house the plant onboard is limited, and therefore the footprint must be considered. Weight affects ship stability and cargo carrying capacity. Sufficient existing electrical power needs to be installed onboard without the need to purchase and install additional generators, which would add to the cost. CapEx needs to be as low as possible. Vessel operating costs are increased as the plant requires maintenance and servicing. The type of re-liquefaction plant selected needs to provide high security and reliability, quick start-up, capable of processing varying quantities of BOG, immune to the sea-state, and maintainable by vessel staff.