There is so much to consider with the various forms of elongation in synthetic ropes - elastic elongation, hysteresis, permanent elongation while working, permanent elongation after relaxed, and cold flow, or creep - but what does the sailor need to know about it? You need consistency from tack to tack, so what happens when a synthetic rope is placed under a load?
The first time a new rope is loaded, the braid compacts slightly, and depending on the construction, small helical changes take place. The result is a permanent extension that will not change over the life of the rope. By cycling the rope under a load a number of times before you use it in competition, this constructional elongation can be eliminated.
Elastic elongation (EE) is a characteristic of the fiber or fibers used in the construction. It is that portion of the extension that is immediately recoverable when the load is released. Elastic elongation is expressed as a percentage of the length at a standard load based on a percentage (10%, 20%, or 30%) of the breaking strength. Elastic elongation can only be reduced by moving up to a larger diameter line, a line with higher breaking strength, or a line with a lower measured elasticity.
Hysteresis, another form of elongation, is not recovered immediately when a load is released, but over hours or even days. This is generally negligible in the scheme of the racing sailor.