Rope, or line as it called aboard a boat, is an essential boat supply. Not only do you need it to moor your boat and tie off the fenders, it has dozens of other boating applications. When outfitting your boat, you should have several different types and sizes of line on board.
Line is made of either natural or synthetic fibers twisted into yarns and grouped together to form strands. To form the line, the strands are twisted, plaited or braided together to form the final product. How the lines are twisted together determines its "lay." Line can be right or left lay, and it is usually plain laid, plaited or double braided depending upon the intended use of the line.
Plain laid line is made of three strands twisted to the left or the right, but the most plain laid lines are right laid. Plain laid lines are also called "three strand" line.
Braided line is usually made from three strands braided together and comes in different construction types such as hollow-braided, stuffer-braided, solid-braided and double braided. The most common type of braided line is double braided nylon.
The construction of the line, along with the material used to make the line, determines the strength of the line and its various uses.
A properly outfitted boat should have at least six dock lines on hand. Two (each) bow and stern lines, and two spring lines. The length of the lines depends upon how and where you moor your boat. Some boaters have custom made lines that are measured specifically for their berthing area, however, you should have designated bow and stern lines that are approximately two-thirds the length of your boat, and spring lines that are the full length for when you moor at unfamiliar places.
Anchor line is also essential when anchoring your boat. Anchor line comes in twisted nylon, solid braided MFP, and polypropylene.
Another type of line to have your boat is general purpose/polypropylene line. This line is great to attach a life ring or other floatation device because it usually comes in bright colors and it floats. This line is also used for skiing, wake boarding and tubing.
If you have the storage, you can never have too much line. Besides designated dock lines, consider varying lengths and sizes of lines to have aboard for practical or emergency use, or to just lend to someone in need.