33 CFR Appendix A to Part 157, Damage Assumptions, Hypothetical Outflows, and Cargo Tank Size and Arrangements
1. Source. The procedures for the damage assumption calculations contained in this Appendix conform to Regulations 24, 25, and 26 of Annex I of the International Convention for the Prevention of the Pollution from Ships, 1973, done at London, November 2, 1973.
2. Assumptions. For the purpose of calculating hypothetical outflow from tank vessels, three dimensions of the extent of damage of a parallelepiped on the side and bottom of the vessel are assumed.
(a) For side damage, the conditions are as follows:
|(1) Longitudinal extent
|(2) Transverse extent (
- or 11.5 m, whichever is less.
|(3) Vertical extent (
||From the base line upwards without limit.|
(b) For bottom damage, two conditions to be applied individually to the stated portions of the vessel, as follows:
|For 0.3L from the forward perpendicular of ship||Any other part of ship|
|(1) Longitudinal extent (
|(2) Transverse extent (
|(3) Vertical extent from the base line (
3. Hypothetical Outflow of Oil.
(a) The hypothetical outflow of oil in the case of side damage (Oc) and bottom damage (Os) is calculated by the following formula with respect to compartments breached by damage to all conceivable locations along the length of the vessel to the extent as defined in section 2 of this Appendix.
(1) For side damages: Formula
(2) For bottom damage: Formula II
(b) If a void space or segregated ballast tank of a length less than lc is located between wing oil tanks, Oc in formula I of this section 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 a collision the value of the actual full volume.
(c) Credit is only given in respect to double bottom tanks which are either empty or carrying clean water when cargo is carried in the tanks above.
(1) If the double bottom does not extend for the full length and width of the tank involved, the double bottom is considered nonexistent and the volume of the tanks above the area of the bottom damage must be included in formula II of this section even if the tank is not considered breached because of the installation of such a partial double bottom.
(2) Suction wells may be neglected in the determination of the value hi if 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 is taken equal to the double bottom height minus the well height.
(d) In the case where bottom damage simultaneously involves four center tanks, the value of Os may be calculated according to formula III as follows:
Os = 1/4(ΣZiWi ΣZiCi)
(e) Credit for reduced oil outflow from bottom damage may be applied to formula III for an installed emergency high suction cargo transfer system that:
(1) transfers within two hours oil equal to one half of the volume of the largest tank involved;
(2) has sufficient ballast or cargo tankage available to receive the transferred oil; and
(3) has the high suction piping installed at a height not less than the vertical extent of bottom damage (vs).
4. Allowable volumes of cargo tanks.
(a) The allowable volume of a wing cargo tank (VOLw) is equal to seventy-five percent of OA. In a segregated ballast tank vessel VOLw may equal OA for a wing cargo oil tank located between two segregated ballast tanks each of length greater than lc and width greater than tc.
(b) The allowable volume of a center cargo tank (VOLc) is 50,000 cubic meters.
5. Allowable length of cargo tanks.
The length of each cargo tank (1 a) must not exceed 10 meters or the distance calculated from (a), (b), or (c), as appropriate, whichever is greater:
(a) Where no longitudinal bulkhead is provided inside the cargo tanks: 1 a=[0.5(bi/B) 0.1] L, but not to exceed 0.2L.
(b) Where a centerline longitudinal bulkhead is provided inside the cargo tanks: 1 a=[0.25(bi/B) 0.15] L, but not to exceed 0.2L.
(c) Where two or more longitudinal bulkheads are provided inside the cargo tanks:
(1) For wing cargo tanks: 1 a = 0.2L.
(2) For center cargo tanks:
(i) If (bi/B) is equal to or greater than 0.2, 1 a = 0.2L.
(ii) If (bi/B) is less than 0.2:
(A) Where no centerline longitudinal bulkhead is provided, 1 a = [0.5(bi/B) 0.1] L.
(B) Where a centerline longitudinal bulkhead is provided, 1 a = [0.25(bi/B) 0.15] L.
(d) “bi” 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 centerline at the level corresponding to the assigned summer freeboard.