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Clasification Society Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, January 2016 - Part 3 FUNCTIONAL UNIT TYPES AND SPECIAL FEATURES - Chapter 10 Positional Mooring Systems - Section 14 Thruster-assist class notation requirements

Section 14 Thruster-assist class notation requirements

Parent topic: Chapter 10 Positional Mooring Systems

14.1 Notation TA(1)

14.1.1 For assignment of the notation TA (1), in accordance with Section 4, the applicable requirements of Pt 3, Ch 10, 12 Electrical and control equipment and Pt 3, Ch 10, 13 Thruster-assisted positional mooring together with Pt 3, Ch 10, 14.1 Notation TA(1) 14.1.2 to Pt 3, Ch 10, 14.1 Notation TA(1) 14.1.2 are to be complied with.

14.1.2 Centralised automated manual control of the thrusters is to be provided to supplement the position mooring system. The manual control system is to provide output signals to the thrusters via the manual controller to change the speed, pitch and azimuth angle, as applicable, as indicated at the central control station, see Pt 3, Ch 10, 13.2 Thrust units.

14.1.3 For electrically driven thruster systems, the total generating capacity of the electrical system is to be not less than the maximum dynamic positioning load together with the maximum auxiliary load. This may be achieved by parallel operation of two or more generating sets, provided the requirements of Pt 6, Ch 2, 2.2 Number and rating of generators and converting equipment are complied with.

14.2 Notation TA(2)

14.2.1 For assignment of the notation TA (2), in accordance with Pt 3, Ch 10, 4 Design aspects, the applicable requirements of Pt 3, Ch 10, 12 Electrical and control equipmentand Pt 3, Ch 10, 13 Thruster-assisted positional mooring together with 14.2.2 to 14.2.8 are to be complied with.

14.2.2 Automatic and manual control systems are to be provided to supplement the positional mooring systems and arranged to operate independently so that failure in one system will not render the other system inoperative, see also 14.1.2 for manual control.

14.2.3 The automatic control system is to utilise automatic inputs from the position reference system, the environmental sensors and line tensions, and automatically provide output signals to the thrusters to change the speed, pitch and azimuth angle, as applicable, such that the line tensions are optimised.

14.2.4 In the event of a failure of a reference or environmental sensor, the control systems are to continue to operate on signals from the remaining sensors without manual intervention.

14.2.5 In the event of line failure or failure of the most effective thruster, the unit is to be capable of maintaining its predetermined area of operation and desired heading in the environmental conditions for which the unit is designed and/or classed.

14.2.6 Control, alarm and safety systems are to incorporate a computer-based consequence analysis which may be continuous or at predetermined intervals and is to analyse the consequence of predetermined failures to verify that the anchor line tensions and position/heading deviations remain within acceptable limits. In the event of a possible hazardous condition arising as a result of the consequence analysis an alarm is to be initiated at the central control station.

14.2.7 The area of operation is to be adjustable, but is not to exceed the specified limits, which are to be based on a percentage of water depth, or if applicable a defined absolute surface movement. Arrangements are to be provided to fix and identify the set point for the area of operation.

14.2.8 For electrically driven thruster systems, the following requirements are to be complied with:
  1. Generating capacity, as defined in 14.1.3.
  2. With one generating set out of action, the capacity of maximum positioning load with the most effective thruster inoperative together with the essential services defined by Pt 6, Ch 2,1.5.
  3. Where generating sets are arranged to operate in parallel, the supplies to essential services are to be protected by the tripping of non-essential loads as required by Pt 6, Ch 2, 6.9 Load management and additionally, on loss of a running generator, a reduction in thrust demand may be accepted provided the arrangements are such that a sufficient level of dynamic position capability is retained to permit the three degrees of manoeuvrability of the unit.
  4. Indication of absorbed electrical power and available on-line generating capacity is to be provided at the main thruster-assisted positioning control station, see 14.4.1.
  5. Means are to be provided to prevent starting of thruster motors until sufficient generating capacity is available.

14.3 Notation TA(3)

14.3.1 For assignment of the notation TA (3), in accordance with Pt 3, Ch 10, 4 Design aspects, the applicable requirements of Pt 3, Ch 10, 12 Electrical and control equipment and Pt 3, Ch 10, 13 Thruster-assisted positional mooring, together with 14.2.3 to 14.2.8 and 14.3.2 to 14.3.8, are to be complied with.

14.3.2 Two automatic control systems are to be provided and arranged to operate independently so that failure in one system will not render the other system inoperative.

14.3.3 In the event of failure of the working system the standby automatic control system is to be arranged to change over automatically without manual intervention and without any adverse effect on the vessel’s station keeping capability. The automatic changeover is to initiate an alarm.

14.3.4 At least two position reference systems as defined by Pt 3, Ch 10, 12.4 Controls of winch and windlass systems, and two gyrocompasses or equivalent, are to be provided.

14.3.5 At least two of each of the sensors as required by 13.4.9 and 13.4.10 are to be provided.

14.3.6 When two voyage recording systems are deployed, their outputs are to be compared and an alarm raised when a significant difference occurs.

14.3.7 The arrangement is to be verified by means of a Failure Mode and Effects Analysis (FMEA). Such components may include, but not be restricted to, the following:
  • Mooring systems.
  • Prime movers, e.g., auxiliary engines.
  • Generators and the excitation equipment.
  • Switchgear.
  • Pumps.
  • Thrusters.
  • Fans.
  • Valves, where power-actuated.

14.3.8 Control, alarm and safety systems are to incorporate a computer-based consequence analysis which may be continuous or at predetermined intervals and is to analyse the consequence of predetermined failures to verify that position and heading deviation remain within acceptable limits. In the event of a possible hazardous condition being indicated from the consequence analysis, an alarm is to be initiated.

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