What is regulations for segregated ballast tanks on ship as per MARPOL?

As per MARPOL annex 1, regulation  18.

The segregated ballast system should be a system which is ‘‘completely separated from the cargo oil and fuel systems’’

1. Every crude oil tanker of 20,000 tonnes deadweight and above and every product carrier of 30,000 tonnes deadweight and above delivered after 1 June 1982, shall be provided with segregated ballast tanks and shall comply with paragraphs 2, 3 and 4, as appropriate, of this regulation.
2. The capacity of the segregated ballast tanks shall be so determined that the ship may operate safely on ballast voyages without recourse to the use of cargo tanks for water ballast except as provided for in paragraph 3 or 4 of this regulation. In all cases, however, the capacity of segregated ballast tanks shall be at least such that, in any ballast condition at any part of the voyage, including the conditions consisting of lightweight plus segregated ballast only, the ship’s draughts and trim can meet the following requirements:
   • the moulded draught amidships (dm) in metres (without taking into account any ship’s deformation) shall not be less than:
     

     dm = 2.0 + 0.02L

   • the draughts at the forward and after perpendiculars shall correspond to those determined by the draught amidships (dm) as specified in paragraph 2.1 of this regulation, in association with the trim by the stern of not greater than 0.015L; and
3. in any case the draught at the after perpendicular shall not be less than that which is necessary to obtain full immersion of the propeller(s).
   • In no case shall ballast water be carried in cargo tanks, except:
     on those rare voyages when weather conditions are so severe that, in the opinion of the master, it is necessary to carry additional ballast water in cargo tanks for the safety of the ship; and
   • in exceptional cases where the particular character of the operation of an oil tanker renders it necessary to carry ballast water in excess of the quantity required under paragraph 2 of this regulation, provided that such operation of the oil tanker falls under the category of exceptional cases as established by the Organization.
4. In the case of crude oil tankers, the additional ballast permitted in paragraph 3 of this regulation shall be carried in cargo tanks only if such tanks have been crude oil washed in accordance with regulation 35 of this Annex before departure from an oil unloading port or terminal.
5. Not with standing the provisions of paragraph 2 of this regulation, the segregated ballast conditions for oil tankers less than 150 metres in length shall be to the satisfaction of the Administration.

Note :

• Crude oil tankers of 40,000 tonnes deadweight and above delivered on or before 1 June 1982
• Product carriers of 40,000 tonnes deadweight and above delivered on or before 1 June 1982