Answer
While IMO is known for mandatory conventions (SOLAS, MARPOL, STCW), it relies heavily on non-mandatory resolutions, recommendations, and circulars. These provide technical guidance and often serve as the foundation for future mandatory legislation.
Key Non-Mandatory Instruments
IMO Resolutions (Assembly/MSC/MEPC): Interpretive guidelines issued to clarify existing treaty ambiguities (e.g., the Revised Guidelines for the Identification and Designation of Particularly Sensitive Sea Areas (PSSAs)).
MSC and MEPC Circulars: Direct technical clarifications, circulars, and Unified Interpretations sent out to provide explicit engineering explanations of complex regulations to classification societies and shipowners.
Technical Codes/Guidelines (Prior to Mandatory Adoption): Specialized operational standards that remain optional until explicitly adopted into a country's national legislation or integrated into a main convention. Examples include:
The IMDG Code (was completely non-mandatory before being forced into compliance via SOLAS Chapter VII amendments).
The Code of Safety for Special Purpose Ships (SPS Code).
Guidelines on cyber risk management onboard ships.