4.1.1 For assignment of DP(AA) notation, the applicable requirements of
Pt 7, Ch 4, 2 Class notation DP(CM) and Pt 7, Ch 4, 3 Class notation DP(AM), together with Pt 7, Ch 4, 4.1 Requirements 4.1.2 to Pt 7, Ch 4, 4.1 Requirements 4.1.11 are to be complied with.
4.1.2 Power, control and thruster systems and other systems necessary for, or
which could affect, the correct functioning of the DP system are to be provided and
configured such that a fault in any active component or system will not result in a loss
of position. This is to be verified by means of a FMEA, see
Pt 7, Ch 4, 1.3 Information and plans required to be submitted 1.3.6. Such components may include, but are not restricted
to, the following:
- Prime movers (e.g. auxiliary engines).
- Generators and their excitation equipment.
- Gearing.
- Pumps.
- Fans.
- Switchgear and controlgear, including their assemblies.
- Thrusters.
- Valves (where power actuated).
Systems which are not part of the DP system but which, in the event of a
fault, could affect the correct functioning of the DP system (for example, fire
suppression systems, engine ventilation systems, shutdown systems, etc.) are to be
included in the FMEA.
4.1.3 Cables, pipes and other components essential for correct functioning of the
DP system are to be located and protected, where necessary, such that the risk of fire
or mechanical damage is minimised.
4.1.4 The electrical generation and distribution arrangements are to be isolatable
such that at least the minimum number of any duplicated, or otherwise replicated, items
required to provide essential services would remain operational in the event of a single
fault. Evidence to verify compliance with this requirement is to be submitted for
consideration when required; for example, where it is intended to operate with the
independent sections required by Pt 7, Ch 4, 2.3 Electrical systems 2.3.12 connected together.
4.1.6 For electrically driven thruster systems:
-
a reduction in position keeping capability may be accepted, but this
is not to result in a loss of position in the environmental conditions in which
the DP system is intended to operate; and
-
provision is to be made for the automatic starting, synchronising and
load sharing of a non-running generator before the load reaches the alarm level
required by Pt 7, Ch 4, 2.3 Electrical systems 2.3.8.
4.1.7 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.
4.1.8 Control systems are to be arranged such that, in the event of failure of
the working control system, the standby system takes control automatically without
manual intervention and without any adverse effect of the ship's station keeping
performance.
4.1.9 At least three position reference systems incorporating at least two
different measurement techniques are to be provided and arranged so that a failure in
one system will not render the other systems inoperative.
4.1.10 At least three heading reference sensors are to be provided and arranged so
that a failure of one sensor will not render the other sensors inoperative.
4.1.11 The DP system is to incorporate a computer based consequence analysis to
determine whether the position of the vessel would remain within the limits set by the
operator in the event of a worst case fault. An audible and visual alarm is to be
initiated where the consequence analysis determines that the limits would be exceeded.
Where applicable to the timescale for safely terminating operations, the consequence
analysis is to allow for manual input of predicted environmental conditions.
4.1.12 The DP system is to include monitoring of all devices where the FMEA shows that the loss
of the device will result in the loss of redundancy provision. Such monitoring is to be
provided for all devices where the loss has the potential for failure of equipment to
perform an on-demand function, such as protective functions in electrical systems and
switchboards, standby equipment, or backup power supplies. The monitoring is to initiate
an alarm in accordance with the requirements of Pt 6, Ch 1, 2.3 Alarm systems, general requirements.