Chock

What a chock actually does

A chock is a fitting through which a mooring or towing line passes so the line runs fair from a winch or bitts to the shore or another vessel, without chafing on deck edges or the ship's own structure. It carries no load itself in the way a bollard or bitt does; its job is to guide and constrain the line's direction while the actual holding load sits on the bitts or winch drum brake behind it.

Main components and types

Closed chock

A fully enclosed oval opening, the most common type, preventing the line from jumping out under a shifting lead angle.

Open (roller or Panama) chock

An open-top fitting, often fitted with a roller, sized and positioned per Panama Canal Authority requirements on vessels that transit the canal, since canal mooring lines are handled by shore locomotives at angles a closed chock cannot accommodate.

Universal chock

Combines a fairlead opening with an integral bollard or bitt point in one casting, saving deck space on vessels with limited mooring deck area.

Roller insert

Where fitted, reduces line friction and chafe damage, at the cost of an extra wear part that needs its own bearing inspection.

Selection and sizing

Selection follows the mooring line's safe working load and material - synthetic fibre ropes need generous bearing radii to avoid heat damage from friction, wire ropes need a harder, smoother bearing surface - plus the deck layout's actual lead angles from winch to chock to the mooring point ashore. Panama or universal types are fitted where trade pattern or class notation calls for them, not as a default choice.

Regulations and class

Chocks fall under the vessel's approved mooring arrangement, assessed against class equipment number calculations and, for canal transits, against the specific fitting positions and dimensions the Panama Canal Authority publishes for its mooring procedure. There is no periodic statutory survey specific to chocks beyond the general condition checks covered in deck equipment and mooring system inspections.

Typical faults

• Sharp or corroded bearing surface - cuts into synthetic line fibres or scores wire rope, a leading and entirely preventable cause of mooring lines parting under load.
• Cracked casting at the base - repeated snap loading from a line running out fatigues the fitting where it is welded or bolted to deck, and a failure here releases the line's full load suddenly.
• Seized roller - a roller-type chock that no longer turns behaves like a fixed chock, defeating the reason it was fitted and accelerating chafe.
• Wrong chock for the lead angle - a line running at a steep angle through a chock sized for a fair lead concentrates wear on one edge and shortens line life significantly.

What to look for in a supplier

• Bearing surface finish and radius matched to the mooring line types actually carried aboard.
• Casting material and load rating documentation tied to the vessel's equipment number, not a generic size chart.
• Panama Canal Authority compliant dimensions and positioning data where the vessel transits the canal.

Run a hand along the chock's bearing surface at every deck round - a nick too small to see is still large enough to start cutting a synthetic mooring line under load.