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Dockline Rope

Dock Line

Dockline from Machovec.comWhen you decide to purchase docklines, it is possible to be overwhelmed by the variety of rope available . If you are after rope to secure your boat to the dock, you can - and should - ignore most of those spools. Most marine cordage is for general or specialized use aboard sailboats, and the less it stretches, the more it gets revered by sailors. For docklines, however, sailors and power boaters alike need a rope that does stretch.

Call Jay at 763-263-9835 for a price quote and shipping information.

Nylon

Incredibly strong

Incredibly stretchy

UV Resistant

Inexpensive

Nylon has three characteristics that make it ideal for dockline. It is incredibly strong, it is very stretchy, and it resists the harmful effects of sunlight.

The value of strength is self-evident, but the benefits of elasticity may not be as obvious. When your boat surges against an unyielding dockline, the load on the line goes from zero to the maximum at the instant the line becomes taut. The likely consequence is a broken line - not unlike how you might snap a piece of thread with a jerk. Even if the rope is strong enough not to break, it is hammering cleats and bitts with every surge. Nylon doesn't become taught suddenly, but dissipates the load by stretching. It is like the difference between hitting the steering wheel or hitting the air bag in an accident.

As for nylon's resistance to ultraviolet damage, docklines - particularly permanent docklines - live in the sun. Nylon enjoys a much longer life in that environment.

Nylon actually has a fourth characteristic that you will surely appreciate; it's less expensive. The only exception is polypropylene.

Polypropylene

Floats

Low breaking strength

Slick surface

Not spliceable

Polypropylene rope is stiff, very slick, and usually bright yellow; but it's most distinguishing characteristic is that it floats. You will be familiar with this rope if you water ski. Polypropylene has a relatively low breaking strength, the quality of the rope is notoriously erratic, and because it is so slick, it does not hold a splice.

Braid or Twisted

Nylon rope is available in both braided and 3-strand twist construction. Each has its advantages.

Nylon braided line looks "dressy". It has better abrasion resistance than 3-strand nylon, and typically is slightly stronger. Braided line can be a good choice for tying up in your home dock, but because braided lines have a tendency to snag on rough pilings, it is not recommended for traveling docklines. As anchor lines, however, braided nylon handles easier and stows more compactly and with less of a tendency to tangle, but at the cost of some elasticity.

The main advantages of 3-strand nylon for docklines are that it doesn't snag, it is easy to splice, and it is considerably less costly than braided rope. 3-strand also has the significant advantage of being more stretchy than braid. As a practical choice for docklines, 3-strand nylon is unbeatable, and how often is the best also the least expensive?

Choose Length

For docklines that are a fixture of your permanent slip, work out the appropriate lengths using old line - making allowances for eye splices. Nothing is more convenient than pulling into your slip and simply drooping eyes over the mooring cleats. If your dock is fixed - not floating - be sure to leave a little extra length for unusually low or high tides.

Choose Size

Since larger diameter line takes longer to chafe through, a case might be made for selecting the largest diameter that will fit your cleats. But as the line diameter gets larger, it also becomes less elastic - making the "right" line diameter a bit of a catch-22. The line diameters shown in the chart should deliver both sufficient strength and the beneficial effects of elasticity.

Choose Dockline Size
Line Diameter Boat Length
3/8" up to 25'
1/2" up to 35'
5/8" up to 45'
3/4" up to 55'
7/8" up to 65'
CAUTION: USE OF WORKING LOADS

Because of the wide range of rope use, rope condition, exposure to the several factors affecting rope behavior, and the degree of risk to life and property involved, it is impossible to make blanket recommendations as to working loads. However, to provide guidelines, working loads are tabulated for rope in good condition with appropriate splices, in non-critical applications and under normal service conditions.

The Cordage Institute Formula for working load is:
Working Load = Minimum Breaking Strength/Safety Factor

A higher working load may be selected only with expert knowledge of conditions and professional estimate of risk. Also, if the rope has not been subject to dynamic loading or other excessive use, has been inspected and found to be in good condition, is to be used in the recommended manner; if the application does not involve elevated temperatures, extended periods under load, or obvious dynamic loading (see explanation below) such as sudden drops, snubs or pickups. For all such applications and for applications involving more severe exposure conditions, or for recommendations on special applications, call Jay at 612-282-4035.

**Many uses of rope involve serious risk of injury to personnel or damage to valuable property. This danger is often obvious, as when a heavy load is supported above one or more workmen. An equally dangerous situation occurs if personnel are in line with a rope under tension. Should the rope fail, it may recoil with considerable force. Persons should be warned against the serious danger of standing in line with any rope under tension. IN ALL CASES WHERE SUCH RISKS ARE PRESENT, THERE IS ANY QUESTION ABOUT THE LOADS INVOLVED OR QUESTIONS ABOUT THE CONDITIONS OF USE, THE WORKING LOAD SHOULD BE SUBSTANTIALLY REDUCED AND THE ROPE PROPERLY INSPECTED.

DYNAMIC LOADING VOIDS NORMAL WORKING LOADS

Normal working loads are not applicable when the rope is subject to significant dynamic loading. Whenever a load is picked up, stopped, moved or swung there is an increased force due to dynamic loading. The more rapidly or suddenly such actions occur, the greater the increase will be. In extreme cases, the force put on the rope may be two, three or even more times the normal involved. Examples could be picking up a tow on a slack line or using a rope to stop a falling object. Therefore, in all such applications such as towing lines, lifelines, safety lines, climbing ropes, etc. working loads as given DO NOT APPLY.

Users should be aware that dynamic effects are greater on a low elongation rope such as polyester than on a high elongation rope such as nylon, and greater on a shorter rope than on a longer one. The working load ratios listed contain provision for very modest dynamic loads. This means, however, that when this working load has been used to select a rope, the load must be handled slowly and smoothly to minimize dynamic effects and avoid exceeding the provision for them.

EFFECT OF TEMPERATURE ON TENSILE STRENGTH

The tensile strength charts apply to ropes tested at normal room temperature (70°F). Ropes have lower tensile strengths at higher temperatures. 30°F (or more) lower at the boiling point of water (212°F) and continuing on down to zero strengths for nylon and polyester at 490°F and 300°F for polypropylene.

Also, continued exposure at elevated temperatures causes permanent damage. TENSILE STRENGTHS shown are average based on new ropes tested under laboratory conditions, minimum can vary by 10%.

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