Trans RINA, Vol 153, Part A1, Intl J Maritime Eng, Jan-Mar 2011


support the regulations and have been designed to give precise information. As a result, many additional items and proposals that were discussed by the drafting group are not included. Proposals have also been made to include these as mandatory but this has not yet been agreed.


3.2 GENERAL PROCESS


The appendix in part B of the Explanatory Notes gives information on what should be submitted for approval. Obviously, approval


authorities will have some


variations on this. What is apparent, especially with complex designs, is the


submission serves as a snapshot at the time of submission. Bearing in mind the numerous items


need to ensure that the to be covered


(systems, structural fire protection etc), any associated plans should be as consistent as possible in order that subsequent discussion items can be easily identified and replicated by the designer and approval authority.


Although Lloyd’s Register uses NAPA as its review tool, submissions


of are also received using other software


products and solutions. In these cases we have to have the ability to not only identify any disparities in the results but to define where the discrepancies lie. Our experience, such as development


our in-house


statutory computational managers (SCMs) mentioned later in this paper, provide us with this ability.


First and foremost, it is important to validate the model and take a disciplined approach, especially for complex designs. Not only is watertight subdivision considered but also items such as A Class fire bulkheads, openings, cross flooding sections, permeabilities, horizontal escape routes, access hatches, emergency switchboard rooms, weather tight openings, air pipes and so on.


Class Rules require that maximum head of water resulting


from the damage stability calculations is


considered when determining the strength of the ship. As a result, the designer has to have a good idea of the stability characteristics and ensure suitable margins are in place at a very early stage of the design process.


Compartment connections must be carefully considered. In passenger ships, certain compartments will be flooded instantaneously, while others will flood in various phases and stages. Due care needs to be taken of flood directions and sequences, finally checking to ensure that generated calculation results are logical.


3.3 SUBDIVISION TABLE


This table determines the extent of all the zones and position


of internal subdivision for addressing the


probability distributions based on the ship dimensions (i.e. ‘pi’ as shown in Figure 3) This, together with the watertight subdivision plan, forms part of the necessary basic information required to be submitted for plan


approval. The subdivision table does not necessarily follow physical boundaries and can be used as a means to take on a reduced ‘p’ probability value in favour of providing a protective location for piping, for example, in order to reduce the number of valves. Automatic damage case generation is based on this table. This process can


prove extremely lengthy without an


automated system. Of the many cases generated, those with the most onerous ‘si’ factor in relationship to ‘pi’ will make up the contribution to the attained index, A.


3.4 WEATHER TIGHT AND UNPROTECTED ITEMS


As mentioned, no margin line is defined in SOLAS 2009 to limit stability margins after a flooding scenario. This is defined by items such as openings, horizontal escapes, pipes and emergency switch rooms. These are treated in different ways


depending on their application and


construction. Generally, they fall into the categories of weather tight and unprotected items. Accordingly, these may or may not be submerged in final,


stages or within the required residual buoyancy range required to achieve a contribution to the index.


Many systems are not considered until later in the design stage and so the designer must make provisions and think carefully how to ensure that adding, for example, air pipes close to the hull shell at a later stage will not have a detrimental impact to the subdivision calculations later on in development. Additionally, where these systems are complex, thought has to be given to their construction and how to provide suitable information at the shop floor to ensure installations are in the right place and quality surveys procedures are maintained. Ad hoc alterations and re-routing can easily have an impact on compliance.


Escape hatch openings are to be designed such that when leaving an undamaged space the hatch opening is not situated in a flooded area. For passenger ships, horizontal escape routes which form part of the main escape routes up to the muster stations also require protection from flooding. It is easy to focus on modelling the regulation precisely as opposed to questioning the intent. For example, towards the forward and aft ends of a cruise liner an escape hatch opening may not be in such close proximity to an immediate access upwards or protected horizontal escape area. Considering questions like these is a necessary process in the plan approval process today and requires


close liaison between the designer and


approval authority. 3.5


CROSS FLOODING ARRANGEMENTS


Recommendations for a standard method for evaluating cross flooding arrangements have been adopted under IMO Resolution MSC.245(83). This is to cater aspects in Chapter II-1 dealing with these points.


for intermediate


A-4


©2011: The Royal Institution of Naval Architects


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