Improved Design for Seakeeping: Seaway Criteria and Related Developments
A major seakeeping workshop was held in 1975 that identified seakeeping deficiencies in our ships compared with those of our NATO allies. The workshop was intended to lead to corrective action with the help of the expertise of the attendees. Because of existing deficiencies in seaway criteria among other problems, the desired results were essentially unattainable at that time. This paper is intended to show that many of these deficiencies can now be overcome (section 2). The approach taken here to improve design for seakeeping is termed a first-principles methodology (FPM), which is derived from the basic elements of military aircraft structural and flying qualities design specifications. Because of the greater complexity of a ship's operating environment, this approach has necessarily been modified to achieve similar overall objectives (section 3). To satisfy the environmental criteria deficiencies cited by Groups 2, 3, and 6 of the workshop, seaway criteria presented here now cover both Survivability and Operability seaway conditions. It is important to note that the measured ocean wave data used for this purpose have been available for only about the last 20 years (section 4). Because of the enormous variability of individual seaway conditions, it is essential that the determination of ship loads and motions be directed toward those particular seaway conditions likely to be critical for design purposes. Seaway criteria suitable for assuring attainment of required military mission performance and survivability are identified (section 5). The results of an investigation of head-seas parametric rolling of a C11 container ship are reviewed to show that FPM design and test elements were successfully employed in that investigation. The role of shipmasters in identifying critical design conditions in severe seaways is illustrated for consideration by naval architects. It is asserted that a beneficial relationship between them is possible when a first-principles design methodology is employed (section 6). Two investigations are recommended for further demonstrating the FPM design and test method using an existing C11 ship model in a Survivability seaway. The first involves a shipmaster's request to determine a ship's ability to maintain a hove-to heading at low speed in a severe seaway. The second is to determine the roll stability of the model in the same seaway at a beam sea heading with complete power loss. The ability of the LAMP-2 or equivalent program to predict the resulting model behavior in each case is to be determined (section 7).
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Document Type: Research Article
Publication date: 2009-04-01
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