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

Chapter: 4 Methodology for Evaluating Effectiveness of Current Stability Regulations

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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
×
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
×
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
×
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Suggested Citation:"4 Methodology for Evaluating Effectiveness of Current Stability Regulations." 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.
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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 31 4 Methodology for Evaluating Effectiveness of Current Stability Regulations Section 212 (b)(1) of the Save Our Seas Act of 2018 requires the U.S. Coast Guard (USCG) to “complete a review of the effectiveness of U.S. regulations, international conventions, recognized organizations’ class rules, and USCG technical policy regarding intact and damage stability standards under Subchapter S.” The USCG asked the study committee to advise on a methodology for conducting this review with a focus on the following questions, which are addressed in turn: • How should “effectiveness” be defined? • What technical studies are needed to review effectiveness? • Should the review methodology vary by vessel type or service? • How should international regulations, class rules, and other requirements outside Subchapter S be addressed in an effectiveness review? DEFINING EFFECTIVENESS Ideally, the effectiveness of a safety regulation or other standard or guidance can be assessed on the basis of its impact in preventing or reducing the occurrence and severity of its targeted safety concern (e.g., a stability-related casualty). However, it can be difficult to isolate the impact of any one regulation, or set of regulations, when that targeted safety problem occurs rarely (although with potentially catastrophic consequences) due to its nature, or when the problem arises from several factors, only some of which may be addressed by the specific regulation or standard.31 There is a challenge too in estimating how observed safety outcomes, such as the number of casualties, would have changed in the absence of a regulation or standard (i.e., the counterfactual) when such an unregulated environment may not have existed for many years. Thus, while such quantitative evaluations are routinely conducted when new regulatory requirements are proposed in rulemaking, they are seldom undertaken in a retrospective manner to measure the overall effectiveness of a longstanding body of requirements and technical and policy guidance. The committee recognizes that the USCG routinely examines casualty data and investigates incidents looking for causal and contributing factors, and expects that incidents involving stability loss are regularly examined to assess the strengths and shortcomings of the specific regulatory requirements. Therefore, rather than try to advise on such quantitative assessments, the committee focused its efforts on the kinds of qualitative assessments that the USCG can make as part of a review of the effectiveness of its stability regulations. The committee believes that qualities such as ease of use, technical accuracy, and scope of application can provide insight into the likelihood of a regulation having its desired safety effect. Ease of Use Ease of use is an important consideration because requirements must be known and understood if they are to be complied with. A review of whether the regulations are written with sufficient 31 See Special Report 234: Designing Safety Regulations for High-Hazard Industries, TRB, 2018.

PREPUBLICATION COPY—Uncorrected Proofs 32 clarity for ease and consistency of use might take into account whether explanatory notes are needed to ensure uniform application. Consideration might also be given to the number of related technical policy documents. A large number of such documents may suggest a set of regulations that demands a great deal of supplemental explanation is lacking in basic clarity. Moreover, the larger the number of such documents, the greater the likelihood that there will be inconsistencies and even conflicts among them, increasing the potential for inconsistent regulatory understanding and varying levels of compliance by users. Technical Accuracy Technical accuracy is another regulatory quality that can be reviewed for the purpose of making inferences about a regulation’s effectiveness. In the case of the USCG’s intact and damage stability regulations and relevant technical documents, one might consider whether the regulations are based on static, quasi-static, or dynamic stability methods and whether they provide realistic and sufficient coverage of intact and damage vulnerabilities associated with vessel size and type. By examining a range of scenarios involving vessel types and sizes that have different susceptibilities to stability problems, such as a partial stability failure (excessive roll/acceleration, vessel heeled only) and a total stability failure (capsize, vessel lost), judgments may be made about the robustness of the requirements. Scope of Applicability The share of a vessel fleet that must comply with the regulations, particularly in cases in which existing vessels receive “grandfather” exemptions, has a direct impact on the effectiveness of a regulation in furthering a desired safety outcome. As discussed in Chapter 3, the intact and particularly the damage stability requirements for ocean-going ships have been updated and significantly expanded in recent years. Probabilistic damage stability requirements were first added in 1992 to the International Convention for the Safety of Life at Sea (SOLAS)32 for new- build freight vessels exceeding 100 m in length, including new roll-on/roll-off (ro-ro) vessels and those undergoing major conversions. The effectiveness of this particular regulatory change, therefore, was limited to a small portion of the fleet. The passage of time has meant that a larger portion of the fleet is now subject to the regulations, and in this regard the regulations can be viewed as having become more effective. The USCG provided the committee with data on the inspected fleet that included the decade of vessel build (see Table 4-1); however, the data do not indicate whether a vessel is SOLAS-certified and whether it was modified later in service such that it is now subject to the latest SOLAS damage stability requirements. Consequently, the records do not provide a fully accurate count of how many vessels meet modern SOLAS damage stability standards. However, based solely on build date, it can be seen that a majority of freight and tank vessels were built after 1990, which suggests that most of the ocean-going fleet is subject to modern damage stability standards. That said, there still appears to be a large number of older vessels that would not be subject to SOLAS damage stability requirements, under the assumption that many have not undergone major modifications. 32 Subdivision and damage stability for cargo ships; resolution MSC.19(58), adopted May 1990 (SOLAS chapter II- 1, Part B-1, Regulations 25-1 to 25-10; applies to cargo ships constructed after February 1, 1992).

PREPUBLICATION COPY—Uncorrected Proofs 33 TABLE 4-1 Active Inspected U.S.-Flag Vessels by Build Date Vessel Type Decade Built Fr ei gh t B ar ge Fr ei gh t S hi p In du st ri al V es se l M ob ile O ffs ho re D ri lli ng U ni t O ffs ho re S up pl y V es se l O il R ec ov er y Pa ss en ge r (I ns pe ct ed ) Pa ss en ge r B ar ge (I ns pe ct ed ) Pu bl ic T an ks hi p/ B ar ge Pu bl ic V es se l, U nc la ss ifi ed R es ea rc h V es se l Sc ho ol S hi p T an k Ba rg e T an k Sh ip T ow in g V es se l A ll V es se l S er vi ce s 1860–1869 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 1870–1879 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 2 1880–1889 0 0 0 0 0 0 6 0 0 0 0 0 0 0 0 6 1890–1899 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 2 1900–1909 1 0 0 0 0 0 5 0 0 0 0 0 0 0 0 6 1910–1919 0 0 0 0 0 0 10 0 0 0 0 1 0 0 0 11 1920–1929 0 0 0 0 0 0 26 0 0 0 0 2 0 0 0 28 1930–1939 1 0 0 0 0 0 24 0 0 0 0 1 0 1 0 27 1940–1949 0 12 1 0 0 0 98 3 0 0 0 0 2 1 5 122 1950–1959 5 13 3 0 0 4 122 6 0 0 0 0 20 0 8 181 1960–1969 4 11 9 0 3 9 327 3 0 0 1 3 136 2 30 538 1970–1979 29 52 26 0 52 19 823 4 1 10 1 0 186 2 76 1,281 1980–1989 33 32 29 1 62 21 1,210 9 0 6 1 11 134 9 72 1,630 1990–1999 33 20 25 0 46 25 1,178 12 1 8 10 4 698 16 37 2,113 2000–2009 38 51 29 1 152 3 1,210 6 3 4 3 6 1,393 28 97 3,024 2010–2019 31 23 26 0 155 9 996 12 2 6 6 2 1,790 33 168 3,259 All Years 175 214 148 2 470 90 6,040 55 7 34 22 30 4,359 92 493 12,231 NOTE: Discrepancies in the tables and charts are due to inconsistencies in the raw MISLE data, such as missing or incorrect entries. SOURCE: USCG, MISLE database (data as of April 2, 2019). NEEDED TECHNICAL STUDIES The committee was asked to identify the kinds of technical studies that are needed for the USCG to review the effectiveness of its stability standards. The committee believes the following studies could be helpful for this purpose. In addition, the USCG could use the risk-based prioritization methodology, presented in Chapter 7, as a basis to evaluate follow-up studies on regulatory effectiveness.

PREPUBLICATION COPY—Uncorrected Proofs 34 A Regulatory Requirements Gap Analysis A systematic and thorough analysis of the differences in the requirements of the various intact and damage stability standards (e.g., the International Maritime Organization [IMO], Class, Subchapter S) would provide a basis for assessing and measuring technical effectiveness among the various stability standards. In the Phase 1 report, many of the differences between Subchapter S, the 2008 Intact Stability Code (IS Code), and SOLAS 2009 were identified. The SOLAS 2020 requirements, which are considered to represent the highest existing intact and damage stability standards for ocean-going vessels, will take effect on January 1, 2020.33 A thorough analysis of the differences among the older, existing, and new requirements would be helpful in reviewing the overall effectiveness of this suite of regulations and in identifying where further improvements are needed to inform development of the next generation of damage and intact stability criteria. By way of example, the USCG could perform stability calculations on a sample of older vessels to determine the level at which they satisfy the current intact or damage stability requirements. Such an analysis would provide some indication of how effective the current standards are in ensuring that the fleet as a whole has adequate stability assurance. Studies of Policy and Guidance Document Relevance Policy and other regulatory guidance documents need to be kept current and consistent with regulatory requirements. Because such documents are essential to furthering the utility and effectiveness of the requirements, periodic assessments of their currency and consistency are equally essential. The Phase 1 report recommended that the USCG carry out a study of stability- related policy documents. The USCG was advised to assess the consistency of the documents within Subchapter S and with one another. Such an assessment would provide the USCG with the opportunity to identify not only those documents that require updating but also those that can be withdrawn or consolidated with other documents. Because this remains an area in which more technical work is needed, the committee suggests a methodology to assess the effectiveness of policy and other guidance documents later in this report (see Chapter 6). Casualty Studies Stability-related casualties are an indicator of the general effectiveness of the regulatory requirements and their application, but they do not necessarily indicate the effectiveness of all of the individual requirements, and particularly the cost effectiveness of regulations. Thus, as a starting point for evaluating effectiveness, the USCG might want to focus on those casualties that cause loss of life or significant injury or property loss. An understanding of the causes of these more serious stability-related incidents will help identify weaknesses in the requirements that have the greatest impact on their overall effectiveness, while pointing to opportunities for cost- effective regulatory enhancements. In addition, the USCG could consider the new Subchapter M regulations for towboats and review accident statistics from before and after the regulations go into effect to gain additional insight on assessing a regulation’s effectiveness when using causality data. Accurate Weight Data Studies Weight data are essential to making stability calculations. A sensitivity study of the impact of inaccurate or uncertain weight data on vessel stability calculations would be helpful in 33 SOLAS 2020; extensive set of amendments to SOLAS Chapter II-1, including revised harmonized damage stability; Resolution MSC.421(98), adopted June 15, 2017(with an in-force date of January 1, 2020).

PREPUBLICATION COPY—Uncorrected Proofs 35 understanding when there is need to improve the accuracy of such data. As discussed in Chapter 3, some vessels such as tankers and bulk carriers have centers of mass at the mid-depth of the vessel or lower due to the nature of the commodities they carry and how they are stowed on the vessel. These vessels have a high margin of stability and a cargo weight that is easily confirmed based on known displacement at measured draft. However, some other vessel types such as container ships, ferries, and ro-ros have distributed units of cargo. The location and weight of these units can affect the location of the vessel’s center of gravity in a manner that may not be readily measured on board. Indeed, due to the potential for significant weight inaccuracy of cargo containers that can affect container ship stability, SOLAS has been amended (Chapter VI, Part A, Regulation 2) to make container weight verification a condition for vessel loading.34 Because some of these vessels operate with a minimum stability margin, the accuracy of the initial lightship incline test can also influence whether the loaded vessel meets stability requirements. The USCG may want to follow up on IMO studies of cargo container weights, coupled with a study of lightship weight data for vessels prone to low stability margins, to determine when and to what extent inaccurate weight data can create a stability risk for different vessel types. VARIABILITY IN STABILITY RISK BY VESSEL TYPES AND SERVICE For reasons previously explained in this chapter and in Chapter 3, some vessel types such as car carriers, container ships, and vessels with large wind area or large deck cargoes, have a lower stability margin, and thus a greater need for close compliance with stability regulations to control stability risks. Both vessel type and service can affect stability risk. Vessels that routinely operate inside the Boundary Lines in protected or partially protected waters are less subject to weather and sea state stability impacts, but they may be more susceptible to grounding, collision, and unexpected high winds. It is therefore important to know how stability requirements account for these different conditions and risk factors. The effects of vessel size and type on stability are illustrated by the following examples: Small Open Passenger Boats Because these vessels typically have very limited freeboard and residual stability after flooding, they depend on benign operating conditions (low wind and waves) for safe operation. The limitation of operations to benign conditions, therefore, requires evaluation when assessing the safety of a vessel and certifying it to carry multiple passengers. Container Ships Modern container ship designs are characterized by fine hull forms with flat transom sterns and extreme bow flare. This design maximizes deck cargo container capacity while minimizing water resistance to achieve high service speeds. It also makes container ships more susceptible to parametric rolling, a form of dynamic instability, which results in extremely high roll amplitudes. Parametric rolling can occur if a container ship is in head, near head, or following seas and encounters waves with lengths similar to the vessel’s own length. Under these conditions, the waterplane area can change significantly, with consequent loss of transverse stability. As 34 See Resolution MSC.380 (94) Amendments to SOLAS as amended, Chapter VI, Part A, Regulation 2. http://www.imo.org/en/KnowledgeCentre/IndexofIMOResolutions/Maritime-Safety-Committee- (MSC)/Documents/MSC.380(94).pdf.

PREPUBLICATION COPY—Uncorrected Proofs 36 stability decreases (i.e., lower righting arm) when the ship is on the wave crest and increases (i.e., higher righting arm) when it is in the wave trough, a resonant roll motion can occur as the varying transverse stability provides impetus to the rolling action at both extremes of the motion. Roll angles as great as 35 to 40 degrees with simultaneous extreme pitching have been reported, in some cases causing heavy damage and loss of containers (France et al. 2003). Operational and design measures, such as modifying course and speed, and the use of passive or active stabilization systems can help mitigate or avoid parametric roll. IMO and many of the classification societies have made recommendations to container ship designers and masters for avoiding parametric rolling situations (IMO 2007; ABS 2019). Parametric roll is also being addressed in the development of the second-generation intact stability criteria. In the meantime, questions remain about the effectiveness of the current stability regulations and operational guidance in avoiding parametric roll. Car Carriers Ro-ro car carriers have experienced losses in stability leading to severe lists (of 40 degrees or more) and casualties. Causes include improper ballasting operations during ballast water exchange,35 underestimating of cargo weights leading to insufficient residual stability margin during a turn,36 and shifting of improperly secured cargo in a storm.37 Although these incidents of stability loss may not have been attributable to shortcomings in the stability regulations per se, they do illustrate the importance of considering human error when developing regulations. In vessel types, such as car carriers, that have a higher susceptibility to stability losses to begin with (because of features such as high freeboard [sail area] and cargo located at high deck levels), the potential for risk arising from human error in regulatory compliance cannot be neglected and should factor into assessments of regulatory content, design, and effectiveness. Bulk Carriers Cargo liquefaction and consequent cargo shifting in bulk carriers transporting mineral concentrates, such as copper, iron, lead nickel, and bauxite that contain some latent moisture (although not visibly wet in appearance), present a stability risk for dry bulk shipping.38 Severe list and even capsizing casualties have occurred in large ocean-going bulk carriers when their cargoes with high latent moisture content are exposed to agitation in the form of ship’s motion, wave impact, and engine vibration during a voyage resulting in compaction of the cargo, causing cargo liquefaction and cargo flow to one side in a roll in heavy seas. To mitigate this risk, IMO has instituted the International Maritime Solid Bulk Cargoes code, which stipulates that shippers are responsible for the testing and sampling of the cargo moisture levels and ensuring that they are below levels at which liquefaction can occur. Nevertheless, casualties arising from cargo liquefaction have continued to occur in bulk carriers carrying mineral concentrates in international ocean trades subject to IMO requirements. It merits considering whether the current 35 For example, see the incident with the car carrier M/V Cougar Ace: https://en.wikipedia.org/wiki/MV_Cougar_Ace or https://safety4sea.com/cm-cougar-ace-how-improper-ballast- water-exchange-can-prove-costly. 36 See the Marine Accident Investigation Branch (MAIB) accident report: https://www.gov.uk/maib-reports/listing-flooding-and-grounding-of-vehicle-carrier-hoegh-osaka. 37 See the example of the Modern Express: https://www.dnvgl.com/article/dnv-gl-salvage-support-for-the-modern- express--89595. 38 See the Bulk Carrier Casualty Report: https://www.intercargo.org/wp-content/uploads/2018/05/bulk-carrier- casualty-report-2017.pdf.

PREPUBLICATION COPY—Uncorrected Proofs 37 regulations governing U.S. flag and domestic vessels are adequate to address the stability concerns arising from cargo liquefaction. ASSESSING THE ROLE OF INTERNATIONAL REGULATIONS AND CLASS RULES As noted earlier in this report, the USCG requires newer ocean-going ships to meet the SOLAS international stability regulations, while older ships (pre-1992) and those without an international convention certificate only have to meet the requirements in Subchapter S. Inasmuch as the SOLAS requirements apply to a segment of the U.S. flag fleet, a review of their effectiveness is within USCG’s purview. Because of the wide variety of vessel types and sizes, as well as operating and environmental conditions, the stability of a ship at sea can involve complex hydrodynamic phenomena that have increasingly been investigated and are now better understood. Most vessels on international voyages are exposed to ocean wind and wave conditions and may be subject to dynamic stability risks. Although the 2008 IS Code was based on the state-of-the-art concepts available at the time it was developed, these were largely based on static and quasi-static stability. The IMO has since recognized that the motion of ships at sea should be treated as a dynamic system and the code should account for ship interactions with environmental conditions such as wave and wind excitations. With this interest in mind, the IMO embarked on improving the 2008 IS Code by adding second-generation stability criteria derived from physics-based numerical simulations and scaled model experiments. The second-generation stability criteria (see Appendix F for an overview) promise to improve the effectiveness of stability regulations to address the true risks to vessels from loss of stability in adverse dynamic operating conditions, and not just from loss of quasi-static stability. If these new international criteria are approved as amendments to SOLAS, they would be applied to U.S. flag vessels with SOLAS certificates, and the variance with the stability regulations in Subchapter S as applied to the domestic fleet will grow. Because both sets of regulation apply to the U.S. flag fleet, the effectiveness of both sets will need to be reviewed periodically. With regard to class rules, SOLAS and the other international conventions permit the flag state to delegate to a recognized class society certain statutory certification and services, including determinations of load line and stability in the intact and damaged conditions. The delegation is allowed in recognition of the fact that many flag states do not have adequate technical expertise, manpower, or global coverage to undertake all the necessary statutory certification services. A class society’s statutory activity, however, is distinct from its own classification requirements. Because of its role as a recognized organization, a class society’s stability rules for ocean-going vessels are the same as those in the international conventions. Similarly, for non-ocean-going domestic vessels the class stability requirements for such vessels are largely the same as those in USCG regulations. REFERENCES Abbreviations ABS American Bureau of Shipping IMO International Maritime Organization IMO MSC International Maritime Organization Maritime Safety Committee SNAME Society of Naval Architects and Marine Engineers

PREPUBLICATION COPY—Uncorrected Proofs 38 Guide for the Assessment of Parametric Roll Resonance in the Design of Container Carriers. ABS, 2019. https://ww2.eagle.org/content/dam/eagle/rules-and- guides/current/design_and_analysis/guide-assessment-parametric-roll-resonance-design- containercarriers/parametric-roll-guide-apr19.pdf. France, W. N., M. Levadou, T. W. Treakle, J. R. Paulling, R. K. Michel, and C. Moore. An Investigation of Head-Sea Parametric Rolling and Its Influence on Container Lashing Systems. SNAME Marine Technology, Vol. 40, No. 1, January 2003. Revised Guidance to the Master for Avoiding Dangerous Situations in Adverse Weather and Sea Conditions. IMO MSC, MSC.1/Circ. 1228, January 11, 2007. http://imo.udhb.gov.tr/dosyam/EKLER/1228.pdf.

Next: 5 Improving the Stability Regulations Outside of Subchapter S »
Review and Update of U.S. Coast Guard Vessel Stability Regulations and Guidance Get This Book
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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.

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