IACS issues requirements for aftmost propeller shaft bearings

The International Association of Classification Societies (IACS) issued a revised UR M52 and new UR M85 setting guidelines for aftmost propeller shaft bearings, detailing both the design specifications (M52) and testing requirements (M85) for various types of bearing materials and lubrications to ensure durability and safety.

UR M52: Design Requirements for Aftmost Propeller Shaft Bearings

Oil-Lubricated Bearings:

White Metal Bearings: Minimum length is 2.0 times the shaft diameter, reducible to 1.5 times if bearing pressure is under 8 bar.
Synthetic Bearings: Similar length requirements apply (2.0 times the shaft diameter, reducible to 1.5 times if pressure is within 6 bar). Synthetic materials must be type-approved under UR M85.

Water-Lubricated Bearings:

The standard length is 4.0 times the shaft diameter. For synthetic materials, length may be reduced to 2.0 times if backed by testing and type-approved per M85.

Grease-Lubricated Bearings:

Minimum length is 4.0 times the shaft diameter.

These design specifications are intended for implementation by January 2026, ensuring uniform standards across IACS member societies.

UR M85: Type Approval Testing for Synthetic Bearing Materials

Testing Scope and Documentation:

UR M85 establishes the type approval testing requirements for synthetic materials used in aftmost propeller shaft bearings, aligning with UR M52. Manufacturers must provide technical documentation, including material type, limits, and operational data.

Testing Program:

A comprehensive testing program is required, covering product descriptions, wear testing (based on ASTM G77-17 or similar), and conditions like material compatibility, lubrication, and performance stability over a minimum of 192 hours.

Material Property Requirements:

For non-elastomeric materials, properties such as compressive strength (≥85 N/mm²) and resistance to swelling (≤3% in water or oil) must be met. Elastomeric materials have specific tensile strength, elongation, and aging resistance criteria.

Laboratory and Product Selection:

Tests must be conducted in accredited labs or under Society supervision on a representative sample of products, ensuring materials meet performance criteria under the operating conditions specified.

Type Approval Certification:

Upon successful testing, the Classification Society issues a Type Approval Certificate detailing material properties, allowable surface pressure, and maximum operating temperature.

Together, UR M52 and UR M85 establish standardized design and rigorous testing protocols for synthetic materials in aftmost propeller shaft bearings, aiming to ensure robust performance and compliance across marine applications by January 2026.