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October 2013 www.sname.org/sname/mt (abstracts) boats. is 9-m craft is capable of operating at speeds up to Froude number 1.7. However, when it begins to maneuver in incident waves near its maximum speed, dynamic instabil- ity occurs immediately. In this instance, the craft trims and rolls to a large heel angle with plow-in,? even with small-amplitude incident waves and small course changes. In this study, a fully nonlinear ship motion model named the Digital Self-consistent Ship Experimental Laboratory (DiSSEL) is used as a numerical tool to understand the physics that cause the dynamic instabilities. DiSSEL showed that when SRB reached Froude number 1.698, acceleration resulting from heading change would cause a dynamic force and moment imbalance, resulting in heel and pitch motion instabilities. DiSSEL also showed that if the heading is fixed, and other conditions remain the same, the instability did not occur. Unfortunately, there is no detailed record of the data or numerical simulation of the ship motions in the stable and unstable regions, except for the description of the ship motions by Codega and Lewis (1987). e simulations by DiSSEL agree well with this description. Optimum Speed Analysis for Large Containerships BY Y.S. KHOR, K.A. DØHLIE, D. KONOVESSIS, AND Q. XIAO PUBLISHED IN THE AUGUST JOURNAL OF SHIP PRODUCTION AND DESIGN During these times of uctuating freight rates and oversupply, selection of optimum speed will give an operator a crucial advantage. Until the recession, the emphasis has always been on larger capacity and higher speed. Now, design innovation and slow steaming are becoming important and this article details new software, which is set up to assist the speed optimization process for large container ships. e software uses both propulsion and revenue-cost anal- ysis with an ultralarge container ship model of 20,000 20-ft.unit (TEU) as a case study to derive the most profitable speed. Shippers costs are also estimated to assess the impact on shippers. is software can be used for new construction or existing ships. e results show that 19.5 knots is the optimum speed, which is a departure from the current trend of 25 knots but supporting the concept of slow steaming. e results are validated by Det Norske Veritas container cost models. Besides that, the multi- variable nature of the optimum speed problem is discussed and further analysis has been car- ried out to determine the range of fuel cost, freight rate, and load factor in which this opti- mum speed is applicable (in this case, 1100TEU < freight rate < 1300TEU, 650MT < fuel cost < 750MT and load factor 40). is will be useful to ship operators for forecasting purposes. A Comparison of Numerical Methods to Predict the Progressive Collapse of Lightweight Aluminium Vessels BY SIMON BENSON, JONATHAN DOWNES, AND ROBERT S. DOW PUBLISHED IN THE AUGUST JOURNAL OF SHIP PRODUCTION AND DESIGN is article presents a comparison of several methods to predict the primary longitudinal bending moment-curvature relationship for a series of box beams with dimensions equiva- lent to a large, lightweight aluminum ship. e comparative study includes the application of an extended progressive collapse methodol- ogy, which has been developed specically to predict the strength behavior of lightweight hull structures under primary bending moment and accounts for compartment-level, gross panel buckling eects of the orthogonally-stiened structure. e approach is based on the princi- ples of the Smith progressive collapse method, which has been shown to be a capable measure of ultimate strength when applied to steel ships. However, a fundamental premise of the Smith method is that buckling forms an interframe. e extended method discards this assump- tion and includes overall gross panel buckling eects in the determination of girder strength. For the case study, both the interframe and compartment behavior of the case study box girders are compared. e results are also com- pared with nonlinear nite element analyses of the box girders. e nonlinear nite element method is being increasingly applied to predict hull girder progressive collapse and, provided computation time is acceptable, will predict collapse modes over an entire compartment. e extended progressive collapse method is shown to compare favorably to the equivalent nite element analysis when overall buckling modes dominate. Minimizing the Cost of Coating Ships BY DARREN BRODERICK, PETER WRIGHT, AND RAOUF KATTAN PUBLISHED IN THE AUGUST JOURNAL OF SHIP PRODUCTION AND DESIGN In the current economic climate, the pres- sures on both shipbuilders and ship owners to minimize the cost of their operations are stronger than ever. Although paint material cost, to coat an entire vessel, only represents a very small percentage of the total for a new build vessel, the labor cost of applying coat- ings to a vessel can represent in excess of 10% to 15% of the total labor costs. In some cases, as much as 30% of this can be attributable to rework. For the ship owner, coatings can have a signicant impact on the operating costs and the availability of the vessel. With greater emphasis being placed on sustain- ability and life cycle costs, it is in the interest of both shipbuilders and the owner/opera- tors to seek ways to minimize the cost of the coatings at both the application stage and maintenance during the service life of the vessel. This article presents work that has been undertaken to examine the life cycle process of designing, building, operating, and recycling a ship and how the activities within the dierent stages aect the application of paint and the inuence this has on costs. Measurement of Hydrodynamic Coecients on a Planing Hull Using Forced Roll Oscillations BY CAROLYN Q. JUDGE AND JOHN A. JUDGE PUBLISHED IN THE JUNE JOURNAL OF SHIP RESEARCHFor planing hulls, dynamic lift reduces the