DOCKLINES

When 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.

Nylon

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

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 3-strand?

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?

What 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.

What 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.