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Mooring and Dock Lines For Your Boat By Captain Bernie Weiss Knowing how to use rope (or, “line” as it called aboard a boat) is an essential component of good boat management. As it comes from the manufacturer on a spool, rope may be found in many different materials, both natural and synthetic; sizes, as measured in diameter and length; type of construction (3-strand, braid, or plait); and colors. Your choice of rope will depend largely on how you plan to use it, because the construction and diameter of the line, along with the material used to make it, determines the strength of the line and its suitability for various purposes. On a boat with many lines, colors help differentiate one particular line from others that are similar. This essay focuses on rope that is to be used as mooring line or dock line, and why the recommendations described below are best for this particular application.

Line Nomenclature and Construction Rope is made of either natural or synthetic fibers twisted into yarns and grouped together to form strands. To create a finished rope, the strands are laid (twisted) together, or sometimes strands are braided or plaited together. The product remains generic “rope” until it is put to use on a boat, at which time it becomes “a (specific) line.” A specific line takes its name from its application. Thus, a “dock line” is a specific length of rope used to secure a boat to the dock. A “towing line” is a specific rope used to tow another boat. An “anchor line” is . . . . get the idea? Plain laid line is made of three strands twisted around each other (usually to the right) and is described as "three-strand" line. On recreational boats like yours and mine, three-strand line is most frequently used for dock lines, mooring lines, and anchor lines. Braided line is usually made from three or more strands braided together. The most common type of braided line is double-braided. The “double” is represented by a braided and compressed core and also a braided hollow cover over the core forming a single line. This unique construction provides superior strength and durability.

Plaited line is made of eight strands. Four strands are twisted to the left and four to the right which are then paired and worked like a four-strand braid. Plaited lines are used most often on larger vessels as heavy-duty anchor lines, towing lines, or dock lines. Braided and plaited lines are less stretchy than three-strand; for dock lines and mooring lines, as well as anchor lines, stretch (elasticity) is important.

Materials Both natural and synthetic fibers are used in rope construction. Natural fiber lines are made from plant fibers such as manila, hemp, and cotton. Manila, made from the fibers of the abaca plant, is the strongest and most expensive of the natural fibers, and until the advent about 50 years ago of synthetic materials for manufacturing rope, manila was the most widely used natural material aboard boats large and small. Manila is rarely seen today. (Before manila, there was cotton! And flax!) Today, synthetic materials such as nylon, dacron (polyester), and polypropylene have taken over this market because they are more practical for use aboard boats. Nylon is inexpensive; has great strength; is highly resistant to weather, including salt water and sunlight, thus has long life. Also, nylon will stretch somewhat under load. (Dacron has many of these same properties.) For these reasons, nylon is usually the material of choice for dock lines, as well as mooring and anchor lines. The stretch factor (elasticity) is an important feature of nylon rope. A nylon line doesn’t suddenly come taut, or snap, when the boat surges; the nylon line stretches a little bit. This helps dissipate the shock over the length of the working line, relieving the stress of a sudden shock -- “shock load” -- when the boat surges against a line and its cleats or other fixtures. After stretching, as the load is relieved, the nylon line returns to its former length and retains its strength. Polypropylene rope is also widely used on recreational boats because of its low cost and strength. Its distinguishing feature: It floats. Because “poly” remains on the surface, its favorite application is for towing lines (water-skiers, dinghies, MOB recovery, etc.). Note that polypropylene quickly deteriorates in sunlight, losing up to half its strength after only one year of continuous exposure. Nor does poly line stretch. For these reasons it is not appropriate for dock lines, mooring, and anchor lines. In recent years rope-makers have introduced a number of lightweight and very strong synthetic rope products, among them Kevlar, Technora, and Spectra. These are usually more expensive than nylon, dacron, and polypropylene; they are usually braided; and they are usually considered “low-stretch” specialty lines. For all these reasons their most appropriate applications are limited, for example, to specialpurpose lightweight sheets and halyards aboard racing yachts. Take-away message: For dock lines, nothing is superior to plain old nylon three-strand rope.

Sizes of Lines (Lengths and Diameters) A properly equipped recreational boat should have at least four -- sometimes six -dock lines. Even if your boat is routinely on a mooring (using two mooring lines from the bow to the buoy), you will occasionally require dock lines. Always have them on board and ready to deploy. When purchasing lines for docking, consider first the required diameter of the line, then the required length of the line. Diameter: This table describes, by length of boat, an appropriate diameter for 3-strand nylon dock line: Length of boat Under 20 feet 20 to 30 feet 30 to 40 feet 40 to 60 feet Over 60 feet

Diameter of line 3/8" 1/2" 5/8" 3/4" 1"

Since larger diameter line is stronger and takes longer to abrade or chafe through, a case might be made for selecting the largest diameter line that will fit your cleats and chocks. But It’s important to remember that as the line diameter gets larger and the line itself becomes thicker and heavier, it also becomes less elastic. The line diameters described here are appropriate for providing sufficient strength and elasticity in most cases. Length: The rule of thumb is that your dock lines should equal the length of your boat. If buying cut lengths of line, be sure to allow for a noose (“eye”) that is to be spliced in one end of each line. However, as with so many things, the length of the lines depends upon personal preference, how and where you berth your boat, your deck and dock layout, and the exact positions of cleats on the deck and on the dock. Or, the distance from your boat’s cleats to the pilings you’ll be using. Many boaters customize the lengths of their dock lines -- measuring, cutting, and splicing them to exact lengths for the “home” berthing area. Nothing is more convenient than pulling into your berth and simply dropping dock line eyes over the cleats. (Or pilings. Or bollards.) If this is your plan, and if your dock is fixed (not floating), be sure to leave a little extra line length for unusually high or low tides. If you have customized the lengths of your dock lines for your home berth, consider those occasions when you will be berthing elsewhere. For such occasions many boaters have a separate set of “cruising dock lines”: These are dedicated bow and stern lines that are at least two-thirds the length of the boat, and dedicated spring lines that are the full length.

Arrangements for dock lines The arrangement of your dock lines will vary depending on your boat, the placement of its deck fittings (chocks, fairleads, cleats), the arrangement of your berth in the marina, and the location of fittings on the dock. Although there are no “rules,” here are two configurations that are typical for dock lines. In the diagram below, the two red lines are the conventional bow and stern lines. The green lines are spring lines. A spring line that leads forward from midships (or anywhere else on the boat) is described as a forward spring, and a spring line that leads aft is described as an after spring. The two springs together prevent the boat from shifting ahead or astern from its desired position. (In this diagram, both the red stern line and the red bow line also serve as spring lines, helping keep the boat in position.)

In the diagram below, you see lines that lead directly to the dock, keeping the boat close to the dock. They are called "breast lines." Breast lines may be forward, midships, or at the stern. Here, lines 2 and 5 are considered breast lines; lines 1 and 6 are considered the bow and stern lines; and lines 3 and 4 are considered spring lines.

Yes. When there are many dock lines in use, for the sake of simple descriptions among the crew, the lines are numbered sequentially from bow to stern.

Eye splice All dock lines should have an eye splice in one end. Some useful guidelines: For a permanent dock line, the eye should be spliced into the boat end of the line, and measure it carefully: The finished eye should be just large enough to fit easily over the horns of the boat’s mooring cleat, so that it is unlikely to come loose. If the eye is large enough, and for complete security, you can feed the eye through an open-based cleat before looping it back over the horns, like this:

For a cruising dock line, the eye generally goes ashore so that you can adjust the exact position of the boat fore and aft while still on board. For these cruising dock lines, twelve inches is a good eye size. Even if a 12” eye won’t fit over another marina’s cleats or pilings, you can pull the standing part of the dock line through the eye to form a bigger loop. Here’s how to splice an eye in the end of a 3-strand nylon dock line:

More detailed splicing instructions are available in many boating publications, and online. On-line, you can even find “animated” step-by-step instructions. For example: http://www.animatedknots.com/splice/index.php?LogoImage=LogoGrog.jpg&Website= www.animatedknots.com

If you don’t want to splice a permanent eye in your dock line, a bowline will work in a pinch, but it is a poor substitute. A bowline significantly reduces the breaking strength of a line, whereas a splice retains 95% of the rope's original strength.

Chafe protection Chafe is the damage caused by lines rubbing on sharp edges and rough surfaces. It is inevitable, and dock line failures are almost always a result of chafe. Unfortunately, it is nearly impossible to rig dock lines so that they never rub against the dock, or a cleat or chock, or even against the boat itself. Sometimes chafing can be reduced by changing the angle of a line so that it does not make an abrupt turn -- providing a nearly straight “fair lead” from the dock cleat to the boat cleat. But most often, we must resort to dock line protection with “chafing gear.” Chafing gear is little more than disposable abrasion-resistant lengths of leather, fabric, rubber, flexible hose, or similar material. For example, a foot or two of any old water hose or garden hose, or even clear vinyl hose, or even a scrap of leather, can be spliced into or sewn over an eye (see illustration below), thus protecting that part of the line which is most subject to wear and tear. Where a dock line is subject to chafe by running over a sharp or abrasive edge, or making an abrupt turn through a chock, a length of hose or tubular fabric can be taped or tied into position to protect the line.

Of course, there are many commercial anti-chafe products, but nearly all of them will cost more than two feet of old hose (with some dutiful application of duct tape). And, although they may appear more “yar,” they likely won’t perform any better. Captain Bernie Weiss USCG-Licensed Master Mariner Date this draft: 4 January 2013