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

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84 APPENDIX D CONTENT AND ORGANIZATION ISSUES WITH SUBCHAPTER S This appendix provides examples of Parts of Subchapter S that have issues with the content or organization that are worth resolving by the U.S. Coast Guard (USCG) as part of an effort to update and improve Subchapter S. The report offers ideas on how to address them. 170.173, Criterion for Vessels of Unusual Proportion and Form In the parts of this section that require a minimum area under the righting arm curve up to 30 or 40 degrees of heel, it is not clear from where the angle ranges are to be started from, upright even list condition or the equilibrium heeled condition. Although not a concern for most vessels that have little to no initial list, there are some classes of vessels such as car ferries that have offset houses and traffic lanes and may at times operate with several degrees or more of list. Doing the area calculations from the upright condition and not the worst-case equilibrium heel angle could result in insufficient area under the righting area curve when heeling to the listed side. 170.295 Special Consideration for Free Surface of Passive Roll Stabilization Tanks and 172.030(b) Grain Exemptions for Certain Vessels These two requirements are difficult to understand, contain confusing requirements and definitions, have formula typographical errors, and employ simplified formulas designed for pencil and paper calculations. For example, in 170.295 (see Box D-1), determining the free surface effect in passive roll stabilization tanks uses a confusing complex hand calculation process that includes hand graphical plotting, and the results in the end are only a modification to be applied to the free surface corrections from Section 170.285. These calculations can now be done easily and accurately using today’s computer-based stability calculation programs.

85 Box D-1 170.295 Special Consideration for Free Surface of Passive Roll Stabilization Tanks (a) The virtual increase in the vertical center of gravity due to a liquid in a roll stabilization tank may be calculated in accordance with paragraph (b) of this section if—(1) The virtual increase in the vertical center of gravity of the vessel is calculated in accordance with § 170.285(a); and (2) The slack surface in the roll stabilization tank is reduced during vessel motions because of the shape of the tank or the amount of liquid in the tank.(b) The virtual rise in the vertical center of gravity calculated in accordance with § 170.285(a) for a stabilization tank may be reduced in accordance with the following equation: E.F.S. = (K)(F.F.S.) where—E.F.S. = the effective free surface, F.F.S. = the full free surface calculated in accordance with § 170.285(a). K = the reduction factor calculated in accordance with paragraph (c) of this section. (c) The factor (K) must be calculated as follows:(1) Plot (I/d)tan T on Graph 170.295 where—(i) (I) is the moment of inertia of the free surface in the roll tank; (ii) (d) is the density of the liquid in the roll tank; and (iii) (T) is the angle of heel.(2) Plot the moments of transference of the liquid in the roll tank on Graph 170.295. (3) Construct a line A on Graph 170.295 so that the area under line A between T = 0 and the angle at which the deck edge is immersed or 28 degrees, whichever is smaller, is equal to the area under the curve of actual moments of transference between the same angles. (4) The factor (K) is calculated by determining the ratio of the ordinate of line A to the ordinate of the curve of (I/d) tan T, both measured at the angle at which the deck edge is immersed or 28 degrees, whichever is smaller. SOURCE: 46 Code of Federal Regulations (CFR), Subchapter S. In 172.030(b)(5) (see Box D-2), the definition of metacentric height (GMR) and metacentric height, increment (GMI) are hard to understand and the required GMR/GMI is not clearly indicated. In addition, the formula in (i) is missing the division sign “/”, as it should read r =

86 (available freeboard) / (beam). The same missing “/” issue also occurs in the formula given in (ii). Box D-2 172.030(b)(5) Exemptions for Certain Vessels (5) The transverse metacentric height (GM), in meters, of the vessel throughout the voyage, after correction for liquid free surface, has been shown by stability calculations to be in excess of the required GM (GMR), in meters. (i) The GMR is the sum of the increments of GM (GMI) multiplied by the correction factor, f and r. Where: r = (available freeboard) (beam) of the vessel and f = 1 if r is >0.268 or f = (0.268 r) if r is <0.268. (ii) The GMI for each compartment which has a slack surface of grain, i.e., is not trimmed full, is calculated by the following formula: GMI = (B3 × L × 0.0661) (Disp. × SF) where: B = breadth of slack grain surface (m) L = Length of compartment (m) Disp. = Displacement of vessel (tons) SF = Stowage factor of grain in compartment (cubic meters/tons) SOURCE: 46 CFR, Subchapter S. Conflicting Definitions of Stability Requirements in Subchapter S Downflooding Definition Conflicting definitions of the same stability requirements located in two or more locations can also cause confusion in the Subchapter S regulations. One such example is the definitions of downflooding and downflooding angle in Subchapter S. Currently downflooding and downflooding angle are defined in the following sections of Subchapter S (see Box D-3 for definition excerpts). 170.055(e) Definitions Concerning a Vessel 174.035(b)(1) Definitions (Mobile Offshore Drilling Units) 174.045(c) Intact Stability Requirements (Mobile Offshore Drilling Units) 170.055(g) Definitions Concerning a Vessel 171.055(f) Intact Stability Requirements for a Monohull Sailing Vessel 172.090(d) Intact Transverse Stability (Hazardous Liquid Barges) 173.095(e) Towline Pull Criterion

87 174.015(b) Intact Stability (Deck Cargo Barges) 174.035(b)(2) Definitions (Mobile Offshore Drilling Units) Box D-3 Downflooding Definition Excerpts from 46 CFR, Subchapter S 170.055(e) Downflooding means, except as provided in 174.035(b), the entry of seawater through any opening into the hull or superstructure of an undamaged vessel due to heel, trim, or submergence of the vessel. 174.035(b)(1) Downflooding means the entry of seawater through any opening that cannot be rapidly closed watertight, into the hull, superstructure, or columns of an undamaged unit due to heel, trim, or submergence of the unit. 174.045(c) For the purposes of this section, openings fitted with weathertight closing appliances specified in 174.100(b) are not considered as openings through which downflooding could occur if they can be rapidly closed and would not be submerged below the unit’s waterline prior to the first intercept angle, except that ventilation intakes and outlets for machinery spaces, crew spaces, and other spaces where ventilation is normally required are considered as openings through which downflooding could occur regardless of location. 170.055(g) Downflooding angle means, except as specified by 171.055(f), 172.090(d), 173.095(e), 174.015(b), and 174.035(b)(2) of this chapter, the static angle from the intersection of the vessel’s centerline and waterline in calm water to the first opening that cannot be closed watertight and through which downflooding can occur. 171.055(f) For the purpose of this section, the downflooding angle means the static angle from the intersection of the vessel’s centerline and waterline in calm water to the first opening that cannot be rapidly closed watertight. 172.090(d) For the purpose of this section, the downflooding angle means the static angle from the intersection of the vessel’s centerline and waterline in calm water to the first opening that does not close watertight automatically. 173.095(e) For the purpose of this section, the downflooding angle means the static angle from the intersection of the vessel’s centerline and waterline in calm water to the first opening that does not close watertight automatically. 174.015(b) For the purpose of this section, the downflooding angle means the static angle from the intersection of the vessel’s centerline and waterline in calm water to the first opening that does not close watertight automatically. 174.035(b)(2) Downflooding angle means the static angle from the intersection of the unit’s centerline and waterline in calm water to the first opening through which downflooding can occur when subject to a wind heel moment (Hm) calculated in accordance with 174.055. SOURCE: 46 CFR, Subchapter S.

88 Downflooding Point In reviewing the downflooding definitions, there are three different definitions for the downflooding point: 1. Any opening, 170.055(e): No mention is made of the ability to be made watertight or weathertight automatically or rapidly, or an opening fitted with no closure. 2. Any opening that cannot be rapidly closed watertight, 174.035(b)(1). 3. Any opening that cannot be rapidly closed weathertight, 171.045(c). Further complicating the issue are the different definitions of downflooding angle throughout Subchapter S, which also includes a definition for the point of downflooding. The additional downflooding point definitions are: 1. Any opening that cannot be closed watertight (with no requirement of how fast the opening must be closed), 170.055(g). 2. Any opening that cannot be rapidly closed watertight, 171.055(f). 3. Any opening that does not close watertight automatically, 172.090(d), 173.095(e), and 174.015(b). 4. Any opening, 174.035(b)(2): No mention is made of the ability to be made watertight or weathertight automatically or rapidly, or an opening fitted with no closure. These conflicting definitions of the downflooding point can even occur in the same section for a particular vessel type, such as in Part 174, Subpart C, Mobile Offshore Drill units, Sections 174.035 and 174.045. In 174.035 the downflooding point is any opening that cannot be rapidly closed watertight while 174.045 defines the downflooding point as any opening that cannot be rapidly closed weathertight. Also note, within many of the definitions the term

89 “rapidly” is used, which is not defined in Subchapter S and is another example of unclear wording. Permeability Factor Another example of conflicting definitions of the same stability requirements located in two or more locations in the Subchapter S regulations are the permeability factors used in the damaged stability calculations. The permeability factors to use are currently defined in the following sections of Subchapter S (see Box D-4 for examples of permeability definitions). 171.072 Calculation of Permeability for Type II Subdivision (Passenger Vessels). 171.080(c) Damaged Stability Standards for Vessels with Type I or Type II Subdivision (Passenger Vessels). 172.065(f) Damage Stability (Vessel Carrying Cargo Under 33 CFR Part 157). 172.140 Permeability of Spaces (Ships Carrying Hazardous Liquids). 172.185 Permeability of Spaces (Ships Carrying Bulk Liquefied Gas). 172.240 Permeability of Spaces (Great Lakes Dry Bulk Cargo Vessels). Box D-4 Permeability Definition Excerpts From Subchapter S - 171.072 When doing calculations to show compliance with 171.070, the following uniform average permeabilities must be assumed: (a) 85 percent in the machinery space. (b) 60 percent in the following spaces: (1) Tanks that are normally filled when the vessel is in the full load condition. (2) Chain lockers. (3) Cargo spaces. (4) Stores spaces. (5) Mail or baggage spaces. (c) 95 percent in all other spaces. - 171.080(c) Permeability. When doing the calculations required in paragraph (a) of this section, the permeability of each space must be calculated in a manner approved by the Commanding Officer, Marine Safety Center or be taken from Table 171.080(c). TABLE 171.080(c) - PERMEABILITY Spaces and tanks Permeability (percent) Cargo, coal, stores 60 Accommodations 95 Machinery 85 Tanks 0 or 95 (1) (1) Whichever value results in the more disabling condition.

90 Box D-4 (continued) Permeability Definition Excerpts From Subchapter S - 172.065(f) Permeability of spaces. When doing the calculations required in paragraph (b) of this section (1) The permeability of a floodable space, other than a machinery space, must be as listed in Table 172.065(b); (2) Calculations in which a machinery space is treated as a floodable space must be based on an assumed machinery space permeability of 85%, unless the use of an assumed permeability of less than 85% is justified in detail; and (3) If a cargo tank would be penetrated under the assumed damage, the cargo tank must be assumed to lose all cargo and refill with salt water, or fresh water if the vessel operates solely on the Great Lakes, up to the level of the tank vessel’s final equilibrium waterline. TABLE 172.065(b) - PERMEABILITY Spaces and tanks Permeability (percent) Storeroom spaces 60 Accommodation spaces 95 Voids 95 Consumable liquid tanks 95 or 0 (1) Other liquid tanks 95 or 0 (2) (1) Whichever results in the more disabling condition. (2) If tanks are partially filled, the permeability must be determined from the actual density and amount of liquid carried. - 172.140 Permeability of spaces. (a) When doing the calculations required in 172.130, the permeability of a floodable space other than a machinery space must be as listed in Table 172.060(b); (b) Calculations in which a machinery space is treated as a floodable space must be based on an assumed machinery space permeability of 0.85, unless the use of an assumed permeability of less than 0.85 is justified in detail. (c) If a cargo tank would be penetrated under the assumed damage, the cargo tank must be assumed to lose all cargo and refill with salt water up to the level of the tankship’s final equilibrium waterline. - 172.185 Permeability of spaces. (a) When doing the calculations required in 172.170, the permeability of a floodable space other than a machinery space must be as listed in Table 172.060(b); (b) Calculations in which a machinery space is treated as a floodable space must be based on an assumed machinery space permeability of 85%, unless the use of an assumed permeability of less than 85% is justified in detail. (c) If a cargo tank would be penetrated under the assumed damage, the cargo tank must be assumed to lose all cargo and refill with salt water up to the level of the tankship’s final equilibrium waterline.

91 One example of conflicting requirements is between Section 171.072 and Section 171.080(c), both of which are for passenger vessels with Type II subdivision. In Section 171.072(b)(1), the permeability for fully loaded tanks is 60% while Section 171.080(c) gives a permeability of either 0 or 95% for tanks. Additional conflicts are also present in the permeability of cargo spaces. Sections 171.072 and 171.080(c) specify a permeability of 60% regardless of condition, while 172.240(c) specifies a permeability of 60% to 95% based on whether the cargo space is full, empty, or somewhere in between. Key Definitions Missing in Subchapter S Tank Runoff in Damaged Stability Calculations Box D-4 (continued) Permeability Definition Excerpts From Subchapter S - 172.240 When doing the calculations required in §172.225, (a) The permeability of a floodable space, other than a machinery or cargo space, must be assumed as listed in Table 172.240; (b) Calculations in which a machinery space is treated as a floodable space must be based on an assumed machinery space permeability of 85% unless the use of an assumed permeability of less than 85% is justified in detail; and (c) Calculations in which a cargo space that is completely filled is considered flooded must be based on an assumed cargo space permeability of 60% unless the use of an assumed permeability of less than 60% is justified in detail. If the cargo space is not completely filled, a cargo space permeability of 95% must be assumed unless the use of an assumed permeability of less than 95% is justified in detail. TABLE 172.240 - PERMEABILITY Spaces and tanks Permeability (percent) Storeroom spaces 60 Accommodations spaces 95 Voids . 95 Consumable liquid tanks (1) 95 or 0 Other liquid tanks (2) 95 or 0 Cargo (completely filled) 60 Cargo (empty) 95 Machinery 85 (1) Whichever results in the more disabling condition. (2) If tanks are partially filled, the permeability must be determined from the actual density and amount of liquid carried. SOURCE: 46 CFR, Subchapter S.

92 Another place where the Subchapter S regulations are missing key definitions is in how a vessel’s intact and damaged stability are to be calculated. For example, in Subchapter S the method of free surface (Subpart I—Free Surface) calculation is explained in detail, including the treatment of spoils in hopper dredges. The treatment of tank runoff in damaged stability calculations is mentioned in Subchapter S for tank barges and tank vessels, but not for passenger vessels. Yet this is critical information for ensuring consistent and correct implementation of the damaged stability criteria. This is particularly true for Subchapter T and K small passenger vessels as USCG’s policy for tank runoff appears counterintuitive to conventional naval architecture damage stability calculations. For small passenger vessels, tanks containing liquids that are damaged for the damaged stability calculations are not to incorporate the emptying of the tanks’ contents, yet still must flood to the damaged equilibrium waterline. This “double” flooding is likely a holdover from the old Ship Hull Characteristics Program (SHCP) stability program constraints and is still the policy required by the USCG MSC even with today’s modern stability calculation programs. Although this policy is not codified in Subchapter S, it is documented in Marine Safety Center (MSC) Plan Review Guidelines, Procedure Numbers H1-01 and H2-03.24 USCG Stability Policy Guidance Located in Multiple Places The USCG policy for small passenger vessel tank runoff is contained in its Plan Review Guidelines H1-01 and H2-03. USCG created these policy documents, as well as others, over time in response to questions about how the Subchapter S regulations are to be interpreted and 24 See https://www.dco.uscg.mil/Our-Organization/Assistant-Commandant-for-Prevention-Policy-CG- 5P/Commercial-Regulations-standards-CG-5PS/Marine-Safety-Center-MSC/Plan-Review-Guides.

93 implemented. Further confusion for the users of Subchapter S is created because these policy decisions are contained in many of the following USCG documents: Navigation and Vessel Inspection Circulars (NVICs); MSC Plan Review Guidelines; Policy File Memorandums (PFMs); Marine Safety Manual, Volume 4; MSC Technical Notes (MTNs); Marine Vessel Investigation Letters; and USCG correspondence, letters, and emails. Having policy decisions established in multiple documents can lead to the following issues: 1. Multiple document types containing policy decisions, making it difficult for the user to search for needed information. 2. Each of the documents can be used to establish policy for all aspects of the USCG’s regulations, not just stability. This broadens the number of documents to be searched for information on a stability topic as only a section of the document may be relevant to stability. 3. The documents are not available at a single location. Some are on the MSC’s website; some are in paper form only. This makes the search process more time consuming. 4. Many are not searchable to locate the desired subject. The user must either have his or her own paper copy library to review or rely on the USCG staff’s institutional knowledge to know which documents are appropriate. 5. A single database summary of the documents does not exist. This again requires the user to rely on the USCG staff’s institutional knowledge, which can be compromised by the normal personnel turnover that occurs over time. Current Stability Requirements Not Aligned with Current Regulatory Approaches Some Subchapter S requirements have been in effect for many years, but may not reflect current regulatory approaches, both domestically and internationally, and the ways a stability analysis

94 would be carried out using newer computational capabilities. For example, Subchapter S still uses static intact stability criteria solely based on initial GM (metacentric height) in multiple locations; more recently developed stability regulations use quasi-dynamic stability criteria that uses the vessel’s righting arm curves. Subchapter S also uses the SOLAS 74 requirements for the Type I subdivision on large passenger vessels; again, this has been superseded by probabilistic damaged stability methods, now used in SOLAS 2009, which will soon be superseded by SOLAS 2020. Static Stability Criteria Static stability criteria is a simple method for evaluating stability, but it contains significant shortcomings: The static-based initial GM intact stability criteria are contained in the following Parts: 170.170—Subpart E Weather Criteria. 171.050—Subpart C Large Passenger Vessels Passenger Heeling Criteria. 172.090(b)—Subpart E Tank Barges Carrying Hazardous Liquids Intact Transverse Stability. 172.095—Subpart E Tank Barges Carrying Hazardous Liquids Intact Longitudinal Stability. 173.095(b)—Subpart E Towing Vessels Towline Pull Criteria. Section 170.170, Weather Criteria, has long been one of the primary methods of assessing a vessel’s criteria for U.S. Flag vessels. These criteria use the vessel’s wind profile and a nominal applied wind force to calculate a heeling moment on a vessel. From this, the minimum required initial GM that will limit the vessel to a specified maximum heel angle and minimum freeboard (typically half the upright freeboard) can be determined using the supplied formulas. Studies indicate that this type of criteria only evaluates the stability of the upright vessel and is not a reliable indicator of a vessel’s critical long-range stability characteristics (i.e., what are the stability characteristics of the vessel as it heels from an applied heeling moment). This is an issue with vessels with a low freeboard, downflooding and deck edge immersion at low heel angles,