5.1 General
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Statutory Documents - IMO Publications and Documents - Resolutions - Marine Environment Protection Committee - Resolution MEPC.110(49) - Revised Interim Guidelines for the Approval of Alternative Methods of Design and Construction of Oil Tankers Under Regulation 13F(5) of Annex I of MARPOL 73/78 - (adopted on 18 July 2003) - Annex - Revised Interim Guidelines for the Approval of Alternative Methods of Design and Construction of Oil Tankers Under Regulation 13F(5) of Annex I Of MARPOL 73/78 - 5 Assumptions for Calculating Oil Outflow Parameters - 5.1 General

5.1 General

  5.1.1 The assumptions specified in this section should be used when calculating the oil outflow parameters.

  5.1.2 Outflow parameters should be calculated independently for collisions and strandings and then combined as follows:

  • .1 0.4 of the computed value for collisions; and

  • .2 0.6 of the computed value for strandings.

  5.1.3 For strandings, independent calculations should be done for 0 m and 2.5 m fall in tide. Outflow parameters for the stranded conditions should be a weighted average, calculated as follows:

  • .1 .7 for 0 m tide condition; and

  • .2 0.3 for 2.5 m fall in tide condition.

  5.1.4 The damage cases and the associated probability factor Pi for each damage case should be determined based on the damage density distribution functions as specified in paragraph 5.2.

  5.1.5 The following general assumptions apply for the calculation of outflow parameters:

  • .1 The ship should be assumed loaded to the load line draught ds with zero trim and heel. All cargo tanks should be assumed loaded to 98% of their volumetric capacity. The nominal density of the cargo oil should be calculated as follows:

  • .2 For the purposes of these outflow calculations, the permeability of each space within the cargo block, including cargo tanks, ballast tanks and other non-oil spaces should be taken as 0.99, unless proven otherwise.

  • .3 For all cases of collision damage, the entire contents of all damaged cargo oil tanks should be assumed to be spilled into the sea, unless proven otherwise.

  • .4 For all stranded conditions, the ship should be assumed aground on a shelf. Assumed stranded draughts prior to tidal change should be equal to the initial intact draughts. Should the ship trim or float free due to the outflow of oil, this should be accounted for in the calculations for the final shipyard design.

  • .5 In general, an inert gas overpressure of 0.05 bar gauge should be assumed if an inert gas system is fitted, otherwise the inert gas overpressure should be taken as zero.

  • .6 For the calculation of oil outflow in case of stranding, the principles of hydrostatic balance should apply, and the location of damage used for calculations of hydrostatic pressure balance and related oil outflow calculations should be the lowest point in the cargo tank.

  • .7 For cargo tanks bounded by the bottom shell, unless proven otherwise, oil outflow equal to 1% of the volume of the damaged tank should be assumed to account for initial exchange losses and dynamic effects due to current and waves.

  • .8 For breached non-cargo spaces located wholly or in part below breached cargo oil tanks, the flooded volume of these spaces at equilibrium should be assumed to contain 50% oil and 50% seawater by volume, unless proven otherwise.

  • .9 If deemed necessary, model tests may be required to determine the influence of tidal, current and swell effects on the oil outflow performance.

  • .10 For ship designs which incorporate cargo transfer systems for reducing oil outflow, calculations should be provided illustrating the effectiveness of such devices. For these calculations, damage openings consistent with the damage density distribution functions defined in paragraph 5.2 should be assumed.

  • .11 Where, for the final shipyard design referred to in 3.3 and in the special cases referred to in paragraph 4.1.3, damage stability calculations are required, the following should apply:

    • A damage stability calculation should be performed for each damage case. The stability in the final stage of flooding should be regarded as sufficient if the requirements of MARPOL regulation I/25(3) are complied with.

    • Should the ship fail to meet the survivability criteria as defined in MARPOL regulation I/25(3), 100% oil outflow from all cargo tanks should be assumed for that damage case.

Parent topic: 5 Assumptions for Calculating Oil Outflow Parameters
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