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SAILING & LINES

Dock Line

The line that holds a boat to the shore — nylon, spliced eyes, and sized for the worst surge.

INSPECT BEFORE LOAD · NEVER EXCEED WLL

Rope, splices and hardware are only as good as their condition. Inspect before every use and retire on evidence.

Dock Line — nautical chart line drawing

Specification

Typical fibreNylon (shock absorption)
ConstructionDouble braid, 3-strand
Diameter range12–24 mm
ElongationHigh — 15–25%
EndsSpliced eye one end, whipped other
Common errorPolyester line where surge absorption is needed

Technical parameters

12 mm nylonMBL ≈ 3,600 kg
16 mm nylonMBL ≈ 6,300 kg
20 mm nylonMBL ≈ 9,600 kg
24 mm nylonMBL ≈ 13,500 kg
Working loadMBL ÷ 5 static, ÷ 8 for surge
Sizing guide≈ 1.5 mm per metre of boat length
SelectLoadInspect

Overview

A dock line ties a boat to a dock, and the load it sees is not the weight of the boat but the energy of the boat moving. Surge, wind, wake and tide combine into repeated snatches, which is exactly the loading nylon is best at absorbing. That is why dock lines are nylon, usually double braid, with a spliced eye at one end and a whipped or heat-sealed end at the other.

Size follows the boat. A rough guide is a diameter in millimetres of about one and a half times the boat's length in metres, so a ten-metre boat wants around fifteen-millimetre line. The number is a starting point; heavy displacement, exposed moorings and storm conditions all argue for more.

The failure mode is almost always chafe, not breakage. A dock line parts where it runs through a chock, over a cleat or against a piling. Chafe gear at those points, and a second line rigged as a spring, are what actually keep a boat on the dock.

Safety notes

  • Elastic energy in a stretched nylon dock line is dangerous. Never stand in line with one that is under load.
  • Fit chafe gear wherever a line passes through a chock or over a rail. Chafe, not strength, is what ends a dock line.
  • In a storm, double up and add springs. One line is never enough for a serious blow.

Using it well

  • Rig a spring line as well as bow and stern lines; the spring is what stops the boat surging fore and aft.
  • Give the eye a thimble if it will bear on a piling or a rough cleat.
  • Coil and stow lines off the deck in sunlight — ultraviolet is what ages nylon fastest.

Suited to

MooringDock workStorm prepTowing (with care)

Typical applications

Dock workMooringStorm prep
Figures are typical catalogue values for new equipment, quoted for comparison and planning. They are not a guarantee for any specific product or any specific load. Always work to the manufacturer’s stated working load limit and to the regulations that apply where you sail.

Related tools

Nylon Rope — nautical chart line drawing

Nylon Rope

High-stretch synthetic with excellent shock absorption — the default for anchor rodes and dock lines.

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The fitting a line is made fast to — horn, cam or jam, each with its own way of holding and releasing.

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Thimble — nautical chart line drawing

Thimble

A metal liner for a spliced eye that spreads the load and stops chafe cutting the rope.

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Fender Line — nautical chart line drawing

Fender Line

Short, adjustable lines that hold fenders at the right height — simple, but they must be right.

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