Section 33(3)(ii) in The Merchant Shipping (Fire Appliances) Rules, 1969
(ii)in the case of a cargo ship, the required fire pumps, other than an emergency pump, shall be capable of delivering a quantity of water, at the appropriate pressure prescribed in sub-rule (2), not less than four-thirds of the quantity required to be dealt with by each of the independent bilge pumps in a passenger ship of the same dimensions when employed on bilge pumping. For this purpose diameter of the bilge main shall be calculated according to the following formulae (the actual internal diameter of the bilge main being the nearest standard size acceptable to the Central Government) :-