Appendix - Arrangements acceptable as alternatives under regulation 13G(7) of Annex I of MARPOL 73/78
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Statutory Documents - IMO Publications and Documents - Resolutions - Marine Environment Protection Committee - Resolution MEPC.64(36) - Guidelines for Approval of Alternative Structural or Operational Arrangements as Called for in Regulation 13G(7) of Annex I of MARPOL 73/78 - (adopted on 4 November 1994) - Annex - Guidelines for Approval of Alternative Structural or Operational Arrangements as Called for in MARPOL 73/78, Annex I, Regulation 13G(7) - Appendix - Arrangements acceptable as alternatives under regulation 13G(7) of Annex I of MARPOL 73/78

Appendix - Arrangements acceptable as alternatives under regulation 13G(7) of Annex I of MARPOL 73/78

 This appendix contains detailed requirements on arrangements accepted by the MEPC as alternatives under the provisions of regulation l3G(7) of Annex I of MARPOL 73/78. At the time of development this appendix contains only one approved alternative method.

  Requirements for application of hydrostatic balanced loading in cargo tanks

 Hydrostatic balance loading is based on the principle that the hydrostatic pressure at the cargo tank bottom of the cargo oil column plus the ullage space inert gas overpressure remains equal to or less than the hydrostatic pressure of the outside water column, thereby mitigating the outflow of oil in case of bottom damage.

 The maximum cargo level in each tank being loaded under this criterion should therefore satisfy the following equation:

where:
h c = is the maximum acceptable cargo level in each tank, measured from the cargo tank bottom, (m)
p c = is the density of the current cargo, (t/m3)
d = is the corresponding draught of the vessel, (m)
h i = is the height of the tank bottom above the keel, (m)
Δp = is the highest normal overpressure in the inert gas system, expressed in bar (normally 0.05 bar), (bar)
p s = is the density of the sea water, (t/m3)
g = is the standard acceleration of gravity (g = 9.81 m/s2).

 Ballast may be carried in segregated ballast tanks to increase draught to a larger value. This may be used to allow more cargo to be taken into cargo tanks within the hydrostatic equilibrium criterion and within the limits of the assigned load line.

 The arrangements and procedures for operation with the hydrostatic balance method should be approved by the Administration. The approval should be based on a system specification and documentation, incorporating also:

  • .1 calculations made to confirm whether or not resonance can occur between the natural period of longitudinal cargo liquid motion and the natural period of pitching of the ship, and also between the natural period of transverse cargo liquid motion and the natural period of rolling of the ship under approved cargo loading conditions and in any cargo tanks. In this context 'resonance can occur' means that the natural period of longitudinal motion of cargo oil is within the range from 60% to 130% of the natural period of pitching of the ship and/or the natural period of transverse motion of cargo is within the range from 80% to 120% of the natural period of rolling of the ship. When resonance can occur between ship's motion and cargo liquid motion, the sloshing pressure caused by such resonance should be estimated, and it should be confirmed that the existing structure has sufficient strength to withstand the estimated sloshing pressure; and

  • .2 calculations of intact and damage stability, including the effects of free surface. Damage stability calculations are however only required for ships defined in regulation 1(6).

 When the accidental outflow reduction requirement can be met by applying hydrostatic loading to a limited number of tanks, wing tanks should have priority, thereby ensuring some reduction also in outflow from a side damage and minimizing sloshing in part loaded centre tanks.

 When operating in a multiport loading or unloading mode using the hydrostatic balance loading method, tanks covering at least 30% of the side of the length of the cargo section should be kept empty until the last loading location or should be unloaded at the first unloading location.

 Copies of certified ullage measurement reports should be kept on board, clearly identified, for at least three years.

Parent topic: Annex - Guidelines for Approval of Alternative Structural or Operational Arrangements as Called for in MARPOL 73/78, Annex I, Regulation 13G(7)
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