IMO I871E-1993 SOLAS EXPLANATORY NOTES TO THE SOLAS REGULATIONS ON SUBDIVISION AND DAMAGE STABILITY OF CARGO SHIPS OF 100 METRES IN LENGTH AND OVER.pdf

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1、 SOLAS EXPLANATORY NOTES TO THE SOLAS REGULATIONS ON SUBDIVISION AND DAMAGE STABILITY OF CARGO SHIPS OF 100 METRES IN LENGTH AND OVER INTERNATIONAL MARITIME ORGANIZATION London, 1993 Published in 7993 by the INTERNATIONAL MARITIME ORGANIZATION 4 Albert Embankment, London SE1 7SR Printed by Intype Li

2、bra Ltd, London 8 10 9 ISBN 92-801-1 2996 IMO PUBLICATION Sales number: 1871 E Copyright 0 International Maritime Organization 1993 Al/ rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior permission in

3、writing from the International Maritime Organization. Foreword The International Conference on Safety of Life at Sea, 1960, recommended that IMO study the extent to which it would be reasonable and practicable to apply subdivision and stability requirements to cargo ships. In pursuance of the recomm

4、endation the work was undertaken and the formulation of appropriate international standards was completed in 1990. The relevant amendments to chapter 11-1 of the International Convention for the Safety of Life at Sea, 1974 (SOLAS 19741, regarding subdivision and damage stability requirements for car

5、go ships based on the probabilistic concept of ship survivability were adopted by the Maritime Safety Com- mittee (MSC) in May 1990 by resolution MSC.19(58). These requirements were intended for cargo ships over 100 metres in length and entered into force on 1 February 1992. ln adopting the above am

6、endments the MSC recognized the necessity of developing appropriate explanatory notes for the implementation of the regulations adopted, in order to ensure their uniform application. Subsequently, the Explanatory notes to the SOLAS regulations on subdivision and damage stability of cargo ships of 10

7、0 metres in length and over were developed by IMO and adopted by the Assembly in November 1991 by resolution A.684(17). This resolution invited govern- ments to apply the explanatory notes when implementing the new SOLAS regulations adopted by resolution MSC.19(58). . III Contents Page Part A . Back

8、ground 1 . Introduction . 2 . Determination of the probability of flooding of ship spaces 3 . Damage statistics . 4 . Probability of capsize . Part B . Guidance on individual regulations Regulation 25-1 . Regulation 25.2 . Regulation 25-4 . Regulation 25.5 Regulation 25.6 . Regulation 25.8 . Regulat

9、ion 25.9 . Appendices Appendix 1 . Transverse subdivision Appendix 2 . I Combined transverse, horizontal and longitudinal subdivision . II Recesses . I I I Damage penetration . Appendix 3 . 1 2 9 27 27 28 31 32 32 32 33 35 39 47 49 52 V Page Annexes Annex 1 - Resolution A.684(17) Annex 2 - Internati

10、onal Convention for the Safety (adopted 6 November 1997). of Life at Sea, 1974, chapter 11-1, part B-1 (Subdivision and damage stability of 59 cargo ships), regulations 25-1 to 25-10 . 61 vi These explanatory notes are divided into two parts. Part A describes the background to the method used while

11、part B contains explanations and amplifications of individual regulations. Part A 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 probabi

12、lity that a damaged ship will not capsize or sink is demonstrated. 1 INTRODUCTION The SOLAS regulations on subdivision and damage stability, as contained in part B-1 of SOLAS chapter 11-1, are based on the probabilistic concept which takes the probability of survival after collision as a measure of

13、ships 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 pr

14、obabilistic approach, with only very few deterministic elements 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

15、 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 sh

16、ip 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

17、. 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. Note: The explanatory notes to the SOLAS regulations on

18、 subdivision and damage stability of cargo ships of 100 metres in length and over comprise the annex to resolution A.WIi), the text of which is reproduced in annex 1 of the present publication. 1 Next, it is assumed that a particular space is flooded. In addition to some inherent characteristics of

19、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 c

20、ombinations 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 of t

21、he 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 mann

22、er 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-di

23、mensional 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

24、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

25、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 wit

26、h 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. 2 All damages which open single compartments of length /; are r

27、epresented in figure 1 by points in triangles with the base /;. Triangles with the base i+j (where j = i+l) enclose points corresponding to damages opening either compartment i, or compartment i, or both of them. Correspondingly, the points in the parallelogram ij represent damages which open both t

28、he compartments i and i. Points in parallelogram / represent all damages Figure 1 3 Damage location x and damage length y are random variables. Their distribution density f(x,y) can be derived from the damage statistics. The meaning of f(x,y) is as follows (see figure 2): the total volume between th

29、e x-y plane and the surface given by f(x,y) equals one and represents the probability that there is damage (this has been assumed to be certain). The volume above a triangle corresponding to damage which opens a compartment represents the probability that this compartment is opened. In a similar man

30、ner for all areas in the x-y plane which correspond to the opening of compartments or group of compartments, there are volumes which represent the probability that the considered compartments or group of compartments are opened. distance of the compartment centre from aft terminal of the ship length

31、 I Figure 2 The probability that a compartment or a group of adjacent compartments is opened is expressed by the factor pi as calculated according to regulation 25-5. 4 Consideration of damage location x and damage length y only would be fully correct inthe case of ships with pure transverse subdivi

32、sion. However, there are very few, if any, such ships - all normally have a double bottom, at least. In such a case, the probability of flooding a compartment should be split up into the following three components: probability of flooding the double bottom only, probability of flooding the space abo

33、ve the double bottom only and probability of flooding both the space above and the double bottom itself (see figure 3). For each of these cases there may be a different probability that the ship will survive in the flooded condition. A way out of this dilemma, which may be used in applying these new

34、 regulations, is to assume that the most unfavourable vertical extent of damage (out of the three possibilities) occurs with the total probability p. Therefore the contribution to survival probability made by more favourable cases is neglected. That the concept is still meaningful for comparative pu

35、rposes follows from the fact that the error made by neglecting favourable effects of horizontal subdivision is not great and the more important influence of longitudinal damage location and extension is fully covered. Some examples for dealing with other cases of horizontal subdivision are given in

36、appendix I. 2.2 Consideration of horizontal subdivision above a waterline In the case where the ship has a horizontal subdivision above a waterline, the vertical extent of damage may be limited to the depth of that horizontal subdivision. The probability of not damaging the horizontal subdivision is

37、 represented by the factor vi, as calculated according to regulation 25-6. This factor represents the assumed distribution function of the vertical extent of damage and varies from zero for subdivision at the level of the waterplane, linearly upwards to the value of one at the level conforming to th

38、e minimum bow height according to the 1966 Load Line Convention (see figure 4). 2.3 Consideration of damage penetration in addition to longitudinal damage location and extent With the simplifying assumption that the damage is rectangular and with the vertical extent of damage according to 2.2, the d

39、amage can be described by the damage location x, the damage length y and the damage penetration z (see figure 5). These variables can be represented in a three- dimensional Co-ordinate system, as shown in figure 6. Each point in the prism, with triangular base, represents a damage. 5 Figure 3 6 m 9)

40、 C .- - -. 7 Figure 5 All damages which open a side compartment correspond to the points of a smaller prism with height b equal to the distance of the longitudinal bulkhead from the ships side, which is erected above a triangle with the base li equal to the length of the side compartment under consi

41、deration. It is not difficult to identify in figure 5 the volumes which correspond to such damage which flood other parts of the ship bounded by transverse and longitudinal watertight structural subdivisions. 8 Damage location x, damage length y and damage penetration z are random variables. The dis

42、tribution density f(x,y,z) can be derived from damage statistics. This distribution density can be illustrated by assuming it to be a density which varies from point to point of the volume shown in figure 6. The “weight” of the total volume is one and represents the probability that there is a damag

43、e (which is assumed to be certain). The “weight“ of a partial volume (representing the flooding of certain spaces) represents the probability that the spaces under consideration are opened. The probability that a side compartment is opened can be expressed as pif, where pi is to be calculated accord

44、ing to regulation 25-5.1 and r according to regulation 255.2. The probability that a centre compartment (extending at least to the ships centreline) is opened, in addition to the adjacent side compartment, can be expressed as pi(l -r). Some examples for the calculation of the probability that side o

45、r side plus centre spaces are opened are given in appendix 2. Again, it must be stated that the probability calculated on the basis of the simplifying assumptions mentioned above is not exact. Nevertheless, it gives a comparative measure of how the probability of opening spaces depends on transverse

46、 and longitudinal structural subdivisions, and thus takes account of the most essential influences, whilst neglecting secondary effects. Neglecting the random variation of longitudinal and transverse damage extent would be a much greater error than that which is caused by neglecting these secondary

47、effects. 3 DAMAGE STATISTICS 3.1 Source of data The following considerations are based on the information contained in various IMO documents. They summarize casualty data reported to IMO on 811 damage cards. There are 296 cases of rammed ships which contain information on each of the following chara

48、cteristics: Ship length -L Ship breadth -B Damage location -x Damage length -Y Damage penetration - z In order to omit inconsistencies in the results derived from the data, which may be caused by the use of different samples, the following investigations have been based only on the aforementioned 29

49、6 cases. However, further investigations have been made using, in addition, the information given for other cases. Despite the random scatter, which is to be expected because of the use of different samples composed at random, they lead to the same conclusion. 9 For the investigation of the dependency of damage length on the year of collision, a different sample was used comprising 209 cases in which i, y and year of collision were given. 3.2 It is clear that the principal factors affecting damage extent are: General consideration of damage extent