Imtech Marine & Offshore B.V. Sluisjesdijk 155 P.O. Box 5054 3008 AB Rotterdam The Netherlands Harbour number 2137 Tel. +31 (0)10 487 19 11 Fax. +31 (0)10 487 17 02
DPT 3500 System User Manual
Blue Giant
Copyright 2008 Imtech Marine & Offshore B.V.
Imtech Marine & Offshore B.V. C.o.C. Rotterdam 24193093
Main title: DPT 3500 System User Manual Sub title: Blue Giant Issue: 1.3.1 Date: 31 July 2008 Total number of pages: 43 Ref. code DPT 3500 System user manual 131 BlueGiant
Author: Imtech Marine & Offshore, F.S. van Schijndel
Quality Control C.J. Koot
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Table of contents Figures ...................................................................................................................................... 4 References................................................................................................................................ 6 Abbreviations ........................................................................................................................... 7 Updates..................................................................................................................................... 8 1.
Introduction ..................................................................................................................... 9 1.1 1.2 1.3 1.4 1.5
2.
System overview ........................................................................................................... 11 2.1 2.2
3.
System Architecture ................................................................................................................11 Functionality overview.............................................................................................................12
Control Modes ............................................................................................................... 14 3.1 3.2 3.3 3.3.1 3.3.2 3.4
4.
General .....................................................................................................................................9 Safety Notes..............................................................................................................................9 System Start and Stop ............................................................................................................10 Version information .................................................................................................................10 Document set up .....................................................................................................................10
Transit modes .........................................................................................................................14 Position control modes............................................................................................................15 Heading control modes ...........................................................................................................16 Optimal Heading mode ...........................................................................................................17 Drift Heading Mode .................................................................................................................17 Speed control modes ..............................................................................................................18
Functional Description.................................................................................................. 19 4.1 Sensor Management...............................................................................................................19 4.1.1 General Principles...................................................................................................................19 4.1.2 Position Reference Systems...................................................................................................19 4.1.2.1 Position reference averaging........................................................................................19 4.1.2.2 Enabling Relative position reference systems..............................................................20 4.2 Automatic Heading control......................................................................................................20 4.3 Automatic Course control........................................................................................................21 4.3.1 Degraded Track Performance.................................................................................................22 4.4 Automatic Route control..........................................................................................................22 4.4.1 Shifting the Route ...................................................................................................................26 4.5 Automatic Speed Control ........................................................................................................27 4.6 Low Speed Control .................................................................................................................28 4.7 Position Control.......................................................................................................................29 4.8 Assist Settings.........................................................................................................................31 4.9 Alarm handling ........................................................................................................................32 4.10 Consequence Analysis ...........................................................................................................35
5.
Control/Settings Details................................................................................................ 36
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5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10
Master/Slave configuration .....................................................................................................36 Sensor filtering ........................................................................................................................37 Accuracy settings ....................................................................................................................37 Actuator Limits ........................................................................................................................38 Heading...................................................................................................................................38 Course/Track...........................................................................................................................39 Dynamic Positioning ...............................................................................................................40 Actuator allocation ..................................................................................................................42 Environmental Compensation.................................................................................................42 Sailing in Adverse Weather Conditions ..................................................................................43
Figures Figure 1 System hardware architecture Figure 2 Valid Initial Target Waypoint Criteria Figure 3 Shift a planned track to Stbd Figure 4 Failure response diagram
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NOTICE This document contains proprietary information. No part of this document may be photocopied, reproduced or translated into another language without the prior written consent of Imtech Marine & Offshore
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References 1. Name: Issue: Date:
Conning 3500 User Manual Blue Giant 3.0.0 31 July 2008
2. Name: Issue: Date:
Application Manager 3500 User Manual 4.0.4 14 July 2008
3. Name: Issue: Date:
DPT 3500 Panel User Manual Blue Giant 1.3.1 31 July 2008
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Abbreviations APP COG CPP DGPS DP DPT DPCS DT DTER DTW ECDIS FU GPS HDG HMI IBC IM&O I/O Kn LAN MFW MRU NFU NMEA OEM PLC PRS ROT RPM SMC SOG STW TID TIU TTER TTW UniMaCS UTC USBL
Aft PerPendicular Course Over Ground Controllable Pitch Propellers Differential GPS Dynamic Positioning Dynamic Positioning and Tracking Dynamic Positioning Control System Dynamic Track Distance To End of Route Distance To Wheel over point Electronic Chart Display Information system Follow Up Global Positioning System Heading Human Machine Interface Integrated Bridge Console Imtech Marine & Offshore Input/Output Knots Local Area Network Multi Functional Workstation Motion Reference Unit Non Follow Up National Marine Electronic Association Original Equipment Manufacturer Programmable Logic Controller Position Reference System Rate Of Turn Rotations Per Minute Ship Motion Control Speed Over Ground Speed Through Water Touchscreen Input Device Thruster Interface Unit Time To End of Route Time To Wheelover point Universal Integrated Monitoring and Control System Universal Time Coordinate Ultra Short Base Line
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Updates Table 1 lists the updates and changes pertaining to the successive document versions. Issue:
Date:
Change:
This document is based on DPT-35-PUM-System-R01300 1.3.1
31 July 2008
First document version for project Blue Giant Table 1 Document changes and updates
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1. 1.1
Introduction General This document describes the DPT 3500 system with DP2 Class certification. The system is a member of the SMC family configured to be used as autopilot, trackpilot, speedpilot and DPT system. The DPT 3500 system is a product of the Imtech Marine & Offshore UniMacs 3000 Integrated Bridge System series. The functionality of the system can be addressed by interfaces like Conning 3500 and DPT 3500 panel [Refs. 1 and 3]. Note: For the sake of brevity, whenever this document mentions a ‘he’ with reference to a person, one should read ‘he or she’.
1.2
Safety Notes System check prior to operation Prior to a start-up of the system, the operator should make sure that the DPT 3500 ON/OFF switch is in the OFF position. No actuator control from the DPT 3500 system will take place as long as this switch is in the OFF position. After each start-up of the system, and/or if the system has been off-line, the operator has to check the alarm list of the system prior to putting the system on line. He has to validate that all required sensors and actuators are ready for use and that the system is fully operational. In case of alarm messages, he has to assess the consequences for the system’s operation. Only after these precautions have been carried out is the operator allowed to use the DPT 3500 system. Maintenance Only instructed service personnel is allowed to perform any maintenance on the system (including the use of the built-in test provisions), and only if the system is off line! Testing while the DPT 3500 system is switched ON may activate the thrusters and lead to dangerous situations. Tests are only allowed after the necessary precautions have been taken. As a matter of principle, the system must be powered down if maintenance involves modifications to any hardware components in the system. Keep the IBC doors closed to prevent dust and oil from entering the system. Abnormal use Never use pointed objects such as pencil, ball-point pen and such, to operate the DPT 3500 panel. Never use excessive force on the joysticks.
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1.3
System Start and Stop Pre-start condition Although the system is designed with utmost attention to safety, its output cannot be guaranteed until the system is ready to be selected. Therefore, it is essential that the ship is in Manual Control mode prior to start up of the system. The DPT 3500 system is then off-line, isolated from the steering and propulsion devices. Start Upon power up of the components of the system (PLC, PC’s and monitors), the system automatically starts all the appropriate programs. At the end of the start-up sequence, the HMI components are activated and they will indicate whether or not the system is ready for automatic control. In control Although the system has been activated, it is not yet fully operational, because it is still off-line. Upon power up, it has no direct control of the steering and propulsion devices. In case more than one control position is present, the active control position will be “Bridge”. The DPT 3500 system becomes operational only after the operator has given command to the system. It then takes command of the steering and/or propulsion devices. This status is clearly indicated on the system’s HMI components. Manual control The operator can always isolate the DPT 3500 system from the steering and propulsion devices by removing the command and switching to Manual Control. Shut down Prior to shut down of the DPT 3500 Server or the DPT 3500 PLC, the system has to be isolated from the steering and propulsion devices by reverting to manual control. The modules running on PC’s (Conning 3500 and DPT 3500 Server) can be stopped by rightclicking in the Application Manager bar at right or left of the screen, and choosing the Exit option in the menu that appears. This will stop all applications running on the specific PC. See for more information the Application Manager User Manual [Ref. 2]. Now the standard Windows 2000 procedure can be followed to safely shut down the PC.
1.4
Version information Version information of the different software components can be found in the respective About boxes. The SmcView information can be requested from any Conning 3500 client, the DPT 3500 server information can only be viewed at the server station. The About boxes also contain the MED Wheelmark information.
1.5
Document set up Chapter 1 contains an introduction. Chapter 2 gives an overview of the system architecture. Chapter 3 describes the different control modes of the system Chapter 4 gives a short description of the system’s functionality. Chapter 5 contains information about advanced control options and settings
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2.
System overview
2.1
System Architecture Any DPT 3500 system forms part of the steering and propulsion control architecture of a ship. Such architecture generally differs from ship to ship. It depends for instance on the number of control positions, the available actuators, and the manual control components. Figure 1 shows the hardware architecture of the Blue Giant vessel. The core of the system consists of type approved PC’s that operate as servers on the LAN. All signal processing and control algorithms run on these PC’s. They will each be able to drive the Conning screens and are connected to one or more PLC’s. The certified industrial DPT 3500 PLC’s serve as I/O devices and provide the interface to the OEM products of the available propulsion devices. The DPT 3500 PC has direct interfaces to: • • • • • • •
The Positioning system (absolute and relative) providing latitude, longitude, ground speed and course. The Gyro, (heading). The motion reference unit (MRU), (roll and pitch). The Anemometer, (relative wind speed and direction). The speed log The sound system (loudspeakers in the IBC), for alarm and auxiliary sounds. PLC connection with platform
The actually interfaces present depend on the ship-specific configuration.
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Ship Sensors 16x NMEA Joystick Controller
UPS JS MSB 1A/1B
DP Operator 2 Station FWD
DP Operator 1 Station AFT
Joystick Station AFT
UPS JS MSB 1A/1B
Ship Sensors 16x NMEA DPT Controller 1
Ship Sensors 16x NMEA DPT Controller 2
UPS PS MSB 1A
UPS SB MSB 1B
UPS SB MSB 1B
UPS PS MSB 1A
Redundant Ring Network UPS PS MSB 1A
UPS PS MSB 1A
UPS PS MSB 1A
TIU 1
TIU 2
TIU 3
Rudder & Propeller Port 4500kW MSB1A
Bow Thruster 1 Berg 1000kW MSB2
UPS JS MSB 1A/1B
UPS SB MSB 1B
UPS SB MSB 1B
TIU 5
TIU 4
TIU 7
Bow Thruster 3 Brunvoll 760kW MSB1A/1B
Stern Thruster 2 Kamewa 600kW MSB3
Bow Thruster 2 Brunvoll new 1000kW MSB3
UPS SB MSB 1B
TIU 6
Thruster Interface Units (TIU) Stern Thruster 1 Kamewa 600kW MSB2
Rudder & Propeller Starboard 4500kW MSB1B
Figure 1 System hardware architecture
2.2
Functionality overview Autopilot The DPT 3500 system contains an autopilot enabling the automatic heading control of a vessel. Setpoints for heading are defined by the operator and processed by the system to provide control signals to the vessel’s steering systems. For this purpose, the system uses data from one or more gyrocompasses, magnetic compasses, and the speed sensors. It automatically calculates the optimal counter rudder/thrusters force and adjusts the control properties to changing environmental conditions. The speed data is used to tune the heading control for different speed ranges. Trackpilot The DPT 3500 system contains a trackpilot enabling the automatic control of a vessel along a pre-planned track or an imaginary line over the ground. Setpoints for course are defined by the operator and processed by the system to provide control signals to the vessel’s steering systems. For this purpose, the system uses data from one or more position sensors, gyrocompasses and speed sensors. It automatically calculates the optimal heading setpoint given the distance and speed to the intended track segment. Subsequently, the internal heading control function is used to calculate the optimal rudder/thruster motions and to adjust the control properties to changing environmental conditions.
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Speedpilot The DPT 3500 system contains a speedpilot enabling the automatic control of the ship’s speed through the water (STW) or relative to the ground (SOG). A speed set point is defined by the operator and processed by the system to provide control signals to the vessel’s propulsion control systems. To do do, the system uses data from one or more ship speed sensors. It automatically calculates the lever setting corresponding to the requested speed and slowly adjusts that output depending on the difference between the requested and the actual ship speed. DP system The DPT 3500 system contains a Dynamic Positioning system enabling station keeping or change of position and heading when the ship's speed is near zero. Any combination of the ship’s surge motion, sway motion and heading can be controlled either automatically or by a single joystick. Set points for position and heading are defined by the operator and processed by the system to provide control signals to the vessel’s available actuators. To do so, the system uses data from one or more position sensors, gyrocompasses and speed sensors. It uses the DP allocation algorithm to generate the optimal rpm, azimuth and propeller pitch setpoints for the available actuators. Assist modes The DPT 3500 system contains an Assist mode for each automatic control system, e.g. Speed, Heading, Track and Route. When not in actual Auto control mode, the Assist options offer the monitoring and alarm functionality of that Auto control mode. Each assist mode can be activated independently, other assist options or auto control modes being on or off has no effect.
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3.
Control Modes
3.1
Transit modes The Transit modes apply when sailing (large) distances. They relate to the functions that are commonly present on board a ship as independent devices such as Autopilot or Trackpilot. In most configurations, the following heading/track control modes are available: NFU/Emergency Steering In NFU/Emergency Steering mode, the operator must use a device that gives direct access to the steering gear valves, in most cases an on/off tiller or push buttons. In this (heading) control mode the DPT 3500 system indicates (auto) heading control mode ‘Off’. The system updates internal settings with the actual conditions in order to be instantaneously ready when an automatic control mode is selected. Manual Direct In Manual Direct mode, the operator generates a heading actuator setpoint, in most cases through a tiller, steering wheel or joystick. From the system’s point of view, this mode is identical to the NFU / Emergency steering mode. The relevant internal settings are updated with the actual conditions and the (auto) heading control indication is ‘Off’. The same applies for any other device used to control the heading and/or track of the ship (bow thrusters, stern thrusters, etc.) N.B. Be careful: if levers not following in autopilot mode, check lever settings before selecting Manual Direct or NFU/Emergency Steering. Manual From the operator’s viewpoint, ‘Manual’ mode is identical to ‘Manual Direct’ mode. However, in ‘Manual’ the heading actuator setpoint is an input of the DPT 3500 system. The DPT system passes this setpoint, generated by the operator (tiller, steering wheel or joystick) to the heading control system and the heading control indication will be ‘Manual’. In case of problems, the DPT system freezes the output. In addition, it generates an alarm, indicating that the operator has to try either ‘Manual Direct’ or ‘Emergency Steering’. The advantage of this mode over ‘Manual Direct’ is that some of the alarm and monitoring functions are activated. Auto Heading In Auto Heading mode, the DPT 3500 system acts as an advanced alternative for the commonly used autopilot. For this mode at least one actuator must be available that has sufficient influence on the ship’s heading. In Auto Heading the operator must specify a heading setpoint. Next, the system tries to achieve this heading.
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Auto Course In Auto course mode, the DPT 3500 system acts as a course pilot. The mode needs at least one actuator that has sufficient influence on the ship’s course. In Auto Course mode, the operator must specify a course setpoint. The system then defines a line over the ground with the requested course, starting at the defined pivot point (usually mid-ship), and tries to follow this line, calculating the required heading setpoint(s). Auto Route In Auto Route mode, the DPT 3500 system acts as an advanced alternative for the commonly used trackpilot. The mode needs at least one actuator that has sufficient influence on the ship’s course. The mode implies that the operator plans a route to be sailed on some planning device (usually an ECDIS, route planning is not included in the DPT 3500 system), and activates this route. The DPT system then checks whether the route can be followed. If no conflicting conditions or requirements are found, the planned route is accepted. The pilot calculates the heading setpoints required to follow this route, and each time a planned course change is encountered, it informs the operator. If the operator does not answer in time, the system generates an alarm. DT Slow For some kinds of special offshore vessel operations, high accuracy track keeping is required. DT Slow mode, also called Drift mode, offers this precision. A special set of control algorithms and settings is activated that has especially been designed for low speed (<4kn) track sailing. This set makes it possible to independently control the ship’s heading and the ship’s course. If required, the operator can sail at low speed, with high accuracy, along a planned track while keeping a constant drift angle with respect to this track. To do so, both a course setpoint and a drift setpoint must be specified. The course setpoint defines the line over the ground to be followed, while the drift setpoint defines the angle that is to be maintained between the ship’s course and heading. This mode can also be used in combination with Auto Route control to sail along a planned route. See also section 4.6. Low Auto (Conning option) With Low Auto mode on, the same control algorithms and settings as designed for low speed track sailing (DT Slow) are activated, the most important feature being that the tunnel thrusters can be used by the pilot system. Low Auto mode, however, is also available when the ship is not sailing along a track, but is simply in Heading Auto control mode. See also section 4.6. 3.2
Position control modes In Position control mode, the DPT 3500 system acts as a Dynamic Positioning system. Any combination of surge motion, sway motion and heading can be controlled automatically, while the control of the remaining components is assigned to a single joystick. Position mode requires that at least one of the ship’s motions that can be controlled automatically in Position mode, can be controlled either automatically or with a joystick.
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Joystick mode In Joystick mode, the system translates the rotation and position of the joystick into an equivalent rotation and translation thrust. Next, it uses the DP allocation algorithm to generate the necessary rpm, azimuth and propeller pitch setpoints for the available actuators in order to realise the requested thrust. Mixed mode In Mixed mode, the operator uses the joystick to position the ship with respect to one motion, while the DP system automatically positions the ship with respect to another motion. For example, during docking operations the operator can control the ship’s sway motion, while the DP system controls the ship’s surge and yaw. This allows the operator to focus on controlling the critical motion component, while the system automatically takes care of the rest. DP-Auto (Automatic mode) DP auto mode implies that the operator requests a position and heading setpoint by activating automatic station keeping. Subsequently, the system will automatically correct for wind, current, position, speed, heading, roll, pitch, draft (manual setting) and rate of turn. The DP allocation algorithm is used to generate the necessary rpm, azimuth and propeller pitch setpoints for the available actuators. In case essential navigation sensors fail, and the dead reckoning period has elapsed, automatic control will revert to manual joystick positioning for surge, sway and heading. Other specialist control modes (optional) Standard included in the DPT 3500 system is the possibility to select a “pivot point” anywhere on or near the vessel, as reference point for DP operations. The DP reference point (pivot point) can either be a fixed position (midships, forward along centreline, or aft along centreline), or a free position, anywhere close to the vessel. As far as the DPT 3500 control system is concerned, the following offshore operations (modes) all have a common characteristic: they all require that control is not based on a fixed reference point on the vessel itself (for instance midships), but is based on a moving reference point outside the ship, like a dredger draghead, underwater ROV or pipe position. Since DPT 3500 was developed in close co-operation with renowned dredging specialist IHC, DPT 3500 excels during these types of operations: - Ploughing - Trenching - Dredging - Follow Sub/Target - Cable laying - Pipe laying 3.3
Heading control modes Apart from Heading Manual (heading input to the actuators from the levers and/or steering wheel) and Heading Auto (heading input to the actuators as user-defined setpoint, see section 3.1), the DPT 3500 system recognises two additional heading control modes: Heading Optimal and Heading Drift, both special modes of automatic heading control.
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3.3.1
Optimal Heading mode
During station keeping operations or low speed track sailing, the heading accuracy is often not of the utmost importance. In such situations, the optimal heading mode can be used to minimise power consumption. With optimal heading mode activated, the DPT 3500 system finds the heading that requires the least effort to maintain within the allowed heading range specified by the operator. This considerably reduces fuel consumption. See also section 3.3.1. Optimal Heading in Track Control During ‘Optimal Heading’ control, the system calculates the global optimum heading that will minimise energy consumption. Only in DT Slow/Low Auto mode can the operator specify a range sector for the required heading. If the optimal heading calculated by the DPT system does not lie within this range sector, the DPT 3500 system will have to generate additional sway force to maintain the track. This situation requires lateral thrust activation. Optimal Heading in Position Control In Position Control, the operator can choose heading control from: ‘Joystick’, ‘Auto’ or ‘Optimal’. If ‘Optimal’ has been selected, the system calculates the heading that will minimise energy consumption. The global optimum heading is limited to a user adjustable sector. For safety reasons, the initial sector value is reset to ± 5° around the present heading when ‘Position’ mode is NOT active. This way, the initial heading change will not be very large when the operator activates the ‘Optimal heading’ function during position control. During DP, the sector can be used to keep the heading within a desired range when it is controlled by the system. This may be required in a narrow channel or during special manoeuvres (e.g. when the vessel is connected to a buoy). Beware The advised heading strongly depends on the estimated current. When this estimation is not correct (caused by sensor deviations or Kalman model behaviour that is not perfect) the optimal heading may keep on varying over a wide range. 3.3.2
Drift Heading Mode
Drift Heading is the Heading mode in DT Slow mode, when the ship sails at low speed, with high accuracy, along a planned track while keeping a constant drift angle with respect to this track. In Drift Heading mode, an option to specify the angle between the ship’s heading and course becomes available. Moreover, the rotation knob on the hardware panel now controls the Drift angle setting.
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3.4
Speed control modes The DPT 3500 system recognises the following speed control modes: Manual Direct In Manual Direct mode, the operator defines a propulsion setpoint, usually through a lever or joystick. The DPT system updates the relevant internal settings with the actual conditions, and the speed control indication is ‘Off’. Manual From the operator’s viewpoint, ‘Manual’ mode is identical to ‘Manual Direct’ mode. However, in this case the lever or joystick is an input of the DPT system. It passes this setpoint, specified by the operator, to the propulsion control system and the speed control indication is ‘Manual’. In case of problems, the DPT system freezes the output. In addition, it generates an alarm, indicating that the operator has to switch to ‘Manual Direct’. The advantage of this mode over ‘Manual Direct’ is that some of the alarm and monitoring functions are activated. Auto STW Auto STW mode requires the availability of at least one actuator that has sufficient influence on the ship’s speed. The operator defines a setpoint for speed relative to the water, and the system tries to achieve this speed. In Auto STW mode, wind and current do not influence the thrust required to keep the ship at setpoint speed. Auto SOG Auto SOG mode requires the availability of at least one actuator that has sufficient influence on the ship’s speed. The operator defines a setpoint for speed over ground, and the system tries to achieve this speed. In Auto SOG mode, wind and current do influence the thrust required to keep the ship at setpoint speed.
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4.
Functional Description This chapter describes the functionality of the heart of the system: the control kernel referred to as SMC Server, the system on which it runs DPT 3500 Server.
4.1
Sensor Management
4.1.1
General Principles
The DPT 3500 Server interfaces with several kinds of navigational/environmental sensors and reference systems, such as GPS, Gyro, wind sensor etc., and platform I/O. When multiple devices providing the same input data are available, the DPT 3500 system has facilities for input selection and automatic switchover in case of sensor failure for each data type where multiple sources are available. The data from the preferred sensor selected by the operator is used by the control algorithms and distributed to other systems (e.g. Radar or ECDIS in case of an integrated system). In case of problems with sensors, the operator should be aware of the following: • When the currently selected sensor fails, and automatic switchover is available, the next sensor is automatically selected, unless the operator has disabled automatic switchover. When 3 or more sensors providing the same data are available the switchover is always to the next available (enabled) sensor with the highest preference. This preference is part of the factory settings. • For position reference systems always the next available PRS with the highest quality is selected. • A sensor that has failed is no longer available for automatic switch-over in case the next active sensor fails. The operator must set the failed sensor to Ready (provided the problem has been solved) to make it selectable for automatic change-over again. 4.1.2
Position Reference Systems
4.1.2.1 Position reference averaging When multiple position reference systems are interfaced to the DPT 3500 system, the system offers the operator the possibility to use a weighted average of the data from the position reference system as a ‘virtual’ reference value, instead of data from a single PRS. This makes the performance of the DPT 3500 system more robust with respect to noise and other disturbances from individual reference systems. All enabled reference systems providing valid data are used to calculate the average. When enabled, the average is always the position reference with the highest preference.
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The data from the individual Position Reference Systems are weighed in the average with a weight factor proportional to their estimated accuracy (higher accuracy _ higher weight). The estimated accuracy is based on a combination of predefined factory settings (e.g. characteristics of the PRS measuring principle) and actual accuracy information, if provided by the reference system (such as the operational mode and HDOP for DGPS). For relative PRSs capable of providing data from multiple targets/beacons/transponders, the weight is increased with the square root of the number of targets (e.g the weight of a Fanbeam system providing data from 2 targets is increased by a factor 1.41). When a PRS is sending data to the DPCS (Dynamic Position Control System) that is of insufficient quality to be used, its data is not automatically rejected from the average calculation. Instead, the weight is reduced rapidly to a very small (but non-zero) value. The only way a PRS can be removed from the average calculation is by the operator disabling the sensor. 4.1.2.2 Enabling Relative position reference systems To facilitate working with Position Reference Systems that provide a relative position reference (e.g. USBL, Tautwire, laser measurements) instead of, or in combination with, an absolute position reference (e.g. DGPS), the following procedure is advised: 1) Activate the relative position reference system: switch the relevant relative position hardware On 2) Make sure that the relative position reference system is working at maximum accuracy (e.g. calibrate USBL system). 3) Upon receiving initial data from the relative position reference system, the data is converted by the DPT 3500 into absolute (WGS84) position reference data, by using the data from absolute position reference system(s). This converted data is shown in the sensor overview. At least 1 (D)GPS must be enabled to provide an absolute reference. 4) When the relative position reference system is working correctly, enable the system: toggle the Enable button in the General mimic, Sensor tab of the Conning On. Now the relative position system can be used as an individual position reference system. Moreover, it can contribute to the calculation of the average position value. 5) Wait a few minutes until the average is settled, then proceed with DP operations. N.B. The distance to the targets used by the relative position reference system must not be more than 1000m. 4.2
Automatic Heading control In “AUTO” heading mode the DPT 3500 Server acts as autopilot, using the available steering systems to control the heading. In principle, heading control can be selected at one of the system’s HMI devices. Upon changing from manual to “AUTO” heading mode, the system takes the actual heading as initial heading setpoint, when automatic setpoint line up has been enabled. File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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The minimum forward speed for adequate heading control depends on the ship’s configuration. Without lateral thrusters, a forward speed above 4 knots is recommended. Below 4 knots the performance will degrade rapidly due to the properties of the ship and its actuators. An absolute minimum requirement is a forward speed of 2 knots relative to the water. With bow, stern or azimuth thrusters, it is possible to maintain heading at low speed, and even at reverse speed. The adaptive control algorithms automatically adjust themselves to the manoeuvring properties of the ship, the speed of the ship and to the wave conditions. This allows the system to use minimum actuator motions to maintain the heading or to execute a manoeuvre. Immediately upon changing the heading setpoint, the system starts the appropriate control action: • A small difference (less than 10º) between setpoint and actual heading results in low control activity. • A large difference results in substantial rudder angles/bow thrusters(s) activity. The ship will turn rapidly unless restrained by the maximum rate of turn (set by the operator). Adaptation to changing manoeuvring properties will only be active during significant heading changes (more than 10º) and a significant speed (more than 5 kn.). In order to activate this mechanism, it is strongly recommended to execute heading changes during automatic heading control. Three or more large heading changes after a docking period (power-up) are in general sufficient to adapt the initial controller gains to fairly good estimates. Filter and controller accuracy settings enable the operator to influence the trade-off between heading control accuracy and actuator fluctuations (see section 5.3). If the control system can no longer control the heading due to problems, it alerts the operator and freezes the output. Thus, when on heading the heading will be maintained (approximately) and during a turn the turning motion will be maintained (approximately), until the operator has resumed command of the steering devices. 4.3
Automatic Course control Auto Course mode is a track control mode in between Auto Heading (i.e. system acting as autopilot) and Auto Route (i.e. system acting as track pilot). Auto Course is normally used as an alternative for Auto Heading. Main advantage is the automatic compensation for the drift induced by current or wind. In principle, Auto Course can be selected at one of the system’s HMI devices. The operator has to be aware of the following: • In Auto Course mode, the operator defines a line over the ground to be followed by the ship. Each time the operator changes the course, a substantial overshoot will occur. The system will bring the ship back to the adjusted line. For other ships in the vicinity, this is not a clear manoeuvre. Therefore, large course changes should be avoided in dense traffic conditions.
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• • •
In that case the operator should revert back to Auto Heading mode, and resume Auto Course once the ship is on heading. With a high lateral current and a low ship speed, the difference between heading and course may be substantial. A sudden lateral current, for instance when crossing the mouth of a river, may cause a sudden change of the heading. This may be confusing for other ships in the vicinity. In case of an obstruction occurring along the path, the operator can simply shift the track any distance to port side or starboard side at the Conning 3500 display (the main HMI device). It is not necessary to revert to manual heading control.
In case of problems, the system will revert to Auto Heading, and the course will be maintained (approximately). When this happens during a course change, the new course setpoint will be used as new heading setpoint and the turn will be completed. 4.3.1 Degraded Track Performance Under the following conditions, the DPT 3500 system will remain in track control but with degraded performance: • • • • • • 4.4
In shallow water. The water flow under the vessel can change rapidly. Thrusters will be less effective. The DGPS fix quality degrades from DGPS to GPS. The position information fails. The DPT 3500 system uses dead reckoning to estimate the ship’s position. The ship’s speed does not match the requirements of the selected track control mode. Poor weather conditions Speed reduction Automatic Route control
Auto Route is the control mode for sailing a planned track. The system is acting as trackpilot as in Auto Course mode, the difference being that the track followed is a planned track possibly consisting of multiple segments, instead of a single straight line or circle. The only way these multiple segments can be created and passed on to the trackpilot is through an ECDIS application. Only if the system has received a valid planned route from a route planning application, route control can be started. Planned Track Data on the Conning When a route file is activated on the ECDIS station, the related track information is automatically sent to the DPT 3500 system. If the route is accepted by the DPT system, it is displayed on the Grid mimic of all available Conning 3500 displays. The route’s waypoints list appears on the Route mimic When a route is not accepted by the DPT 3500 system, it does not appear in the Grid mimic, and a ‘Received Route’ alarm is generated. The waypoint list, however, can be inspected on the Route mimic, where information is provided as to why the route was not accepted. A possible File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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reason may for instance be that the route requires a rate of turn that exceeds the current limit settings of the ship. When a planned route is being sailed, new routes can be received, but not be activated. An ‘Unexpected Route received’ alarm is generated. See also ref [1]. The system will continue to sail along the active route, though the received route can be viewed on the Route mimic. Starting route control In principle, route control can be selected at any of the HMI components. However, a number of conditions must be met before the system accepts an initial target waypoint as a valid waypoint from which to start sailing the route: • The ship’s position must lie in an area defined by a cross-track distance of one nautical mile. • The ship must be able to reach the target waypoint with a drift angle less than 45º. • The ship may not be further than 500m away in front of the track. • The angle between the track segment and the ship course must be less than 90º. • The manoeuvring properties of the ship must be able to let the ship sail the circle segments at wheel-over points. (See also Figure 2.) On the main HMI device (see ref. [1]), an InRange indicator lights up as soon as the received route meets the requirements. Accept route When a new route is received from a planning device, the operator has to accept it before it can be activated. If no other route is active, the received route automatically becomes the active route. If a new route is received while the ship is already in Auto Route mode, the new route is not automatically activated. The system warns the operator that it has received a route, and the operator has to accept it as the new (future) route. The next time ‘Auto Route’ is selected (after having been switched off), this new route will be used. Clear route Independent from the planning device, the operator may decide to clear a received route. In that case, the planning device has to send a new route before the operator can select Auto Route. Reverse route The operator can decide to sail a route in reverse direction. Thus, one and the same planned route can be used to sail back and forth between two places. The operator has to be aware that a route that can be executed in one direction cannot automatically be executed in the reverse direction as well. The ship’s course and heading have to match the track control requirements first. Auto approach The DPT 3500 system is rather lenient with respect to the maximum allowed distance between the ship and the planned track and with respect to the angle between ship course and track course. Nevertheless, as mentioned above, there are several constraints that have to be met for an initial target waypoint to become a valid starting point: • The ship’s position must lie in an area defined by a cross-track distance of one nautical mile. File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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• • •
The ship must be able to reach the initial target waypoint with a drift angle less than 45º. The ship may not be further than 500m away in front of the track. The angle between track segment (in the sailing direction) and ship course must be less than 90º. In Figure 2 the area defined by these criteria is shown in white. If Auto Route mode is activated while the function Auto Approach is on, the system calculates itself how it is going to approach the currently active route, i.e. from which waypoint it is going to start sailing the route. It selects the nearest track segment if: It has a valid initial target waypoint. The angle of attack to the track segment is smaller than 60º. If Auto Approach is not activated, the operator has to specify the initial waypoint and sail the ship the ship to a position where it is In Range.
planned track target waypoint wheel-over points
45º
allowed position 1 NM
<90º
ship
Initial waypoint 500m
Figure 2 Valid Initial Target Waypoint Criteria
Wheelover points In Auto Route mode, the conning shows the distance and estimated time to the next wheelover point as a DTW and TTW value, respectively. Once TTW reaches 5 minutes, an acknowledge button (Early Course Change: ECC) starts flashing, warning the operator that he is approaching a wheelover point. The operator must press the button to acknowledge the warning, and the File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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button remains lighted until the wheelover point has been reached. If the operator does not acknowledge the warning, the ‘Course change accept’ alarm is generated when the TTW drops below 30s. When TTW reaches 1 minute, the operator is again required to acknowledge a warning. If not done before the wheelover point is reached, an alarm is generated. However, the planned manoeuvre will be executed anyway. When the ship is sailing along the last segment of a planned track, the TTW and DTW indications change to TTER (Time To End of Route) and DTER (Distance To End of Route), respectively. When the TTER drops below 5 minutes, an ‘End of route’ alarm is generated. Route Interrupts The intentions of a navigator must be clear to other traffic. Other ships interpret these intentions based on their observations of speed, heading and rate of turn. For this reason it is recommended not to stay in Auto Track or Auto Route control mode when a collision avoidance manoeuvre is required. The operator should take control in Auto Heading mode or Manual mode, and make his intentions clear by turning to a safe heading. Once the area is clear, the operator has to bring the vessel close to the planned route again, where a manual or automatic approach can be used as described earlier in this chapter. When the avoidance manoeuvre was required close before or during a wheel-over, it is recommended to complete the whole wheel-over manually before an attempt is made to return to the planned route. Off-Route Alarms A planned route may contain guard limits. These limits are defined on the planning station and usually indicate a boundary that should for some reason not be crossed. When the route guard limits are set to zero on the ECDIS planning station, they are not monitored by the DPT system. The DPT system itself also has off-track limit settings, which can be defined by the user. In Auto Route mode, the guard limits and the off-track limits are monitored independently.
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4.4.1
Shifting the Route
In some cases, the operator may want to sail not on a planned route, but at a certain distance away from it. A typical example is a route planned through a channel. In one direction, the operator is obliged to use the left lane, in the opposite direction he is obliged to use the right lane. Another example is when dredging trenches: the operator may want to dredge over a track that is only a few meters removed from the last track.
original track
2
1 shifted track
3
0
Figure 3 Shift a planned track to Stbd With the DPT 3500 system, the operator can shift the original track that was planned on the ECDIS planning station. This involves moving all individual track segments to a parallel position at identical distances. The new waypoint co-ordinates and the total direction and size of the shift can be inspected on the Route conning mimic. The wheel-over distances are not adjusted. The new route data is shown on the conning. The DPT system will steer the ship to the new track after one of the track keeping modes, Auto track or Auto Route, has been activated and control is transferred to the ECDIS route. Exit Automatic route control The operator can stop route control by selecting one of the other control modes: • •
When ‘Auto Heading’ is selected, the initial heading setpoint is indicated at each of the HMI components. When ‘Auto Course’ is selected, the ship will continue along the current leg of the track.
If the conditions for track/route control are no longer met, the system will warn the operator. In case of problems, the system will revert to ‘Auto Heading’. Thus, the course will be maintained (approximately). However, when that happens during a course change, the course setpoint of the next leg of the track/route will be used as the new heading setpoint and the turn will be completed.
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Degraded Track Performance The DPT 3500 system will remain in track control but with degraded performance under the following conditions: • • • • • • 4.5
In shallow water. The water flow under the vessel can change rapidly. Thrusters will be less effective. The DGPS fix quality degrades from DGPS to GPS. The position information fails. The DPT 3500 system will use dead reckoning to estimate the ship’s position. The ship speed does not match the requirements of the selected track control mode. Poor weather conditions Speed reduction Automatic Speed Control
The DPT 3500 system provides automatic speed control in transit operations by sending pseudo lever commands to the propulsion control systems. These systems regard the commands as if coming from a standard lever and will control setpoints of propulsion system (i.e. CPP pitch and shaft rpm of the main propellers) accordingly. In order to realise a smooth switchover with minimum initial change to propulsion settings, the speed setpoint is lined up with actual vessel speed before the speedpilot is turned on. When Auto Speed mode is selected, actual vessel speed becomes the initial speed setpoint. The speed setpoint values can range from zero to a maximum value that depends on the ship’s maximum speed. Off Speed alarm When the speedpilot has steadily maintained a speed near the speed setpoint, the ‘Off speed alarm threshold EXCEEDED’ algorithm will become active, i,e the Off Speed alarm becomes armed. This alarm is inactive as long as the speed pilot is still busy bringing the ship to setpoint speed. The Off Speed alarm is raised only when a substantial speed deviation occurs. When the ship is steady on course, a speed deviation of 1 knot is used as threshold for an ‘Off speed’ alarm. If the ship’s configuration includes an Off Speed Limit control setting, the user can define the off speed alarm threshold himself. One shaft in Auto, one shaft in Manual The speed pilot can operate with control of one propulsion actuator while others are in manual mode, i.e. not ready or disabled for DPT. The speedpilot compensates for thrust generated by the manually controlled actuator. Slow down behaviour The slow down behaviour depends on the ship’s configuration and its forward speed. Normally, no reverse thrust is allowed for deceleration. A minimum forward thrust is maintained to avoid losing all steering capabilities. Only with special configurations, for instance DP or DT control File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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modes, will reverse thrust be used to decelerate the ship. Consequently, track keeping accuracy may suffer. At slow speed all thrusters are used to control speed. More extreme solutions may be applied by the system if the accuracy setting HIGH is selected (ref section 5.3). 4.6
Low Speed Control Low Auto In Low Auto (conning option) mode the same control algorithms and settings as designed for low speed track sailing (DT Slow) are activated, meaning that the tunnel thrusters can be used by the pilot system. • Low Auto in Heading Auto control mode is identical to the (hardware) panel option Medium Pilot. If Low Auto is selected in Heading Auto mode the DP/DT panel automatically reverts to Medium Pilot mode, and vice versa. The operator has control over the tunnel thrusters, for instance to very accurately perform a heading change at low speed. Speed is not limited, but at increasing speed, the tunnel thrusters become less effective, and are then not used by the pilot system anymore. If Low Auto is switched off, the DP/DT panel automatically reverts to Sail Pilot mode, and vice versa. • Low Auto in Track Auto control mode is identical to the (hardware) panel option DT Slow. When Low Auto is selected in Track Auto mode, the DP/DT panel automatically switches to DT Slow mode. See below. • In Low Auto ànd Track Auto mode, the operator can also select an intermediate mode in the DP/DT panel: DT Medium mode. In this mode speed is not limited, although at increasing speed the tunnel thrusters become less effective. Heading mode automatically turns to Optimal, but the operator cannot specify a range sector for the optimal heading. See also section 3.3.1. • If, in Track Auto mode, Low Auto is switched off, the DP/DT panel automatically reverts to DT Sail mode, and vice versa. DT Slow (ship in Track Auto control) The Low Speed Track control mode DT Slow comprises a special set of control algorithms and settings, especially designed for low speed track sailing. The most important feature of this mode is that the ships heading and course are controlled independently. Contrary to the other modes, DT Slow mode has no built-in thruster limitations. It is also the only control mode where reverse thrust from the main propulsion actuators is used to decelerate to a lower speed. The effectiveness of this mode depends on the effectiveness of the tunnel thrusters. The theoretical limit for forward speed in DT Slow mode is 4kn, but if the tunnel thruster performance degrades quickly with increasing forward speed, the practical limit may be as low as 2kn. In DT Slow mode operator speed input is limited to 5 kn. Heading options in DT Slow mode Once the DT Slow settings have been activated, it is possible to switch between Auto Heading, Optimal Heading and Drift angle, while maintaining the DT Slow control settings. • When activated, DT Slow will automatically switch heading control to Drift angle mode. This mode makes it possible to specify the ship’s heading at an angle to the ship’s course (the drift angle). The operator has to specify both a course setpoint and a drift setpoint. The File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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•
•
4.7
course setpoint defines the line over the ground that is to be followed, while the drift setpoint defines the angle that is to be maintained between the ship’s course and heading. With Heading Optimal, the operator can specify a range sector for the optimal heading. See also section 3.3.1. The Optimal heading parameters will be permanently displayed, regardless of the selected Heading mode (see section Error! Reference source not found. for information on optimal heading). With Auto Heading control activated, the system will keep the ship’s heading fixed, regardless of the course setpoint. Position Control
If the operational mode is Position mode, control of the ship’s position is shared between the DPT 3500 system and a user-operated joystick. Any combination of the ship’s surge motion, sway motion and heading can be controlled automatically by the DPT system while control of the remaining components is assigned to the single joystick. Joystick control With Joystick control surge, sway and heading, i.e. all individual actuators, can (individually) be controlled with a single joystick. The system translates the rotation of the joystick and the position of the joystick into an equivalent rotation and translation thrust. Next, it uses the DP allocation algorithm to generate the necessary rpm, azimuth and propeller pitch setpoints for the available actuators in order to realise the requested thrust. It is not possible to realise 100% thrust simultaneously in all directions. Nor is it advisable to request a thrust in more than one direction at any given time. In that case, the response of the ship will be difficult to predict. If the operator wants to apply thrust in more than one direction, the ship’s behaviour will be better predictable if one of the motions is controlled by joystick, while the others are maintained by the DP system, i.e. set to DP Auto mode (mixed control). In case both a lateral and a forward or reverse thrust are requested, the angle of the joystick will indicate the approximate direction of the ship through the water. Be aware that the actual ship motion is also influenced by wind, current, water under the keel, vessel load, anchors, tugs, etc. This may cause a deviation of the direction. Joystick control during operational mode ‘Position’ is a strict manual control method with predictable thruster allocation behaviour. No automatic corrections for wind, current, position, speed, heading, roll, pitch, draught or rate of turn will take place. It will also work when the gyro, the GPS, the MRU or the speed LOG are down. Automatic control In “Auto” mode the ship’s surge, sway and/or heading are controlled automatically. In this mode the system tries to minimize the position difference between a pivot point relative to the ship and the requested position, and between the ship’s heading and the heading setpoint. As initial position setpoint the ship’s position upon selecting automatic position control is taken. File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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One motion at a time (mixed control) In principle, the DPT 3500 panel and the joystick give the operator full freedom to modify the ship speed in the horizontal plane. He may control, even simultaneously, the ship’s yaw, surge and sway. Alternatively, he may let the DPT 3500 system ‘hold’ one or more of these three motions by selecting AUTO mode for that motion. Best procedure Joystick control is a form of open loop control. Although the DPT 3500 system is tuned to let the ship follow the direction of change of the joystick, many factors (external disturbances, ship load, pivot point selection etc.) will cause deviations from the intended end result. Therefore, it is difficult for the operator to assess how the ship will react if he uses the joystick to control more than one motion at the time. On the other hand, ‘AUTO’ is closed loop control and therefore much less sensitive to disturbances. Thus, the operator can be fairly sure about what the ship will do if he uses the joystick to control only one motion and let the DPT 3500 system deal with the others. The preferred way to use the system can be summarised as follows: Let the operator control one and only one of these motions and let the system ‘hold’ the others. The best procedure in using the system is to use the setting ‘Auto’ to maintain position and heading and, if necessary, use the setting ‘Joystick’ for one of the motion directions (most probably Surge or Sway) to keep the ship at (or move the ship back to) its DP point. Thus, to use dynamic positioning in the preferred way, proceed as follows: •
Assess the limitations of the DP operation Prior to starting DP operations, the operator should assess the limitations of the DP operation. How strong are wind and current and is it possible to execute the intended operations? Should a different initial heading be selected to avoid a lateral current larger than the ship can deal with?
•
Start from zero speed For the system, it is difficult to assess which motion is more important, rate of turn, forward speed or lateral speed. Starting a DP operation with a high forward speed will certainly give a large position error before the system is able to recuperate. Good practice is to reduce the forward speed manually to approximately zero prior to starting the operation i.e. before selecting DP Auto. In starting with DP AUTO, the operator lets the system compensate for wind and current. By looking at the behaviour of the actuators in relation to the position accuracy of the ship, the operator may confirm his initial assessment about the limitations of the DP operation.
•
Compensate for wind and current first The first thing the operator has to do upon selecting joystick control for one of the ship motions, is to try to set the joystick in the position that compensates for wind and current. Once that setting is found and the speed of the vessel is close to zero, he may apply force in
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the intended direction by placing the joystick gradually, in small steps, in the appropriate position. Always keep the speed over the ground below 2.5 kn. •
Be cautious and beware of reaching thruster limits After each small change in joystick setting, the operator has to wait for the result and assess the situation. A big change is only allowed to oppose a large ship motion in the wrong direction. If the system requires a high actuator setting to compensate for wind or current, not much room may be left for moving the ship in the intended direction with the joystick. A large joystick deflection may result in reaching the actuator limits. This will have a negative effect on the ship motions controlled by the DPT 3500 system.
Be very cautious in shallow water conditions Actuator allocation has been validated, and if necessary tuned, in open water conditions with hardly any wind or current and plenty of water under the keel. Be aware the, in particular in shallow water conditions, the behaviour of ship, actuators and sensors can differ considerably: • The impact of the current, in particular of a lateral current, will be noticeably higher,. • Ground - hull interaction will change the ship’s response to actuator settings. In DP Auto mode, this will have a negative effect on the control accuracy. In DP Joystick, the ship’s response to joystick settings may be more sluggish and the direction of the joystick may no longer be a proper indication of the direction of the ship speed. • Some sensors such as log and echo sounder become seriously affected by the water turbulence. • Often large changes in water current will occur when entering or leaving a channel. • Nearby structures or other vessels may disturb or block the water flow of the thrusters. • Large buildings may disturb the quality of the DGPS reading.
4.8
Assist Settings The Assist settings activate the full monitoring and alarm functionality normally associated with an Auto mode control setting, without actually activating that Auto control mode. The system functions as an alarm system, as if in Auto mode. Each Assist setting can be activated independent of other Assist settings or control mode. Heading Assist With Heading Assist selected and not in Auto Heading or Auto Track/Route mode, the DPT 3500 system assists the user in keeping heading to a specific setpoint. The system provides the monitoring and alarm functions associated with Auto Heading mode, but control of the actuators is left to the operator. The navigator specifies a heading setpoint and operates the actuators to keep within the off-heading limits. If this fails, the system generates the relevant alarms.
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Track Assist With Track Assist selected and not in Auto Track mode, the DPT 3500 system assists the user in sailing along a line over the ground. The system provides the monitoring and alarm functions associated with Auto Course mode, but control of the actuators is left to the operator. The navigator specifies a course setpoint and operates the actuators to keep within the off-course and off-track limits. If this fails, the system generates the relevant alarms. Route Assist The Route Assist setting can only be activated if the conditions as required for ‘Auto Route’ have been met. Thus, if the ship is not In Range of a valid route, Route Assist cannot be selected. With Route Assist on and not in Auto Route mode, the system provides the monitoring and alarm functions associated with ‘Auto Route’ mode, but control of the actuators is left to the operator. The navigator provides the system with a course setpoint (i.e. the Route waypoints) and operates the actuators to keep within the off-course and off-track limits. If this fails, the system generates the relevant alarms. The Early Course Change warnings and associated alarms are activated as well. Speed Assist With Speed Assist selected and not in Speed Auto mode, the system assists the operator in keeping speed to a specific sped (SOG or STW) setpoint. The system provides all monitoring and alarm functions associated with Auto Speed mode, but control of the actuators is left to the operator. The navigator specifies a speed setpoint and operates the actuators to keep within the off-speed limits. If this fails, the system generates the relevant alarms. DP Assist In DP Assist mode, the DP Guard Limit alarm is armed, warning the operator if the ship’s pivot point moves within the guard limit range around the selected DP point. Once this limit is exceeded, a DP Guard alarm is generated. The alarm is not affected by the active control mode. DP Assist can be selected even if the DPT 3500 system is in Transit mode. 4.9
Alarm handling The DPT 3500 system continuously checks whether the hardware of the system (PLC, PC, software modules), the interfaces, the connected sensors, and the control devices are fully operational and whether the requirements for a specific control mode are met. Different methods are applied such as: • Out of range detection (to detect hardware problems) • Out of limits detection (the limits can in some cases be defined by the operator) • Comparison with expected values as calculated by one of the internally present mathematical models (to assess, and if necessary reject, sensor data or to check a (in)correct actuator response). As soon as the system detects a problem, it will automatically assess the relevance of that problem and determine the proper course of action: • It may wait a (predefined) time to check whether or not the problem persists. • It may reject input or replace it by an available alternative.
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Figure 4 shows the system’s reaction to failures. Component Failure
Condition Failure System
In use?
y
Alternative?
n
n
y
Essential n
y
Operator
Degrades to Lower Level
Immediate Action
Continues, Probably with Degraded Performance
Judge, take action if needed
Uses Alternative No action
Figure 4 Failure response diagram Once the system recognises a persisting problem, it will alarm the operator with a red blinking button at the top of the Conning screen and (optionally) an alarm sound. An alarm message appears in the Alarm list. Each alarm message has to be acknowledged by the operator even if the underlying problem has disappeared. If not acknowledged, the message remains in the alarm list. The DPT 3500 Server distinguishes four kinds of alarms: • System alarms - If an I/O interface is lost, a driver alarm will be generated. For instance the NMEA driver alarm and the PLC driver alarm belong to this group. - If a particular sensor fails (e.g. wire break), that sensor will generate an • Sensor alarms alarm. A sensor alarm is suppressed (i.e. it does not appear in the alarm list) when it is caused by a driver alarm. If a functional alarm is generated, this in most cases means that the • Functional control mode cannot be maintained or that the controller performance alarms degrades. Examples are: • Steering gear follow up alarm; • Vessel heading alarm (no valid heading available); • Steering gear not ready alarm •
Other alarms
- The DPT 3500 Server can be used as an alarm device for other systems.
Every alarm is listed in the following format: • A marker pointing out the selected alarm message • Time indicating when the alarm was generated • Short description of component in alarm File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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•
Status of component in alarm
Alarm sequence When an alarm occurs the following happens: • A sound alert is generated (only at the active control position) • Conning 3500: the Alarm button at the top of the mimic screens turns red and starts blinking, and a red blinking alarm message (+timestamp) appears in alarm list on the Alarms mimic. If the alarm is not accepted but the alarm condition has disappeared, the alarm message in the alarm list turns a dim grey. • Conning 3500: Field for which information is no longer available displays red stars “****”. To accept an alarm (only at the active control position): • Hardware panel: press the ALARM button. • Conning 3500: Switch to the alarm mimic and click in the alarm list. Accepting alarms(s) will stop the alarm sound. The alarm indication stops flashing but remains lit. The alarm message stops blinking. As soon the alarm condition is rectified, the alarm message automatically disappears from the alarm list. When all alarms are removed the Alarm button turns grey again. Degradation If the system decides that the current control mode requirements are no longer met, it will degrade to a lower control mode, for instance from Auto Track to Auto Heading. The operator is warned to take action immediately. A “fatal” sound alert is generated at the active control position to inform the operator when Auto mode can no longer be maintained and that manual control must be assumed. No Degradation Alarm messages are generated in the same way as mentioned above under “Degradation”. However, a different alarm sound is generated and the control mode stays unaffected. Dead reckoning When all position devices or all heading devices fail, dead reckoning starts in order to provide the relevant input (position or heading). The sensor indicator reads “DEAD” as position or heading source and shows estimated data. After the dead reckoning time has elapsed the data is replaced by red stars: “****”. Server – client connection The DPT 3500 Server acts as any server: it builds up and sends the alarm information for display purposes to clients like Conning 3500. If the connection between client and server is lost, all information on the client conning will be displayed as red stars “****” and an alarm will appear in the alarm list (only on the client that has lost communication). This alarm can only be accepted on the client that has lost the communication.
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4.10
Consequence Analysis
The consequence analysis function analyses the vessel’s capability to maintain current heading and position setpoint after the worst-case single equipment failure. It continuously monitors the power and thrust required for station keeping under the prevailing environmental conditions and compares this with the hypothetical remaining power and thrust after a single failure. If the thrust remaining after single failure is not sufficient for station keeping, the “DP2 Consequence” alarm is raised. Other aspects of the DP control system influencing the station keeping ability, such as the number of control servers or sensors available, are not part of the consequence analysis function. The single failures analysed by the consequence analysis are predetermined according to the vessel’s power generation, distribution and thruster configuration. Typically, the worst-case failure is the loss of a switchboard, engine, or group of thrusters The consequence analysis function fulfils the requirements for DP equipment class 2 and 3. Operation The consequence analysis function can only be active when the system is in ‘DP-auto’ mode for all degrees of freedom (surge, sway and yaw) and the vessel is on position and heading setpoint. When the vessel is moving from one position and/or heading setpoint to another, the analysis is temporarily suspended, until the vessel is on position and heading again. The analysis is performed each process cycle of the control system. In order to prevent false alarms, e.g. due to a temporary increase in required thrust resulting from a short wind gust, the alarm is only raised when the analysis result is continuously positive for 10 seconds Consequence Analysis is not automatically activated. The operator must switch the functionality on. As soon as the pre-conditions as mentioned above are met, the analysis is started.
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5.
Control/Settings Details
5.1
Master/Slave configuration In a configuration that contains two DPT 3500 servers, one server will act as Master system and the other as the Slave system. All operator actions and control actions are executed by the Master system. The servers change roles in the following situations: • •
The operator selects the Slave system to become Master. In that case, the other system automatically becomes the Slave. The Master system has a problem that causes a mode degradation (such as from ‘Auto Heading’ to ‘Manual’). In that case, the system checks whether the Slave system has the same problem. If not, the Slave system becomes Master and the Master system becomes a locked Slave system. A locked Slave system requires operator intervention to be unlocked again. This is only possible if the system has no serious fault.
The system generates a warning when the slave system becomes locked. Procedure If the Master server has a problem, its ‘Fault’ button turns red, its Standby Off light turns yellow. If the Slave Server (at that moment) has no (relevant) problem, the servers automatically change role, the former Slave Server becomes Master, the former Master server becomes Slave. When the problem has disappeared, the Fault button of the former-Master-now-Slave server turns grey again, though the Standby Off button remains yellow. The server remains locked. The locked Slave system requires operator intervention to get unlocked: press the Standby Off button. The server is now available for automatic changeover again. (This is only possible if the system has no serious fault.) Lock as Slave In some cases, automatic role change is undesirable, for instance: • if a server was forced to become a slave because it had a problem that the other server did not have • if the operator has a preference for a specific server to be Master (or Slave). To prevent automatic Master-Slave switching, a Slave system can be locked by the operator. Unlocking also required operator intervention. This is only possible if the system has no serious fault.
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5.2
Sensor filtering Sensor Filtering defines the level of filtering that is applied to the fluctuations in the sensor values. ‘Normal’ is the setting that in general results in a good balance between the degree to which sensor fluctuations are taken into account, and the actuator response to these fluctuations. If the setting is ‘Less’, filtering is limited to what is needed to protect the control algorithms against sensor errors. A minimum amount of filtering is applied to the sensor values. In adverse conditions, this may lead to rapid fluctuations in the steering devices. If the setting is ‘More’, filtering suppresses the sensor fluctuations as much as deemed necessary to reduce fluctuations of the steering devices. The high frequency sensor fluctuations are filtered out. This may have some negative consequences on the control accuracy, as the control algorithm will now act on low-frequency disturbances only.
5.3
Accuracy settings Controller accuracy The Controller Accuracy settings define the amount of rudder, or other steering or propulsion device, used to oppose the fluctuations from the setpoints. The Accuracy setting is available for each of the ‘Auto’ control modes: Heading Track, Speed. • The setting ‘NORM’ gives the best compromise between on the one hand fair accuracy and on the other hand reasonable actuator response. The initial Accuracy setting after power-up will be ‘NORM’. • If the Accuracy setting is ‘LOW’ the control sensitivity is low. The steering and propulsion devices are controlled in a gentle and smooth way. Larger deviations from setpoints may be the result. • If the Accuracy setting is ‘HIGH’ the control sensitivity is high. The steering and propulsion devices are controlled intensively, possibly up to the maximum allowable limits. Smaller deviations from the setpoints will be the result. The operator should be aware of the following limitations of these settings: • The achieved control accuracy also depends on the accuracy of the steering devices and the sensor data, as may be indicated by a small but constant heading offset or a small constant track error. The effect will be particularly noticeable in light weather conditions. • Selecting the accuracy setting ‘low’ will not always result in less rudder motion. Depending on the prevailing conditions, the heading fluctuations may increase such that more rudder is required to oppose these fluctuations. • In case of sudden, large constant disturbances (dredging, current), the setting LOW may result in temporary large position, track or heading errors. • The Filter Accuracy setting also influences the effect of the Controller Accuracy setting (see below). • In particular if a ship has a tendency to drift strongly during a turn, the accuracy setting ‘high’ may result in off track fluctuations. In that case, the operator should select a lower accuracy. • In adverse weather conditions, the setting HIGH may result in excessive actuator motions. File: DPT 3500 System user manual 131 BlueGiant Copyright 2008 Imtech Marine & Offshore B.V.
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5.4
Actuator Limits Azimuth thruster limits The azimuth thruster limits (propulsion and angle) enable the operator to define a hard limit for the required thruster setpoints as calculated in Auto pilot mode. The limit settings should be used with care because a narrow limit may interfere with the pilot control requirements, leading to a reduced performance. The system automatically adjusts the actuator motions to the ship’s speed: at higher speeds, less correction is applied to address the same error. Rate of turn limit At a high rate of turn, a ship may heel considerably. The rate of turn (ROT) limit enables the operator to define how fast the ship may turn, and thus what amount of heel is acceptable. The rate of turn limit has other benefits as well: • •
By applying a low rate of turn limit, the operator can impose a well-defined curve to be sailed by the ship. The amount of rudder used by the system will be reduced to match the limited rate of turn.
The operator should be aware that the actual rate of turn might be less than the set rate of turn limit. This happens for instance at relative low ship speeds when the potential rate of turn of the ship is low. In adverse conditions, this may lead to rapid fluctuations in the steering devices 5.5
Heading Heading setpoint Heading setpoint changes are limited to ± 175º. The operator should be aware that this limitation is monitored and executed in the server. Due to a delay between the input device and the server it may seem that a larger change is accepted. However, after that delay it will be noted that the induced change is indeed limited or even ignored. Heading deviation alarm The heading deviation alarm is armed once the ship is ‘on heading’. The operator can set the allowed deviation at one of the available input devices. The range is limited between 5 and 15 deg. Preferably, the selected deviation limit value should match the accuracy setting (i.e. low accuracy = high deviation limit) and the prevailing weather conditions (i.e. low sea-state = low deviation limit). If a new heading setpoint is defined, the heading deviation alarm is automatically suppressed until the ship is ‘on heading’ again.
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5.6
Course/Track Course setpoint Course setpoint changes are limited to ± 175º. The operator should be aware that this limitation is monitored and executed in the server. Due to a delay between the input device and the server it may seem that a larger change is accepted. However, after that delay it will be noted that the induced change is indeed limited. Course deviation alarm The course deviation alarm is armed once the ship is ‘on course’. The operator can set the allowed deviation at one of the available input devices. The range is limited between 5 and 45 deg. Preferably, the selected deviation limit value should match the prevailing weather and current conditions (i.e. low sea-state and low current = low deviation limit). If a new course setpoint is defined, the course deviation alarm is automatically suppressed until the ship is ‘on course’ again, or if a certain time limit (configured to match the manoeuvring properties of the ship) has expired. Route shift The operator can shift a received planned track prior to switching to Auto Route mode. It is not possible to do so while sailing in ‘Auto Route’ mode. Route Shift does not change the received track itself, it only “creates” another the route to be sailed. Thus, it is simple to revert back to the original route. The main HMI input device contains the option to select a shift distance. Each time the shift order is given, the track is shifted over this distance. Line shift The setting ‘Line shift’ is similar to ‘Route shift’, and used in combination with ‘Auto Course’. This setting can only be used if ‘Auto Course’ is activated. Immediately upon giving the line shift command, the ship will move the new track line. Track Pivot Point The DPT 3500 system uses a fixed point, relative to the ship, for use in Auto Track sailing. It aims to move this so-called pivot point over the intended track. The pivot point and the actual setpoint determine the error that has to be dealt with by the control system. For track control only mid ship can be selected (fixed point). The controller accuracy is tuned for a pivot point at mid ship.
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5.7
Dynamic Positioning Position Error presentation The operator can select to present the DP position error relative to the ship’s heading in one of two ways: • As surge and sway error. • As range and bearing. Saved DP Positions Up to four DP locations can be stored as favourite positions. The present DP setpoint can be stored in the Saved DP Points list. Saved DP locations can be edited by changing the position co-ordinates. Line-up DP setpoint By using the surge, sway or heading line-up functions, the system changes the current DP setpoint to a new setpoint with surge, sway or heading error reduced to zero. DP Auto Speed Limit The DP Auto Speed Limit determines the maximum speed allowed to steer the ship towards the DP position setpoint. It depends on the properties of the ship and the actuators and on the environmental conditions whether the maximum speed can be reached. The potential speed in forward direction is much larger than a speed in lateral direction. Thus, it is more difficult to compensate for a lateral current then for a longitudinal current. The DP Auto Speed Limit should preferably not be set higher than the potential lateral speed minus the speed of the actual current. In doing so, the operator will force the DPT 3500 system to a position change behaviour that is approximately the same in all directions. DP Guard Limit The setting ‘DP Guard Limit’ determines a circle around the DP position setpoint representing the maximum allowed position error. The off-position alarm is activated (circle colour goes from grey to red) when the ship is steady on DP. If the alarm is armed, an alarm is generated to inform the operator that the position error has become too large as soon as the ship crosses the guard circle. DP Pivot Point The operator can select a point relative to the ship to be used for DP operations. This so called pivot point and the actual setpoint determine the error that has to be reduced by the control system. During DP Auto, the system tries to minimise the distance between the pivot point and the DP position setpoint. The pivot point is also used as centre of rotation. The operator can choose between a number of fixed pivot points and a free pivot point. For DP control three predefined, standard pivot point locations are available as fixed point:
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• • •
Bow Mid ship Stern
On the ship axis at the bow. On the ship axis at mid ship. On the ship axis at the stern.
For a free pivot point, the operator can select any point within a certain range: ± 40 m from the axis and ± 80 m from mid ship. The origin of the pivot co-ordinates can be set at mid ship or at the APP (the aft of the vessel). For safety reasons, the pivot point that is used during DP mode operations automatically reverts back to mid ship when another control mode is selected. If the pivot point is changed during DP, the DP setpoint is changed accordingly to avoid a position change of the vessel. The controller accuracy (section 5.3) is tuned for a pivot point at mid ship. Selecting another pivot point may have an adverse effect on the controller accuracy. Heading In Position Control (DP), the operator can choose heading control from: ‘Joystick’, ‘Auto’ or ‘Optimal’. If ‘Optimal’ has been selected, the system calculates the heading that will minimise energy consumption. The global optimum heading is limited to a user adjustable sector to keep the heading within a desired range when it is controlled by the system. This may be required in a narrow channel or during special manoeuvres (e.g. when the vessel is connected to a buoy). For safety reasons, the initial sector value is reset to ± 5° around the present heading when ‘Position’ mode is NOT active. This way, the initial heading change will not be very large when the operator activates the ‘Optimal heading’ function during position control. Beware The advised heading strongly depends on the estimated current. When this estimation is not correct (caused by sensor deviations or Kalman model behaviour that is not perfect) the optimal heading may keep on varying over a wide range.
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5.8
Actuator allocation Actuator allocation contains two types of settings: 1. Ready, enable and forced data for each actuator (rudder, propeller, thrusters, etc). 2. Controls to fix the actuator angle. The DPT 3500 system will only use those thrusters that are enabled by the operator. Beware Thruster pitch and rpm limits are valid for all control modes. A small value may have a deteriorating effect on low speed operations and on DP operations.
5.9
Environmental Compensation Manual True Wind In order to improve control accuracy, the DPT 3500 control system automatically compensates for wind disturbances. However, this is not possible if wind sensor input is unreliable. In this is the case, the operator must either accept a degraded controller performance, or he must assist the system. Unreliable data can be caused by malfunctioning of the sensor, by a rapidly fluctuating wind direction, or by interference of the anemometer's readings due to nearby obstructions. To solve such problems, wind speed and wind direction may be entered manually, so enforcing a smoother control action. I present, the option called True Wind, is found in the Conning, General mimic, Manual tab. If True Wind is On, the indication ‘MANUAL’ appears in the Wind display on the conning. Manual True Current In practice, there is an unavoidable steady state error that must be reduced as much as possible by the control system. This error is caused by unknown but more or less constant disturbances. In theory, if the applied ship models are very accurate and the influence of rudders, thrusters, actuators, wind forces and forces of attached equipment (like dredge pipes, mooring lines, winches, towing lines etc.) is exactly known, the only unknown cause of such steady state errors is the water current. This explains the name ‘Current compensation’. The control system is rather sensitive to a proper estimate of these unknown constant disturbances. When the current suddenly changes, it takes time before that change has been estimated, and during that time controller performance suffers. Also, if the behaviour of the internal ship model deviates from the actual ship behaviour (possibly during acceleration/deceleration or dredging), an unjustified estimation of a considerable ‘current’ component may result. To rectify a situation like this, an option True Current may be present, enabling the operator to assist the system in estimating a proper current value and thereby improving performance. If present, True Current is found in the Conning, General mimic, Manual tab. If True Current is On, the indication ‘MANUAL’ appears in the Set and Drift display on the conning.
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The other options available are Manual Draught and Manual Water Speed, which allow the operator to enter a manual value when the relevant sensor fails. Be aware that using manual input for sensor data may have a negative effect on the adaptive character of the autopilot system and that system performance may be impaired. 5.10
Sailing in Adverse Weather Conditions
In adverse weather conditions, the performance of the DPT 3500 system may suffer. For instance, a strong wind can cause a considerable yaw moment that is difficult to oppose, in particular if ship speed is low and/or if lateral thrusters are off line. Moreover, it may induce a considerable lateral force, and large waves induced by heavy wind will cause considerable ship motions. Such weather conditions may have the following consequences: • The ship continuously shows a large heading error, track error, position error or speed error. • The average rudder/azimuth angles are large. • The actuator fluctuations are large and continuously reach their limits. The operator has some means to oppose these negative effects: • By selecting the accuracy ‘Normal’ or even ‘Low’ he informs the system that accuracy is less important. This will reduce the actuator motions. Moreover, if the actuators continuously reach their limits, a High Accuracy setting has not much effect on the accuracy anyway. • By setting one lever more forward than the other (speed control in ‘Lever’), the operator can induce a yaw moment to oppose a wind induced moment. As a consequence, the average rudder angle will be less and the heading or track keeping properties may improve considerably. • Track keeping is easier if heading control is in ‘Optimal’ than in ‘Auto’ or ‘Drift’ mode. Thus, the heading control setting also influences the track control accuracy.
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