National Academies Press: OpenBook

Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance (2019)

Chapter: Appendix F: Current State of Second Generation Stability Criteria

« Previous: Appendix E: Cargo Ship Weight-Tracking Programs
Page 114
Suggested Citation:"Appendix F: Current State of Second Generation Stability Criteria." National Academies of Sciences, Engineering, and Medicine. 2019. Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25565.
×
Page 114
Page 115
Suggested Citation:"Appendix F: Current State of Second Generation Stability Criteria." National Academies of Sciences, Engineering, and Medicine. 2019. Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance. Washington, DC: The National Academies Press. doi: 10.17226/25565.
×
Page 115

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

PREPUBLICATION COPY—Uncorrected Proofs 114 Appendix F Current State of Second Generation Stability Criteria The International Maritime Organization (IMO) has been undertaking a significant effort to develop its so-called Second Generation Ship Stability Criteria. These criteria have the potential to dramatically improve both the accuracy and realism of existing quasistatic approaches, which mainly consider the calm water hydrostatic restoring moment arm curve compared with a steady heeling moment. This new approach, under consideration by the IMO, consists of three levels of accuracy beginning with the first level, which is essentially the current prescriptive criteria of the 2008 Intact Stability Code (IS Code), and ending with the third level, a direct stability assessment using physical model testing and numerical simulation. The second level is an improvement on the first level, but would not be as expensive or time consuming to apply as the third level. The essential aspect of the second-generation criteria is to identify five vulnerabilities or failure modes: 1. Pure loss of stability, 2. Parametric roll, 3. Surf-riding/broaching, 4. Dead ship condition, and 5. Excessive accelerations. Discussions at the recent sixth session of the IMO’s Committee on Ship Design and Construction (SDC) (IMO SDC 6, February 4–8, 2019) resulted in approval of many of the recommendations of an experts group that were based on a request by the IMO’s Marine Safety Committee (MSC). The goal of the next meeting of the seventh SDC will be to draft an interim guideline in the form of an MSC Circular, which will consist of three items: 1. Guidelines of ship vulnerability failure. 2. Specification for direct stability assessment. 3. Operational guidance. These three items will be a summary of the contents of the report of the expert group SDC-6 WP6 and will include three annexes. The mandatory Part A of the existing 2008 IS Code will continue to be mandatory. The new MSC Circular to be submitted to the seventh SDC that describes some of the aspects of the Second Generation Ship Stability Criteria will remain in a trial stage. However, not all five vulnerabilities may be addressed, with only the surf- riding/broaching and parametric rolling to be definitely addressed. The eighth session of the SDC may have a goal of producing explanatory notes, which will address extreme conditions and an assessment of how rare these various vulnerabilities are. Although the three levels of assessment are to be performed sequentially with each yielding a more accurate and less conservative judgment, there has been some concern that this may not be the case. Specifically, in some rare cases, it has been found that a vessel may satisfy level one but fail level two. Moreover, the interim guidelines for direct assessment are being exposed to a three-level Verification, Validation, and Accreditation. To comment on the goals and effectiveness of the IMO Second Generation Ship Stability Criteria may be premature. The U.S. Coast Guard (USCG) and the U.S. Navy are represented as part of the international group of experts and therefore the USCG is closely following the

PREPUBLICATION COPY—Uncorrected Proofs 115 development of these criteria. In theory, the availability of such a “first principles” ship stability assessment is long overdue. However, for over two decades, the specific details have been debated and will continue to be debated. These criteria may be particularly relevant to vessels with unique hull forms and hydrodynamic characteristics. Examples include advanced marine vehicles, non-mono-hull displacement hulls, floating offshore platforms with unique geometry, and also possibly smaller vessels such as fishing vessels that may be exposed to extreme environmental conditions. Unfortunately, such a physics-based first principles approach may require a level of training beyond what is the norm for vessel designers, particularly at the smaller firms. Therefore, an effort must be made to simultaneously refine the accuracy and realism of these criteria while making them understandable and usable to a wider audience without an undue investment in time and cost. It merits noting that implementation of a dynamic response-based criteria is not new. The American Bureau of Shipping (ABS) undertook such a project in the 1980s to develop response- based criteria for column stabilized mobile offshore drilling units (MODUs). Although not widely accepted by industry, the criteria have been applied by some organizations. Moreover, in the 1990s the U.S. Navy, in order to consider the dramatically different motions characteristics of its new destroyer hull form, implemented response-based criteria. Unfortunately, the U.S. Navy’s methodology was both time consuming and expensive to implement and has only been applied to that single hull. Therefore, a more general approach, especially for the second level analysis, must be relatively simple to implement but also must consider three important characteristics of the response: accurate hydrodynamic modeling, the inherently nonlinear character of the dynamics, and a realistic wave and wind environment and its resulting stochastic character. Such a comprehensive approach would be required as part of further developments of the IMO Second Generation Criteria. Specifically, the second level analysis approach would need to be more accurate than the first level (prescriptive), but more time and cost efficient than the third level (physical model testing and numerical simulation). Moreover, this approach would need to be easily applied and understandable by the practicing naval architect.

Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

U.S. Coast Guard (USCG) ship stability regulations governing the ability of a vessel to return to an upright position after being disturbed is the focus of a new TRB publication, Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance. The authors advise the USCG on how it can make its stability regulations more usable and complete in meeting the requirements of different types of vessels and those vessels that have undergone weight changes that can affect their stability characteristics.

The USCG has safety regulatory jurisdiction over vessels registered in the United States. One of its oldest regulatory functions is to ensure these ships, boats, and other floating vessels remain upright as they encounter both expected and unexpected loading, operating, and weather conditions, including wind and wave conditions and unexpected failure of watertight integrity.

Stability standards have been improved over time - particularly in the past 30 years - and the USCG remains keenly interested in making sure the regulations are kept updated based on the latest technical knowledge, well aligned with international standards, and organized and presented in a manner that facilitates compliance and enforcement. The recommendations in the report are intended to further these aims. The USCG earlier commissioned a National Academies study to identify options for improving vessel stability regulations, and after receiving that study in September 2018, the USCG asked for this second study to provide more in-depth advice on applying these options.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!