IMO DEVELOPMENT OF EXPLANATORY NOTES FOR HARMONIZED SOLAS CHAPTER II-1

Transcription

1 INTERNATIONAL MARITIME ORGANIZATION E IMO SUB-COMMITTEE ON STABILITY AND LOAD LINES AND ON FISHING VESSELS SAFETY 51st session Agenda item 3 SLF 51/3/2 10 April 2008 Original: ENGLISH DEVELOPMENT OF EXPLANATORY NOTES FOR HARMONIZED SOLAS CHAPTER II-1 Report of the SDS Correspondence Group (SOLAS chapter II-1 regulations for possible future improvement) Submitted by Sweden and the United States Executive summary: Strategic direction: 5.2 High-level action: Planned output: Action to be taken: Paragraph 5 Related documents: SUMMARY This document provides the SDS Correspondence Group s report regarding the list of SOLAS chapter II-1 regulations identified for possible future improvement. SLF 50/19, SLF 50/3 and SLF 50/WP.1 Introduction 1 The Sub-Committee, during its fiftieth session, re-established the Correspondence Group on Subdivision and Damage Stability (SLF 50/19, paragraph 3.23). Sweden and the United States have jointly co-ordinated the group. 2 Sweden and the United States would like to thank the following Member States and non-governmental organizations for their participation in the correspondence group: the Bahamas, Canada, China, Cyprus, Denmark, Finland, France, Germany, Greece, Italy, Japan, the Marshall Islands, the Netherlands, Norway, Poland, the Republic of Korea, the Russian Federation, Spain, the United Kingdom, CLIA and IACS. For reasons of economy, this document is printed in a limited number. Delegates are kindly asked to bring their copies to meetings and not to request additional copies.

2 - 2-3 The terms of reference for the correspondence group included instructions, inter alia, to consider the list of SOLAS chapter II-1 regulations identified as needing future improvement and make relevant recommendations, taking into account document SLF 50/WP.1. This document provides the results of the correspondence group s consideration of this matter. SOLAS chapter II-1 regulations for future improvement 4 In the process of developing Explanatory Notes for the new SOLAS chapter II-1 subdivision and damage stability regulations, various regulations have been identified as either needing or potential candidates for future improvement. An initial list of these SOLAS chapter II-1 regulations and associated comments was provided in annex 2 to document SLF 50/3. This list has now been updated to include the additional items agreed to at SLF 50 (see SLF 50/19, paragraph 3.17), and other additional items arising from the correspondence group s further development work on the explanatory notes. The updated list of SOLAS chapter II-1 regulations identified for possible future improvement and associated comments are attached in the annex. Action requested of the Sub-Committee 5 The Sub-Committee is invited to consider the information provided and take action as appropriate. ***

3 SOLAS CHAPTER II-1 REGULATIONS IDENTIFIED FOR POSSIBLE FUTURE IMPROVEMENT Regulation 1 Application Paragraph This provision, regarding cargo ship subdivision and damage stability in the context of alterations and modifications of a major character, is not currently in line with the principles recently agreed to at SLF 50 and approved at MSC 83 in new MSC.1/Circ.1246 (which superseded MSC/Circ.650). This provision should be revised to reflect the principles in MSC.1/Circ.1246 (see SLF 50/19, paragraph ). Regulation 5-1 Stability information to be supplied to the master Paragraph 3 This provision that the influence of various trims on the stability information need only be taken into account if the operational trim range exceeds +/- 0.5% of L s should be revisited (also in regulation 7.2). Associated comment from the United Kingdom: In our experience, particularly with ro-ro passenger ships, the influence of trim can become important at much lower % L s values. Paragraph 4 In order to allow/be consistent with the proposal from Norway (under regulation 7.2 below) regarding calculation of A for different trims, it is proposed to re-word last sentence of this paragraph as follows: If the subdivision index is calculated for different trims, a single envelope curve for required GM should be developed. If required KG is produced, then several required KG curves will be established. Because the limiting GM (or KG) guidance provided to the master in accordance with regulation 5-1 could be impacted by the requirements in regulations 8 and 9 (and the partial attained subdivision indices in regulation 6.1), the following text was added to the Explanatory Notes under regulation 5-1.2: Any limiting GM (or KG) requirements arising from provisions in regulation 6.1 (regarding partial attained subdivision indices), regulation 8 or regulation 9, which are in addition to those described in paragraph 4, shall also be taken into account when developing this information. In this regard, the text stability requirements of part B-1 in regulation could be replaced by stability requirements of these regulations (because regulation 9 is located in part B-2, not part B-1).

4 Page 2 Regulation 7 Attained subdivision index A Paragraph 2 The treatment of trim in the damage stability calculations is an item that has been identified for further consideration (this item is also related to the stability information required under regulation 5-1). At SLF 49, Norway made an oral proposal leading to extensive discussions regarding GM limiting curves for different trims (see figure/proposal below). There was extensive support for the proposal but it was dropped for not being exactly in line/allowed by the wording of the last sentence in regulation (see proposed revision to regulation above to allow this). This issue and proposal should be revisited. 0.5%L s 1%L s 0.5%L s d s Min service trim Max service trim d p 0.5%L s 1%L s 1%L s 0.5%L s Service trims trim Trims used in calculations Related comments from the United Kingdom: We have seen examples in stability information booklets based on the current regulations where only level trim minimum GM curves are shown. The booklet then shows a loading condition where the vessel has some stern trim and seems to comply with the minimum GM curve and yet if the trim is taken off by shifting a load horizontally, the condition would not comply. The reason is that KM generally increases as the ship trims by the stern and so therefore does GM, while KG remains fixed. Some yards/owners take advantage of this effect and it can lead to discrepancies with the onboard stability computer. We can envisage a similar loophole being exploited in the SOLAS 2009 regulations where regulation requires trimmed information only if the operational trim range exceeds +/- 0.5% of Ls. For these reasons we would like to suggest that only maximum allowable KG curves/tables be used.

5 Page 3 We propose a further simplification for presenting the limiting KG curves to make them easier to read (see figure below). It can be seen that calculations for 9 points are required encompassing the entire range of draught and trim. The curves are derived by linear interpolation between trims for each of the 3 draughts and compliance can easily be checked by spotting on the trim and KG from the loading condition and interpolating the critical KG curve at the actual draught. Any restrictions in trim at a particular draught can also be shown easily by simple use of shading to indicate prohibited ranges of operation. Critical KG s can also arise from regulation 8 (minor damage), regulation 9 (bottom damage) and may arise from the new stability criteria to be introduced into regulation 8-1 (return to port). Intact stability could also influence the critical KG curves. All of these extra curves could be incorporated into this simple diagram with the worst critical KG at each draught/trim combination being plotted but still with only 3 limiting curves for the master to use. Max Allowable KG (A=R) vs Trim dl dp ds Crit KG (m.) Trim (m.) In our experience, particularly with ro-ro passenger ships, the influence of trim can become important at much lower %Ls values. Our proposed method of plotting limiting KG against trim for the three calculated draughts at three trims would therefore always be applied to every ship, regardless of the size of the operational trim range (on the basis that all ships have some trim at some time).

6 Page 4 Paragraph 6 The assumption/simplification that only one free surface need be assumed in the flooding calculations should be reconsidered However, associated with including this item for future reconsideration were several additional concerns as follows: a. If the use of multiple free surfaces were to be adapted in the future, then the basis for how the R-index was developed would also have to be reconsidered. What would the GM requirement level for SOLAS 90 ships be if instead of one free surface, multiple free surfaces were applied? b. It has been assumed in the SOLAS 2009 regulations some generally approved simplifications. This seems to be in line with the whole harmonization work; i.e. what has been done over the last 15 years. To account for multiple free surfaces is quite a complicated matter. For example in the cabin area the space has been considered as one room. Because the space is extending from side to side the effect of multiple free surfaces is very large in the calculations. But in reality there are cabin blocks, which certainly will change the calculated value. Regulation 7-1 Calculation of the factor p i Paragraph 1 In the definition of b, the term deepest subdivision load line should be replaced by deepest subdivision draught. Paragraph 1.2 Reduction factor r for damages of transverse extent limited to b is dependent on the length of the damage. This takes into account the fact that a breach of limited longitudinal extent cannot have a deep penetration. On the contrary, very long damages are raking type damages, so the probability to have a deep penetration may be reduced for very long damages. If minor damage above an intermediate deck is considered, depth of the breach below the waterline may be limited, so it can be obtained either from a raking damage or from a breach generated by a ramming ship with shallow draft. In both cases, the probability to have a deep penetration is low. This is not taken into account in the regulation. In all cases, the r factor should take account of the structural resistance of the ship to an external impact. Regulation 7-2 Calculation of the factor s i Paragraph 2 s intermediate should vary progressively as a function of heel. Therefore the proposal would be to have a K factor as for s final :

7 Page 5 s int = K int GZ 1/4 max. Range where: K int = ( θ max. int θe) /( θ max. int θ min. int) For final equilibrium θ max is of 15 degrees compared to 12 deg in present SOLAS. For intermediate stages, maximum angle of 15 deg would give a θ max of deg. Proposed values may be: θ min-int = 10 degrees θ max-int = 18 degrees Stability in intermediate stages of flooding for cargo ships: Although it was decided not to include a requirement for cargo ship intermediate stage flooding calculations in regulation 7-2.2, there were views that this important issue should be revisited in the future (see SLF 47/WP.6, paragraph 6 below). Paragraph 4 6 Several delegations believed that intermediate stages of flooding should be considered for some cargo ships and that this issue should be revisited in any future revision of the regulations. The draft text of regulation 4, paragraph 2, permits some flexibility by the Administrations and there was general support to include the following in the Explanatory Notes: If the Administration considers that the stability in intermediate stages of flooding may be insufficient, it may require further investigation thereof. Clarify the item that is now addressed in the Explanatory Notes: The displacement is the intact displacement at the subdivision draught in question (d s, d p and d l ). Paragraph Clarify the item that is now addressed in the Explanatory Notes: The beam B used in this paragraph means breadth as defined in regulation 2.8. Paragraphs 5.2 and 5.3 The fact that part of escape routes or control systems of watertight doors or valves may be within the damage extent is not taken into account. It is specified in explanatory notes that Horizontal evacuation routes do not include corridors within the damaged spaces. Is this acceptable if the corridor within the damaged space is used for evacuation from another undamaged space?

8 Page 6 Regulation 8 Special requirements concerning passenger ship stability Paragraphs 3.2 to 3.5 Clarify the item that is now addressed in the Explanatory Notes: The number of persons carried, which is specified in these paragraphs, equals the total number of persons on board (and not N = N 1 + 2N 2 as defined in regulation 6) Note: See regulation 12 regarding the issue of a requirement for full survivability (s = 1) in case of damages forward of the collision bulkhead (which is an issue for both passenger and cargo ships. Regulation 9 Double bottoms in passenger ships and cargo ships other than tankers Paragraph 8 The assumed extent of damage; the longitudinal and vertical extent is the same all along the ship. This should be verified referring to damage statistics. Regulation 12 Peak and machinery space bulkheads, shaft tunnels, etc. New paragraph? Japan would again like to draw attention to the issue that the revised SOLAS chapter II-1 does not contain a requirement for full survivability (s = 1) in case of damages forward of the collision bulkhead; this should be identified for future improvement of the SOLAS text (see SLF 49/17, paragraph 3.5.3). Also see SLF 49/3, paragraph 10 below: 10 In addition, Japan provided further information to the group regarding the issue that the new revised SOLAS chapter II-1 does not contain a requirement for full survivability (s = 1) in case of damages in front of the collision bulkhead (see SLF 48/21, paragraph 3.35). This information was circulated to the group and comments were requested. From the group s comments, there were three general conclusions: (1) there was general agreement that s = 1 for damages forward of the collision bulkhead should be a basic SOLAS chapter II-1 requirement for all ships; (2) this chapter II-1 regulatory omission is generally not viewed as a serious weakness/problem; and (3) this problem cannot be addressed in the Explanatory Notes; it will require a SOLAS amendment (consistent with the SLF 48 view). Note: This is already covered by damage of 0.08L from the forward perpendicular for passenger ships carrying more than 400 persons.

9 Page 7 Regulation 17 Internal watertight integrity of passenger ships above the bulkhead deck Paragraph 3 The requirement in this paragraph should be reviewed to determine if it, or a comparable provision, is still necessary under the new probabilistic damage stability methodology. If it is necessary, determine whether it needs revision to properly fit and be consistent with the probabilistic damage stability methodology. (Note: Background information on this item is provided below.) Associated background information: At SLF 48 the prevailing view was to delete this paragraph (see SLF 48/21, paragraph 3.41): 3.41 The Sub-Committee found that paragraph 3 of regulation 17 was not relevant with respect to the new damage stability requirements. As a temporary solution, the EN should advise that the referenced waterline could be taken from conditions where s = 1. As a result, the text agreed to at SLF 49 and included in the Interim Explanatory Notes (MSC.1/Circ.1226) for regulation 17.3: These provisions are generally already accounted for in an alternative probabilistic manner by paragraphs and of regulation 7-2. Therefore, instead of the specified waterline, the waterline from conditions where s = 1 can be used. The open end of air pipes means pipes without any weathertight valve. Then based on further discussions at SLF 50, the prevailing view on this item changed (see SLF 50/19, paragraphs and below) internal watertight integrity of passenger ships above the bulkhead deck the deterministic way to be included, replacing the existing text, noting also that regulation 17 has been included in the list of SOLAS regulations to be further considered in the future (SLF 50/3, annex 2) it should be reconsidered whether regulation II-1/17.3 should be deleted or not. As a result of these decisions at SLF 50, the current text in the draft Explanatory Notes submitted for consideration at SLF 51 is as follows: These provisions regarding the open end of air pipes should be applied only to damages of longitudinal and transverse extent as defined in regulation 8.3 but limited to the bulkhead deck and involving tanks having their open end terminating within the superstructure. Regulation 22 Prevention and control of water ingress, etc. Due to the similarity of headings for regulations 22 and 24, it is proposed to clarify the regulation 22 heading as follows: Prevention and control of water ingress, etc., in passenger and cargo ships.

10 Page 8 Regulation 24 Prevention and control of water ingress, etc., in cargo ships Due to the similarity of headings for regulations 22 and 24, it is proposed to clarify the regulation 24 heading as follows: Additional measures for the prevention and control of water ingress, etc., in cargo ships only. Regulation 35-1 Bilge pumping arrangements Modification may be necessary for application to ships fulfilling the probabilistic damage stability regulations. Paragraph 3.10 The term deepest subdivision load line should be replaced by deepest subdivision draught.