Marina Articles

Dock Lines (Summarized)

By US Boat Panel Expert, Don Casey

When it comes to dock lines, sailors and power boaters alike need a rope that stretches. The right rope for dock lines is plain old nylon. Nylon has three characteristics that make it ideal for dock lines. It is incredibly strong, it is very stretchy, and it’s very good at resisting harmful effects of sunlight. Most importantly, nylon doesn’t come taut suddenly, but dissipates the load by stretching. Also it is less expensive than most other ropes. Nylon is available in both braided and three-strand twist construction. Each has its advantages. Braided line looks “dressy”, has better abrasion resistance than three-strand, and is typically a little stronger; but it does have a tendency to snag on rough piling.

On the other hand, three-strand nylon doesn’t snag and is easy to splice. Also, it has more stretch and costs considerably less than braided rope. So as a practical choice for dock lines, three-strand nylon is unbeatable. For rope size, see the following chart to determine an adequate line diameter that provides the best strength and rope elasticity to the size of your boat.

For dock lines that are a fixture of your permanent slip, work out appropriate lengths using old line or light flag halyard line, making allowance for eye splices, then cut your nylon lines to those lengths. If the dock is fixed–not floating—be sure to leave a little extra for unusually high or low tides. For dock lines that travel with the boat, it’s recommended they are equal to the length of the boat; this is essential for spring lines. The inconvenience of a line that’s too long is less than one that’s too short.

Additionally, all dock lines should have an eye splice in one end. It should be just large enough to fit over the horn of the boat’s mooring cleats. Twelve inches is a good eye size, making it easy to pull the line through the eye to form a loop. See the following illustration. NOTE: A knot isn’t a good substitute for a proper splice. It reduces strength by about 40%, while a splice retains 95% of the rope’s strength.

Finally, protect your investment—your dock lines and your boat—by sliding a foot or two of heavy-duty hose over each line and tying it in position, so as to better handle the abuses of abrasion.

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