Section 1 General

101. General

1. Units are to be provided with positioning systems Chapter.

complying with the requirements given in this

102. Mooring systems

1. Mooring systems are to be sufficiently capable of all of the design conditions for positioning as well

positioning Units at a specific location against as all of the safety conditions for systems em-

bedded on the seabed and the ships laden with offloaded crude oil from such Units.

2. In the case of mooring systems of Units operated in sea areas where low temperature, freezing, ice formation, etc. are predicted, the effects of such things are to be taken into consideration or appro- priate countermeasures are to be provided.

103. Conditions to be considered for mooring system analysis

1. The various conditions of a Floating Installation which are important for the designer to consider are as follows.

(1) Intact Design

A condition with all components of the system intact and exposed to an environment as de- scribed by the design environmental condition (DEC).

(2) Damaged Case with One Broken Mooring Line

A condition with any one mooring line broken at the design environmental condition (DEC) that would cause maximum mooring line load for the system. The mooring line subjected to the maximum load in intact extreme conditions when broken might not lead to the worst broken mooring line case. The designer should determine the worst case by analyzing several cases of broken mooring line, including lead line broken and adjacent line broken cases. For a dis- connectable mooring system with quick release system, the mooring analysis for a broken line case may not be required. For unusual (non-symmetric) mooring pattern, mooring analysis for the broken line case for the disconnectable environmental condition may be required. For a sys- tem utilizing the SALM concept, the case with one broken mooring line is not relevant. A case considering loss of buoyancy due to damage of a compartment of the SALM structure should be analyzed for position mooring capability. The loss of thruster power or mechanical failure on thruster-assisted position mooring systems will be considered on a case-by-case basis.

(3) Transient Condition with One Broken Mooring Line

A condition with one mooring line broken (usually the lead line) in which the moored in- stallation exhibits transient motions (overshooting) before it settles at a new equilibrium position. The transient condition can be an important consideration when proper clearance is to be main- tained between the moored installation and nearby structures. An analysis for this condition un- der the design environmental condition (DEC) is required. The effect of increased line tensions due to overshoot upon failure of one mooring line (or thruster or propeller if mooring is pow- er-assisted) should also be considered.

2. The proper clearances between Units and any near-by structures and ships are to also be verified.

3. In the case of SALM, cases considering a loss of buoyancy due to damage of a compartment of the SALM structure should be analyzed for position mooring capability instead of cases with one broken mooring line.

4. Mooring system analysis in combination with the assistance of propulsion systems, thrusters, etc. is to be as deemed appropriate by the Society.