Overview
ISO 13713:2020 - Ships and marine technology - Ship's mooring and towing fittings - Mooring chocks - defines the types, nominal sizes, dimensions, materials, construction, manufacturing, inspection and marking requirements for mooring chocks used to lead mooring and towing ropes from a ship’s inboard to outboard. The standard applies to chocks for synthetic ropes (nylon and similar) and complements guidance for wire rope fittings (see ISO 13729).
Key topics and technical requirements
- Types and sizes
- Two installation types: Type A (deck‑mounted) and Type B (bulwark‑mounted).
- Nominal opening sizes (L × H) specified (e.g., 250×200, 300×250 … 500×250A/B).
- Dimensions and geometry
- Detailed dimensional tables and figures define opening, radii and edge requirements (minimum radii where not shown: 25 mm).
- Materials
- Steel casting material with yield point ≥ 235 N/mm² and carbon ≤ 0.23% for weldability (per ISO 4990 references).
- Construction and foundations
- Foundations and weld connections must transmit maximum loading without plastic deformation or cracks; welding methods may be adapted provided equivalent strength/volume.
- Manufacturing and inspection
- Surfaces (including welded areas) must be free of visible flaws; rope-contact surfaces must be smooth to avoid abrasion.
- External anti‑corrosion protective coating required.
- Marking and SWL
- Safe Working Load (SWL) guidance: SWL to be recorded on the ship’s towing and mooring plan (IMO MSC/Circ.1175) and marked clearly on the chock or foundation in tonnes.
- Actual onboard SWL depends on foundation and under‑deck reinforcement and shall not exceed values indicated in the standard.
- Strength assessment
- Strength basis uses finite element model (FEM) analysis (2D shell modelling, mesh ≈ 2×thickness) and considers horizontal and vertical load cases individually.
- Stress criterion: combined stress under SWL limited to 85% of material yield. Wear and corrosion margins are incorporated into the criterion.
- Rope bending
- Rope tensile strength reduction due to bend radius (D/d ratio) should follow the rope manufacturer’s guidance.
Applications and users
ISO 13713:2020 is used by:
- Shipbuilders, shipyards and naval architects specifying deck and bulwark fittings
- Mooring‑fitting manufacturers and foundries
- Classification societies, marine engineers and surveyors for acceptance checks
- Ship operators and masters for operational SWL and mooring plans
Practical use cases include selection of correctly sized chocks, design of foundation reinforcement, fabrication quality control, and marking/ documentation for safe mooring and towing operations.
Related standards
- IMO MSC/Circ.1175 (shipboard towing and mooring equipment guidance)
- ISO 13729 (closed chocks - wire ropes)
- ISO 4990 (steel castings delivery requirements)
- IACS UR A2 and OCIMF MEG4 (industry guidance)