Section3 Design of Mooring Lines, etc.

301. Components of mooring lines and seabed mooring points

1. Each component of mooring systems is to be designed using design methods by which the severest loading condition can be verified. The strength of connecting shackles, links, etc. used at the con- necting points between the mooring lines and hull structures of Units and between mooring lines and seabed mooring points are, in principle, to have safety factors against the breaking loads of such mooring lines or the ultimate strength of structures not less than those indicated in the Table 6.3.

Table 6.3 Safety Factor

2. In the case of catenary mooring systems, mooring lines are to be sufficiently long so that no up- lifting forces act on the parts of the mooring line around the mooring point on the seabed un- der design conditions. In the case of soft clay conditions (like in the Gulf of Mexico), a small an- gle for the one broken mooring line condition may be considered in cases where deemed accept- able by the Society.

3. Information verifying that the holding power of seabed mooring points is sufficient against the ex- pected tension from the mooring lines in accordance with 204. is to be submitted to the Society for reference.

4. In the case of seabed mooring points which rely on friction with the seabed surface, if the sub-

merged unit weight of mooring lines is constant, the maximum load at the seabed mooring point

ÁŴŸẄYŸZ can be calculated as follow:

ÁŴŸẄYŸZ G ĀŶYŸẀ G BZŹẄBǼ G ÁXZYẄŹYŸŸ

ÁXZ YẄŹ YŸŸ G XZŶÄẄẀ ẀBZŹ Ẅ

ĀŶYŸẀ : Maximum mooring line tension

WD

XZŶ

ÄẄẀ Ẁ

BZŹẄ

: Water depth

: Friction coefficient of mooring line on seabed at sliding which is to be determined in consideration of soil conditions, the type of mooring line, etc. In the case of soft mud, sand, and clay, the values of XZŶ , and the coefficient of friction at the start XZŹ , indicated in the Table 6.4 may be used.

: Length of mooring line on seabed at design storm conditions, not to exceed 20% of

the total length of a mooring line.

: Submerged unit weight of mooring line

In cases where submerged mooring lines are not a single line, or those cases where using inter- mediate sinkers/buoys, the above equation is to be applied in consideration of such effects.

5. The safety factors for the horizontal holding power capacity of the seabed mooring points of cate- nary mooring systems and taut mooring systems are, in principle, to be in accordance with Table

6.5. However, the above may not be complied with in cases where required ultimate holding ca-

pacity is to be determined based on mooring loads derived from dynamic analysis taking into ac- count mooring line dynamics.

6. The safety factors for the vertical holding power capacity of the seabed mooring points of taut mooring systems are, in principle, to be in accordance with Table 6.6.

Table 6.4 Coefficient of Friction X

Table 6.5 Safety Factor for the Horizontal Holding Capacity of the Seabed Mooring Points of Catenary Mooring Systems and Taut Mooring Systems

Table 6.6 Safety Factor for the Vertical Holding Capacity of the Seabed Mooring Points of Taut Mooring Systems