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Review of U.S. Coast Guard Vessel Stability Regulations (2018)

Chapter: APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS

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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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Suggested Citation:"APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS." National Academies of Sciences, Engineering, and Medicine. 2018. Review of U.S. Coast Guard Vessel Stability Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25258.
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128 APPENDIX H WEIGHT GROWTH IN PASSENGER VESSELS International Maritime Response to Weight Growth and Lightship Verification Schemes International Regulations Because of the potentially negative impacts that weight growth (or weight creep) can have on a ship’s stability, many maritime nations have mandated lightship verification schemes for various classes of vessels. The following represent a list of international lightship verification regulations for passenger vessels. - International Convention for the Safety of Life at Sea (SOLAS), chapter II-1, regulation 5, paragraph 5; resolution MSC.421(98), adopted on 15 June 2017 - International Maritime Organization (IMO), International Code on Intact Stability, 2008 (2008 IS Code), part B, chapter 8, paragraph 8.1.5; resolution MSC.267(85), adopted 4 December 2008 - Canada, Transport Canada TP 10943, Part III, Section 20.(1) to 20.(3) - UK, Maritime and Coastguard Agency (MCA) Large Commercial Yacht Code (LY3) 11.5.3 Large Commercial Yachts Carrying Passengers - Cayman Islands, The Passenger Yacht Code (PYC) Chapter 4, Part II, 4.3(3)(a) Large Commercial Yachts Carrying Passengers - Australia, National Standard for Commercial Vessels (NSCV), Part 6, Subsection 6C, 3.4.1(a) - Danish Maritime Authority, Chapter II-1, Part B-1, Regulation 18 - Polish Registry, Rules for the Classification and Construction of Small Sea-Going Vessels, Part IV, 1.5.5 - UK Marine Safety Notice (MSN) 1823, Safety Code for Passenger Vessels Operating Solely in UK Waters, 10.4.1(1) and 10.4.2(1)(c) - India Ministry of Shipping, Construction, Survey, Certification and Operation of Indian River Sea Passenger Vessels Type 3 and 4, 4.18.4

129 A majority of the regulations listed use a verification scheme that involves a periodic lightship deadweight survey on a 5-year interval. Other forms of lightship verification include a weight tracking program, the use of lightship verification freeboards, or a declaration by the owner that either no changes or only minor changes have occurred to the vessel’s lightship. These regulations are largely a result of the Herald of Free Enterprise disaster. The United Kingdom’s Department of Transportation Report40 found that the vessel and her sistership’s lightship weight had increased an average of 0.3% per year, or about 1.5% every 5 years. Written Declaration for Periodic Lightship Verifications A vessel’s owner could use this lightship verification option when no changes have occurred to the vessel since the last lightship verification. The option could also be used when only minor changes, well below the 2% weight change threshold, have occurred and these changes, in general, can be documented. In this case the documentation for changes need not be detailed, only sufficient enough to allow verification of what the changes were and that the weights involved were small. The declaration would need to be made in writing by the vessel’s owner and would have to be reviewed and accepted by the U.S. Coast Guard (USCG) inspector (Officer in Charge, Marine Inspection [OCMI]) as part of a formal walk through survey of the vessel for weight change as part of the 5-year Certificate of Inspection (COI) renewal survey. It is important that this declaration cover the period from the last inclining or simplified stability test, not just from the last declaration. This is critical to ensure that all of the possible changes are captured since the vessel’s last known lightship condition. The written declaration option could cover a vast majority of the existing U.S. passenger vessel fleet, particularly those 40 See https://www.gov.uk/maib-reports/flooding-and-subsequent-capsize-of-ro-ro-passenger-ferry-herald-of-free- enterprise-off-the-port-of-zeebrugge-belgium-with-loss-of-193-lives.

130 with simple outfitting, such as charter fishing vessels or excursion-only passenger vessels with only basic food service. The written declaration is currently used in the following maritime regulations as an option for periodic lightship verification:  Canada, Transport Canada, Passenger Vessels less than 24 Meters Long  UK, MSN, Vessels Subject to Stability Heel Test Weight Tracking Program Lightship Verification Scheme The basic weight tracking program consists of the owner or master recording the changes made to the vessel after the vessel’s initial inclining. At a minimum, the following information would be required to be recorded. 1. A description of the weight change. 2. The weight of the change added or removed. 3. The location of weight change. Documentation of the current state of weights at the time of the survey could be supplemented with video of spaces and equipment. This minimal weight-tracking program would require the calculations to check if the lightship condition has changed more than the 2% weight change or had a 1% change in longitudinal center of gravity (LCG). The weight-tracking program could be enhanced by the use of a suitable form that would allow the owner or master to perform the required calculations to verify the lightship condition. This would require the owner or master to have advanced knowledge of basic stability LCG/vertical center of gravity (VCG) moment calculations and sufficiently detailed and scaled plans of their vessel to measure the local LCG and VCG of each weight change accurately.

131 Several important factors would need to be considered when developing a weight- tracking program for a specific vessel. The first is how small a weight change must be included. Too low a cutoff will be too burdensome for the master or owner to track. Too high a cutoff value will affect the accuracy of the tracking, as many small changes may not be recorded. The second is developing a weight-tracking program that allows the master or owner to record the changes easily. Operators of small passenger vessels are busy at the height of the season and have less time to update weight-tracking documentation. Third, as with the written declaration, the record of weight changes would need to be cumulative from the last inclining or simplified stability test, not just from the last time the weight tracking program’s results were compared to the inclined lightship condition. This is critical to ensure all of the possible changes are captured since the vessel’s last known lightship condition. The weight-tracking program seems best suited to vessels of modest complexity that would not be expecting to make a large number of changes in a 5-year period. Dinner or excursion vessels with onboard food preparation and enclosed seating areas could be likely candidates for a weight-tracking program. A weight-tracking program scheme is currently used in the Australian National Standard for Commercial Vessels (NSCV) for vessels less than 12 m long. The weight-tracking program scheme was also mandated for use by new U.S. towing vessels in the USCG’s Subchapter M regulations. Lightship Verification Marks or Freeboards Scheme While the maximum stability loading marks are not a practical tool for lightship verification, a similar approach using “lightship verification” marks or freeboards could be used to check a change in lightship weight or a shift in a vessel’s LCG. For this scheme, an easily repeatable loading condition would be developed for the vessel from the approved inclining or simplified

132 stability test data. For example, fuel could be at 50% and water tanks, pressed full, and sewage at 25%. In addition, no passengers and only a limited crew would be in the lightship verification loading condition. The lightship verification loading condition would also have the maximum 2% weight growth built in for ease of verification. It would be reasonable for the master or owner to configure his or her vessel to match this loading condition at each of the 5-year COI renewal inspections. It would also be reasonable for the OCMI to be able to verify that the vessel was at the required loading condition. The OCMI would only need to verify that the tank soundings and the general stores matched those of the lightship verification loading condition, the same as would be required for an inclining or deadweight survey. Verification of any changes in the lightship weight or the LCG would then depend on whether loading marks or freeboard measurements were being used. In the case of using lightship verification loading marks, these marks would be applied to the vessel at the time of the initial COI based on the approved lightship condition and the desired lightship verification loading condition to be used. The lightship verification marks would be located at the bow and stern of the vessel similar to maximum stability loading marks. Verification is then readily apparent by visual inspection of the lightship verification loading marks. If both bow and stern marks are at or above the waterline, the current lightship condition is within the 2% allowable weight change and there has been no significant change in the LCG. If bow or stern marks are not visible, the vessel’s lightship must be checked by a formal stability review because either the lightship has increased by more than 2% or the LCG has shifted significantly. The alternative to using physical marks would be to use freeboards measured at defined locations along the hull. The baseline freeboards would be calculated using the same repeatable

133 lightship verification loading condition as described above. This method does require the taking of a series of freeboards as opposed to just looking at a set of physical marks. This is possible using the vessel’s crew with verification by the OCMI, thus not requiring the services of a professional naval architect and minimizing the costs to the vessel owner. The OCMI must already verify the freeboard readings and marks used in the simplified stability test for small Subchapter T passenger vessels, so verifying the lightship verification freeboards to the necessary degree of accuracy is realistic. The advantages to using lightship verification loading marks or freeboards are the low cost to the vessel owner both in time required to prepare the vessel and in performing the verification. Preparing the vessel can be done during the week before the COI inspection and primarily would involve cleaning up the vessel, putting items where they belong, and removing items that do not belong, which is good seamanship practice. To verify that the vessel is in the correct loading condition takes approximately an hour, while the actual verification takes just minutes when using physical marks on the hull. The use of the freeboards version may require an additional hour or two to take the freeboards and compare the results. The lightship verification loading method will also not require any outside professional assistance, such as a naval architect, further minimizing costs to the vessel owner. The other advantage to using lightship verification marks or freeboards is that this method always compares the results to the last approved inclining or simplified stability test lightship condition. However, there are two drawbacks to using the lightship verification loading marks or freeboards for lightship verification. First, the only variable in this method that may be difficult to control is the density of the water at the time of the lightship verification check for two reasons. One, the water density at the time of initial inclining where the vessel was built is likely

134 to be different from the density at the time of periodic checks where the vessel operates. Two, the vessel may operate at different locations throughout its life, which could have significantly different water densities. An allowance for these differences will need to be factored into any lightship verification program that uses loading marks or freeboards. The second drawback is that the approach will only indicate if the lightship is different from the original lightship condition used in the stability calculations. This approach cannot tell how much the lightship conditions have changed to revise the stability calculations. The master or owner may get a sense of whether the change is relatively small or large, but that is all. The lightship verification freeboard method is used by the United Kingdom in its Safety Code for Passenger Ships Operating Solely in UK Categorized Waters, MSN 1823. This method is only applicable to small vessels utilizing the heel test for initial stability verification (similar to the USCG simplified stability test). At the time of the heel test, freeboard measurements are taken at the bow, stern, and amidships along with the locations used and recorded. At the required 5-year intervals, the vessel is placed into the original heel test condition and freeboards are taken at the previously documented locations. The UK method considers the freeboards to be unchanged if they are within 2 cm (3/4 in.) at the bow and stern of the initial recorded values. Lightship Verification by a Deadweight Survey The last method is the verification of a vessel’s lightship condition by a formal deadweight survey. The deadweight survey is more involved than the use of lightship verification marks or freeboards, weight tracking, or a written declaration. The deadweight survey has several advantages over these other lightship verification schemes: 1. The vessel would not have to be configured to a particular loading condition.

135 2. The results would not only tell if the lightship condition has changed, but also by how much the lightship has actually changed. The drawbacks of a deadweight survey include: 1. The deadweight survey requires the use of a professional naval architect, making this option more expensive than other lightship verification methods. 2. The vessel would be out of service longer than for the lightship verification loading marks or freeboards. This time could be mitigated somewhat, however, as the vessel does not have to be loaded to a particular configuration before the deadweight survey. The deadweight survey would be most applicable to large vessels, such as cruise ships, with multiple tanks, large stores, and significant amounts of outfitting. The deadweight survey would also be applicable to any vessel where it is likely the vessel is near the 2% allowable weight change, as it would be the most accurate method of determining weight change. This method is the one required by IMO for use on international passenger vessels, as well as the one required by the majority of the maritime regulations previously noted. Examples of Weight Growth in Ships All boats and ships, whether large or small, private or commercial, power or sail, can and likely do undergo weight growth over their lifetime. This weight growth can come from three typical sources. One, “major conversions,” involves a change in a vessel’s service or mission, such as converting an Offshore Supply Vessel (OSV) to an inter-island passenger or cargo ferry or a fishing vessel. A second source involves “significant alterations” to a vessel, such as to meet new regulations or to meet changes in market requirements. Examples of this source would include the installation of exhaust gas scrubbers or the addition of roll on/roll off (ro-ro) space and ramps to a container vessel to allow for additional market capabilities at the ports served. A third source

136 involves the slow increase in a vessel’s weight from the accumulation of many small changes or the onboard accumulation of parts that may occur over time. Usually the first two sources of weight growth are readily apparent and would require a full stability review by attendant regulatory authorities. The last source of weight growth is a concern to the long-term safety of a ship. The accumulation of the many small changes and the spare parts and other items that can occur over a vessel’s lifetime can easily go undetected by the master and crew of the vessel and is often referred to as “weight creep.” Notional Effects of Weight Creep on a Passenger Vessel’s Stability Weight creep can adversely affect a vessel’s stability, particularly in passenger vessels, for two reasons. First, the increase in weight will lower the vessel’s freeboard when carrying the permitted full deadweight loads, which reduces both the range of positive stability and lowers the righting arms (GZ) throughout the GZ curve. This would not apply to vessels with a Load Line certificate, which are prohibited from sailing with a deeper draft than the Load Line. Second, the changes typically occur in the passenger spaces, which for most U.S. small passenger vessels are located on and above the main deck. The resulting increase in the vessel’s VCG has the same impact on the GZ curve as the loss of freeboard, i.e., lower righting arms and range of positive stability. Passenger vessels, particularly those with accommodation spaces, are constantly seeing small changes in their outfitting to respond to changing market conditions and passenger expectations. For example, where plastic tables and chairs were acceptable in the past, maybe metal-framed cushioned chairs with glass-topped tables are now expected. The potential effect that upgrades to the tables and chairs have on board an excursion vessel is an interesting question. For this illustration, the operator is replacing 200 chairs and 50 tables. Upgrading the

137 chairs by just 10 lbs apiece and the tables by 30 lbs apiece results in a weight growth of 3,500 lbs. On the surface, this change appears to be a small and insignificant one, particularly on a vessel that would have a lightship weight of approximately 250 long tons (560,000 lbs). This change alone, about 0.6% of lightship, would have a very small impact on the vessel’s stability. However, this could be only one change among many that may occur over the 20-year life of the vessel. Other changes could include additional furnishings, upgrades to the food service areas (bars and buffets), renovated toilet spaces, and changes to draperies and carpeting. Over a 20-year period, the overall weight increase will add up to a larger number. This is in addition to weight creep from the typical accumulation of “stuff,” such as spare parts. Coupled with the fact that the majority of these changes occur in the passenger spaces located in the upper portions of the vessel, a significant long-term negative impact on the vessel’s stability. A Notional Study of the Impact of Lightship Weight Growth on the Intact Stability of a Small Passenger Vessel The use of a sensitivity study is provided as an example to explore the potential impacts of small, incremental weight growth on an USCG inspected (under Subchapter K or T) passenger vessel's intact trim and stability. This type of study could provide the USCG a guide for determining which classes or types of passenger vessels might be more susceptible to weight growth. Wide varieties of small passenger vessels exist, all with a variety of hull designs, particularly among the Subchapter T vessels. Many of these small passenger vessels are day excursion boats, and do not include accommodations. This sensitivity study example illustrates the impact of weight growth on one type of vessel and the results presented may not be indicative of results for other types of small vessels. The study’s purpose is to provide a methodology for an expanded study that could be conducted for a wider variety of vessel designs.

138 The notional weight growth to be added to the vessel for this example would be based on the vessel's lightship weight, because a percentage increase in lightship weight is one of the triggers for determining if a vessel must undergo an additional stability review. To capture a vessel’s sensitivity to weight growth, a possible range for the weight growth for this example is 0.25% to 6%. Because small incremental weight changes in passenger vessels are likely to occur in the passenger spaces, the vertical and longitudinal center of the weight growth for this example will be biased toward the center of the passenger spaces. As part of an expanded sensitivity analysis, the weight growth center of gravity could vary by the type of vessel and the different mechanisms that could cause weight growth. For example, on vessels without accommodation spaces, weight growth could occur more in the hull from machinery upgrades or additional stores and spares carried onboard. The subject vessel for the sensitivity study example is a 280-ft overnight river cruise boat (see Figure H-1) with the lightship at 1,842 long tons. To evaluate the vessel's sensitivity to weight growth, the vessel’s intact trim and stability were calculated at the following loading conditions:  Baseline Condition: Vessel at her design full load departure condition.  2% Growth: 2% of the vessel’s lightship weight was added to the baseline.  4% Growth: 4% of the vessel’s lightship weight was added to the baseline.  6% Growth: 6% of the vessel’s lightship weight was added to the baseline. Figure H-1 Subject vessel for the hypothetical sensitivity study: 280-ft overnight river cruise boat. NOTE: CG = center of gravity.

139 The weight growth was added at the approximate vertical and longitudinal center (see Figure H-1) of the passenger spaces above the main deck as this is where most of the weight growth will likely occur. Figure H-2 shows the resulting GZ curves for each of the loading conditions described above. Figure H-2 The GZ curves for each of the hypothetical loading conditions. From these righting arm curves and additional stability criteria results, such as downflooding angles and the angle of maximum and vanishing righting arm (GZ), an evaluation of the subject vessel’s sensitivity to weight growth can occur. A detailed review of some of the trim and stability impacts are calculated as follows. In this example, the increase in draft for the first 2% of weight growth is 1-3/8 in. If this were to occur over a 5-year period, that is a little more than 1/4 in. per year (see Table H-1).

140 Table H-1 Effect of Weight Growth on the Vessel’s Midships Draft Midship’s Increase in Percent Increase Condition Draft—Feet Midships Draft from Baseline (BL) Baseline 8.28 — — +2% Growth 8.39 1-3/8” +1.3% +4% Growth 8.50 2-5/8” +2.7% +6% Growth 8.61 4” +4.0% This small change in draft is not likely to be noticed by the crew or the USCG OCMI, and with the same weight growth rate over 10 or 15 years, it is unlikely this increase in draft would be noticed either. It is not unimaginable that a weight growth of 4% or 6% could occur and be unnoticed by the crew or the OCMI over a period of more than 20 years. The effect of weight growth on the vessel’s VCG did result in a 6 to 8 in. increase for weight growth in the 4% to 6% range (see Table H-2) as the vertical center of the passenger spaces is significantly higher than the lightship VCG. This increase in VCG is part of the reason for the reduction in the GZ curves, with the other being the increase in draft (and thus reduction in freeboard) previously discussed. Table H-2 Effect of Weight Growth on the Vessel’s VCG VCG Above Increase in Percent Increase Condition Baseline (BL)–Feet VCG from BL from BL Baseline 20.92 — — +2% Growth 21.15 2-3/4” +1.1% +4% Growth 21.38 5-1/2” +2.2% +6% Growth 21.60 8-1/8” +3.3% The impact on the vessel’s LCG though was basically nil (see Table H-3), as the longitudinal center of the passenger spaces is fairly close to the vessel’s lightship LCG. Table H-3 Effect of Weight Growth on the Vessel’s LCG LCG Aft Increase in Percent Change Condition Amid–Ft LCG from Baseline of LBP (268 ft) Baseline –9.51 — — +2% Growth –9.61 1-1/4” <0.00% +4% Growth –9.71 2-1/2” <0.00% +6% Growth –9.81 3-3/8” <0.00% NOTE: LBP = length between perpendiculars.

141 The reduction in area under the GZ curve is very significant as the weight growth enters the 4% to 6% range (see Table H-4). At a 6% weight growth the reduction in area is about 25% from the baseline loading condition. The rapid reduction in area is due to the GZ curves becoming both lower and having a shorter range of positive stability from both a reduction in freeboard and an increase in the VCG, as well as the point of downflooding occurring at a lower heel angle. Table H-4 Effect of Weight Growth on the Vessel’s Area Under the GZ Curve from 0 Degrees to the Angle of Downflooding Angle of Area 0 Degs to Percent Reduction Condition Downflood Downflood–FtDeg from Baseline Baseline 15.8 21.46 — +2% Growth 15.5 19.48 –9.2% +4% Growth 15.2 17.66 –17.7% +6% Growth 14.9 15.96 –25.6% Similar to the impact on the area to the downflood point, the area under the GZ curve to the point of maximum GZ also shows a significant reduction as the weight growth enters the 4% to 6% range (see Table H-5) . At a 6% weight growth, the reduction in area is even greater at about 28% from the baseline loading condition. The reasons for this reduction are the same as for the area to downflooding, lower GZ curves in addition to the angle of the maximum GZ also becoming lower. Table H-5 Effect of Weight Growth on the Vessel’s Area Under the GZ Curve from 0 Degrees to the Angle of Maximum GZ Angle of Area 0 Degs to Percent Reduction Condition Max GZ Max GZ–FtDeg from Baseline Baseline 15.8 27.36 — +2% Growth 15.5 25.54 –6.7% +4% Growth 15.2 22.01 –19.6% +6% Growth 14.9 19.68 –28.1% The example vessel in the weight growth sensitivity study did exhibit some significant reductions in stability at the higher levels of weight growth. Interestingly, the example vessel did not fail any of the Part 170.173 criteria for vessels on a protected route until the weight

142 growth was at 6%. In addition, this failure was only in the required downflooding angle just going below the 15-degree minimum (14.9 degrees). The area to the downflooding point is still more than 50% of that required, 15.96 ft-degs versus the minimum required 10.0 ft-degs. This result is due to the vessel’s conservative design that included an allowance for the potential future weight growth being explored in this sensitivity study. This notional study does indicate that a similar vessel, which initially was just meeting the minimum stability requirements, might have potential stability issues because the loss in stability levels is relative to the increase in weight growth. Table H-6 summarizes the resulting trim and stability values and includes the actual values for the various parameters calculated, as well as the percent change from the baseline loading condition.

143 Table H-6 Summary Results from Sensitivity Study of the Impact of Lightship Weight Growth on the Intact Stability of a Small Passenger Vessel

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On September 12, 2018, TRB released a letter report that reviews regulations and policy documents that establish vessel stability requirements for U.S. Flag vessels. The review, conducted at the request of the U.S. Coast Guard Office of Design and Engineering Standards, considers options to make and keep stability requirements current, align them better with international standards, and improve their consistency, clarity, and usability. In addition to identifying a series of promising options for these purposes, the report makes recommendations to the Coast Guard on coordinating with industry advisory groups and collecting, managing, and analyzing data to inform regulatory decisions.

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