Section
14 Thruster-assist class notation requirements
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) 14.1.3 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 Class Notations.
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)
14.2.2 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:
- Generating capacity, as defined in 14.1.3.
- 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.
- 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 bPt 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.
- 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.
- 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, 11 Anchor winches and windlasses and Pt 3, Ch 10, 12 Electrical and control equipment, 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.
14.3.5 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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