Regulation 25 - Hypothetical outflow of oil
Clasification Society 2024 - Version 9.40

Regulation 25 - Hypothetical outflow of oil

  1 The hypothetical outflow of oil in the case of side damage (Oc) and bottom damage (Os) shall be calculated by the following formulae with respect to compartments breached by damage to all conceivable locations along the length of the ship to the extent as defined in regulation 24 of this Annex.

  • .1 For side damages:

    O c = ΣW i + Σ K i C i
  • (I)
  • .2 For bottom damages:

    O s = 1/3 (Σ Z i W i + Σ Z i C i)
  • (II)
  • where:
    W i = volume of a wing tank in cubic metres assumed to be breached by the damage as specified in regulation 24 of this Annex; Wi for a segregated ballast tank may be taken equal to zero.
    C i = volume of a centre tank in cubic metres assumed to be breached by the damage as specified in regulation 24 of this Annex; Ci for a segregated ballast tank may be taken equal to zero.
    K i = 1 bi/tc when bi is equal to or greater than tc, Ki shall be taken equal to zero.
    Z i = 1- hi/vs, when hi is equal to or greater than vs, Zi shall be taken equal to zero.
    b i = width of wing tank under consideration, in metres, measured inboard from the ship's side at right angles to the centreline at the level corresponding to the assigned summer freeboard.
    h i = minimum depth of the double bottom under consideration, in metres; where no double bottom is fitted hi shall be taken equal to zero.
  • Whenever symbols given in this paragraph appear in this chapter, they have the meaning as defined in this regulation.

  2 If a void space or segregated ballast tank of a length less than l c as defined in regulation 24 of this Annex is located between wing oil tanks, Oc in formula (I) may be calculated on the basis of volume Wi being the actual volume of one such tank (where they are of equal capacity) or the smaller of the two tanks (if they differ in capacity) adjacent to such space, multiplied by Si as defined below and taking for all other wing tanks involved in such collision the value of the actual full volume.

S i = 1 - l i/l c
where l i = length in metres of void space or segregated ballast tank under consideration.
  • 3.1 Credit shall only be given in respect of double bottom tanks which are either empty or carrying clean water when cargo is carried in the tanks above.

  • 3.2 Where the double bottom does not extend for the full length and width of the tank involved, the double bottom is considered non-existent and the volume of the tanks above the area of the bottom damage shall be included in formula (II) even if the tank is not considered breached because of the installation of such a partial double bottom.

  • 3.3 Suction wells may be neglected in the determination of the value hi provided such wells are not excessive in area and extend below the tank for a minimum distance and in no case more than half the height of the double bottom. If the depth of such a well exceeds half the height of the double bottom, hi shall be taken equal to the double bottom height minus the well height.

    Piping serving such wells if installed within the double bottom shall be fitted with valves or other closing arrangements located at the point of connection to the tank served to prevent oil outflow in the event of damage to the piping. Such piping shall be installed as high from the bottom shell as possible. These valves shall be kept closed at sea at any time when the tank contains oil cargo, except that they may be opened only for cargo transfer needed for the purpose of trimming of the ship.

  4 In the case where bottom damage simultaneously involves four centre tanks, the value of Os may be calculated according to the formula:

O s = 1/4Z i W i + Σ Z i C i)
  • (III)

  5 An Administration may credit as reducing oil outflow in case of bottom damage, an installed cargo transfer system having an emergency high suction in each cargo oil tank, capable of transferring from a breached tank or tanks to segregated ballast tanks or to available cargo tankage if it can be assured that such tanks will have sufficient ullage. Credit for such a system would be governed by ability to transfer in two hours of operation oil equal to one half of the largest of the breached tanks involved and by availability of equivalent receiving capacity in ballast or cargo tanks. The credit shall be confined to permitting calculation of Os according to formula (III). The pipes for such suctions shall be installed at least at a height not less than the vertical extent of the bottom damage vs. The Administration shall supply the Organization with the information concerning the arrangements accepted by it, for circulation to other Parties to the Convention.

  6 This regulation does not apply to oil tankers delivered on or after 1 January 2010, as defined in regulation 1.28.8.


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