AUTOPILOTS:
This is intended to remove the need for the operator to assess the correct control settings. In effect the autopilot ‘learns’ the vessel’s handling characteristics in calm weather and then, when the weather deteriorate, can distinguish between those errors in heading due to the weather and those due to vessel’s normal handling characteristics. It has been found that in heavy weather the vessel’s head deviates very little ‘relative to the water’.T4 the adaptive autopilot concerns itself primarily with those errors in heading resulting from normal handling characteristics, so reducing the work and hence drag of the rudder.
For example in Sperry model auto tuning software is fitted. The software performs dynamic tuning of the autopilot during a modest series of initial maneuvers, then automatically continues to retune the tuning throughout the voyage in response to the ship’s behavior. System also maintains two different tunings, one for light and one for loaded condition.
Limitations of auto pilot: Auto pilot should not be used under following circumstances:
(WASTV MNS)
In rough weather
During large alterations of courses
At slow speeds
In heavy traffic areas
In conditions of reduced visibility
While maneuvering the vessel
In narrow channels and confined waters.
In shallow waters
CONTROL UNIT:
1)PROPORTIONAL CONTROL: Output of the controller is proportional to the offcourse error from the course to steer ( deviation)
Controller ouput = constant (Kp) x Deviation
2) INTEGRAL CONTROL: Output of the controller is proportional to the summation of all instantaneous values of error ( deviation ) for as long as error persists.
Controller output = constant ( Ki ) x error x Time
3) DERIVATIVE CONTROL: Output of the controller is proportional to the rate of change of error ( deviation ).
Controller output = constant ( KD ) x change of error / time
THREE TERM CONTROLLER ACTION: Output signal is proportional to the deviation, persists as long as deviation persists and also depends on rate of change of deviation i.e.
Proportional + Integral + Derivative
CONTROLS:
WEATHER SETTING CONTROL: When steering in heavy weather with wind and sea at an angle to the vessel’s heading, there is a tendency for the vessel’s head to be turned in a particular direction. The effect of this can be offset by maintaining some permanent value of rudder angle; this angle is set using ‘weather helm’ after a period of trial and error.
SYNCHRONISATION CONTROL: Temporairly disconnects gyro repeater from main gyro for sync of heading. Required for sync and when gyro switched off and restarted.
SPEED: Usually from log and manual if log fails
COURSE SELECTOR KNOB: For setting course to be steered.
DIMMER: For illumination of panel
AUTO/FOLLOW UP/ NON FOLLOW UP : For choosing steering mode
RUDDER LIMIT: Purpose is to prevent a maneuver more radical than is compatible with:
Speed loss
Comfort on ship
Safety of ship
Rudder angle greater than 15 to 20 deg do not improve course alteration but result in excessive speed loss.This control limits the number of degrees of helm that can be applied by auto pilot computer in any mode. Limits are : 5, 10, 15 and 20 degrees.
OFF COURSE ALARM: It gives alarm if ship deviates from set course by a pre determined limit. Setting depends on Wx condition, open/coastal waters.
RUDDER CONTROL: This is proportional controller which transmits a signal which is proportional to course error
Controller ouput = constant (Kp) x Deviation
The ratio can be changed by settings ( i.e. the ratio between instantaneous heading error and rudder command)
Also called rudder multiplier
Control knob alters the ratio of output.
Higher setting -- Larger rudder angle ( results in overcorrecting – overshooting )
Lower setting – Less rudder angle ( Long time to return to set Co – Sluggish )
Therefore optimum setting required.
COUNTER RUDDER: This is Derivative control.
Purpose is to apply a relatively greater amount of helm at the beginning of a course alteration to get the ship turning. Once the ship is turning, just enough helm is applied in order to keep her coming around. When new heading is approached, opposite helm is applied to stop the swing. As the ship settles on new heading and the yaw rate disappears, the helm is removed.
Produces an output when course of vessel is changing.
Depends on rate of change of course:
Controller output = constant ( KD ) x change of error / time
Determines amount of counter rudder to steady the ship on set course.
Keeps over shoot to minimum.
Greater the ship’s inertia, greater the setting required. If ship has good dynamic stability, relatively small settings of counter rudder will be sufficient. If the ship is unstable, higher settings will be required.
Depends on ship’s characteristics, loaded/ballast conditions and rate of turn.
Too high setting will bring the ship to set Co slowly
Too low setting allows overshoot
As counter rudder settings increase , counter rudder increases.
KD – Counter rudder time constant ( Calibration done at sea trial to set KD )
PERMANENT HELM: This is integral controller.( In NFU this control is out of action)
When ship has known imbalance to one side, requiring a certain amount of bias helm ( e.g. TT of propeller or extreme case of trawlers working their trawl over one side) manual setting of the approximate bias speed up the effect of the AUTOMATIC PERMANENT HELM calculator, because it started off nearer to its target.
Whether the control setting is estimated correctly or left at zero has no effect on the final steering accuracy but only in the time it takes to reach this heading accuracy.
If not used as described above , the permanent helm should be left at ZERO and the automatic permanent helm will function normally.
Produces output as long a course error persists
Used when beam winds; couple formed causing ship to turn into wind.
Rudder position required to counteract is permanent helm.
Continuous control calibrated from 20 (P) to 20 (S).
Changing over from Hand Steering to Auto Steering :
Before changing over from hand steering to auto steering, the settings on the auto pilot panel must be adjusted for weather and traffic conditions.
The vessel must be made steady on the course on which she has to be set on auto steering.
Changing over to emergency steering system :
When the steering panel gives an alarm, it must be read carefully to see as to what has gone out of order, operation must be changed-over to the other/ alterative steering gear/ motor or transmission system/ telemotor, engineroom must be informed immediately.
If the Auto-pilot gives an alarm or the off-course alarm goes off, adjust the settings on the Auto-pilot panel accordingly.
If the Auto-pilot fails, change-over to hand steering.
If the Follow-up system doesn’t work (the feedback leg of the steering gears doesn’t function properly), change-over to Non-Follow-Up mode.
If the steering transmission systems or telemotors stop working, emergency steering has to be performed by trick-wheel arrangement or solenoids after bringing the rudder mid-ships.
Further, if the steering hydraulic or electric motors also stop working, rudder will have to turned by some mechanical arrangement like chains and blocks, this is not possible in case of large rudders (large ships). As the last resort, Jury rudder is used, which means some arrangement/ structural changes, which overside work as an alternative rudder arrangement e.g. wooden planks on the stern turned/ rotated like a rudder.
Changing over (handing over/ taking over) of a watch between the OOWs whether at sea or at anchor is done in compliance with the ISM checklists onboard which, in general, include the following :
Use of the Automatic Pilot
4.- (1) The master shall ensure that an automatic pilot, where fitted, shall not be used in area of high traffic density, in conditions of restricted visibility nor in any other hazardous navigational situation unless it is possible to establish manual control of the ship's steering within 30 seconds.
(2) Before entering any area of high traffic density, and whenever visibility is likely to become restricted or some other hazardous navigational situation is likely to arise, the master shall arrange, where practicable, for the officer of the watch to have available without delay the services of a qualified helmsman who shall be ready at all times to take over the manual steering.
(3) The change-over form automatic to manual steering and vice versa shall be made by, or under the supervision of, the officer of the watch, or, if there is no such officer, the master.
(4) The master shall ensure that the manual steering gear is tested (a) after continuous use of the automatic pilot for 24 hours and (b) before entering any areas where navigation demands special caution.
Operations of Steering Gear
5. In areas where navigation demands special caution, the master shall ensure that the ship shall have more than one steering gear power unit in operation when such units are available and capable of simultaneous operation.
Steering Gear - Testing and Drills
6.-(1) The master shall, within 12 hours before departure of the ship, cause the steering gear to be checked and tested so as to ensure that it is working satisfactorily:
Provided that in the case of ships regularly making more than one voyage a week to or from the same port a check and test of the steering gear need only be made once in that week unless a part of the steering gear or its control system has been dismantled or change since the last test.
1764 MERCHANT SHIPPING
The test procedure shall include, where applicable, the operation of the following:
(a) the main steering gear;
(b) the auxiliary steering gear;
(c) the remote steering gear control systems
(d) the steering positions located on the navigating bridge
(e) the emergency power supply
(f) the rudder angle indicators in relation to the actual position of the rudder
(g) the remote steering gear control system power failure alarms
(h) the steering gear power unit failure alarms; and
(i) the automatic isolating arrangements and other automatic equipment required for steering gear.
(2) The checks and tests shall include:
(a) the full movement of the rudder according to the required capabilities of the steering gear;
(b) a visual inspection of the steering gear and its connecting linkage; and
(c) the operation of the means of communication between the navigating bridge and the steering gear compartment.
(3) The owner shall provide simple operating instructions, with a block diagram showing the changeover procedures, for the remote steering gear control systems and steering gear power units, and the master shall ensure that they are permanently displayed on the navigating bridge and in the steering gear compartment.
(4) A person shall not supervise the operation or maintenance of the steering gear unless that person is familiar with the operation of the steering systems fitted on the ship, and, where applicable, with the procedures for changing form one system to the other.
(5) In addition to the routine checks and tests prescribed in paragraphs (1) and (2) of this regulation, the master shall ensure that emergency steering gear drills which practise emergency steering gear procedures take place at least once every three months. These drills shall include, where applicable, use of direct control form within the steering gear compartment, the communications procedure with the navigating bridge and the operation of alternative power supplies.
(6) (a) The date time and place that the said routine checks and tests are carried out and the date and details of emergency steering drills carried out shall be recorded by the master in the official logbook.
(b) In ships not required to keep an official logbook, a record of each check, test and drill shall be made by the master and be retained on board for a period of six months and be available for inspection on demand by a superintendent, proper officer or surveyor of ships.
This is intended to remove the need for the operator to assess the correct control settings. In effect the autopilot ‘learns’ the vessel’s handling characteristics in calm weather and then, when the weather deteriorate, can distinguish between those errors in heading due to the weather and those due to vessel’s normal handling characteristics. It has been found that in heavy weather the vessel’s head deviates very little ‘relative to the water’.T4 the adaptive autopilot concerns itself primarily with those errors in heading resulting from normal handling characteristics, so reducing the work and hence drag of the rudder.
For example in Sperry model auto tuning software is fitted. The software performs dynamic tuning of the autopilot during a modest series of initial maneuvers, then automatically continues to retune the tuning throughout the voyage in response to the ship’s behavior. System also maintains two different tunings, one for light and one for loaded condition.
Limitations of auto pilot: Auto pilot should not be used under following circumstances:
(WASTV MNS)
In rough weather
During large alterations of courses
At slow speeds
In heavy traffic areas
In conditions of reduced visibility
While maneuvering the vessel
In narrow channels and confined waters.
In shallow waters
CONTROL UNIT:
1)PROPORTIONAL CONTROL: Output of the controller is proportional to the offcourse error from the course to steer ( deviation)
Controller ouput = constant (Kp) x Deviation
2) INTEGRAL CONTROL: Output of the controller is proportional to the summation of all instantaneous values of error ( deviation ) for as long as error persists.
Controller output = constant ( Ki ) x error x Time
3) DERIVATIVE CONTROL: Output of the controller is proportional to the rate of change of error ( deviation ).
Controller output = constant ( KD ) x change of error / time
THREE TERM CONTROLLER ACTION: Output signal is proportional to the deviation, persists as long as deviation persists and also depends on rate of change of deviation i.e.
Proportional + Integral + Derivative
CONTROLS:
WEATHER SETTING CONTROL: When steering in heavy weather with wind and sea at an angle to the vessel’s heading, there is a tendency for the vessel’s head to be turned in a particular direction. The effect of this can be offset by maintaining some permanent value of rudder angle; this angle is set using ‘weather helm’ after a period of trial and error.
SYNCHRONISATION CONTROL: Temporairly disconnects gyro repeater from main gyro for sync of heading. Required for sync and when gyro switched off and restarted.
SPEED: Usually from log and manual if log fails
COURSE SELECTOR KNOB: For setting course to be steered.
DIMMER: For illumination of panel
AUTO/FOLLOW UP/ NON FOLLOW UP : For choosing steering mode
RUDDER LIMIT: Purpose is to prevent a maneuver more radical than is compatible with:
Speed loss
Comfort on ship
Safety of ship
Rudder angle greater than 15 to 20 deg do not improve course alteration but result in excessive speed loss.This control limits the number of degrees of helm that can be applied by auto pilot computer in any mode. Limits are : 5, 10, 15 and 20 degrees.
OFF COURSE ALARM: It gives alarm if ship deviates from set course by a pre determined limit. Setting depends on Wx condition, open/coastal waters.
RUDDER CONTROL: This is proportional controller which transmits a signal which is proportional to course error
Controller ouput = constant (Kp) x Deviation
The ratio can be changed by settings ( i.e. the ratio between instantaneous heading error and rudder command)
Also called rudder multiplier
Control knob alters the ratio of output.
Higher setting -- Larger rudder angle ( results in overcorrecting – overshooting )
Lower setting – Less rudder angle ( Long time to return to set Co – Sluggish )
Therefore optimum setting required.
COUNTER RUDDER: This is Derivative control.
Purpose is to apply a relatively greater amount of helm at the beginning of a course alteration to get the ship turning. Once the ship is turning, just enough helm is applied in order to keep her coming around. When new heading is approached, opposite helm is applied to stop the swing. As the ship settles on new heading and the yaw rate disappears, the helm is removed.
Produces an output when course of vessel is changing.
Depends on rate of change of course:
Controller output = constant ( KD ) x change of error / time
Determines amount of counter rudder to steady the ship on set course.
Keeps over shoot to minimum.
Greater the ship’s inertia, greater the setting required. If ship has good dynamic stability, relatively small settings of counter rudder will be sufficient. If the ship is unstable, higher settings will be required.
Depends on ship’s characteristics, loaded/ballast conditions and rate of turn.
Too high setting will bring the ship to set Co slowly
Too low setting allows overshoot
As counter rudder settings increase , counter rudder increases.
KD – Counter rudder time constant ( Calibration done at sea trial to set KD )
PERMANENT HELM: This is integral controller.( In NFU this control is out of action)
When ship has known imbalance to one side, requiring a certain amount of bias helm ( e.g. TT of propeller or extreme case of trawlers working their trawl over one side) manual setting of the approximate bias speed up the effect of the AUTOMATIC PERMANENT HELM calculator, because it started off nearer to its target.
Whether the control setting is estimated correctly or left at zero has no effect on the final steering accuracy but only in the time it takes to reach this heading accuracy.
If not used as described above , the permanent helm should be left at ZERO and the automatic permanent helm will function normally.
Produces output as long a course error persists
Used when beam winds; couple formed causing ship to turn into wind.
Rudder position required to counteract is permanent helm.
Continuous control calibrated from 20 (P) to 20 (S).
Changing over from Hand Steering to Auto Steering :
Before changing over from hand steering to auto steering, the settings on the auto pilot panel must be adjusted for weather and traffic conditions.
The vessel must be made steady on the course on which she has to be set on auto steering.
Changing over to emergency steering system :
When the steering panel gives an alarm, it must be read carefully to see as to what has gone out of order, operation must be changed-over to the other/ alterative steering gear/ motor or transmission system/ telemotor, engineroom must be informed immediately.
If the Auto-pilot gives an alarm or the off-course alarm goes off, adjust the settings on the Auto-pilot panel accordingly.
If the Auto-pilot fails, change-over to hand steering.
If the Follow-up system doesn’t work (the feedback leg of the steering gears doesn’t function properly), change-over to Non-Follow-Up mode.
If the steering transmission systems or telemotors stop working, emergency steering has to be performed by trick-wheel arrangement or solenoids after bringing the rudder mid-ships.
Further, if the steering hydraulic or electric motors also stop working, rudder will have to turned by some mechanical arrangement like chains and blocks, this is not possible in case of large rudders (large ships). As the last resort, Jury rudder is used, which means some arrangement/ structural changes, which overside work as an alternative rudder arrangement e.g. wooden planks on the stern turned/ rotated like a rudder.
Changing over (handing over/ taking over) of a watch between the OOWs whether at sea or at anchor is done in compliance with the ISM checklists onboard which, in general, include the following :
Use of the Automatic Pilot
4.- (1) The master shall ensure that an automatic pilot, where fitted, shall not be used in area of high traffic density, in conditions of restricted visibility nor in any other hazardous navigational situation unless it is possible to establish manual control of the ship's steering within 30 seconds.
(2) Before entering any area of high traffic density, and whenever visibility is likely to become restricted or some other hazardous navigational situation is likely to arise, the master shall arrange, where practicable, for the officer of the watch to have available without delay the services of a qualified helmsman who shall be ready at all times to take over the manual steering.
(3) The change-over form automatic to manual steering and vice versa shall be made by, or under the supervision of, the officer of the watch, or, if there is no such officer, the master.
(4) The master shall ensure that the manual steering gear is tested (a) after continuous use of the automatic pilot for 24 hours and (b) before entering any areas where navigation demands special caution.
Operations of Steering Gear
5. In areas where navigation demands special caution, the master shall ensure that the ship shall have more than one steering gear power unit in operation when such units are available and capable of simultaneous operation.
Steering Gear - Testing and Drills
6.-(1) The master shall, within 12 hours before departure of the ship, cause the steering gear to be checked and tested so as to ensure that it is working satisfactorily:
Provided that in the case of ships regularly making more than one voyage a week to or from the same port a check and test of the steering gear need only be made once in that week unless a part of the steering gear or its control system has been dismantled or change since the last test.
1764 MERCHANT SHIPPING
The test procedure shall include, where applicable, the operation of the following:
(a) the main steering gear;
(b) the auxiliary steering gear;
(c) the remote steering gear control systems
(d) the steering positions located on the navigating bridge
(e) the emergency power supply
(f) the rudder angle indicators in relation to the actual position of the rudder
(g) the remote steering gear control system power failure alarms
(h) the steering gear power unit failure alarms; and
(i) the automatic isolating arrangements and other automatic equipment required for steering gear.
(2) The checks and tests shall include:
(a) the full movement of the rudder according to the required capabilities of the steering gear;
(b) a visual inspection of the steering gear and its connecting linkage; and
(c) the operation of the means of communication between the navigating bridge and the steering gear compartment.
(3) The owner shall provide simple operating instructions, with a block diagram showing the changeover procedures, for the remote steering gear control systems and steering gear power units, and the master shall ensure that they are permanently displayed on the navigating bridge and in the steering gear compartment.
(4) A person shall not supervise the operation or maintenance of the steering gear unless that person is familiar with the operation of the steering systems fitted on the ship, and, where applicable, with the procedures for changing form one system to the other.
(5) In addition to the routine checks and tests prescribed in paragraphs (1) and (2) of this regulation, the master shall ensure that emergency steering gear drills which practise emergency steering gear procedures take place at least once every three months. These drills shall include, where applicable, use of direct control form within the steering gear compartment, the communications procedure with the navigating bridge and the operation of alternative power supplies.
(6) (a) The date time and place that the said routine checks and tests are carried out and the date and details of emergency steering drills carried out shall be recorded by the master in the official logbook.
(b) In ships not required to keep an official logbook, a record of each check, test and drill shall be made by the master and be retained on board for a period of six months and be available for inspection on demand by a superintendent, proper officer or surveyor of ships.
3 comments:
very helpfull,could you please mail the exact procedure followed for testing and setting of off course alarm..thanks.
I have learnt something concerning auto pilot parameters,in which conditions to be used.I like it
A great helpful to we all mariners sir. My regard is to do so for all important question of all subject.
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