Mooring lines construction and stretch
Mooring lines and docklines are being produced in various constructions (3-strand, 8-strand, 12-strand, double-braided) and materials like polyester, nylon, and Dyneema. Which one is the right one for your boat?
First of all stretch in mooring lines is very important. The mooring line should be able to absorb shocks that are generated by wind or swell. The amount of stretch required is defined by the situation your yacht is moored. Marinas and harbors with good protection require minimal stretch, while mooring in places where you might experience big swells it is important to have good stretch. In this case even extra items may be required such as rubber stretchers.
The type and shape of yacht is also important. Sailing yachts with furling sails have quite some projected area for the wind, while low motoryachts won’t catch much wind.
The amount of stretch greatly varies by the construction and material used in the docklines. 3-strand, 8-strand and 12-strand construction gives very good stretch. The 3-strand construction is the oldest way of making ropes and still very effective for mooring lines.
The disadvantage of 3, 8 and 12-strand is that it might get a stiff after a while.
The more modern double-braided ropes have 12-strand “woven” core and 32-strand braided cover. This makes the rope very flexible and strong.
Mooring lines materials
Having the right material is quite important. Common choices are materials such as Nylon, Polyester and Dyneema.
Nylon is a great material, with excellent break loads and very good stretch properties. The main disadvantage is Nylon has a tendency to shrink and harden due to UV radiation, also the break load is greatly affect when wet. This is why Nylon is losing market share as docklines for yachts.
Polyester is the successor to Nylon, Polyester still provides very good stretch properties. Polyester offers great resistance against abrasion, is less affected by UV radiation, doesn’t lose strength when wet and is very soft to the touch.
Dyneema SK75 and SK78 fibers are more than twice as strong as Polyester in the same diameter but less than half the weight. Dyneema has the best abrasive resistance but is to slippery to handle. Therefore our Dyneema mooring lines are protected with a polyester cover.
Plain Dyneema will absorb no water and can even float, making it great for tow or ground lines.
The main downside to Dyneema is the lack of stretch, when using Dyneema as a mooring line we recommend using polyester loops as stretchers. The length and diameters of these loops depend on the required stretch, which again is defined by the yacht and mooring properties.