2.3.4 Per paragraph 7.3.2 of regulation 21, the cargo level after damage, measured in meters above Zl, is calculated as follows:

　

where:

　

2.3.5 For the condition with the tidal change tc equal to O m, the cargo level after damage hc is 20.153 m. The remaining volume for each cargo tank after damage, in m³, the oil outflow OB(i) are as follows:

　

　

 For the condition with tidal change tc equal to -2.5m, the remaining volume for each cargo tank after damage, in m³, and the oil outflow OB(i) is as follows:

　

　

2.3.6 In accordance with paragraphs 7.1 and 7.2 of regulation 21, the mean outflow from bottom damage is calculated as follows:

　

　

2.3.7 It is recognized that a portion of the oil escaping from a cargo tank may be entrapped by a double bottom tank below, thereby preventing the oil from reaching the sea. In accordance with paragraph 7.4 of regulation 21, CDB(i) is to be taken as 0.6 when a cargo tank is bounded from below by a non-oil compartment.

　

　

　

2.3.8 In accordance with paragraph 5.2 of regulation 21, mean outflow values from the 0.0 m and -2.5 m tide conditions are combined in a 70%:30% ratio to obtain the bottom damage mean outflow:

　

　

2.4 Mean oil outflow parameter OM

　

2.4.1 The non-dimensional mean oil outflow parameter OM is calculated as follows in accordance with paragraph 5.1 of regulation 21.

　

　

2.4.2 For oil tanker of 5,000 metric tons deadweight and above, the required mean oil outflow parameter is calculated in accordance with paragraph 3.1 of regulation 21.

　

　

 Since C is equal to 333,200 m³, the required mean oil outflow parameter OM is as follows.

　

　

 The vessel is therefore in compliance with the
"Accidental oil outflow performance" regulation 21.

　

　

　

　

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 Interim Guidelines^(2)*.

　

6.2 In accordance with paragraph 6 of regulation 21, the mean outflow from side damage is calculated as follows:

　

　

 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 21, 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 21 without consideration of the C3 factor, and also calculated based on the hypothetical sub-compartment methodology specified in paragraph 10.1 of regulation 21. The vessels with capacities of under 200,000 m³ which have a single centerline bulkhead show good correspondence. The simplified regulation 21 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.