In the world of maritime operations, mooring chocks play a vital role in ensuring the safe and efficient berthing of vessels. Often underestimated, these simple yet robust fittings are essential for guiding and protecting mooring lines as they pass through the ship's hull or bulwark. With different vessel types requiring specific mooring configurations, selecting the right type of chock is crucial to ensure both operational reliability and compliance with international maritime standards.

What Is a Mooring Chock?

A mooring chock is a fixed, typically cast steel or cast ductile iron device designed to lead mooring lines from the vessel’s deck to the berth. It ensures minimal wear and friction on the mooring rope, reduces the risk of damage to the hull, and provides controlled routing of lines during mooring and towing operations.

Common Types of Mooring Chocks

Mooring chocks come in several designs, each suited to specific operational and vessel requirements:

1. Closed Chock

Features: Enclosed design with a rounded inner surface

Applications: Commonly used on large commercial vessels like bulk carriers, tankers, and container ships

Advantages: Provides secure rope guidance, reduces rope jumping

2. Open Chocks

Features: U-shaped or open-top designs

Applications: Typically found on smaller vessels, tugboats, and fishing boats

Advantages: Easy to rig and unrig ropes; suitable for quick operations

3. Deck Chocks

Features: Mounted directly on deck

Applications: Found on smaller workboats, pilot boats, and service vessels

Advantages: Compact and ideal for deck-level line handling

4. Bulwark Chocks

Features: Installed on or through the ship’s bulwark

Applications: Frequently used on cargo ships and ferries

Advantages: Guides lines over the edge of the vessel without damaging the structure

5. Roller Chocks

Features: Equipped with rollers to reduce friction

Applications: Used where frequent mooring and line movement occur (e.g., tugboats)

Advantages: Minimizes wear on both lines and chock surfaces

Mooring Chocks for Specific Vessel Types

Mooring chocks are critical components of a vessel’s mooring system, acting as guides that safely lead ropes and wires from the ship to the shore or another vessel. While they may appear as simple fixtures, mooring chocks must be carefully selected and positioned based on the type of vessel, its function, and operational environment. Each vessel class imposes unique requirements that influence the design, size, and location of the chocks.

1. Oil Tankers

Key Requirements:

High-strength mooring chocks to handle large loads

Resistance to corrosion from harsh marine environments

Preferred Chock Types:

Closed chocks (Panama chocks): Ensures rope security and minimizes slippage

Bulwark chocks: Helps guide ropes over vessel’s sides without damaging the structure

Standards:

Often built to comply with OCIMF and IMO regulations due to strict safety demands in the oil industry

2. Container Ships

Key Requirements:

Efficient line management during quick port turnarounds

Chocks designed for high-tension synthetic ropes or wire ropes

Preferred Chock Types:

Closed chocks: Common on both stern and bow to ensure safe mooring during dynamic loading

Deck-mounted chocks: Placed strategically to align with container bay design

Considerations:

Smooth inner surface finish to minimize abrasion on high-load mooring lines

3. Bulk Carriers

Key Requirements:

Chocks capable of withstanding static mooring while at anchor or port

Often require heavy-duty fittings for long mooring durations

Preferred Chock Types:

Closed chocks

Roller chocks (for regions experiencing tidal movements)

Additional Features:

Designed for heavy use with fiber ropes or steel wire in rough environments

4. Tugboats

Key Requirements:

Flexible line handling and resistance to heavy dynamic forces

Compact design for limited deck space

Preferred Chock Types:

Open chocks: Allow for quick rope release and handling

Roller chocks: Minimize friction and line wear during frequent movements

Notes:

Often integrated into towing winch systems or stern fittings

5. Offshore Supply Vessels (OSVs)

Key Requirements:

Operate under dynamic positioning conditions

Require multi-directional mooring capabilities

Preferred Chock Types:

Closed chocks

Deck-mounted chocks with reinforced bases

Engineering Focus:

Materials with high corrosion resistance due to harsh offshore environments

6. Passenger Ferries

Key Requirements:

Smooth, quick mooring in busy terminals

Aesthetic integration with vessel’s structure

Preferred Chock Types:

Deck chocks

Closed chocks with recessed or hidden designs

Safety Consideration:

Chocks must be placed to minimize interference with passenger movements and gangway operations

7. Fishing Vessels

Key Requirements:

Frequent port calls and rugged handling

Low-maintenance, easy-to-access fittings

Preferred Chock Types:

Open chocks

Deck-mounted chocks

Field Insight:

Must allow for rope flexibility during trawling or anchoring operations in harsh seas

Selection Criteria

When selecting mooring chocks, key factors to consider include:

Rope Type and Diameter – Chock opening must match line size to avoid jamming or slippage.

Mooring Load – Chocks must be tested for expected static and dynamic loads.

Material & Coating – Galvanized or painted cast steel is common; marine-grade stainless steel is used for corrosion-prone environments.

Compliance – Ensure adherence to standards like IMO, ISO 13713, or JIS F 2005.

Summary

Mooring chocks may appear simple, but their role is critical in vessel mooring safety. From massive oil tankers to nimble pilot boats, every vessel type requires chocks tailored to its mooring needs. Understanding the unique characteristics of each chock type and their applications ensures safe, efficient, and long-lasting mooring systems.