Section 2 Class notation DP(CM)

2.1.1 For assignment of DP(CM) notation, the requirements of Pt 7, Ch 4, 2.1 General 2.1.2 and Pt 7, Ch 4, 2.2 Thrusters to Pt 7, Ch 4, 2.5 Control system are to be complied with.

2.1.2 Control engineering systems, electrical and piping installations and machinery items are to be designed, constructed, installed and tested in accordance with the relevant requirements of Pt 5 Main and Auxiliary Machinery and Pt 6 Control, Electrical, Refrigeration and Fire.

2.2.1 Thruster installations are to be designed, constructed, installed and tested in accordance with the requirements of Pt 5, Ch 20 Azimuth Thrusters, as applicable.

2.2.2 Thruster installations are to be designed to minimize potential interference with other thrusters, sensors, hull or other surfaces, which could be encountered in the service for which the ship is intended.

2.2.3 Thruster intakes are to be located at sufficient depth to reduce the possibility of ingesting floating debris and vortex formation.

2.2.4 The response and repeatability of thrusters to changes in propeller pitch or propeller speed/direction of rotation are to be suitable for maintaining the area of operation and heading within specified limits.

2.2.5 Failure of a thruster system including pitch, azimuth and/or speed control is not to cause an increase in thrust magnitude or change in thrust direction of the failed thruster.

2.2.6 Thrusters are to be provided with individual emergency stop systems in the DP control station. The emergency stop system is to be provided with loop monitoring facilities that will initiate an alarm in accordance with the requirements of Pt 6, Ch 1, 2.3 Alarm systems, general requirements. In the event that the loop monitoring alarm is initiated the thruster output is to remain unaltered.

2.2.7 Alternative energy storage (e.g. batteries and fly-wheels) may be used as sources of power to thrusters.

2.3.1 This Section applies to the electrical generation and distribution system associated with the Dynamic Positioning System, whether this generating system is dedicated to the DP system or forms a central generating arrangement for all loads on the ship.

2.3.2 The electrical installation is to be designed, constructed and installed, in accordance with the requirements of Pt 6, Ch 2 Electrical Engineering, together with the requirements of Pt 7, Ch 4, 2.3 Electrical systems 2.3.3 to Pt 7, Ch 4, 2.3 Electrical systems 2.3.12.

2.3.3 Where thrusters are electrically driven, the relevant requirements, including surveys, of Pt 6, Ch 2, 16 Electric propulsion are to be complied with.

2.3.4 Essential services are those defined in Pt 6, Ch 2, 1.6 Definitions, as applicable, together with thruster auxiliaries, computers, generator and thruster control equipment, reference systems, environmental sensors and electrically driven thrusters.

2.3.5 The number and rating of generator sets, transformers and converter equipment are to be sufficient to ensure the operation of essential services, even when one generating set, transformer or converter equipment is out of action.

2.3.6 For electrically driven thruster systems, the generator rating is to be determined by the maximum dynamic positioning load, together with the maximum ancillary load.

2.3.7 There are to be arrangements to prevent overloading of the running generator(s). The tripping of non-essential loads and the temporary reduction in the load demands of electrically driven thrusters may form part of these arrangements. The arrangements are to ensure that sudden load changes resulting from single faults or equipment failures do not create a loss of electrical supplies.

2.3.8 An alarm is to be initiated when the total electrical load exceeds a preset percentage of the running generator(s) capacity. This alarm is to be adjustable between 50 and 100 per cent of the running capacity and is to be set with regard to the number of generators in service and the effect of the loss of any one generator.

2.3.9 On loss of power due to the failure of the operating generator(s), there is to be provision for the automatic starting and connection to the switchboard of a standby set and the automatic sequential restarting of essential services. Consideration may be given to cases where arrangements for automatic re-starting of thrusters would not be practicable. Details are to be submitted in such cases to show that manual means for the immediate re-starting of thrusters would be available at the control station from where the dynamic positioning system would be operated.

2.3.10 Any loads that require an uninterrupted electrical power supply are to be provided with uninterruptible power systems (UPS) having a capacity for a minimum of 30 minutes' operation following loss of the main supply. A UPS is to be provided for each control computer system.

2.3.11 An indication of the absorbed power and the available on-line generating capacity is to be provided at the main dynamic positioning control station.

2.3.12 Essential services are to be served by individual circuits. Essential services that are duplicated are:

1. to be supplied from independent sections of their switchboard or section board;

2. to have their circuits separated throughout their length as widely as is practicable; and

3. not to depend upon common feeders, transformers, converters, protective devices, control circuits or controlgear assemblies to operate.

2.4.1 Control stations from which the dynamic positioning system may be operated are to be designed in accordance with sound ergonomic principles, and are to be provided with sufficient instrumentation to provide effective control and indicate that the systems are functioning correctly. Colour schemes and screen layouts are to be selected such that necessary information is readily available and clearly displayed. See also Pt 6, Ch 1, 2.10 Programmable electronic systems - General requirements for general ergonomic requirements.

2.4.2 Control station(s) are to be located such that the operator has a good view of the ship's exterior limits and surrounding area.

2.4.3 Indication of the following is to be provided at each station from which it is possible to control the dynamic positioning system:

1. The heading and location of the ship relative to the desired reference point or course.

2. Vectorial thrust output, individual and total.

3. Operational status of position reference systems and environmental sensors.

4. Environmental conditions, e.g. wind speed and direction.

5. Availability status of standby thrusters.

2.4.4 At least one position reference system, heading reference sensor and wind sensor are to be provided to ensure that the specified area of operation and heading can be effectively maintained.

2.4.5 Position reference systems are to incorporate measurement techniques suitable for the service conditions for which the ship is intended.

2.4.6 Where necessary for the correct functioning of a position reference system, a vertical reference sensor is to be provided to correct for the pitch and roll of the ship. There are to be at least as many vertical reference units as there are associated position reference systems.

2.4.7 Alarms, in accordance with the requirements of Pt 6, Ch 1, 2.3 Alarm systems, general requirements, are to be provided for the following fault conditions as applicable:

1. When the ship deviates from the area of operation.

2. When the heading exceeds the allowable deviation.

3. Position reference system fault (for each reference system).

4. Heading reference sensor fault.

5. Vertical reference sensor fault.

6. Wind sensor fault.

7. Taut wire excursion limit.

8. Automatic changeover to a standby position reference system or environmental sensor.

A record of the occurrences of alarms and warnings, and of status changes is to be provided.

2.5.1 A centralised remote manual control system is to be provided such that changes in the vectorial thrust output may be readily effected by a single operator action.

2.5.2 Suitable processing and comparative techniques are to be provided to validate the control system inputs from position and other sensors. Abnormal signal errors revealed by the validity checks are to operate alarms.

2.5.3 The control system for dynamic positioning operation is to be stable throughout its operational range and is to meet the specified performance and accuracy criteria.

2.5.4 Automatic controls are to be provided to maintain the heading of the ship within specified limits.

2.5.5 The allowable deviation from the desired heading is to be adjustable, but should not exceed the specified limits, see Pt 7, Ch 4, 1.1 Application 1.1.4. Arrangements are to be provided to fix and identify the set point for the desired heading.

2.5.6 Alarms, in accordance with the requirements of Pt 6, Ch 1, 2.3 Alarm systems, general requirements, are to be provided for the following fault conditions:

1. Control computer system fault.

2. Automatic changeover to a standby control computer system, as applicable, see Pt 7, Ch 4, 4.1 Requirements 4.1.8.

2.5.7 Safeguards are to be implemented to ensure the integrity of the control system by preventing the connection of unauthorised or unapproved devices or systems.