Do-It-Yourself: Upgrading Your Dock Lines

By Tom Burden, Last Updated 8/8/2019

Do your dock lines look a bit green and covered with algae, or stiff and gray? Do they look like a hungry rat has discovered a taste for nylon? If they meet any of these (or other) embarrassing criteria, then it may be time to consider replacing them. This West Advisor is part of West Marine’s Do It Yourself Project series, and our topic is how to improve your dock lines so that they hold your boat securely, last a long time and look professional. Here is a quick dock line refresher course.

Skill Level Description
Tying a cleat hitch: 1 out of 10
Tying a boat to a dock using bow, stern, and spring lines: 2 out of 10
Assembling a permanent set of dock lines: 5 out of 10
Tools RequiredShopping List
Three strand eye splices:
  • Hollow Fid
  • Rigging or Electrical Tape
  • Hot Knife or Soldering Iron
  • Rigging Knife

Whipping the bitter end:

  • Whipping Twine
  • Rigging Knife
  • Hot Knife or Soldering Iron

Cutting chain:

  • Hack Saw or Bolt Cutters

Fiber and Construction

Dock lines should be made from nylon, a synthetic fiber that has a superior combination of strength and stretch. Nylon is strong (although it shrinks and loses about 10-15% of its strength when wet), durable, and stretchy (three-strand nylon stretches up to 16% of its length when loaded to 15% of its breaking strength), so it absorbs shocks. Low-stretch lines, like old worn-out polyester double braid used for sailboat running rigging, are less desirable because they transmit shocks from waves, loading up and loosening dock cleats and your boat's deck hardware. There are three main types of rope construction for dock lines: three-strand, double braid and Mega Braid.

Three-strand line has a knobby finish, is easy to splice and is the most affordable.

Double braid is somewhat stronger for a given size, has about half of three-strand's stretch, and is available in many colors so you can color-coordinate your dock lines to match the color of your trim or canvas.

Mega Braid is a 12-strand single braid from New England Ropes. Single braids are very supple and limp, so they are easy to coil and handle. Mega Braid is frequently the choice for boats above 70'. It is harder to splice, so boaters may want to order custom Mega Braid from West Marine Rigging. Mega Braid comes in white or black.

Transient and Permanent Dock Lines

When your boat is away from its regular slip or mooring, you need to have some designated dock lines aboard, preferably with spliced eyes, ready for use wherever you tie up. We call these transient dock lines.

Transient dock lines are generally purchased pre-made with an eye splice at one end and a whipped end on the other. The eye in the end is easily passed around a cleat or piling by someone on the dock and the bitter end is then adjusted on board. There are dozens of combinations of diameters and lengths.

Permanent dock lines, as their name implies, are permanently attached to the hardware of your slip. They differ from transient dock lines in several ways. First, they must be protected from chafe, the enemy of all lines in constant use. This calls for leather, rubber or fabric chafe gear where the line passes through the chocks, and possibly a chafe sleeve on the eye where it goes around the cleat on deck. At the dock, lines should be protected from chafe using eye splices and shackles if the dock has rings, or eye splices and short lengths of chain if the dock has cleats. Permanent dock lines should be cut to fit the particular boat in the slip. Trailerable boats that don't have a permanent berth may only have transient dock lines.

Length of your Dock Lines

Bow and stern lines should be about two thirds of the length of the boat. Spring lines, used to keep the boat parallel to the dock, are run aft from the bow to the dock (this is called an after spring) and forward from the stern to the dock (this is called a forward spring). Spring lines should be as long as the boat.

This basic selection rule works pretty well. On Chuck's 21' Zodiac, he bought 15' white three-strand lines for the bow and stern, and 20' lines for the springs, and it's perfect. Tom uses blue double braid dock lines for his Newport 30 sailboat, which is in between the best size for pre-made dock lines. He bought bow and stern lines that were 25' long, and then trimmed them back to 20', whipped the ends with some waxed whipping twine, burned the ends with a lighter and dipped them in Flexible Vinyl Rope Dip for a clean, professional look. The spring lines were 35' long, trimmed back to 30' with the ends similarly customized.

Dock Line Diameter

We’ve found that the same general rule that applies to anchor lines also works well for dock lines. We recommend 1/8" of line diameter for every 9' of boat length. Larger lines will wear longer but stretch less, and stretch is important for absorbing the shocks caused by waves and the wakes from passing boats. See the chart below:

Boat LengthDock Line Dia.
Up to 27'3/8"
28'–31' 7/16"

Once again, this rule works really well for the boats we have owned. And even if your boat is shorter than 20' or so, 3/8" line is a nice size to hold and handle. Lines that are too small will stretch excessively and wear out prematurely. Lines that are too large may not fit on your cleats correctly, and won't have sufficient stretch to absorb shock loads.

Just to confuse the issue a bit, heavier boats may need larger diameter lines, so a heavy Grand Banks trawler or cruising sailboat might select lines based on 1/8" of line diameter for every 8' of boat length. That means that you can use 3/8" diameter for boats to 24' long; 1/2" diameter for boats to 32' long; and 5/8" diameter for boats to 40' long.

Customizing Your Permanent Dock Lines

Transient dock lines are simple and generic; just choose the right length and diameter and that’s all. At home with your boat in your own slip, it’s best to customize your permanent lines. When you return home, there's no adjusting or fiddling with the lengths of the lines. You simply throw them over the cleats or bollards on your boat and you’re done.

Chafe is the Enemy

Chafe is the damage caused when lines rub on surfaces. It is inevitable, but can be reduced by not changing the angle of a line abruptly and by using abrasion-resistant pads, such as lengths of leather or hose, called chafing gear. Even smooth, large radius surfaces will abrade nylon and polyester lines over time.

Chafe guards provide a sacrificial surface that can take the damage without reducing the breaking strength of the line. Commonly, docks will have eyebolts, rings, or galvanized cleats where the dock lines are made fast. The type of hardware on the dock or piling determines the best type of dock line splice and chafe protection. For example, you may want to have an eye splice around a thimble, and a galvanized shackle when connecting to a ring or eyebolt. If there is a large cleat, you may choose to take a short loop of chain around the base of the cleat and through a galvanized thimble. Either of these methods will last far longer than simply tying the line around the dock hardware.

Connecting to the Dock Hardware

You have a choice on how to prevent chafe at the dock. In our local harbor, we have large galvanized dock cleats, so we use a loop of chain about a food in diameter through the center of the cleat and the thimble. We close the loop of chain with chain link or a common shackle. At some point if we need to replace the chain, we can cut if off with a hacksaw. Note that this method of attachment completely reduces the chafe at the dock, and also prevents dock lines from being stolen. Your harbor or marina may use galvanized eyes or other connection points, so you may be able to use shackles or some other means of attachment.

Tied Up at the Dock

The spring lines run from the same cleats but in the opposite direction. They keep the boat from yawing, and hold it in a parallel orientation to the dock. While you may not use four lines every time you tie up for lunch or fuel, using a forward spring will make your boat sit more securely at a dock.

We know that this is understood by most of you, but here's the correct way to make a line fast to a cleat. Take a full turn around the base, then a turn across the cleat, and then a locking. While you can make a cleat hitch more complicated, this is all you have to do, and it’s simplest to untie. If you can’t remember how to do this, remember the boater’s refrain: “If you can't tie knots, tie lots!”

Washing Your Dock Lines

If your double braid dock lines have become stiff and dingy, you can make them look like new again by throwing them in an old pillowcase and running them through your washing machine with liquid laundry detergent and a little fabric softener (the pillowcase is to keep the lines from wrapping around the agitator and binding up your washer). A couple of considerations: Do not try this with a front-loading washer (our friends ruined their marina’s community washing machine this way). Use more than one pillowcase to balance the load and spread the weight around the agitator.