Attained index
“DEEPEST SUBDIVISION DRAUGHT.”
Any final comments / objections?
US: Fully agree with this conclusion.
China: No
Regulation 7-1.1.1 [Coordinators Note: the following paragraphs 1-12, including the diagrams, are all EN]
1. The coefficients b11, b12, b21 and b22 are coefficients in the bi-linear probability density function on normalized damage length (J). The coefficient b12 is dependent on whether Ls is greater or less than L* (i.e. 260 m); the other coefficients are valid irrespective of Ls
Longitudinal subdivision
2. In order to prepare for the calculation of index A, the ship’s subdivision length Ls
is divided into a fixed discrete number of damage zones. These damage zones will determine the damage stability investigation in the way of specific damages to be calculated.
3. There are no rules for the subdividing, except that the length Ls defines the extremes for the actual hull. Zone boundaries need not coincide with physical watertight boundaries. However, it is important to consider a strategy carefully to obtain a good result (that is a large attained index A). All zones and combination of adjacent zones may contribute to the index A. In general it is expected that the more zone boundaries the ship is divided into the higher will be the attained index, but this benefit must be balanced against extra computing time. The figure below shows different longitudinal zone divisions of the length Ls
4. The first example is a very rough division into three zones of approximately the same size with limits where longitudinal subdivision is established. The probability that the ship will survive a damage in one of the three zones is expected to be low (i.e. the s-factor is low or zero) and, therefore, the total attained index A will be correspondingly low.
5. In the second example the zones have been placed in accordance with the watertight arrangement, including minor subdivision (as in double bottom, etc.). In this case there is a much better chance of obtaining higher s-factors.
6. Where transverse corrugated bulkheads are fitted, they may be treated as
equivalent plane bulkheads, provided the corrugation depth is of the same order as the stiffening structure.
[7. Pipes and valves directly adjacent to a transverse bulkhead can be considered to be part of the bulkhead, provided the separation distance is of the same order as the bulkhead stiffening structure. The same applies for small recesses, drain wells, etc.]
[Coordinator’s Note:. There is a new proposal to harmonize the text with reg. 7.7 EN1 and reg. 1.1.2 EN 12, as highlighted in green, below. For full discussion see reg 7-1.1.2 EN12, below under CLIA Q6D. Support is good but Norway has some reservations on the proposed amendments in green below for this EN ]:-
7. Pipes and valves directly adjacent to a transverse bulkhead or to a deck can be considered to be part of the bulkhead or deck, provided the separation distance on either side of the bulkhead or deck is of the same order as the bulkhead or deck stiffening structure. The same applies for small recesses, drain wells, etc.]
8. For cases where the pipes and valves are outside the transverse bulkhead stiffening structure, when they present a risk of progressive flooding to other watertight compartments that will have influence on the overall attained index A, they should be handled either by introducing a new damage zone and accounting for the progressive flooding to associated compartments or by introducing a gap.
9. The triangle in the figure below illustrates the possible single and multiple zone damages in a ship with a watertight arrangement suitable for a seven-zone division. The triangles at the bottom line indicate single zone damages and the parallelograms indicate adjacent zones damages.
Z 1 Z2 Z3 Z4 Z5 Z6 Z7
Figure illustrates the possible single and multiple zone damages in a ship.
10. As an example, the triangle illustrates a damage opening the rooms in zone 2 to the sea and the parallelogram illustrates a damage where rooms in the zones 4, 5 and 6 are flooded simultaneously.
11. The shaded area illustrates the effect of the maximum absolute damage length.
The p-factor for a combination of three or more adjacent zones equals zero if the length of the combined adjacent damage zones minus the length of the foremost and the aft most damage zones in the combined damage zone is greater than the maximum damage length. Having this in mind when subdividing Ls could limit the number of zones defined to maximize the attained index A.
12. As the p-factor is related to the watertight arrangement by the longitudinal limits of damage zones and the transverse distance from the ship side to any longitudinal barrier in the zone, the following indices are introduced:
END OF EN for Regulation 7-1.1.1
Regulation 7-1.1.2 (ref. SLF 51/3/2 Annex – US and Sweden)
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.
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Regulation 7-1 para 1.2 (ref. SLF 52/17/5 Annex - Norway)
Document SLF 51/3/2 contains a proposal that the “r” factor should take account of the structural resistance of the ship to an external impact. Although this Administration would agree that this principle could be made an option in the future, it is believed that extensive work is required to develop a unified method suitable for inclusion in the regulation.
R7-1.1.2 (Should raking damage and structural resistance be taken into account?) Q29. In SLF 51/3/2 it is suggested:-
(a) that the regulations as they stand do not take into account the possibility that long raking damages will tend to have a shallower depth of penetration and (b) that the “r” factor should take into account structural resistance to side
impact.
In 52/17/5, Norway agrees with point (b) in principle but points out that it would require a great deal of work to bring into force.
(a) Does “r” need modifying for raking damages? Yes or No:- Yes: Germany (with comments), MI, US, Sweden
No: China, Finland, Japan, Norway (not now), CLIA, Italy, Spain, Denmark, UK (b) Does “r” need modifying for structural resistance? Yes or No:- Yes: Germany (with comments), Sweden
No: China, Finland, Japan, Norway, CLIA, Italy, Spain, Denmark, UK, US, MI (may be too difficult, see comments)
(a) Comments / suggestions / proposals / more consideration needed?:-
China: The probabilistic damage stability regulations of Part B-1 mainly deal with collision casualties; raking damages need not be considered. Therefore “r” need not be modified for raking damages.
Finland: Before doing any changes to “r” more investigation is needed. It is preferable first to see effect of SOLAS2009 on design, before modifying “r”-factor.
Germany: More investigations and data to support the approach needed.
Norway: More extensive work is required; cf. SLF 52/17/5.
“r” was never intended for raking damages as that was not within the TOR. Modification will be required if it is decided to include raking damages in the chapter.
Spain:- S-2009 is a result of a lot of years of research. We know that the method involves many simplifications, but to change these assumptions of the method will involve a lot of new studies (new comparisons with the existing fleet, new statistic data, etcetera). From a practical point of view we prefer to maintain the basics assumptions and simplifications of S-2009.
Denmark: We would prefer to see some research into the statistics, mechanics and implications before considering a change. Particularly since with probability, the frequency of raking damages compared to other damages is important
US: The issue of raking damage should be further considered.
France: [comment added in Round 2] Comment in SLF 51/3/2 was related to minor damages above intermediate decks which may not result from collision with a large ship. In this case, breach penetration probability should be linked to the position of the intermediate deck below the waterline.
Round 1 Discussion: (a) Does “r” need modifying for raking damage? Four members agree that “r” should be modified for raking damage and nine disagree. However, of the 9 opposed to the idea 3 think that the issue needs some further research as do 2 of the 4 in favour.
So the vote actually splits into 2 totally in favour, 5 require more research before deciding and 6 are totally opposed. So 11 out of 13 are not in favour of either immediate action or any action being taken at all. This suggests that the issue should be flagged up to SLF with a recommendation for it to be put on the “back burner” for now until more pressing issues are resolved.
(b) Comments / suggestions / proposals / more consideration needed?:- China: This is too complicated, absolutely “No”.
Finland: Before doing any changes to “r” more investigation is needed. It is preferable first to see effect of SOLAS2009 on design, before modifying “r”-factor.
Germany: More investigations and data to support the approach is needed.
Japan: As Norway points out, this study requires a great deal of work.
MI: The structural resistance to side impact will vary along the length of a ship depending on whether it occurs mid way between transverse bulkheads or near a bulkhead and is totally dependent on the size, trajectory and speed of the impacting ship. Suggest that this proposal may be too difficult to develop any further.
Norway: There seems to be no imminent need to modify “r” for structural resistance, but we support that an option be developed at a later stage.
Spain: Same comments as previous paragraph. Additionally, to evaluate the structural resistance of a certain area of a vessel (taking into account all the ship’s service life) is very complicated.
Denmark: Structural resistance is indeed important and we would welcome research into how it could be accounted for. It seems though that having different r factors for different types of vessels is a move away from harmonisation (which may indeed be needed), is likely to increase complexity and may have undesired consequences and implications; we are thinking about vessels with changes in structure along the length of the vessel, vessels fitted with sponsons and of cruise vessels where a revision of the r factor may boost the A index.
Round 1 Discussion: (b) Does “r” need modifying for structural resistance? Here