However, for vessels of 30.5 m (100 ft) in length or greater, no bilge main suction pipe is to be less than 63 mm (2.5 in.) internal diameter.
5.5.1(b) Bilge system serving only engine room. Where the engine room bilge pumps are fitted primarily for drainage within the engine room, L may be reduced by the combined length of the cargo tanks or cargo holds. In such cases, the cross sectional area of the main bilge line is not to be less than twice the required cross sectional area of the engine room branch bilge lines.
5.5.1(c) Direct bilge suction. The diameter of the direct bilge suction [see 4-6-4/5.3.5(a)] is to be not less than that determined by the equation in 4-6-4/5.5.1(a).
5.5.1(d) Bilge branch. The diameter of the bilge branch suction for a compartment is to be determined by the following equation. If the compartment is served by more than one branch suction, the combined area of all branch suction pipes is not to be less than the area corresponding to the diameter determined by the following equations: