SPAR MOORING

Mooring Design

6. Evaluate mooring alternatives

Mooring lines

The most common tension member lines used are synthetic fiber ropes and wire rope. Synthetic lines have the advantage of easy handling and some types have stretch, which can be used to fine tune static and dynamic mooring behavior and aid in load sharing between tension members. Wire rope has the advantage of durability.

  • Synthetic Fiber Ropes

Mooring lines are formed by weaving a number of strands together to form a composite tension member. Lines are made of different types of fiber and various constructions. The size and type of synthetic line specified in a given design will depend upon parameters such as those shown in table below.

  • Wire Ropes

Wire rope is composed of three parts: wires, strands, and a core. The basic unit is the wire. A predetermined number of wires of the proper size are fabricated in a uniform geometric arrangement of definite pitch or lay to form a strand of the required diameter. The required number of strands are then laid together symmetrically around a core to form the rope. Refer to NAVSEA NSTM 613 for additional information.

  • Factors considered for selection

  • Some important issues

1.Polyester rope stiffness is a function of many variables unlike spiral strand. For a spar, currents will usually control the design. As a result, the static stiffness of the polyester rope become much more important than the dynamic stiffness.

2.To date the largest polyester rope ever made and put into a service is 1000 tonnes with 1250 tonnes ropes being produced.

3. The last issues is development of adequate assurance that the mooring could be safely operated over the field life.

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