ISO 13729 Type A Deck-Mounted Cast Steel Closed Chock | Ship Mooring and Towing

Product Specification

ISO 13729 Type A Deck-Mounted Cast Steel Closed Chock | Ship Mooring and Towing

Product Overview

The ISO 13729 Type A closed chock is a deck-mounted cast steel mooring and towing fitting installed at the ship side to guide a rope from the inboard deck area to the outboard lead. Its closed opening keeps the line within a defined passage, while the rounded rope-contact geometry is intended for ships using wire ropes and for arrangements where controlled lead direction is required.

The current ISO 13729:2020 edition defines Type A as deck-mounted and provides 14 nominal sizes from 250 × 200 × 214 to 500 × 400 × 525B. The supplied table covers standard SWL values from 23 t to 144 t, recommended wire-rope diameters from 18 mm to 44 mm, and calculated weights from 73 kg to 825 kg. Final selection must also consider the actual rope lead angle, load direction, deck foundation, under-deck reinforcement, welding details, rope manufacturer's bend-radius guidance, coating system, and class inspection scope.

Quick Specifications

• Standard and type: ISO 13729:2020 Type A → current deck-mounted closed chock configuration; ISO 13729:2012 has been replaced by the 2020 edition.
• Nominal size range: 14 sizes from 250 × 200 × 214 to 500 × 400 × 525B → opening width, opening height, and chock depth are used for size designation.
• Standard SWL range: 226–1,413 kN / 23–144 t → the actual onboard SWL is limited by the chock, foundation, welding, and under-deck reinforcement.
• Recommended wire-rope diameter: 18–44 mm → initial rope compatibility reference; final D/d and bend-radius checks follow the rope manufacturer's guidance.
• Standard material basis: cast steel with yield point not less than 235 N/mm² and carbon content not more than 0.23% → supports strength and weldability requirements.
• Calculated weight: 73–825 kg → useful for handling, lifting planning during installation, packing, and freight estimation.
• Rope-contact design: closed opening with smooth radiused surfaces → guides the line and reduces local abrasion or sharp contact at the chock.
• Installation and marking: deck-welded foundation with SWL marking → actual load direction, seat/foundation design, weld details, and marking position must be confirmed before production.

Main Technical Parameters

Selection & Inquiry Guide

Step 1: Confirm ISO 13729:2020 Type A, the required nominal size, and whether the fitting is for mooring, towing, or both according to the vessel towing and mooring arrangement.

Step 2: Provide the design line load, intended onboard SWL, rope type, wire-rope diameter, rope MBL, rope manufacturer, and actual inboard/outboard lead angles so that the size and D/d relationship can be checked.

Step 3: Confirm deck installation details, actual load direction, foundation or seat arrangement, under-deck reinforcement, weld interface, and available installation space. If a separate seat is used, provide the ISO 23113 or project seat drawing.

Step 4: Confirm material: ISO cast-steel basis, project-specific stainless cast steel, or special low-temperature/ice-service steel. Alternative materials require mechanical properties, weldability, temperature rating, and class approval confirmation.

Step 5: Confirm surface treatment, final vessel coating system, rope-contact finishing, NDT or inspection scope, material traceability, maker certificate, and classification society requirement before quotation.

Step 6: Provide vessel type, newbuilding or replacement status, quantity, GA/installation drawing or reference photos, delivery destination, Incoterms, and required delivery time.

Structure

Cast steel closed body | Radiused wire-rope contact surfaces | Type A deck-mounted base | Reinforced casting transitions | Deck welding interface | SWL marking area | Anti-corrosion protective finish

Casting, Rope Contact & Installation Advantages

• The closed opening maintains a defined rope passage and helps keep the wire rope within the guide when the lead direction changes during mooring or towing operations.
• The chock geometry is based on a wire-rope bending relationship of not less than twelve times the rope diameter; final selection should also follow the rope manufacturer's permitted D/d ratio and strength-reduction guidance.
• Rope-contact surfaces are to be smooth and free from roughness or irregularities likely to damage the rope by abrasion. Grinding and finishing should preserve the specified radii and casting geometry.
• The ISO material basis uses cast steel with a minimum yield point of 235 N/mm² and carbon content not exceeding 0.23%, supporting the strength and weldability requirements of the deck-mounted fitting.
• Foundation design is checked against the actual load direction so that the chock, weld connection, seat or deck foundation, and under-deck structure transfer the maximum design load without plastic deformation or cracking.
• The 14-size range supports coordinated selection by opening geometry, SWL, recommended wire-rope diameter, deck space, and calculated handling weight rather than by SWL alone.
• SWL identification is marked by weld bead or equivalent at the chock foundation or deck and coordinated with the vessel towing and mooring plan.

Custom Attributes

• Standard: ISO 13729:2020 → current international standard for shipboard closed chocks; final production should use the licensed project edition.
• Type: Type A deck-mounted → differentiated from Type B bulwark-mounted closed chocks.
• Nominal Size: 250 × 200 × 214 to 500 × 400 × 525B → designated by opening width × opening height × chock depth.
• SWL: 23–144 t standard table range → actual onboard SWL depends on the fitting, foundation, welds, under-deck reinforcement, and approved arrangement.
• Wire Rope Diameter: 18–44 mm recommended → rope MBL, construction, D/d requirement, and manufacturer guidance remain part of final selection.
• Material: Cast steel as ISO basis → cast stainless steel or special ice-service steel is project-specific and subject to confirmed properties and class acceptance.
• Surface Treatment: Sa 2.5 blasting + epoxy shop primer as supply reference → final coating follows vessel paint specification; stainless surfaces may be polished when specified.
• Inspection & Certification: According to project requirement → maker certificate, material certificate, NDT, class survey, and approval scope must be confirmed before quotation.
• Marking: SWL in tonnes on foundation or deck → marking shall remain visible during operation and correspond with the approved towing and mooring plan.

How It Works

Mooring or towing line approaches from the inboard deck → Wire rope passes through the closed radiused opening → Smooth contact surfaces guide the line to the outboard lead → Local rope force is transferred through the cast body and welded foundation → Reinforced deck structure distributes the load into the hull

Applications

Bulk carriers | Tankers | Container vessels | General cargo ships | Ocean-going commercial vessels | Deck mooring stations | Shipboard towing arrangements | Newbuilding and replacement projects

Certifications & Advantages

Certificates and inspection can be arranged according to project requirement, material traceability, manufacturer approval status, class survey plan, and the agreed order scope. Class approval or a class certificate is not assumed unless specified and accepted before production.

Certification: CCS, NK, BV, ABS, DNV, LR, KR, IRS, RS, RINA, CRS, Makers Test Certificate.

Drawing & Photos

FAQ

Q1: How should the correct ISO 13729 Type A size and SWL be selected?

A1: Start with the vessel towing and mooring plan, intended line load, rope diameter and MBL, actual lead angles, and available deck space. Then select a nominal size whose standard SWL is adequate. The approved onboard SWL must also account for the foundation, welds, seat, and under-deck reinforcement and cannot exceed the standard table value.

Q2: What is the difference between ISO 13729 Type A and Type B?

A2: Type A is deck-mounted and transfers load through a deck foundation or seat. Type B is bulwark-mounted and uses a different hull interface. The correct type must follow the vessel arrangement drawing; the two configurations should not be interchanged without structural review.

Q3: Can stainless steel or special steel for ice-service vessels be supplied?

A3: Project-specific alternatives can be discussed, but they are not automatic substitutes for the ISO cast-steel basis. The exact grade, design temperature, mechanical properties, corrosion requirement, weldability, NDT, heat treatment, and class approval scope must be confirmed before quotation.