Answer
Propeller immersion requirements are explicitly mandated and quantified under MARPOL Annex I (Prevention of Pollution by Oil).
Regulation 18: Segregated Ballast Tanks (SBT)
Specifically, it is found in MARPOL Annex I, Regulation 18, which outlines the mandatory draft and trim requirements for tankers operating in a ballast condition (without cargo).
It states that the draught at the after perpendicular must be sufficient to obtain full immersion of the propeller.
This requirement applies principally to:
Crude-oil tankers of 20,000 DWT and above
Product tankers of 30,000 DWT and above
which are required to have segregated ballast tanks under MARPOL Annex I Regulation 18
Context and Other InstrumentsPurpose in MARPOL: The minimum draught and propeller immersion criteria were established to ensure tankers can navigate safely on ballast voyages without needing to fill oil cargo tanks with water ballast (thus preventing operational oil pollution).
Ballast Water Management Convention (BWM Convention): BWM guidelines (e.g., BWE / Ballast Water Exchange) reference these MARPOL Annex I Regulation 18 parameters to ensure that during sequential or flow-through exchange steps, the vessel maintains 100% propeller immersion and proper trim for safe maneuvering.
Classification Rules & IACS Unified Requirements (e.g., UR S25): Standardize these minimum ballast draught and propeller immersion requirements across general cargo vessels and bulk carriers during design and loading manual approvals.