NVIC 04-93: Damage stability explanatory notes for dry cargo ships

Commandant (G-MTH-3) MAILING ADDRESS: United States Coast Guard 2100 SECOND STREET SW WASHINGTON DC 20593-0001 202) 267-2988 COMDTPUB P16700.4 NVIC 4-93 MAY 25, 1993 NAVIGATION AND VESSEL INSPECTION CIRCULAR NO. 4-93 Subj: Subdivision and Damage Stability of Dry Cargo Vessels

Subdivision and Damage Stability of Dry Cargo Vessels — PURPOSE. The purpose of this Circular is to promulgate

International Maritime Organization (IMO) Resolution A.684(17), "Explanatory Notes to the SOLAS Regulations on Subdivision and Damage Stability of Dry Cargo Ships of Over 100 Meters (328 feet) in Length."

Subdivision and Damage Stability of Dry Cargo Vessels — BACKGROUND.

a. In 1985, the Maritime Safety Committee (MSC) of the IMO instructed the technical Sub-Committee on Stability and Load Lines and on Fishing Vessels Safety (SLF) to develop a subdivision and damage stability standard based on the probabilistic analysis method. The standards that were developed are based on the research work done for the probabilistic rules for passenger ships (IMO Resolution A.265(VIII)). b. IMO Resolution MSC.19(58), "Regulations for the Damage Stability Requirements of Dry Cargo Ships," became effective on February 1, 1992, as an amendment to the International Convention for the Safety of Life at Sea, 1974 (SOLAS). The U.S. Coast Guard published a final rule (58 FR 17316) on April 1, 1993, which adopted this international standard into 46 CFR Part 174. c. The SLF Sub-Committee developed the consolidated text of the explanatory notes to the regulation on subdivision and damage stability of dry cargo ships which was published as Resolution A.684(17).

Subdivision and Damage Stability of Dry Cargo Vessels — DISCUSSION.

a. The probabilistic approach of the regulations takes into account the probability of various extents of damage occurring anywhere along the ship's length and the resulting flooding. At the same time it takes into account the probability that the ship will survive the damage given its stability and draft. This provides a rational means of assessing the safety of ships, where flooding is concerned, no matter what their arrangements might be. For instance, a ship may be designed with less subdivision in part of its length, provided it has additional subdivision in areas shown to have a higher probability of damage. In this respect, it frees designers and operators from unnecessarily arbitrary restrictions on arrangements. b. This Circular is initial guidance for the marine shipping industry, ship designers, and the U.S. Coast Guard. As experience with the probabilistic method is gained this information will be updated accordingly. c. Any questions concerning the regulations on subdivision and damage stability should be directed to the U.S. Coast Guard's Marine Safety Center (MSC). The MSC will review all questions from the civilian marine industry concerning the new regulations on subdivision and damage stability and will consult with the U.S. Coast Guard's Marine Technical Hazardous Materials Division if further clarification is necessary.

Subdivision and Damage Stability of Dry Cargo Vessels — IMPLEMENTATION.

a. Enclosure (1), IMO Resolution A.684(17), has been promulgated as international policy to assist interpretation of the SOLAS regulations on the subdivision and damage stability of dry cargo vessels including Ro/Ro ships of over 100 meters (328 feet) in length. These explanatory notes shall be used in conjunction with both part B-1 of chapter zz-1 of SOLAS 1974 and 46 CFR 174. /s/ R. C. NORTH ACTING CHIEF, OFFICE OF MARINE SAFETY, SECURITY & ENVIRONMENTAL PROTECTION Encl: (1) IMO Resolution A.684(17) Non-Standard Distribution: C:e New Orleans (90); Hampton Roads (50); Baltimore (45); San Francisco (40); Philadelphia, Port Arthur, Honolulu, Puget Sound (35); Miami, Houston, Mobile, Morgan City, Los Angeles/Long Beach, Portland OR (25); Jacksonville (20); Boston, Portland NE, Charleston, Galveston, Anchorage (15); Cleveland (12); Louisville, Memphis, Paducah, Pittsburgh, St. Louis, San Juan, Savannah, Tampa, Chicago, Buffalo, Detroit, Duluth, Milwaukee, San Diego, Juneau, Valdez (10); Providence, Huntington, Wilmington, Corpus Christi, Toledo, Guam (5). C:m New York (70); St. Ignace (5); Sturgeon Bay (4). D:d Except Baltimore, Moriches. D:1 CG Liaison Officer MILSEALIFTCOMD (Code N-7CG), CG Liaison Officer RSPA (DHM-22), CG Liaison Officer FARAD (MAR-742), CG Liaison Officer JUSMAGPHIL, CG Liaison Officer World Maritime University, CG Liaison Officer ABS (1). ABS (260). NOAA Fleet Inspection Officer (1). U.S. Merchant Marine Academy (1). Resolution A.684(17) Adopted on 6 November 1991

(Agenda item 10) EXPLANATORY NOTES TO THE SOLAS REGULATIONS ON SUBDIVISION AND DAMAGE STABILlTY OF CARCO SHIPS OF 100 METRES IN LENGTH AND OVER THE ASSEMBLY, Recalling Article 15(j) of the Convention on the International Maritime Organization concerning the functions of the Assembly in relation to regulations and guidelines concerning maritime safety, Recalling further that by resolution A.265(VIII) the Assembly adopted regulations on subdivision and stability of passenger ships, which may be used as an equivalent to part B "Subdivision and stability" oil chapter II-1 of the 1974 SOLAS Convention, NOTING that by resolution MSC.19(58) the Maritime Safety Committee at its fifty-eighth session adopted amendments to the 1974 5OLAS Convention to include, as part B-1 of chapter II-1.

Regulations for subdivision and damage stability of cargo ships which apply to cargo ships of 100 m in length and over, Nothing further that the Maritime Safety Committee, in adopting the above amendments to the 1974 SOLES Convention, recognized the necessity of development of appropriate explanatorv notes for implementation of the regulations adopted, in order to ensure their uniform application, Having considered the recommendations made by the Maritime Safety Committee at its fifty-ninth session, 1.

Adopts the explanatory notes to the SOLAS regulations on subdivision and damage stability of cargo ships of 100 m in length and over set out in the annex to the present resolution; 2.

Invites Governments to apply the explanatory notes when implementing the regulations for subdivision and damage stability contained in the amendments to chapter II-1 of the 1974 SOLAS Convention adopted by resolution MSC.19(5S).

Annex EXPLANATORY NOTES TO THE SOLAS REGULATIONS ON SUBDIVlSION AND DAMAGE STABILITY OF CARGO SHIPS OF 100 METRO IN LENGTH AND OVER These explanatory notes are divided into two parts.

Part A describes the background to the method used while part B contains explanations and amplifications of individual regulations.

In this part of the explanatory notes, the background of the subdivision index is presented and then the calculation of the probability of damage is developed.

Finally, the development of the calculation of the probability that a damaged ship will not capsize or sink is demonstrated. 1 INTRODUCTION The SOLC regulations on subdivision and damage stability, as contained in part B-1 of SOLAS chapter II-1, are based on the probabilistic concept which takes the probability of survival after collision as a measure of ship's safety in the damaged condition, hereinafter referred to as the "attained subdivision index A".

This is an objective measure of ship safety and therefore there is no need to supplement this index by any deterministic requirements.

These new regulations, therefore, are primarily based on the probabilistic approach, with only very few deterministic element- which are necessary to make the concept practicable.

The philosophy behind the probabilistic concept is that two different ships with the same index of subdivision are of equal safety and therefore there is no need for special treatment for specific parts of the ship.

The only areas which are given special attention in these regulations are the forward and bottom regions which are dealt with by special rules concerning subdivision, provided for the cases of ramming and grounding.

In order to develop the probabilistic concept of ship subdivision, it is assumed that the ship is damaged.

Since the location and size of the damage is random.

It is not possible to state which part of the ship becomes flooded.

However, the probability of flooding a space can be determined if the probability of occurrence of certain damages is known.

The probability of flooding a space is equal to the probability of occurrence of all such damages which just open the considered space.

A space is a part of the volume of the ship which is bounded by undamaged watertight structural divisions.

Next, it is assumed that a particular space is flooded.

In addition to some inherent characteristics of the ship, in such a case there are various factors which influence whether the ship can survive such flooding; they include the initial draught and GM, the permeability of the space and the weather conditions, all of which are random at the time when the ship is damaged.

Provided that the limiting combinations of the aforementioned variables and the probability of their occurrence are known, the probability that the ship will not capsize or sink, with the considered space flooded can be determined.

The probability of survival is determined by the formula for entire probability as the sum or the products for each compartment or group of compartments of the probability that a space is flooded multiplied by the probability that the ship will not capsize or sink with the considered space flooded.

Although the ideas outlined above are very simple, their practical application in an exact manner would give rise to several difficulties.

For example, for an extensive but still incomplete description of the damage, it is necessary to know its longitudinal and vertical location as well as its longitudinal, vertical and transverse extent.

Apart from the difficulties in handling such a five-dimensional random variable, it is impossible to determine its probability distribution with the presently available damage statistics.

Similar conditions hold for the variables and physical relationships involved in the calculation of the probability that a ship with a flooded space will not capsize or sink.

In order to make the concept practicable, extensive simplifications are necessary.

Although it is not possible to calculate on such a simplified basis the exact probability of survival, it is possible to develop a useful comparative measure of the merits of the longitudinal, transverse and horizontal subdivision of the ship. 2 DETERMINATION OF THE PROBABILITY OF FLOODING OF SHIP SPACES 2.1 Consideration of longitudinal damage location and extent only The simplest case is to consider the location and length of damage in the longitudinal direction.

This would be sufficient for ships with no longitudinal and horizontal watertight structural divisions.

With the damage location x and damage length y as defined in figure 1, all possible damages can be represented by points in a triangle which is also shown in this figure.

All damages which open single compartments of length l; are represented in figure 1 by points in triangles with the base l , Triangles with the base l , r i +l (where j=i+1) enclose points corresponding to damages opening either j compartment i, or compartment j, or both of them.

Correspondingly, the points in the parallelogram ij represent damages which open both the compartments i and j.