Dock Lines                                                                                    (excerpt from West Marine catalog)

How they work
When your boat is away from its regular slip or mooring, you need to have some designated nylon lines aboard, preferably with spliced eyes, ready for use when you tie up somewhere.  We call these transient dock lines.  The eye in the end is easily passed around a cleat or piling by someone on the dock and the bitter end is adjusted on board.  There are dozens of combinations of diameters and lengths.

Permanent dock lines are also made of nylon, but 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.

What to look for
Dock lines should be made from nylon, which has a superior combination of strength and stretch.  Both three-strand and braided construction are common.  Three-strand stretches more, is very abrasion- and snag-resistant and less expensive.  Braided nylon is stronger, comes in colors, and has a nice feel or “hand”.

Diameter
We recommend 1/8" of line diameter for every 9' of boat length.  Larger lines will wear longer but stretch less.  See the chart below:

Length
Transient dock lines should be about 2/3 of the boat’s length when used on the bow and stern. Spring lines should be equal to your boat’s length.

Glossary
Chafe is the damage caused by rubbing lines or sails 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.

Eye splices are loops woven into the ends of line by passing the strands of the line in and out of the strands on the standing part. They retain a high percentage of the strength of the line compared to knots, and cannot come apart accidentally when properly spliced.

Nylon is a synthetic fiber that has high strength, high stretch and good abrasion resistance.

Spring lines are dock lines that run forward from the stern, or aft from the bow of the boat to the dock. They oppose the tension on the bow and stern lines and keep the boat from surging fore and aft.