K.B. FERRIE, CDR, Chief, Hull Division References: a. 46 CFR Subchapter T, Parts 178, 179 b. 46 CFR Subchapter S, Parts 170, 171 c. Marine Safety Manual (MSM), Vol. IV d. Navigation and Vessel Circular No. 14-81, CH 1, Stability Tests; Waiving of for Sister Vessels, dated December 2, 1981 e. Navigation and Vessel Circular No. 17-91, CH 1, Guidelines for Conducting Stability Tests, dated November 4, 1991 f. ASTM F1321-92, Standard Guide for Conducting a Stability Test (Lightweight Survey and Inclining Experiment) to Determine the Light Ship Displacement and Centers of Gravity of a Vessel g. Federal Register, Vol. 75, No. 239, Passenger Weight and Inspected Vessel Stability Requirements; Final Rule, dated December 14, 2010 h. Office of Vessel Activities (CG-543) Policy Letter 11-03, Implementation of Revised Passenger Weight Standards for Existing Passenger Vessels, dated April 8, 2011 Contact Information: If you have any questions or comments concerning this document, please contact the Marine Safety Center by e-mail or phone. Please refer to Procedure Number: H1-16. E-mail: msc@uscg.mil Phone: 703-872-6729 Website: http://homeport.uscg.mil/msc Applicability: This Plan Review Guideline is applicable to stability calculations reviewed by MSC for catamaran sailing vessels certificated under 46 CFR Subchapter T. If the vessel s stability is being reviewed under Navigation and Vessel Inspection Circular (NVIC) No. 3-97, Stability Related Review Performed by the American Bureau of Shipping for U.S. Flag Vessels, then MSC review of stability items is not required unless the submittal has been targeted for MSC oversight. In accordance with 46 CFR 178.310(a) and (b), catamaran sailing vessels must in each condition of loading and operation comply with the intact stability requirements of 46 CFR Subchapter S to include: 46 CFR 170.170 (Weather Criteria), 170.173 (Righting Energy Criteria), 171.050 (Passenger Heel Criteria), and 171.057 (Catamaran Sailing Vessel Criteria). Vessels meeting the applicability of 46 CFR 179.210 must also comply with the collision bulkhead requirements of 179.310 (Collision Bulkhead). Additionally, vessels meeting the applicability of 179.212(a) must comply with the subdivision
and damage stability requirements of 46 CFR 171.070 (Type II Subdivision) and 171.080 (Damage Stability) in each condition of loading and operation. In accordance with 46 CFR 178.310(c), subchapter T catamaran sailing vessels do not meet the applicability to comply with alternate stability criteria to 46 CFR Subchapter S. Specifically, it is not permitted for a catamaran sailing vessel to undergo a simplified stability proof test or operational test to meet stability requirements. Submittal Checklist: Check that the following items are included in the submittal package: Letter of intent identifying what is included in the submittal and requested actions to be taken by the Marine Safety Center; Copy of Application for Inspection submitted to the OCMI; Description of the vessel operating envelope including route designation and classification, number of passengers, total persons carried, and any operating limits and/or restrictions previously provided (such as maximum draft, trim, wave height, speed, geographical boundaries); All possible loading conditions for each particular operation of the vessel; Lines plan of the hull to at least the bulkhead deck. See reference (c), Section 6.B.1.a regarding possible inclusion of deck houses and superstructure in buoyant volume; Computerized hull model (recommended, but not required); Hydrostatics or Curves of Form and Righting Arm Curves (tabulated data may be accepted); Tank Capacity Tables including liquid volume or weight, center of gravity location, and free surface factor for relevant tank filling levels; General Arrangement and relevant plans showing: Outboard Profile; Compartmentation (at least plan and profile views); Location and extent of bulkhead deck; Location and extent of watertight bulkheads including collision bulkhead; Watertight and weathertight doors, hatches, scuttles, and similar closures; Weather deck freeing port and/or scupper sizes and locations (as applicable); Downflooding points and other openings into the hull such as vents or windows; Locations and reference points of any draft or loading marks. See 46 CFR 185.602(b) and (c), and reference (d), Section 6.B.6. 2
Sail Plan: Ensure that sail areas used in stability analysis match sail areas shown on the sail plan; Fixed Ballast Plan or Listing (if applicable): Ensure that fixed ballast shown on ballast plan or listing matches the fixed ballast used in lightship calculation; Foam flotation material information (if applicable); Approved lightship values or stability test lightship calculations; Intact Stability Calculations; Collision Bulkhead Calculations (if applicable); Subdivision and Damage Stability Calculations (if applicable). Lightship Verification: Ensure that lightship characteristics were (or are to be) determined using one of the following methods: Acceptance as a sister to a vessel with known characteristics (reference (c), Section 6.D.2 and reference (d)) Deadweight survey combined with a conservatively assumed vertical center of gravity (VCG) height (references (e) and (f)) Inclining (full stability test) (references (e) and (f)) In accordance with 46 CFR 170.085, a written stability test procedure must be sent to the Coast Guard Marine Safety Center at least two weeks before the stability test. Reference (f) provides guidance on the required elements for the stability test procedure. The procedure shall be approved by the MSC prior conducting the test or survey. In accordance with 46 CFR 170.175(b), arrangements should be made with the OCMI for an acceptable Coast Guard representative to witness the stability test. Hull Model: MSC will generate a hull model in GHS from the lines, offsets or provided computer model information to verify the stability of the vessel. Passenger/Crew Weight Guidance: The assumed average weight per person (AAWP) of passengers and crew must not be less than 185 pounds in accordance with 46 CFR 170.090 (d)(1). All passengers must be assumed to be standing in order to check the worst case Vertical Center of Gravity (VCG) condition. For all vessels built or having undergone a major conversion after March 14, 2011 the VCG for all passengers must be at least 39 inches (1 meter) above the highest deck to which they are allowed access. For all other vessels, the VCG for all passengers must be at least 36 inches above the highest deck to which they are allowed access. 3
Loading Conditions: Ensure that the vessel s loading conditions cover the entire range of operation. This includes, but is not limited to the following conditions: a. Full load with 100% consumables; b. Mid Voyage with 50% consumables; c. Arrival (Burned Out) with 10% consumables Attention should be given to the vertical distribution of passengers. In general, assuming all passengers are on the uppermost deck will allow no restrictions in the stability letter. However, vessels may be sensitive to carrying a high percentage of passengers on upper decks with few or no passengers carried on the lower decks. In these cases, operating restrictions will need to be developed accordingly. For light vessels, additional loading conditions should include minimal passenger counts. Ensure that loading conditions incorporate liquid free surface in accordance with 46 CFR 170.285 for intact stability and 46 CFR 170.290 for damage stability. Intact Stability: In accordance with 46 CFR 178.310(a) and (b), calculations shall be submitted for each condition of loading and operation that demonstrate compliance with the following criteria: Weather Criteria: 46 CFR 170.170: 1. Ensure correct use of weather criterion variables for intended route. 2. Sailing vessel or auxiliary sailing vessel must be assumed to be under bare poles or if the vessel has no auxiliary propulsion, to have storm sails set and trimmed flat. 3. Ensure available GM meets or exceeds the minimum acceptable value. Righting Energy Criteria: 46 CFR 170.173 (only if vessel has auxiliary power): 1. Ensure stability characteristics meet the minimum requirements for intended route and that all criteria are addressed: a. Exposed Route: 46 CFR 170.173(b) or (c) b. Partially Protected Route: 46 CFR 170.173(e)(1) c. Protected Route: 46 CFR 170.173(e)(2) 2. Ensure these calculations correctly reflect submergence of any potential downflooding points. 4
3. In accordance with 46 CFR 170.173(c)(2), passenger vessels are required to have an angle of maximum righting arm of not less than 15 degrees. Due to the separation of the hulls on a catamaran, the shape of its righting arm curve is normally much steeper at low angles of heel than would be the case for a comparable monohull, often resulting in an angle of maximum righting arm less than 15 degrees. For catamarans with an angle of maximum righting arm less than 15 degrees, an equivalent level of safety to 46 CFR 170.173(c)(2) must be demonstrated and included in the submittal for our approval in accordance with 46 CFR 170.010. Passenger Heel Criteria: 46 CFR 171.050 (only if vessel has auxiliary power): 1. Ensure correct use of passenger criterion equation variables. 2. Ensure available GM meets or exceeds the minimum acceptable value. Catamaran Sailing Vessel Criteria: 46 CFR 171.057: 1. Ensure correct use of monohull sailing vessel criterion equation variables for intended route and that all criteria are addressed: a. Protected Route: 46 CFR 171.057(a) b. Partially Protected and Exposed Routes: 46 CFR 171.057(b) Ensure the intact stability calculations submitted comply with the maximum free surface corrections in accordance with 46 CFR 170.285. Ensure drainage of weather decks is in accordance with 46 CFR 178 Subpart D Collision Bulkhead: In accordance with 46 CFR 179.210(a) and (b), include calculations demonstrating the collision bulkhead location complies with 46 CFR 179.310(b) (collision bulkhead location) if the vessel meets one or more of the following criteria: Is more than 65 feet in length; Is not more than 65 feet in length if it: Carries more than 49 passengers; Operates on exposed waters; Is not more than 40 feet in length and operates on partially protected waters; or Is constructed of wood on or after March 11, 2001, and operates in cold water. 5
Ensure the collision bulkhead is constructed in accordance with 46 CFR 179.310(a). Additional information on collision bulkhead requirements is included in reference (c), Section 6.E.9.g. Subdivision/ Damage Stability: In accordance with 46 CFR 179.212(a), include calculations in the submittal package demonstrating compliance with 46 CFR 170.070 (Type II Subdivision) and 46 CFR 171.080 (Damage Stability) in each condition of loading and operation if the vessel meets one or more the following criteria: Is more than 65 feet in length; Carries more than 49 passengers; Is constructed of wood on or after March 11, 2001, and operates in cold water; or Is constructed before January 1, 2009 and carries more than 12 passengers on an international voyager. For catamarans, subdivision is not applied from side shell to side shell, because of the distance between hulls (with the exception of the bow compartments, which could be damaged simultaneously by a frontal collision). Rather, for catamarans that have a separation between the individual hulls greater than the beam of a single individual hull, subdivision is applied by requiring surviving a one-compartment standard by damaging both bow compartments simultaneously, and then one compartment at a time down one side of the vessel, with a bottom damage whose vertical extent is B/15 or 30 inches (whichever is greater, where B is the total buoyant beam of each hull at the highest waterline). Catamarans that have a separation between the individual hulls less than the beam of a single individual hull are treated as a single conventional hull, with equivalent beam twice that of a single individual hull, for the purpose of subdivision and damage stability. Damage stability is applied by requiring meeting the criteria in 46 CFR 171.080 by damaging both bow compartments simultaneously, then one compartment at a time down one side of the vessel, using the extents of damage in 46 CFR 171.080: Existing vessels, as defined in 46 CFR 171.080(a), shall ensure that damage stability calculations meet or exceed the standards required in 171.080(e). New vessels, as defined in 171.080(a), shall ensure that damage stability calculations meet or exceed the standards required in 171.080(f). Ensure the correct placement of the margin line in accordance with 46 CFR 171.015. Ensure the appropriate standard of flooding is used for subdivision calculations in accordance with 46 171.070(a) and (b) and 46 CFR 171.017. 6
Ensure subdivision and damage stability calculations do not incorporate the emptying of tank contents (run-off) for any damaged tanks. Subdivision calculations must comply with the permeability requirements of 46 CFR 171.072. Damage stability calculations must comply with the permeability requirements of 46 CFR 171.080(c). Main transverse watertight bulkhead (MTWB) minimum spacing requirements of 46 CFR 171.070(e)(1) (if the LBP of the vessel is 143 feet or more) or 171.070(e)(2) (if the LBP of the vessel is less than 143 feet). In cases where the MTWBs are spaced closer than the minimum allowed, some of those MTWBs are to be considered ineffective in the subdivision stability analysis in order to meet the minimum spacing requirement. Ensure the damage stability calculations comply with the extent and character of damage required in 46 CFR Table 171.080(a). Definitions: Downflooding: The entry of seawater through any opening into the hull or superstructure of an undamaged vessel [or portion of a vessel] due to heel, trim, or submergence of the vessel. Downflooding Point: Any opening in the hull or superstructure of the vessel that cannot be closed watertight and through which downflooding can occur. For monohull sailing vessel intact stability calculations, openings that cannot be rapidly closed watertight are considered downflooding points. For damage stability calculations, openings that are fitted with weathertight closures and that are not submerged during any stage of flooding will not be considered downflooding points. Weathertight: Water will not penetrate into the vessel in any sea condition. This also means being able to resist boarding seas. As addressed in reference (d), windows are not accepted as weathertight closures and, without the provision of deadlight covers, must be considered as potential downflooding points. Ball check valves used in tank vent lines are generally accepted as weathertight closures. Watertight: Capable of preventing the passage of water through the structure in any direction under a head of water for which the surrounding structure was designed. 7
Special Consideration: In accordance with 46 CFR 175.550, the cognizant Officer in Charge, Marine Inspection (OCMI) may give special consideration to authorizing departures from the specific requirements of 46 CFR Subchapter T when unusual circumstances or arrangements warrant such departures and an equivalent level of safety is provided. The OCMI of each marine inspection zone in which the vessel intends to operate must approve any special consideration granted to the vessel. Disclaimer: This guidance is not a substitute for applicable legal requirements, nor is it itself a rule. It is not intended to nor does it impose legally-binding requirements on any party. It represents the Coast Guard s current thinking on this topic and may assist industry, mariners, the general public, and the Coast Guard, as well as other federal and state regulators, in applying statutory and regulatory requirements. You can use an alternative approach for complying with these requirements if the approach satisfies the requirements of the applicable statutes and regulations. If you want to discuss an alternative, you may contact the Marine Safety Center, the unit responsible for implementing this guidance. 8