Part II - Double Hull Construction Requirements for New Oil Tankers

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6. Application

6.1 The requirements of this Part shall apply to oil tankers delivered on or after 6 July 1996.

6.2 This Part reflects the provisions of regulation 19 of Annex I of MARPOL .

7. Requirement to be Double Hulled or have Alternate Arrangements

7.1 Unless it is subject to the provisions of sections 9 or 10, every oil tanker delivered on or after 6 July 1996 shall comply with the requirements of section 8 and also comply, if applicable, with the requirements of section 11.

8. Dimensions of Protective Spaces

8.1 The entire cargo tank length shall be protected by ballast tanks or spaces other than cargo and oil tanks as follows:

Wing Tanks or Spaces

1. wing tanks or spaces shall extend either for the full depth of the vessel’s side or from the top of the double bottom to the uppermost deck, disregarding a rounded gunwale where fitted, and arranged that the cargo tanks are located inboard of the moulded line of the side shell plating, nowhere less the distance w which, as shown in Figure 1, is measured at any cross-section at right angles to the shell, specified as follows:

1. vessels of 5,000 tonnes deadweight ( DWT ) and above
   
    
   
   
   
   or 2.0 m whichever is the lesser, with a minimum value of w = 1.0 m ;
2. vessels of less than 5,000 tonnes deadweight ( DWT )
   
    
   
   
   
   with minimum value of w = 0.76 m ;

Double Bottom Tanks or Spaces

2. at any cross-section the depth of each double bottom tank or space shall be such that the distance h between the bottom of the cargo tanks and the moulded line of the bottom shell plating measured at right angles to the bottom shell plating as shown in Figure 1 is not less than specified as follows:

1. oil tankers of 5,000 tonnes deadweight ( DWT ) and above h = B/15 ( m ) or 2.0 m , whichever is the lesser, with a minimum value of h = 1.0 m ;
2. oil tankers of less than 5,000 tonnes deadweight ( DWT ) h = B/15 ( m ), but in no case less than 0.76 m ;

3. at the turn of the bilge area, or at locations without a clearly defined turn of the bilge, when the distances h and w are different,

1. for oil tankers of 5,000 tonnes deadweight and above, the distance w shall have preference at levels exceeding 1.5h above the baseline as shown in Figure 1; and
2. for oil tankers of less than 5,000 tonnes deadweight, the cargo tank boundary line shall run not less than the distance h above and parallel to the line of the midship flat bottom as shown in Figure 2, and at levels greater than h above the line of the midship flat bottom, the cargo tanks shall be located not less than the distance w inboard of the moulded line of the side shell plating as shown in Figure 2.

Figure 1 Cargo tank boundary lines for the purpose of section 8

Figure 2 Cargo tank boundary lines within the turn of bilge for oil tankers under 5,000 tonnes deadweight

8.2 On crude oil tankers of 20,000 tonnes deadweight and above and product carriers of 30,000 tonnes deadweight and above, the aggregate capacity of wing tanks, double bottom tanks, forepeak tanks and afterpeak tanks shall not be less than the capacity of segregated ballast tanks necessary to meet the requirements of Regulation 18 of Annex 1 of MARPOL , and wing tanks or spaces and double bottom tanks used to meet the requirements of Regulation 18 of Annex I of MARPOL shall be located as uniformly as practicable along the cargo tank length; additional segregated ballast capacity provided for reducing longitudinal hull girder bending stress, trim, etc., may be located anywhere within the vessel.

8.3 Suction wells in cargo tanks may protrude into the double bottom below the boundary line defined by the distance h provided that such wells are as small as practicable and the distance between the well bottom and bottom shell plating is not less than 0.5 h.

8.4 Ballast piping and other piping such as sounding and vent piping to ballast tanks shall not pass through cargo tanks; nor shall cargo piping and piping to cargo tanks pass through ballast tanks, except that exemptions may be granted for short lengths of piping, provided that they are completely welded or equivalent.

9. Alternative Arrangements For Double Bottom Spaces

9.1 Double bottom tanks or spaces as required by paragraph 8(1)(b) may be dispensed with, provided that the design of the tanker is such that the cargo and vapour pressure exerted on the bottom shell plating forming a single boundary between the cargo and the sea does not exceed the external hydrostatic water pressure, as expressed by the following formula:

f × h_c × ρ_c × g + Δp ≤ d_n × ρ_s × g where:

h_c = height of cargo in contact with the bottom shell plating
ρ_c = maximum cargo density (tonnes per cubic metre, t / m ³)
d_n = minimum operating draught under any expected loading condition (metres)
ρ_s = density of seawater (tonnes per cubic metre, t / m ³)
Δp = maximum set pressure of pressure/vacuum valve provided for the cargo tank (kilopascals, kPa )
f = safety factor = 1.1
g = standard acceleration due to gravity (9.81 metres per second squared, m / sec ²).

9.2 Any horizontal partition necessary to fulfil the above requirements shall be located at a height of not less than B /6 or 6 m , whichever is the lesser, but not more than 0.6 D , above the baseline where D is moulded depth amidships.

9.3 The location of wing tanks or spaces shall be as defined in paragraph 8(1)(a) except that below a level 1.5 h above the baseline, where h is as defined in paragraph 8(1)(b), the cargo tank boundary line may be vertical down to the bottom plating, as shown in figure 3.

Figure 3 Cargo tank boundary lines for oil tankers adopting alternative arrangements for double bottom spaces (Section 9 refers)

10. Alternative Designs

10.1 Other methods of design and construction of oil tankers may also be accepted by the Minister as alternatives to the requirements prescribed in section 8, provided that such methods ensure at least the same level of protection against oil pollution in the event of collision or stranding and are approved in principle by the Marine Environment Protection Committee of the International Maritime Organization, based on guidelines developed by the Organization (resolution MEPC .110(49) as may be amended from time to time).

11. Assumptions For Bottom Raking Damage

11.1 For oil tankers of 20,000 tonnes deadweight and above the damage assumptions prescribed in Regulation 28.2.2 of Annex I of MARPOL shall be supplemented by the following assumed bottom raking damage:

1. longitudinal extent shall be
   1. for ships of 75,000 tonnes deadweight and above, 0.6 L measured from the forward perpendicular, and
   2. for ships of less than 75,000 tonnes deadweight, 0.4 L measured from the forward perpendicular;
2. transverse extent shall be B /3 anywhere in the bottom; and
3. vertical extent shall only include breach of the outer hull.

12. Cargo Location Relative to Collision Bulkhead

12.1 Oil shall not be carried in any space extending forward of a collision bulkhead located in accordance with regulation II-1/11 of the International Convention for the Safety of Life at Sea, 1974, as amended, and an oil tanker that is not required to have a collision bulkhead in accordance with that regulation shall not carry oil in any space extending forward of the transverse plane perpendicular to the centreline that is located as if it were a collision bulkhead located in accordance with that regulation.

13. General Safety Aspects

13.1 In approving the design and construction of oil tankers to be built in accordance with the provisions of these Standards, due regard shall be given to the general safety aspects including the need for the maintenance and inspections of wing and double bottom tanks or spaces (refer to IMO Resolution MSC .158(78)).

14. Limitation of Size and Arrangement of Cargo Tanks

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

1. where no longitudinal bulkhead is provided inside the cargo tanks,
   
    
   
   
   
   but l is not to exceed 0.2 L ; or
2. where a centreline longitudinal bulkhead is provided inside the cargo tanks,
    
   
3. where two or more longitudinal bulkheads are provided inside the cargo tanks,
   1. for wing cargo tanks,
      l = 0.2 L , and
   2. for centre cargo tanks,
      1. if
         
         is equal to or greater than one fifth,
         then l = 0.2 L , or
      2. if
         
         is less than one fifth, then,
         where no centreline longitudinal bulkhead is provided,
         
          
         
         
         
         or;
         
         where a centreline longitudinal bulkhead is provided,
          
         

where:

"b_i" means 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;

" B " means "breadth" as defined in section 2; and

" L " means "length" as defined in section 2.

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