Regulation 23 - Accidental oil outflow performance
Clasification Society 2024 - Version 9.40

Regulation 23 - Accidental oil outflow performance

  1 This regulation shall apply to oil tankers delivered on or after 1 January 2010, as defined in regulation 1.28.8.

  2 For the purpose of this regulation, the following definitions shall apply:

  • .1 "Load line draught (d S)" is the vertical distance, in metres, from the moulded baseline at mid-length to the waterline corresponding to the summer freeboard to be assigned to the ship. Calculations pertaining to this regulation should be based on draught d S, notwithstanding assigned draughts that may exceed d S, such as the tropical loadline.

  • .2 "Waterline (d B)" is the vertical distance, in metres, from the moulded baseline at mid-length to the waterline corresponding to 30% of the depth D S.

  • .3 "Breadth (B S)" is the greatest moulded breadth of the ship, in metres, at or below the deepest load line d S.

  • .4 "Breadth (B B)" is the greatest moulded breadth of the ship, in metres, at or below the waterline d B.

  • .5 "Depth (D S)" is the moulded depth, in metres, measured at mid-length to the upper deck at side.

  • .6 "Length (L)" and "deadweight (DW)" are as defined in regulations 1.19 and 1.23, respectively.

  3 To provide adequate protection against oil pollution in the event of collision or stranding the following shall be complied with:

  • .1 for oil tankers of 5,000 tonnes deadweight (DWT) and above, the mean oil outflow parameter shall be as follows:

    OM ≤ 0.015 for C ≤ 200,000 m3
    OM ≤ 0.012 + (0.003/200,000) (400,000–C) for 200,000 m3 < C < 400,000 m3
    OM ≤ 0.012 for C ≥ 400,000 m3

    for combination carriers between 5,000 tonnes deadweight (DWT) and 200,000 m3 capacity, the mean oil outflow parameter may be applied, provided calculations are submitted to the satisfaction of the Administration, demonstrating that after accounting for its increased structural strength, the combination carrier has at least equivalent oil out flow performance to a standard double hull tanker of the same size having a OM ≤ 0.015.

    OM ≤ 0.021 for C ≤ 100,000 m3
    OM ≤ 0.015 + (0.006/100,000) (200,000–C) for 100,000 m3 < C < 200,000 m3
    where:
    OM = mean oil outflow parameter
    C = total volume of cargo oil, in m3, at 98% tank filling.

  • .2 for oil tankers of less than 5,000 tonnes deadweight (DWT):

    The length of each cargo tank shall not exceed 10 m or one of the following values, whichever is the greater:

    • .2.1 where no longitudinal bulkhead is provided inside the cargo tanks:

      but not to exceed 0.2L

    • .2.2 where a centreline longitudinal bulkhead is provided inside the cargo tanks:

    • .2.3 where two or more longitudinal bulkheads are provided inside the cargo tanks:

      • .2.3.1 for wing cargo tanks: 0.2L

      • .2.3.2 for centre cargo tanks:

        • .2.3.2.1 if

        • .2.3.2.2 if

          • .2.3.2.2.1 - where no centreline longitudinal bulkhead is provided:

          • .2.3.2.2.2 - where a centreline longitudinal bulkhead is provided:

      b i is the minimum distance from the ship's side to the outer longitudinal bulkhead of the tank in question measured inboard at right angles to the centreline at the level corresponding to the assigned summer freeboard.

  4 The following general assumptions shall apply when calculating the mean oil outflow parameter:

  • .1 The cargo block length extends between the forward and aft extremities of all tanks arranged for the carriage of cargo oil, including slop tanks.

  • .2 Where this regulation refers to cargo tanks, it shall be understood to include all cargo tanks, slop tanks and fuel tanks located within the cargo block length.

  • .3 The ship shall be assumed loaded to the load line draught dS without trim or heel.

  • .4 All cargo oil tanks shall be assumed loaded to 98% of their volumetric capacity. The nominal density of the cargo oil ( ρ n) shall be calculated as follows:

    ρ n = 1000 (DWT)/C (kg/m3)

  • .5 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 shall be taken as 0.99, unless proven otherwise.

  • .6 Suction wells may be neglected in the determination of tank location provided that such wells are as small as practicable and the distance between the well bottom and bottom shell plating is not less than 0.5h, where h is the height as defined in regulation 19.3.2.

  5 The following assumptions shall be used when combining the oil outflow parameters:

  • .1 The mean oil outflow shall be calculated independently for side damage and for bottom damage and then combined into the non-dimensional oil outflow parameter OM, as follows:

    OM = (0.4 OMS + 0.6 OMB)/C
    where:
    OMS = mean outflow for side damage, in m3; and
    OMB = mean outflow for bottom damage, in m3.

  • .2 For bottom damage, independent calculations for mean outflow shall be done for 0 m and minus 2.5 m tide conditions, and then combined as follows:

    OMB = 0.7 OMB(0) + 0.3 OMB(2.5)
    where:
    OMB(0) = mean outflow for 0 m tide condition; and
    OMB(2.5) = mean outflow for minus 2.5 m tide condition, in m3.

  6 The mean outflow for side damage OMS shall be calculated as follows:

OMS =
where:
i = represents each cargo tank under consideration;
n = total number of cargo tanks;
PS(i) = the probability of penetrating cargo tank i from side damage, calculated in accordance with paragraph 8.1 of this regulation;
OS(i) = the outflow, in m3, from side damage to cargo tank i, which is assumed equal to the total volume in cargo tank i at 98% filling, unless it is proven through the application of the Guidelines referred to in regulation 19.5 that any significant cargo volume will be retained; and
C3 = 0.77 for ships having two longitudinal bulkheads inside the cargo tanks, provided these bulkheads are continuous over the cargo block and Ps(i) is developed in accordance with this regulation. C3 equals 1.0 for all other ships or when Ps(i) is developed in accordance with paragraph 10 of this regulation.

  7 The mean outflow for bottom damage shall be calculated for each tidal condition as follows:

  • .1

    where:
    i = represents each cargo tank under consideration;
    n = the total number of cargo tanks;
    PB(i) = the probability of penetrating cargo tank i from bottom damage, calculated in accordance with paragraph 9.1 of this regulation;
    OB(i) = the outflow from cargo tank i, in m3, calculated in accordance with paragraph 7.3 of this regulation; and
    CDB(i) = factor to account for oil capture as defined in paragraph 7.4 of this regulation

  • .2

    where:
    i, n, PB(i) and CDB(i) = as defined in subparagraph .1 above;
    OB(i) = the outflow from cargo tank i, in m3, after tidal change.

  • .3 The oil outflow OB(i) for each cargo oil tank shall be calculated based on pressure-balance principles, in accordance with the following assumptions:

    • .1 The ship shall be assumed stranded with zero trim and heel, with the stranded draught prior to tidal change equal to the load line draught ds.

    • .2 The cargo level after damage shall be calculated as follows:

      hc = {(ds + tc - Zl) ( ρ s) – (1000 p) / g }/ ρ n
      where:
      hc = the height of the cargo oil above Zl, in metres;
      tc = the tidal change, in metres. Reductions in tide shall be expressed as negative values;
      Zl = the height of the lowest point in the cargo tank above baseline, in metres;
      ρ s = density of seawater, to be taken as 1,025 kg/m3;
      p = if an inert gas system is fitted, the normal overpressure, in kPa, to be taken as not less than 5 kPa; if an inert gas system is not fitted, the overpressure may be taken as 0;
      g = the acceleration of gravity, to be taken as 9.81 m/s2; and
      ρ n = nominal density of cargo oil, calculated in accordance with paragraph 4.4 of this regulation.

    • SEE INTERPRETATION 47

    • .3 For cargo tanks bounded by the bottom shell, unless proven otherwise, oil outflow OB(i) shall be taken not less than 1% of the total volume of cargo oil loaded in cargo tank i, to account for initial exchange losses and dynamic effects due to current and waves.

  • .4 In the case of bottom damage, a portion from the outflow from a cargo tank may be captured by non-oil compartments. This effect is approximated by application of the factor CDB(i) for each tank, which shall be taken as follows:

    CDB(i) = 0.6 for cargo tanks bounded from below by non-oil compartments;
    CDB(i) = 1.0 for cargo tanks bounded by the bottom shell.

  8 The probability PS of breaching a compartment from side damage shall be calculated as follows:

  • .1 PS = PSL PSV PST

    where:
    PSL = 1 - PSf - PSa
    = probability the damage will extend into the longitudinal zone bounded by Xa and Xf;
    PSV = 1 - PSu - PS1
    = probability the damage will extend into the vertical zone bounded by Zl and Zu; and
    PST = 1 - PSy
    = probability the damage will extend transversely beyond the boundary defined by y.

  • .2 PSa, PSf, PSl, PSu and PSy shall be determined by linear interpolation from the table of probabilities for side damage provided in paragraph 8.3 of this regulation,

    where:
    PSa = the probability the damage will lie entirely aft of location Xa/L;
    PSf = the probability the damage will lie entirely forward of location Xf/L;
    PSl = the probability the damage will lie entirely below the tank;
    PSu = the probability the damage will lie entirely above the tank; and
    PSy = the probability the damage will lie entirely outboard of the tank.
    = Compartment boundaries Xa, Xf, Zl, Zu and y shall be developed as follows:
    Xa = the longitudinal distance from the aft terminal of L to the aftmost point on the compartment being considered, in metres;
    Xf = the longitudinal distance from the aft terminal of L to the foremost point on the compartment being considered, in metres;
    Zl = the vertical distance from the moulded baseline to the lowest point on the compartment being considered, in metres;
    Zu = the vertical distance from the moulded baseline to the highest point on the compartment being considered, in metres. Zu is not to be taken greater than Ds; and
    y = the minimum horizontal distance measured at right angles to the centreline between the compartment under consideration and the side shell in metres; footnote

  • .3 Table of probabilities for side damage

    Xa /L PSa   Xf /L PSf   Zl /DS PSl   Zu /DS PSu
    0.00 0.000   0.00 0.967   0.00 0.000   0.00 0.968
    0.05 0.023   0.05 0.917   0.05 0.000   0.05 0.952
    0.10 0.068   0.10 0.867   0.10 0.001   0.10 0.931
    0.15 0.117   0.15 0.817   0.15 0.003   0.15 0.905
    0.20 0.167   0.20 0.767   0.20 0.007   0.20 0.873
    0.25 0.217   0.25 0.717   0.25 0.013   0.25 0.836
    0.30 0.267   0.30 0.667   0.30 0.021   0.30 0.789
    0.35 0.317   0.35 0.617   0.35 0.034   0.35 0.733
    0.40 0.367   0.40 0.567   0.40 0.055   0.40 0.670
    0.45 0.417   0.45 0.517   0.45 0.085   0.45 0.599
    0.50 0.467   0.50 0.467   0.50 0.123   0.50 0.525
    0.55 0.517   0.55 0.417   0.55 0.172   0.55 0.452
    0.60 0.567   0.60 0.367   0.60 0.226   0.60 0.383
    0.65 0.617   0.65 0.317   0.65 0.285   0.65 0.317
    0.70 0.667   0.70 0.267   0.70 0.347   0.70 0.255
    0.75 0.717   0.75 0.217   0.75 0.413   0.75 0.197
    0.80 0.767   0.80 0.167   0.80 0.482   0.80 0.143
    0.85 0.817   0.85 0.117   0.85 0.553   0.85 0.092
    0.90 0.867   0.90 0.068   0.90 0.626   0.90 0.046
    0.95 0.917   0.95 0.023   0.95 0.700   0.95 0.013
    1.00 0.967   1.00 0.000   1.00 0.775   1.00 0.000

    PSy shall be calculated as follows:

    PSy = (24.96 -199.6 y/BS) (y/BS)
    • for y/BS ≤ 0.05
    PSy = 0.749 + {5 -44.4 (y/BS - 0.05)} (y/BS - 0.05)
    • for 0.05 < y/BS < 0.1
    PSy = 0.888 + 0.56 (y/BS - 0.1)
    • for y/BS ≥ 0.1

    PSy shall not be taken greater than 1.

  9 The probability PB of breaching a compartment from bottom damage shall be calculated as follows:

  • .1 PB = PBL PBT PBV

    where:
    PBL = 1 - PBf - PBa
    = probability the damage will extend into the longitudinal zone bounded by Xa and Xf;
    PBT = 1 - PBp - PBs
    = probability the damage will extend into the transverse zone bounded by Yp and Ys; and
    PBV = 1 - PBz
    = probability the damage will extend vertically above the boundary defined by z.

  • .2 PBa, PBf, PBp, PBs, and PBz shall be determined by linear interpolation from the table of probabilities for bottom damage provided in paragraph 9.3 of this regulation, where:

    PBa = the probability the damage will lie entirely aft of location Xa/L;
    PBf = the probability the damage will lie entirely forward of location Xf/L;
    PBp = the probability the damage will lie entirely to port of the tank;
    PBs = the probability the damage will lie entirely to starboard of the tank; and
    PBz = the probability the damage will lie entirely below the tank.

    Compartment boundaries Xa, Xf, Yp, Ys, and z shall be developed as follows:

    Xa and Xf are as defined in paragraph 8.2 of this regulation;

    Yp = the transverse distance from the port-most point on the compartment located at or below the waterline dB, to a vertical plane located BB /2 to starboard of the ship's centreline, in metres;
    Ys = the transverse distance from the starboard-most point on the compartment located at or below the waterline dB, to a vertical plane located BB /2 to starboard of the ship's centreline, in metres; and
    z = the minimum value of z over the length of the compartment, where, at any given longitudinal location, z is the vertical distance from the lower point of the bottom shell at that longitudinal location to the lower point of the compartment at that longitudinal location, in metres.

  • .3 Table of probabilities for bottom damage

    Xa /L PBa   Xf /L PBf   Yp /BB PBp   Ys /BB PBs
    0.00 0.000   0.00 0.969   0.00 0.844   0.00 0.000
    0.05 0.002   0.05 0.953   0.05 0.794   0.05 0.009
    0.10 0.008   0.10 0.936   0.10 0.744   0.10 0.032
    0.15 0.017   0.15 0.916   0.15 0.694   0.15 0.063
    0.20 0.029   0.20 0.894   0.20 0.644   0.20 0.097
    0.25 0.042   0.25 0.870   0.25 0.594   0.25 0.133
    0.30 0.058   0.30 0.842   0.30 0.544   0.30 0.171
    0.35 0.076   0.35 0.810   0.35 0.494   0.35 0.211
    0.40 0.096   0.40 0.775   0.40 0.444   0.40 0.253
    0.45 0.119   0.45 0.734   0.45 0.394   0.45 0.297
    0.50 0.143   0.50 0.687   0.50 0.344   0.50 0.344
    0.55 0.171   0.55 0.630   0.55 0.297   0.55 0.394
    0.60 0.203   0.60 0.563   0.60 0.253   0.60 0.444
    0.65 0.242   0.65 0.489   0.65 0.211   0.65 0.494
    0.70 0.289   0.70 0.413   0.70 0.171   0.70 0.544
    0.75 0.344   0.75 0.333   0.75 0.133   0.75 0.594
    0.80 0.409   0.80 0.252   0.80 0.097   0.80 0.644
    0.85 0.482   0.85 0.170   0.85 0.063   0.85 0.694
    0.90 0.565   0.90 0.089   0.90 0.032   0.90 0.744
    0.95 0.658   0.95 0.026   0.95 0.009   0.95 0.794
    1.00 0.761   1.00 0.000   1.00 0.000   1.00 0.844

    PBz shall be calculated as follows:

    PBz = (14.5 - 67 z/DS) (z/DS )
    • for z/DS ≤ 0.1,
    PBz = 0.78 + 1.1 (z/DS - 0.1)
    • for z/DS > 0.1.

    PBz shall not be taken greater than 1.

  10 This regulation uses a simplified probabilistic approach where a summation is carried out over the contributions to the mean outflow from each cargo tank. For certain designs such as those characterized by the occurrence of steps/recesses in bulkheads/decks and for sloping bulkheads and/or a pronounced hull curvature, more rigorous calculations may be appropriate. In such cases one of the following calculation procedures may be applied:

  • .1 The probabilities referred to in 8 and 9 above may be calculated with more precision through application of hypothetical sub-compartments. footnote

  • .2 The probabilities referred to in 8 and 9 above may be calculated through direct application of the probability density functions contained in the Guidelines referred to in regulation 19.5.

  • .3 The oil outflow performance may be evaluated in accordance with the method described in the Guidelines referred to in regulation 19.5.

  11 The following provisions regarding piping arrangements shall apply:

  • .1 Lines of piping that run through cargo tanks in a position less than 0.30Bs from the ship's side or less than 0.30Ds from the ship's bottom shall be fitted with valves or similar closing devices at the point at which they open into any cargo tank. These valves shall be kept closed at sea at any time when the tanks contain cargo oil, except that they may be opened only for cargo transfer needed for essential cargo operations.

  • .2 Credit for reducing oil outflow through the use of an emergency rapid cargo transfer system or other system arranged to mitigate oil outflow in the event of an accident may be taken into account only after the effectiveness and safety aspects of the system are approved by the Organization. Submittal for approval shall be made in accordance with the provisions of the Guidelines referred to in regulation 19.5.

Parent topic: Part A - Construction
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