6 Calculation of mean outflow from side damage
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Statutory Documents - IMO Publications and Documents - Resolutions - Marine Environment Protection Committee - Resolution MEPC.122(52) - Explanatory Notes on Matters Related to the Accidental Oil Outflow Performance under Regulation 23 of the Revised MARPOL Annex I - (Adopted on 15 October 2004)Amended by Resolution MEPC.146(54) - Annex - Explanatory Notes on Matters Related to the Accidental Oil Outflow Performance under Regulation 23 of the Revised MARPOL Annex I - Part A - Background - 6 Calculation of mean outflow from side damage

6 Calculation of mean outflow from side damage

  6.1 There were no available data on the percentage of outflow from a tank subject to side damage, and theoretical calculation of the portion of retained liquid was considered impractical. Therefore, it is conservatively assumed that for side damage, total (100%) of the oil outflows from each damaged cargo tank. This is consistent with the approach applied in the Revised Interim Guidelines.

  6.2 In accordance with paragraph 6 of regulation 23, the mean outflow from side damage is calculated as follows:

(6.2)

Where Ps(i) is the probability of penetrating cargo tank i from side damage, and Os(i) is the outflow from side damage to cargo tank i.

  6.3 In accordance with the simplified approach prescribed in regulation 23, the probability that damage will extend transversely into a cargo tank is calculated based on the minimum horizontal distance between the compartment and the side shell. Where the distance to the shell is not uniform, this assumption will result in over-estimates of oil outflow. This is most evident in way of the forward and aft cargo tanks, where hull curvature is most pronounced.

  6.4 More rigorous calculations carried out to validate the methodology showed that tankers with two continuous longitudinal bulkheads within the cargo tanks (i.e. with a three across cargo tank arrangement) are most affected by this conservative approach . Figure 13 presents the mean outflow parameters for a series of tankers calculated using the simplified approach as per regulation 23 without consideration of the C3 factor, and also calculated based on the hypothetical sub-compartment methodology specified in paragraph 10.1 of regulation 23. The vessels with capacities of under 200,000 m3 which have a single centreline bulkhead show good correspondence. The simplified regulation 23 approach overestimates the outflow performance of vessels over 300,000 m3 capacity, all of which have two longitudinal bulkheads within the cargo tanks. Therefore, in the case of such designs the outflow from side damage is multiplied by the C3 factor 0.77.

Comparison of calculations using the simplified method and hypothetical sub-compartments

Parent topic: Part A - Background
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