Towing Pin / Norman Pin

What a towing pin does

When a tow wire runs off the centreline of the stern roller, under load it can walk sideways until it saws against the roller flange or pulls at an angle the winch and fairleads were never built for. Towing pins are raised in pairs either side of the wire's working position on the stern roller, physically boxing the wire onto the centreline during payout and recovery. They are not load-bearing in normal operation, since the winch and roller carry the tow load, but they become critical the moment the tow angle changes sharply, such as during a rig move or when the towed vessel yaws.

Main components

Pin assemblies

Vertical steel posts, usually one pair per stern roller, raised and lowered by individual hydraulic rams so they can be positioned to match the wire's actual working point rather than a single fixed slot.

Hydraulic power and control

Driven from the same hydraulic power pack serving the towing winch and shark jaw, with independent control so the pins can be raised, lowered or held at partial height from the winch control console.

Roller integration

Pins are set into or immediately beside the stern roller structure itself, so their alignment is fixed relative to the roller at build or installation and cannot simply be adjusted by eye during operations.

Selection and sizing

Pin height and the clear gap between the raised pair are matched to the largest wire or chain diameter the vessel is expected to handle, with enough clearance that the wire runs freely but cannot ride up and over the pin under a sideways load spike. Hydraulic ram capacity is sized against the sideways force expected from the vessel's rated bollard pull and typical tow angles, not against the tow load itself.

Regulations and class

Towing pins fall under the same class notation and survey regime as the towing winch and shark jaw on anchor handling and towing vessels, inspected for wear, hydraulic ram condition and structural attachment to the stern roller frame as part of the vessel's periodic deck machinery survey.

Typical faults

• Hydraulic ram seal wear lets a pin sag under sideways load, so the wire escapes the intended track
• Pin surface wear or scoring from repeated wire contact, so sharp edges begin to damage the wire itself
• Control interlock failure lets a pin retract under load rather than only when commanded, causing sudden loss of centring
• Misalignment after a stern roller repair, so the pins no longer match the wire's actual working line

What to look for in a supplier

• Ram capacity rated against the vessel's actual tow angle and bollard pull figures, not a generic package
• Pin and roller supplied as a matched, aligned assembly rather than pins retrofitted to an existing roller
• Wear surface material and replacement procedure for pins in heavy wire-contact service
• Control integration with the existing winch console and interlock logic

Never treat towing pins as load-bearing: they centre the wire, they do not hold the tow, and a crew that leans on that distinction during an emergency release finds out the difference the hard way.