Overview - ISO 13733:2020 (Universal fairleads with upper roller)
ISO 13733:2020 specifies requirements for universal fairleads with upper roller(s) used to lead mooring ropes on ships. The standard defines types, nominal sizes, dimensions, materials, construction, manufacturing/inspection and marking requirements for ship’s mooring and towing fittings. It is intended to ensure safe, durable and compatibility‑checked fairleads that are suitable for shipboard mooring operations.
Key technical topics and requirements
- Scope and classification
- Covers fairleads with upper rollers installed to lead the mooring rope.
- Four types are defined: Type 4R, 5RL, 5RR, and 7R (single or double rope openings, with optional side guide roller).
- Nominal sizes and dimensions
- Nominal sizes are specified by the main roller outside diameter (Dn) with a defined preferred-number series (examples: 140, 160, 180, 200, 250, 300A/300B, 400A/400B/400C).
- Detailed dimensional tables and assembly figures provide mounting and roller geometry.
- Materials and mechanical properties
- Frame/plates, rollers and axles have minimum yield point requirements (e.g., frame/rollers generally ≥235 N/mm²; select sizes require ≥315 N/mm²; axle ≥345 N/mm²).
- Bushes specified as brass, bronze or equivalent.
- Construction and strength
- Rollers may be formed from plate or steel tube.
- Manufacturer determines foundation and welding to ensure loads transmit to hull without plastic deformation or cracks.
- Annex A provides the basis for strength assessment (includes guidance on FEM and strength calculation updates in this edition).
- Operational guidance
- D/d ratio (roller diameter to rope diameter) must be considered to mitigate bending loss of rope strength; rope manufacturer guidance affects tensile strength through bends.
- Manufacturing, inspection and finish
- Surfaces (including welded areas) must be free of visible flaws; rope contact surfaces must be smooth to avoid abrasion.
- External anti‑corrosion coating required and rotating parts must be greased.
- Marking and SWL
- Safe Working Load (SWL) must be documented in the ship’s towing and mooring plan (IMO Circular MSC/Circ.1175 referenced) and marked on the fitting in tonnes.
Practical applications and who uses this standard
ISO 13733:2020 is used by:
- Shipbuilders and naval architects for specifying mooring fitting layouts and hull strengthening.
- Mooring equipment manufacturers and suppliers for design, fabrication and QA.
- Ship operators, shipmasters and shipowners for selecting fittings consistent with mooring plans and rope characteristics.
- Classification societies, inspectors and port/state authorities for verification of SWL marking, mounting and structural integrity.
- Marine engineers and offshore support vessel designers integrating mooring systems.
Related standards and references
- Normative reference: IMO Circular MSC/Circ.1175 (Guidance on shipboard towing and mooring equipment).
- Prepared by ISO/TC 8 (Ships and marine technology), Subcommittee SC 4 (Outfitting and deck machinery).