Detail
Article 19.03(7), (8) and (10) - Calculation of intermediate stages of flooding
Article 19.03(7) stipulates that the calculation of damage stability shall be based on the “lost buoyancy” method.
According to Article 19.03(8): "… mathematical proof of sufficient stability shall be determined for the three intermediate stages of flooding (25, 50 and 75 % of flood build-up) … "
Article 19.03(10)(a), stipulates that:
“The heeling angle φ at the equilibrium position of the intermediate stage in question shall not exceed 15°."
Most commercially available software uses an algorithm to calculate equilibrium. The computer only displays the result once equilibrium has been reached.
An intermediate stage of flooding is not an equilibrium position. Equilibrium is only reached at the final stage of flooding.
Consequently, the requirement in article 19.03(10)(a) makes no sense in the event of the lost buoyancy method being used. Only one method can provide an intermediate result, for example for flooding of 25%. This is the “added mass method”.
Can the “added mass method” be used as an alternative for calculating intermediate stages of flooding? (See also question 3b above).
If the “added mass method” can be used, can the criteria mentioned in article 19.03(10)(a), (b) and (c) be calculated in their entirety using this method?
Conclusions:
When calculating damage stability, the notion of “free surface effect” is part of the added mass method and not part of the “lost buoyancy” method. The “added mass method” is no longer recognised by the IMO. In the IMO context, calculations are to be made using the “lost buoyancy method”.
The requirement for “intermediate stages of flooding” is crucial. Yet, intermediate stages of flooding can only be calculated using the “added mass method”.
If the “lost buoyancy method” is also to be used for intermediate stages of flooding, it will be difficult to find software for this purpose and shipbuilding engineers capable of performing these calculations. The cost for vessel owners could be high!
Given article 19.03(7), which recommends use of the “loss buoyancy method” the current text of ES-TRIN is very confusing. The calculation methods need to be clarified.
Answer:
It is true that an intermediate stage of flooding is not an equilibrium position. The notion of “equilibrium stage of the intermediate state” is purely theoretical but it can be calculated and therefore the criterion is verifiable.
In order for the text to be clearer and consistent with practice, it should be explained that it is stability in the final state of flooding that is to be calculated using the lost buoyancy method.
In the current wording of article 19.03(9)(c), the notion of final stage of flooding is only used for the bulkhead deck and not for the windows, which could create the impression that as far as the latter are concerned the requirement also applies to the intermediate stages. Moreover, the conditions to be complied with for the intermediate stages and final stage are clarified in (10) and (11) respectively whereas (9) in its entirety, except for (c), relates to how to perform the calculations. It would be more logical to relocate the content of (9)(c) to (c) in (10) and (11). There would then no longer be any doubt as the stage to which the requirements apply.
RV/G (07) 84 rev. 1
The explanations are not proposed amendments of the requirements but comments. These explanations are correct.
RV/G (07) 90
CCNR Inspection Regulations Working Group RV/G, stability, damage stability, flooding
