Splices and Loops are on of the most used techniques in marlinspike seamanship and can be made in any line.
Lines on vessels come in two types. One is twisted yarns laid back on themselves and it resembles a continuous spiral along the length of the line. The second is braided line which has the smooth appearance of fabric on the surface.
Lines that need to run fast in blocks or need to look nice for aesthetic purposes are often braided types. Larger size lines are almost always twisted and are meant to carry the heaviest of loads.
Both of these types of lines can be spliced with strength greater than the original material. This is because the yarns which make up the lines are doubled in the splice and with proper construction the splice will constrict more as the load increases.
Splicing a Twisted Line
The most common line in commercial applications is a three stranded twist. This is available in most hardware stores and your local boat supply shop. Lines made for maritime use have significantly more resistance to ultraviolet rays than their cheaper counterparts. If you are learning splices go ahead and use the cheap stuff, if you are making a set of mooring pendants for a large boat buy high quality material. It will remain flexible much longer and that leads to better strength and durability.
To begin take two lengths of line and place them on a flat surface. Cut the finished ends off one side of both lines. Take these cut ends and place them in line with each other so it forms a continuous straight line.
Now you will open both rope ends, one at a time to reveal three strands as the rope untwists. Use a wire tie or piece of masking tape to keep the rope from unraveling more than about eight inches for a half inch rope. If you have more than three strands then refinish the ends and find some three strand line.
You can splice as many strands as a line has, it is only limited by your patience and eyesight. The problem is like juggling with too many balls to start, so no more than three strands while learning.
Once the yarns are exposed then the tape or wire ties should be pulled close together so the yarns overlap.
The next step is to twist the line opposite the lay so the yarns open up and make spaces between themselves. You can use a tool called a fid which is a wooden or metal spike with a handle. For smaller line golf tees work well and are easy to find.
Whatever keeps the line from unraveling needs to be tight since this is where the weaving starts. The strands should be paired up and each side should roughly follow the path of its pair as the lines are woven together. Each yarn is passed over its neighbor strand once per revolution around the splice. When the twist is allowed to return to the rope all yarns should be worked into a round shape and stretched progressively tighter. Some riggers wet the rope, pull tight, release and let dry for a rock hard splice.
Loops in Twisted Lines
If you already completed the twisted splice above you already know how to make a spliced loop, or eye, at the end of a line.
This time we will unravel the end of the line like you would for splicing. Instead of weaving it into a different line this time the lay is twisted open at the desired diameter of the loop and the yarns are woven in using the same splicing technique. When the twist returns to the line there will be a strong and neat loop once the ends of the yarns are trimmed flush with the splice.
Splices and Loops in Braided Lines
Compared to twisted splices braided splices are easy. The technique is the same for both results, it's similar to the twisted process except there is no weaving.
To make an end splice the braided sheath that covers the core of the line needs to be pushed back to make some working room. This will be easy once the finished end is cut. Put some tape or a wire tie on this line so the sheath doesn't get baggy too far up the line. This takes a lot of time to fix so it's best to avoid it.
The next step is to take a hollow fid or splicing needle and pass the core of one side through the core of the other in a wave pattern. In one side and out the other at least three times.
Pull the sheath back together and whip the sheath together with fine cord for at least three times the diameter of the line.
A loop or eye is the same technique just with one line like the twisted loop.
Some braided lines have loosely bundled core yarns to make them super flexible by reducing internal friction. In this case a knot that lays flat is used to tie the cores together. A figure eight knot makes a good choice since the sheath can be worked back over the splice easily.