Nt921g Operating Manual 47506s

NAVITRON SYSTEMS LTD NT921G AUTOPILOT OPERATING MANUAL

Osborn House 25e Brockhampton Lane Havant, Hants, U.K. PO9 1JT ed in England No. 2607869

Tel: (023) 9249 8740 FAX: (023) 9249 8783 Int. Code: +44 23 E-mail: [email protected] Web: www.navitron.co.uk

0107 / 6

NAVITRON SYSTEMS LTD. NT921G AUTOPILOT OPERATING MANUAL

- Contents -

Section 1:

Short Operating Instructions.

Section 2:

Operator Controls and Sea Trials.

Section 3:

Display Messages, Alarms and Status Indicators.

NB: Whilst all efforts have been made to ensure the safety and reliability of the NT921G Autopilot system, it should be noted that the installation of any such system, should never be permitted to detract from the adequate provision of sound and continuous watch keeping duties.

NT921G AUTOPILOT OPERATING MANUAL

Section 1: Short Operating Instructions.

1.1

Initial Control Settings.

1.2

Switching On.

1.3

Engaging Autopilot.

1.4

Adjusting Steering Performance.

1.5

Matching Heading Steered with Heading Set.

1.6

Avoiding Unnecessary Rudder Correction.

1.7

Altering to a New Heading.

1.8

Adjusting Rate of Turn using the Rudder Limit Control.

1.8A Programmable Automatic Rate of Turn Control. 1.9

Adjusting Overshoot & Undershoot.

1.10

Using Track Function.

1.11

Cancelling an Audible Alarm.

1.12

Using NT920NFU Dodge and Power Steer Functions (If fitted).

NT921G AUTOPILOT OPERATING MANUAL Section 1: Short Operating Instructions. These Short Operating Instructions provide a quick reference guide to setting up and operating the NT921G autopilot. The locations in the manual where more detailed descriptions can be found are shown against each heading in brackets, e.g. (Section X.XX). 1.1

Initial Control Settings (Section 2.15). Unless alternative settings have been established from experience during sea ages with the autopilot in operation, the controls should be set as shown: -

COUNTER 1

RUDDER 3

RUDDER LIMIT 25° (or max safe setting)

YAW 1 MODE SWITCH

MAG/GYRO (as appropriate)

1.2

Switching On (Sections 2.16 and 2.17). Before engaging the autopilot the equipment must first be switched on by switching to standby mode: (i)

Turn the MODE switch to STANDBY.

(ii)

Wait for SELF TEST to complete alignment of the Course Selector (Heading Setter) Card.

In this mode Heading Setter functions as a magnetic or gyro com repeater (depending on how the Heading Reference switch is set) until the autopilot is engaged. 1.3

Engaging Autopilot (Section 2.18). To engage the autopilot: (i)

Steady the vessel on the required heading.

(ii)

Turn the MODE switch from STANDBY to ON.

TO DISENGAGE the AUTOPILOT at any time turn the MODE switch to STANDBY or OFF.

NT921G AUTOPILOT OPERATING MANUAL 1.4

Adjusting Steering Performance (Sections 2.19 to 2.21).

Understeer Characteristics

Oversteer Characteristics

Large deviations or protracted periods off the Heading Set due to insufficient rudder application in response to Yaw: -

Autopilot applying too much rudder causing vessel ‘weave’ which may increase to a tight ‘S’ pattern: -

Typical stretched ‘S’ characteristic of Understeer

Typical tight ‘S’ characteristic of Oversteer

Action required: -

Action required: -

Increase Rudder Control Setting.

Reduce Rudder Control Setting.

3

3

4

2

5

1 RUDDER

4

2

5

1 RUDDER

To adjust steering performance If vessel oversteers

-

Reduce RUDDER control setting (turn Anticlockwise).

If vessel understeers

-

Increase RUDDER control setting (turn Clockwise).

In both cases turn RUDDER control one step only and monitor steering performance before adjusting again if necessary.

NT921G AUTOPILOT OPERATING MANUAL 1.5

Matching Heading Steered with Heading Set (Section 2.22). When the autopilot is engaged the TRIM function continuously monitors any long-term differences between the heading set and the mean course actually steered. Any long-term difference is automatically adjusted by the TRIM function applying the appropriate amount of permanent helm. To speed up this automatic trim process: (i)

Wait for vessel to settle on steady heading.

(ii)

Press TRIM SET key.

Pressing the TRIM ZERO key immediately cancels any trim adjustment (permanent helm) that has been automatically set and the automatic monitoring and adjustment process will restart. Pressing and holding down the TRIM ZERO and SET keys together for 5 seconds will switch the TRIM function to OFF. 1.6

Avoiding Unnecessary Rudder Correction (Section 2.24). Frequent rudder movements when the vessel is yawing either side of the set heading in a seaway indicates that the autopilot sensitivity is set too high for the sea conditions being experienced. This can cause premature wear of the steering gear and is therefore undesirable. To decrease the frequency of rudder movement due to yawing: (i)

Increase the YAW setting (turn CLOCKWISE).

N.B. Don’t forget to reduce the YAW setting when yawing decreases as the vessel moves from rougher to calmer sea conditions. 1.7

Altering to a New Heading (Section 2.28). To alter course to a new heading using the autopilot: (i)

Check that the RUDDER LIMIT is set to a safe limit (Section 2.25)

(ii)

Press and hold down the knob on the Course Selector (Heading Setter) to engage the mechanism (safety device to prevent accidental turning) then:

(iii)

Turn CLOCKWISE to alter course to STARBOARD or ANTICLOCKWISE to alter course to PORT.

N.B. The Autopilot will order the vessel to turn in the same direction as the Course Selector knob is turned for any amount of Course change up to 359°. The result is that if the course change is more that 180° the vessel will continue to take the “long way” round to the new course.

NT921G AUTOPILOT OPERATING MANUAL 1.8

Adjusting Rate of Turn using the Rudder Limit Control (Section 2.25). To adjust the rate of turn when altering course using the autopilot: If vessel turns too quickly

-

If vessel turns too slowly

-

reduce RUDDER LIMIT setting (turn ANTICLOCKWISE).

increase RUDDER LIMIT setting (turn CLOCKWISE). NB See also Menu Programmable ROT (section 2.25A) 1.8A Programmable Automatic Rate of Turn Control. The Autopilot is equipped with a programmable Rate Of Turn (ROT) facility which can be accessed via the normal Set Up mode when the Autopilot is in STANDBY or via a special Set Up mode when the Autopilot is engaged. It is essential that the ROT control facility is correctly calibrated before use (see section 2.25A for details). 1.9

Adjusting Overshoot & Undershoot (Section 2.23). To adjust overshoot (vessel goes past new heading) or undershoot (vessel stops short of new heading) when altering course using the autopilot: If vessel overshoots

-

increase COUNTER RUDDER setting (turn CLOCKWISE).

If vessel undershoots

-

reduce COUNTER RUDDER setting (turn ANTICLOCKWISE).

1.10 Using Track Function (Section 2.29). N.B. This function can only be used if the vessel is also fitted with separate electronic position fixing equipment (GPS or Loran C) and this equipment has been correctly connected to the autopilot (2.9 and 2.29). The TRACK function operates using information received from the electronic position fixing equipment (GPS or Loran C) to keep the vessel on a predetermined track between two positions (waypoints) and will not work unless the electronic position fixing equipment is also in operation. (Refer to the electronic position fixing equipment manufacturers own manual for details of how to set-up and operate this equipment.) The track computer within the autopilot continuously checks the direction (left/port or right/starboard) together with the distance the vessel is offset from the required track and automatically orders heading corrections in a series of 3° steps. As a general rule, the more frequent the correction the closer the vessel will keep to the required track. Therefore in normal operation the TRACK function should be set to HI. However, too frequent a correction in the case of long distance open sea navigation or very slow vessels will produce an unnecessarily large number of heading adjustments. In these cases the TRACK function should be set to LO.

NT921G AUTOPILOT OPERATING MANUAL 1.10 Using Track Function (Section 2.29) Continued. If the input from the electronic position fixing equipment (GPS or Loran C) fails or the heading correction needed to regain the required track exceeds 30° the audible alarm will sound and a message (DATA FAIL or HC30) will be displayed in the ACTUAL HEADING window. Should this happen the TRACK function should be switched OFF. This will result in the realignment of the Course Selector (Heading Setter) with the vessels current heading and the vessel will be steered on this heading until the autopilot is disengaged (MODE switch is turned to STANDBY or OFF). N.B. If a DATA FAIL or HC30 alarm occurs the vessel could be a long way off the intended track. Therefore immediate steps should be taken to check the vessel’s position and take any corrective action needed to keep the vessel from running into danger. Disengaging the autopilot (turning the MODE switch to Standby or OFF) when the TRACK function is in operation will also automatically switch off the track function. Re-engaging the autopilot will not automatically reengage the TRACK function. This will require the TRACK function to be separately engaged as described below. The operational status of the TRACK function is shown by the illumination of 4 LED’s next to the TRACK ON/OFF key, which responds to single presses as follows: Track ON/OFF key

LED Illuminated ‘OFF’

Press 1

‘LO’

Press 2

‘HI’

Press 3

‘OFF’

Track mode Operational Status Track function disengaged Track LO mode active Track HI mode active Track function disengaged

When the RESET LED flashes pressing the ON/OFF key once will restore the TRACK function to the HI or LO setting that was in operation prior to the RESET. To engage the TRACK function: (i)

Check that the electronic positioning fixing equipment (GPS or Loran C) is operating and that the desired waypoint has been entered.

(ii)

Check that the autopilot has been engaged (Section 1.3)

(iii)

Press the Track ON/OFF key to select HI or LO as required.

Illumination of the HI or LO LED indicates that the TRACK function is operating.

NT921G AUTOPILOT OPERATING MANUAL 1.10 Using Track Function (Section 2.29) Continued.

To disengage the TRACK function at any time press the TRACK ON/OFF key until the OFF LED is illuminated or turn the MODE switch to STANDBY or OFF.

N.B. Turning the MODE switch to STANDBY or OFF disengages the autopilot and the vessel must be hand steered until the autopilot is reengaged. 1.11 Cancelling an Audible Alarm (Section 2.30). To cancel an audible alarm: (i)

Press the ALARM CANCEL key.

Audible alarms may be permanently muted as described in Section 2.30 but this function should be used with extreme caution. A permanently muted alarm may result in a missed alarm condition with dire consequences.

NT921G AUTOPILOT OPERATING MANUAL 1.12 Using NT920NFU Dodge and Power Steer functions (if fitted – Section 2.31).

NT920NFU Operating Instructions: N.B. The NT920NFU(s) will only function when the Autopilot MODE switch is set to REMOTE. Any other MODE switch position (ON, STANDBY or OFF) will immediately disable the NFU(s). DODGE MODE: (i)

Check that the Autopilot MODE switch is in the REMOTE position.

(ii)

Select DODGE on the NT920NFU selector switch. (Confirmed by illumination of DODGE READY LED).

(iii)

Move and hold the NT920NFU Jog Lever right (STBD) or Left (PORT) to apply corresponding rudder and override the Autopilot.

(iv)

Release the Jog Lever to centre when ready for the Autopilot to return the vessel to the original Autopilot heading.

NFU MODE: (i)

Check that the Autopilot MODE switch is in the REMOTE position.

(ii)

Select NFU on the NT920NFU selector switch. (Confirmed by illumination of the POWER STEER LED).

(iii)

Move the NT920NFU Jog Lever Right (STBD) or Left (PORT) and release the Jog lever to centre when the required angle of applied rudder is attained.

(iv)

Repeat Jog Lever operation as necessary to align the vessel on the new heading required.

(v)

Select DODGE or OFF to return heading control to the Autopilot which will maintain the vessel on the new (current) heading.

NT921G AUTOPILOT OPERATING MANUAL Section 2.0: Operator Controls and Sea Trials. Operator Controls and Displays Defined: 2.1

Autopilot Mode Switch.

2.2

Rudder Control.

2.3

Yaw Control.

2.4

Rudder Limit Control.

2.5

Gyro/Mag Switch.

2.6

Counter Rudder Control.

2.7

Illumination Control.

2.8

Automatic Trim (Automatic Permanent Helm).

2.9

Track (RadioNav Interface) Function.

2.10

Off Heading (Off Course) Alarm.

2.11

Actual Heading Indicator.

2.12

Rudder Angle Indicator.

2.13

Alarm Test and Cancel Keys.

2.14

Incremental (+1°/-1°) Keys.

NT921G AUTOPILOT OPERATING MANUAL Section 2.0: Operator Controls and Sea Trials. Sea Trials 2.15

Sea Trials.

2.16

Mag Heading Assessment.

2.17

Gyro Heading Assessment.

2.18

Autopilot Engagement.

2.19

Initial Heading Control (Course Keeping) Performance.

2.20

Optimising the Rudder Control Setting.

2.21

Optimising the Rudder Control Range.

2.22

Trim (Automatic Permanent Helm) Assessment. Manual Trim Cancellation. Automatic Trim Cancellation

2.23

Counter Rudder Control Setting.

2.24

Yaw Control Setting.

2.25

Rudder Limit Control Setting.

2.25A Programmable Automatic Rate of Turn Control. 2.26

Standard and Independent Off Heading Alarm Operation.

2.27

Magnetic Deviation Correction.

2.28

Course Selector (Heading Setter) Operation.

2.29

Track (RadioNav) Operation and Optimisation.

2.30

Alarm Test and Cancel Key Operation.

NT921G AUTOPILOT OPERATING MANUAL Section 2.0: Operator Controls and Sea Trials.

FIG 2 – NT921G Control Layout 2.1

The Autopilot Mode Switch. (i) OFF

All Autopilot functions are inoperative.

(ii) STANDBY

Servo Heading (Course setter card), repeater and digital displays operational. Heading data and Rudder angle output signal operational. Manual steering required.

(iii) ON

All Autopilot functions operational. Automatic steering in process.

(iv) REMOTE

Permits remote power steer/override of Autopilot steering when requested from remote station. Automatic steering in process provided no remote station(s) switched on.

Three red LED’s adjacent to the Rudder Angle display window confirm the operational status of the steering mode. O MANUAL

O AUTO

O REMOTE

NT921G AUTOPILOT OPERATING MANUAL 2.2

The Rudder Control. The Rudder Control defines the angle of Rudder that shall be applied in relation, or proportion to course error (degrees off course). The Control is graduated 1 to 5 and minimum Rudder is applied at a setting of 1. Maximum Rudder is therefore applied at a setting of 5 and a 3:1 ratio exists between minimum and maximum settings. Factory default (Set up table) calibration of the Rudder Control initially provides 0.5° to 1.5° of Rudder per degree course error. The Rudder Control is principally employed to prevent Autopilot “Understeer” and “Oversteer” and, the operator control band may be optimised by use of the programmable Loop Gain adjustment (Section 2.19).

2.3

The Yaw Control. This control defines the sensitivity of the Autopilot to course error. Graduated 1 to 5, a setting of 1 specifies minimum Yaw (maximum sensitivity) when the Autopilot will respond to course error of ± 0.5°. At maximum Yaw (5) a deadband of ± 10° is prescribed. (Whilst the term “Deadband” is used it should be noted that provided the Automatic Permanent Helm (Trim) feature is operational, the Autopilot will ensure that the average course is maintained whilst disregarding short term course errors arising from pitch and roll etc. thus avoiding unnecessary Rudder movement.) As a general rule the Yaw control should be set to provide good sensitivity, which would normally be reduced in heavy weather. See section 2.24.

2.4

The Rudder Limit Control. This control sets the maximum rudder angle that can be applied by the Autopilot other than counter rudder, The maximum rudder angle can be set between 5° and 45° in 5° steps and therefore limits the maximum rate of turn of the vessel. The Rudder limit LED will illuminate when the specified rudder limit angle is reached. The Rudder Limit function can also be turned off and is confirmed by the Rudder limit Off LED. NB The Rudder Control Limit LED will also illuminate when the ROT control algorithm is active.

NT921G AUTOPILOT OPERATING MANUAL 2.5

The Heading Sensor Selector Switch (Mag/Gyro). This switch selects the source of the heading reference signal used by the Autopilot, which is either Magnetic Com (MAG) or Gyrocom (GYRO).

2.6

The Counter Rudder Control. The Counter Control prescribes how much opposite rudder is applied to prevent overshoot in a turn or how much additional rudder is applied to arrest a sudden or fast and unspecified departure from the set heading. Minimum opposite (counter) rudder is applied at a control setting of N°1 (Maximum effect at 5). Section 2.23 refers.

2.7

The Illumination Control. The Illumination Control (ILLUM) provides the operator with a variable intensity control illumination enabling optimum day/night settings to be specified. When fully anticlockwise, all red signal LED’s are at maximum brilliance. All other legends are unlit. When the control is rotated clockwise, the LED’s dim and then increase in brilliance at the same rate as the control legends. In this manner all aspects can be unobtrusively illuminated in all conditions. The illumination control is not operational when the Autopilot MODE switch is ‘OFF’.

2.8

The Trim Function. Permanent Helm (TRIM) is automatically applied over a period of time when underway to offset the rudder and eliminate heading errors caused by windage or vessel trim etc. The trim function can be permanently switched off if required (confirmed by illumination of the red TRIM OFF LED) or can be instantaneously cancelled or set using the ZERO and SET keys on the Control . (See section 2.22).

2.9

The Track Function. RadioNav (Track) steering is switched on from the Control when the Autopilot is required to maintain a track between two waypoints (i.e. automatically correcting for drift etc.). Cross Track Error data input is required from a GPS or Track Plotter for this purpose. Two levels (LO and HI) of track retention are available and the Heading Indicator display is updated every 15 seconds with actual Cross Track Error and the angle of correction automatically applied to the Heading set to maintain the required track (direction over the ground). Section 2.28 refers.

NT921G AUTOPILOT OPERATING MANUAL 2.10 The Off Course Alarm. This function continuously monitors any difference between actual heading and heading specified (Course Set) when the Autopilot is steering the vessel. A visual and audible alarm is initiated if the heading error exceeds the level specified. (See section 2.26). 2.11 The Heading Indicator. This 4-digit LCD display provides continuous Mag or True heading identified by the appropriate red LED adjacent to the display window. When the RadioNav function is engaged (Track ON) the heading indicator is interrupted at 15-second intervals to display Cross Track Error (nm) and the angle of automatic correction currently applied to close to, or maintain track. The red TRACK DATA LED adjacent to the display window confirms RadioNav data display status. 2.12 The Rudder Indicator. Rudder Angle information is continuously displayed in the STANDBY and ON modes. A 2-digit display above a bar graph provides precise angular data whilst the coarser bar graph provides immediate visual appreciation of rudder direction (Port or Stbd) and rate of change. 2.13 Alarm Test and Cancel. Pressing and holding down the Alarm TEST key for 5 seconds will test all alarm functions. During normal operation, any audible alarm generated by the Autopilot system can be cancelled for a predetermined period (installation programmable) by a single press of the CANCEL key. If required, all audible alarms with the exception of POWER FAIL can be permanently muted by pressing and holding the CANCEL key for 5 seconds confirmed by illumination of the red CANCEL ALARMS LED. 2.14 The +1°/-1° Keys. These keys enable 1° step course changes to be specified to Port (-1°) or Stbd (+1°). Larger course changes can also be instructed by holding the key depressed for 3-seconds beyond which the new heading instruction will clock up or down at the rate of 1 degree per second. Corresponding movement of the Course Setter card automatically confirms all key instructions.

NT921G AUTOPILOT OPERATING MANUAL 2.15 Sea Trials. All necessary set up parameters and installation procedures should now have been completed in accordance with Section 3 of the Installation and Technical Manual. (i)

Set the NT921G Operator Controls as follows: -

RUDDER YAW COUNTER RUDDER LIMIT HEADING REFERENCE

N°3 N°1 N°1 25°

(mid travel) (fully anticlockwise) (fully anticlockwise) MAG or GYRO as required/appropriate

(ii)

Check that the Autopilot Isolators are on.

(iii)

Set the Mode Switch from OFF to STANDBY.

A 10-second self test will elapse signalled by the SELF TEST message in the Heading Indicator display window and the Course Setter Card will rotate and reverse before automatically aligning with ships head. Self test completion and operational readiness is confirmed by normal ships head display, which agrees with the Course Setter Card. 2.16 Mag Heading Assessment. With the Autopilot set to STANDBY and self-test completed: (i)

Set the GYRO/MAG switch to MAG (provided Mag input used).

(ii)

Manually steer the vessel and check that the digital heading Display and Course Setter Card follow ships head movement accurately and in unison.

N.B. Deviation correction is not immediately necessary but can be programmed either manually or automatically dependent upon heading inputs used (See section 2.27). (iii)

The source of the magnetic heading information currently in use by the Autopilot can be inspected at any time during normal operation by a single press of the TEST key and resultant display message: HSC1 or HSC2 = Sensor Coil on mag com HDG, HDM, HCC, HDT = NMEA data source Followed by the status of the ROT control: -

or

ROT SET XX.X ROT OFF

if ROT control is ENABLED if ROT control is DISABLED

The heading source message will automatically revert to normal heading display after approx 2 seconds.

NT921G AUTOPILOT OPERATING MANUAL 2.17 Gyro Heading Assessment. With the Autopilot set to STANDBY and self-test completed: (i)

Set the GYRO/MAG switch to GYRO (Provided GYRO input used)

(ii)

Manually steer the vessel and check that the digital heading display and Course Setter Card follow ships head movement accurately and in unison.

(iii)

The source of the Gyro heading information currently in use by the Autopilot can be inspected at any time during normal operation by a single press of the TEST key and resultant display message: SYNC = 1:1 Synchro HDT, HDG, HDM, HCC = NMEA data source Followed by the status of the ROT control (ROT SET XX.X or ROT OFF)

The heading source display will automatically revert to normal heading display after approx 2 seconds. 2.18 Autopilot Engagement. When the Autopilot is in the STANDBY mode, the Course Setter Card will continuously ‘follow’ ships head. (Sections 2.16 and 2.17 refer). Manually steer the vessel dead ahead at normal/typical operating speed with the operator controls set as follows: RUDDER YAW COUNTER RUDDER LIMIT HEADING REFERENCE

N°3 N°1 N°1 25°

(mid travel) (fully anticlockwise) (fully anticlockwise) (or as otherwise considered appropriate) MAG or GYRO as required/appropriate

To engage the Autopilot: Set the mode switch from STANDBY to ON. The Autopilot should now steer the vessel dead ahead. (The automatic TRIM function is always ON when the Autopilot is switched from STANDBY to ON. As a result, provided the rudder is positioned to steer the vessel dead ahead immediately prior to Autopilot engagement, any rudder offset angle (trim) manually determined for this purpose will be sampled and held by the Autopilot and the vessel will continue to steer dead ahead).

NT921G AUTOPILOT OPERATING MANUAL 2.19 Initial Course Keeping Performance (Control of Heading). Provided the Autopilot YAW control is set to N°1 (minimum Yaw) corrective rudder will be demanded and applied by the Autopilot system for any short term yaw angle in excess of 0.7 degree*. PORT Yaw will result in STBD rudder application confirmed by illumination of the GREEN chevron situated immediately above the Course Setter Card. Conversely Starboard Yaw will initiate PORT rudder and the RED chevron. The actual angle of corrective rudder applied to correct Yaw will be directly proportional to the Yaw angle and to the control setting of the RUDDER control. Too much applied rudder will promote OVERSTEER (Overcorrection) Insufficient applied rudder will promote UNDERSTEER (Undercorrection). *

The ultimate addition of Counter rudder and Automatic Trim significantly increases heading resolution in practice.

Understeer Characteristics

Oversteer Characteristics

Large deviations or protracted periods off the Heading Set due to insufficient rudder application in response to Yaw: -

Autopilot applying too much rudder causing vessel ‘weave’ which may increase to a tight ‘S’ pattern: -

Typical stretched ‘S’ characteristic of Understeer

Typical tight ‘S’ characteristic of Oversteer

Action required: -

Action required: -

Increase Rudder Control Setting.

Reduce Rudder Control Setting.

3

3 4

2

5

1 RUDDER

4

2

5

1 RUDDER

NT921G AUTOPILOT OPERATING MANUAL 2.20 Optimising the Rudder Control Setting. The RUDDER control provides the operator with the means to increase or decrease the angle of rudder applied in relation to course error and should be adjusted to provide positive correction of Yaw without oversteer (Section 2.19 refers). N.B Certain types of vessel steering characteristics benefit greatly from the anticipation afforded by a competent helmsman in applying short term exaggerated angles of rudder in order to check or ‘counter’ yaw inertia as soon as ‘felt’. The Autopilot Counter Rudder control produces a similar effect and it may prove beneficial at this stage to increase the COUNTER setting by an amount, which fully optimises the initial straight-line steering performance. Under normal operating conditions (normal cruising speed and average sea state) the RUDDER control will ideally be set at approximately mid travel (N°3) to provide operator scope for increase or decrease in significantly changed operating conditions. In heavy following sea conditions or at very slow speeds it is likely that the operator will need to increase the RUDDER control setting whereas at full speed or when beating into sea the RUDDER control setting will need to be decreased. If it is found that the maximum (N°5) RUDDER setting typically does not produce enough rudder or, conversely if the minimum (N°1) RUDDER setting typically provides too much rudder, the entire band of control available to the operator can be increased or decreased by corresponding Loop Gain adjustment via access to the Set Up programme as specified in Section 2.21. 2.21 Optimising the RUDDER Control Band. A RUDDER control setting of N°1 will produce 1/3rd (33%) of the angle of rudder otherwise produced by a control setting of N°5. The resultant 3:1 range available to the operator can be calibrated by access to the Set Up programme to produce actual degree of rudder per degree of course error ranges as follows: Minimum 0.33°(N°1) to 1°(N°5) of rudder per degree of course error (Loop Gain) Maximum 1°(N°1) to 3°(N°5) of rudder per degree of course error The factory default range setting for loop gain provides 0.5° to 1.5° of rudder per degree of course error but as a general rule, the operating band via Loop Gain calibration should initially be set as follows: Fast planing/semi planing vessels Deep sea fishing vessels etc Heavy displacement ocean going vessels -

0.33° to 1° per degree 0.5° to 1.5° per degree 1.0° to 3.0° per degree

NT921G AUTOPILOT OPERATING MANUAL 2.21 Optimising the RUDDER Control Band (Continued). Loop Gain Calibration. (i)

Switch the Autopilot MODE switch to STANDBY (Vessel now under manual steering control)

(ii)

Enter the Set Up mode (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display)

(iii)

Press TEST key to step through SET UP programme until LOOP GAIN is displayed.

(iv)

Set the RUDDER control fully clockwise (N°5) (The display now reads the maximum angle in degrees of rudder that will be applied for each degree of course error).

(v)

Use the SET key to increase the value or the ZERO key to decrease.

(vi)

When the new maximum value required is displayed for RUDDER setting N°5 turn the rudder control fully anticlockwise (N°1) to display the new minimum value which will be 1/3rd of that observed at maximum (N°5). (This is the recalibrated band of control available to the operator).

(vii)

Use the TEST key to step to the next Set Up parameter if required or exit the Set Up programme by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships heading display.

(viii)

The Autopilot can now be reengaged when required by switching the MODE switch from STANDBY to ON.

2.22 Trim (Automatic Permanent Helm) Assessment. Functional Description. The Autopilot system is equipped with an Integrator, which enables the electronic control stages to monitor the instantaneous position of the rudder in the STANDBY mode and to control the mean position of the rudder in the ON mode. In the STANDBY mode, the permanent helm (TRIM) integrator memorises and adopts any angle of rudder offset (up to 30°) which exists at the instant that the Autopilot is switched from STANDBY to ON.

NT921G AUTOPILOT OPERATING MANUAL 2.22 Trim (Automatic Permanent Helm) Assessment (Continued). This function is always operational when the Autopilot is switched from STANDBY to ON and permits the Autopilot to copy the angle of offset rudder manually applied to steer the vessel dead ahead on the desired heading (i.e. Trim compensated) at the instant of Autopilot engagement. In the ON mode, the Autopilot TRIM function (unless TRIM switched off) continuously monitors any long term differences between the Autopilot Heading Set and the mean course actually steered. Any apparent long-term difference is compensated for by automatic trim reassessment over a period of time to ensure the correct mean direction of the vessel through the water. The correction time is factory set at 300 seconds (5 minutes) for a maximum of 30° of rudder, but is re-programmable via the Set Up mode and is identified as APH (Automatic Permanent Helm) secs. APH timing periods of less than 300 seconds (5 minutes) are likely to degrade Autopilot steering performance on vessels other than highspeed craft with planing/semi planing hull forms. Timing periods greater than 300 seconds may benefit larger ocean going displacement vessels subject to seagoing appraisal. (Section 2.23 refers) Trim Operating Modes. (i) Autopilot switched from STANDBY to ON

-

Trim function operational.

(ii) SET (TRIM) key operation

-

Overrides APH timing period and immediately updates rudder-offset angle.

(iii) ZERO (TRIM) key operation

-

Immediately cancels any permanent helm rudder offset angle.

(iv) Simultaneous ZERO and SET operation for 5 seconds -

Switches TRIM function OFF (Confirmed by illumination of TRIM OFF Led).

NT921G AUTOPILOT OPERATING MANUAL 2.22 Seagoing Trim (APH) Assessment (Continued). (i)

Note the mean & steady course manually steered in the STANDBY mode by reference to the Autopilot ACTUAL HEADING display immediately prior to Autopilot engagement.

(ii)

Engage the Autopilot (switch from STANDBY to ON) and note that the mean and steady course now steered is as previously observed. (This confirms that any permanent helm rudder offset manually determined to steer the vessel dead ahead has been copied by the Autopilot).

(iii)

If the mean course steered ultimately differs from the Autopilot Heading Set (Magnetic deviation excluded) this will be automatically corrected over the timing period associated with the TRIM (APH) integrator. Alternatively – and provided the vessel is settled on a stable course – operation of the SET key will override the timing period and initiate immediate TRIM reassessment to correct the mean direction through the water. (i.e. the mean course actually steered will be the same as the course actually set).

N.B. When the SET key is operated, repeat operation is automatically prevented for a period of 20 seconds to allow the new mean rudder offset angle to initiate vessel response. Manual Cancellation of TRIM (APH) Rudder Offset. Press the ZERO key to initiate immediate cancellation of any existing permanent helm rudder offset beyond which the time based reassessment and correction process will automatically recommence. N.B. If not required, the TRIM function can be turned off by simultaneous 5-second operation of the SET and ZERO keys until confirmed by illumination of the TRIM OFF LED. Automatic Cancellation of TRIM (APH) Rudder Offset. A permanent Helm Offset angle, which is correct on an existing heading, may prove to be totally incorrect on a new heading particularly when large course changes are ordered. This might result in the wrong mean direction through the water when initially setting on the new heading but would ultimately be automatically corrected by the time based automatic TRIM correction process or by manual operation of the SET key.

NT921G AUTOPILOT OPERATING MANUAL 2.22 Automatic Cancellation of TRIM (APH) Rudder Offset (Continued). However, the Autopilot is equipped to automatically ‘trip’ or cancel any existing TRIM (APH) rudder offset for any course change ordered in excess of 60° (i.e. 60° to Port or Stbd of the current course). This automatic trip point is reprogrammable via the Set Up mode and can be lowered in onedegree steps from ±60° to ±10°. N.B. Lowering of the trip level should normally be avoided unless it is determined that the operational performance of the vessel will benefit accordingly. Automatic APH Trip level calibration. (i)

Switch the Autopilot MODE switch to STANDBY. (Vessel now under manual steering control).

(ii)

Enter the Set Up mode (Simultaneous 5-second operation of TEST and CANCEL keys until confirmed by ‘Set Up’ display)

(iii)

Press TEST key to step through Set Up programme until ‘APH TRIP xx’ is displayed (Where xx is the current two-digit trip level in degrees).

(iv)

Use the Set key to increase or the ZERO key to lower the APH trip level).

(v)

When the new value required is displayed use the TEST key to step to the next Set Up parameter if required or exit the Set Up programme by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships heading display.

(vi)

The Autopilot can now be reengaged when required by switching the MODE switch from STANDBY to ON.

NT921G AUTOPILOT OPERATING MANUAL 2.23 The Counter Rudder Control Setting. The Autopilot Counter rudder function continuously monitors the rate of change of heading (Rate of Turn) of the vessel and is principally responsible for the application of ‘Counter’ or ‘Opposite’ rudder as follows: Counter

-

Counters or ‘checks’ any sudden departure from the steady course steered by applying exaggerated short-term angles of rudder measured against the rate of turn away from the specified heading.

Opposite -

Monitors the closing rate towards a new course to prevent ‘overshoot’ by removing rudder early and applying opposite rudder to ‘meet’ and stabilise the vessel on the new heading specified.

Optimising the Counter Rudder Setting. The Counter Rudder effect may be increased or decreased by adjustment of the Counter control from N°1 (Zero effect) to N°5 (maximum effect). (i)

With the Autopilot engaged (ON) and the vessel underway on a stable heading, set the RUDDER LIMIT control to the highest level that will permit a rudder induced turn within the safe turning capability of the vessel.

NB If the ROT Control is ENABLED it will be necessary to ensure that this is set to the highest value permitted within the safe turning capability of the vessel (see section 2.25 to adjust the ROT value). (ii)

Use the Autopilot Course Setter to order a course change of 30° Port or Stbd of the current heading.

(iii)

Observe the response of the vessel noting whether overshoot occurs or whether the vessel is prematurely arrested in it’s turn to the new heading.

(iv)

Repeat the 30° course change in the opposite direction to gain an average evaluation.

Vessel Consistently Overshoots

-

Increase the Counter setting (Clockwise)

Vessel Prematurely Arrested

-

Decrease the Counter setting (Anticlockwise)

The optimum Counter setting has been achieved when the vessel turns efficiently to the new heading and stabilises without overshoot. N.B. If overshoot persists despite a maximum (N°5) Counter setting it is likely that the APH TRIP Level or the APH Timing Period require adjustment via access to the Set Up mode after further evaluation as follows: -

NT921G AUTOPILOT OPERATING MANUAL 2.23 The Counter Rudder Control Setting (Continued). (i)

Prepare to operate the ZERO (TRIM) key immediately prior to ordering another 30° course change.

(ii)

With the vessel stable on heading, press the ZERO key and immediately order a 30° course change via the Autopilot Course Setter.

If there is now no overshoot: The APH TRIP Level requires to be lowered to 20°. (See Automatic APH TRIP Level Calibration in Section 2.22) If overshoot persists: The APH Timing Period requires to be increased by 50% as follows: TRIM (APH) Timing Period Calibration. (i)

Switch the Autopilot MODE switch to STANDBY. (Vessel now under manual steering control)

(ii)

Enter the Set Up mode. (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display).

(iii)

Repeatedly press TEST key to step through SET UP programme until APH secs xxx is displayed. (Where xxx is the current APH timing period in seconds).

(iv)

Use the SET key to increase or the ZERO key to decrease the APH timing period as required.

(APH timing periods of less than 300 seconds (5 minutes) are likely to degrade Autopilot steering performance on vessels other than high-speed craft with planing/semi planing hull forms. Timing periods greater that 300 seconds may benefit slower turning displacement vessels subject to seagoing appraisal). (v)

When the new required value is displayed, use the TEST key to step to the next parameter if required or exit the Set Up mode by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships heading display.

(vi)

The Autopilot can now be reengaged when required by switching the MODE switch from STANDBY to ON.

NT921G AUTOPILOT OPERATING MANUAL 2.24 Optimising the YAW Control Setting. The YAW control setting defines the Autopilot sensitivity to short term yaw or course error and determines how much short term error will be tolerated before corrective rudder is ordered. A minimum YAW setting (N°1) prescribes maximum Autopilot sensitivity (±0.7°) increasing linearly to a maximum setting (N°5) for minimum sensitivity (±10°) (i.e. minimum yaw = maximum sensitivity and vice versa). N.B.

The minimum yaw setting limit of ±0.7° referred to above does not restrict the Autopilot in it’s ability to maintain heading control more accurately than ±0.7°. In practice, the cumulative effects of Counter Rudder and Automatic Trim (APH) combine to produce an overall resolution of ±0.2°. This combined effect is particular important in heavy sea conditions when the YAW control setting can be increased to prevent unnecessarily frequent rudder movements in response to sea state induced yaw. In such conditions and despite the wider deadband (increased tolerance to natural yaw) the Autopilot will continue to monitor and control the mean course accuracy as a function of the Automatic trim (APH Integrator) with a higher long term resolution than the Yaw control setting would suggest. As a general rule, the Yaw control should be set at the lowest number that provides the required course keeping sensitivity and ‘straight wake’ performance but avoids unnecessary rudder movements in response to natural Yaw.

2.25 Setting the Rudder Limit Control. The Rudder Limit Control defines the maximum angle of rudder that the Autopilot is able to apply with the exception of Counter Rudder, which overrides the Rudder Limit setting. N.B. This results in a safe operating mode wherein rudder angle is limited for any angle of course change ordered to a new heading and for any angle of rudder ordered by the Automatic Trim process (APH). However, high rates of departure from the course steered will continue to attract large angles of ‘check’ rudder that might be necessary to quickly arrest the vessel in a potential broach condition etc. The Rudder Limit control can be set from 5° to 45° in 5° increments or switched OFF confirmed by illumination of a red Rudder Limit ‘OFF’ LED positioned adjacent to the control. A second ‘Rudder Limit’ LED is also located adjacent to the control and illuminates when the limit of prescribed angle is reached (see also section 2.25A).

NT921G AUTOPILOT OPERATING MANUAL 2.25 Setting the Rudder Limit Control (Continued). As a general rule, the Rudder Limit control should be set to limit the angle of rudder applied such that any angle of course change ordered can be safely executed within the turning capability of the vessel and it’s operational considerations (warp tensions if towing etc.) 2.25A Programmable Automatic Rate of Turn Control. The Autopilot is equipped with a programmable Rate of Turn (ROT) facility which is accessible via the Set Up mode and has a factory default setting of 5 degrees per second (5°/sec) The ROT value can be inspected during normal Autopilot operation and can be changed (via entry to the Set Up mode) to any desired value from 0.2°/sec to 10°/sec (0.1°/sec steps) or can be switched off. When the desired ROT value is programmed, the Autopilot will continuously monitor and control the actual rate of turn of the vessel to accord with the ROT value set even when large course changes are ordered. The Rudder limit control must be set to a high enough value to allow enough rudder to be applied to achieve the desired ROT. To inspect the value of ROT: The setting of ROT currently programmed can be inspected at any time during normal operation by use of the TEST key and resultant ACTUAL HEADING display message as follows: (i)

Press the TEST key to display heading source in the ACTUAL HEADING display window (for approximately 2 seconds) after which the current ROT limit status will also be displayed in the format rot SEt XX.X. (rot OFF will be displayed if ROT control is not enabled).

To alter the value of ROT: (i)

Switch the Autopilot MODE switch to STANDBY (vessel now under manual steering control).

(ii)

Enter the Set Up mode (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display.

(iii)

Press the TEST key to step through SET UP programme until ROT ON or ROT OFF is displayed.

(iv)

Press the ZERO or SET key to select ROT ON or OFF as required (if automatic ROT control is required select ROT ‘ON’).

(v)

Press the TEST key to display the value of ROT SET. Use the ZERO (decrease) or SET (increase) key until the desired ROT is displayed.

NT921G AUTOPILOT OPERATING MANUAL 2.25A Programmable Automatic Rate of Turn Control (Continued). (vi)

Press the TEST ALARMS key to save the value and step to the next Set Up parameter.

(vii)

Exit the Set Up mode (simultaneous 5 second operation of TEST and CANCEL keys).

Indication of ROT control activation: Initial indication of ROT control activation is by illumination of the RUDDER LIMIT LED accompanied by an audible bleep. The ROT limit status will also be displayed simultaneously in the ACTUAL HEADING window in the format rot XX.X where XX.X is the set limit. To alter the ROT calibration value: It is essential that the ROT calibration value accurately reflects the vessels characteristics in order that the specified ROT can be achieved as quickly and efficiently as possible whilst minimising overshoot and rudder movement. A particular value of ROT CAL will only be optimum for the vessel for a limited range of speeds and laden states. The ROT CAL value is affected by the RUDDER control setting and this will therefore help to compensate for changes in the characteristics of the vessel. The value of ROT CAL can be adjusted manually or can be calculated automatically during sea trials. To optimise the value of ROT CAL automatically at normal steaming speed proceed as follows: Automatic ROT calibration: (i)

Set the Autopilot MODE switch to STANDBY. With the vessel at normal steaming/cruising speed and when safe to do so manually steer the vessel in a circle at a high ROT well within the safe turning capabilities of the vessel.

(ii)

When the Rate Of Turn has become constant, enter the Autopilot setup mode via simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display.

(iii)

Press the TEST key to step through SET UP programme until ROT CAL XX.X is displayed.

(iv)

Simultaneously press the ZERO and SET key to select automatic calibration of ROT CAL value.

(v)

Exit the Set Up mode (simultaneous 5 second operation of TEST and CANCEL keys).

NT921G AUTOPILOT OPERATING MANUAL To adjust the ROT CAL value manually proceed as follows: Manual ROT calibration: (i)

Enter the Autopilot setup mode (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display).

(ii)

Press the TEST key until the display shows “ROT CAL XX.X”.

(iii)

Use the SET key to increase or the ZERO key to decrease the ROT CAL value as required.

(iv)

Exit the Set Up mode (simultaneous 5 second operation of TEST and CANCEL keys).

Altering ROT SET and ROT CAL during normal Autopilot operation: Provision has been made to allow the value of ROT SET and ROT CAL to be altered quickly and easily whilst the Autopilot is engaged. Proceed as follows: (i)

Ensure the Autopilot MODE switch is set to ON.

(ii)

Press the TEST and CANCEL ALARMS keys for 2 seconds. A bleep will be heard and heading display will show “ROT SET XX.X”. NB If automatic ROT control is not enabled the display will briefly show “ROT OFF” and then revert to normal heading display. Refer to section 3.5A of the Installation and Technical Manual to enable ROT control.

(iii)

Use the ZERO and SET keys to alter ROT SET until the required value is shown. NB If the vessel is already making a ROT controlled turn then the Autopilot will ‘ramp’ the vessels ROT up or down to achieve the new ROT SET value.

(iv)

Press TEST ALARM to step to the ROT CAL value or press TEST and CANCEL ALARMS for 2 seconds to exit this special setup mode.

(v)

If ROT CAL is to be adjusted use the ZERO and SET keys to alter the value until the required value is shown. Press TEST and CANCEL ALARMS for 2 seconds to exit this special setup mode.

NT921G AUTOPILOT OPERATING MANUAL 2.26 Optimising the Off Heading (Off Course) Alarm. The OFF HEADING ALARM (OHM) continuously monitors and compares the difference between the heading set and the actual heading steered and generates an audible and visual alarm if the specified limit is exceeded. Alarm Trip Level. The specified limit (Alarm trip level) is operator selectable at 1.5°, 3°, 5°, 10°, 15°, 20°, 25° and 30°. Alarm Cancellation. The audible alarm can be cancelled by operation of the CANCEL (ALARMS) key but will sound again after a programmable mute period (10-60 seconds) if the heading error condition is still present. If required, the audible alarm can also be permanently muted by 5-second operation of the CANCEL key but this will also mute all other audible alarm functions. Standard and Independent Operating Modes Two modes of OHA are available: Standard -

If only one heading input is connected to the Autopilot System (Mag or Gyro) the OHA must be programmed for STANDARD operation via the Set Up mode since the heading set and heading steered will share the same heading input information.

Independent -

Provided two (or more) heading inputs are connected to the Autopilot (Mag and Gyro) the OHA can be programmed (Set Up mode) for independent operation. (In the Independent mode the Autopilot system will automatically ensure that the heading set and heading steered references are independent such that a heading input fault affecting the Autopilot course would not affect the ability of the OHA to detect and signal an Off Heading condition).

NT921G AUTOPILOT OPERATING MANUAL 2.26 Optimising the Off Heading (Off Course) Alarm (Continued). To Select Standard or Independent OHA Operation. (i)

Switch the Autopilot MODE switch to STANDBY. (Vessel now under manual steering control).

(ii)

Enter the Set Up mode. (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display).

(iii)

Repeatedly press TEST key to step through Set Up programme until ‘OHA Type Ind/Stnd’ is displayed.

(iv)

Use the SET or ZERO keys to select Stnd (STANDARD) or Ind (INDEPENDENT) as required.

(v)

When the correct operating mode is displayed, use the CANCEL keys to step back to OHA Secs if the Alarm mute period is to be altered

OR Exit the Set Up mode by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships head display. To Alter the OHA Alarm Mute Period. (i)

Enter the Set Up mode (if appropriate) as (i) and (ii) above.

(ii)

Repeatedly press the TEST key (If appropriate) to display OHA Secs xx (where xx is the mute period in seconds).

(iii)

Use the SET or ZERO keys to increase or decrease the alarm mute period as required.

(iv)

When the required value is displayed, use the TEST key to step to the next parameter if required or exit the Set Up mode by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships heading display.

2.27 Deviation Correction. A Navitron Heading Sensor Coil (type HSC1 or HSC2) attached above or below a magnetic com to transmit heading information to the Autopilot system will be subject to any deviation errors associated with the com. Provided such errors are not totally abnormal they can be electronically corrected by the Autopilot system via access to the Set Up mode.

NT921G AUTOPILOT OPERATING MANUAL 2.27 Deviation Correction (Continued). Two deviation correction procedures are available in the Set Up mode as follows: Automatic Deviation Correction. This is only available when heading information is connected to the Gyro input of the Autopilot (1:1 Synchro or NMEA type) in addition to the Sensor Coil information connected to the Mag input. (i.e. when swinging the vessel, the Sensor Coil information can automatically be compared with the 1:1 Gyro or NMEA input and electronically corrected accordingly). Manual Deviation Correction. This is the only facility for electronic deviation correction if the Sensor Coil is the solitary heading input to the Autopilot. Deviation Correction Procedure. (i)

Switch the Autopilot MODE switch to STANDBY (Vessel now under manual steering control).

(ii)

Enter the Set Up mode. (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display).

(iii)

Repeatedly press TEST key to step through SET UP programme until AUTO DEV ON/OFF is displayed.

(iv)

Use the SET or ZERO key to switch Auto Deviation ON or OFF as appropriate (Auto deviation OFF = Manual Correction)

(v)

Refer to Automatic or Manual Procedure following: -

Auto Deviation Procedure. If Auto deviation has been selected (AUTO DEV ON) the display will now read REF xxx.x (where xxx.x is the magnetic heading in degrees) (i)

Use the SET or ZERO keys to alter the reference heading (REF xxx.x) until the heading display is correct with actual steady ships magnetic heading.

Press the TEST key when correct following which the display will read TURN STBD. (ii)

Manually set the vessel in a slow and steady rate of turn to Stbd (5 degrees per second or less) through 360°and continue the turn until the display reads END.

NT921G AUTOPILOT OPERATING MANUAL 2.27 Deviation Correction (Continued). (iii)

Use the TEST key to save the deviation table and exit the Set Up mode by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships heading display.

Manual Deviation Procedure. If Manual deviation has been selected (AUTO DEV OFF) the display will now read 360 alternating with 01 (360↔01). (i)

Manually steer the vessel on 360° (000°) and press the ZERO or SET key when steady on 360°.

(ii)

Display will now read 030 alternating with 02 (030↔02). Manually alter course to 030° and press the ZERO or SET key when steady on 30°.

(iii)

Repeat the foregoing on the next heading shown (060°) pressing ZERO or SET when steady and continue in 30° steps (090°, 120°, 150°, 180°, 210°, etc) through 360° until the display reads END.

(iv)

Use the TEST key to save the deviation table and exit the Set Up mode by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships heading display.

NT921G AUTOPILOT OPERATING MANUAL 2.28 The Autopilot Course Selector (Heading Setter). The Autopilot is equipped with a rotary Course Selector which is clearly marked in 1° increments and is used to specify the required heading when the Autopilot MODE switch is in the ‘ON’ position. In the STANDBY position, the Course Selector card functions as a card repeater by following any movement of Ships head. This feature – in addition to offering a convenient heading repeater facility to the helmsman when steering manually – provides an important safety consideration by ensuring that the Course Selector is always in the correct position to steer the vessel on the current heading, when the MODE switch is set from STANDBY to ON. Initial Heading (Course) Selection. (i)

Provided the Autopilot MODE switch is set to STANDBY, the Course Selector will track ships head.

(ii)

Manually steer the vessel on the required heading.

(iii)

Set the Autopilot MODE switch from STANDBY to ON to engage the Autopilot and steer the current heading.

N.B. If the vessel is turning at the instant of Autopilot engagement the wrong heading will initially result – particularly if a significant angle of rudder is responsible for the turn. The Automatic Trim process will automatically correct this over a period of minutes unless the Trim SET key is employed (Section 2.22 refers). Subsequent Heading (Course) Alteration. To prevent inadvertent operation, the Course Selector (Heading Setter) knob is a spring-loaded mechanism, which rotates freely unless depressed to engage. Depressing and turning the Course Selector (Heading Setter) knob CLOCKWISE will order a vessel course change to STARBOARD. Conversely, depression and rotation of the Course Setter ANTICLOCKWISE will order a vessel course change to PORT.

knob

The amount (angle) of course change will be accurately specified by the new position of the Course Selector Card. N.B. Any angle of course change specified up to 359° will result in the vessel turning to the new heading in the direction specified by the direction in which the Course Selector knob has been rotated.

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function. Functional Description. The Track function involves an integral Radio Navigator Interface (RNI), which enables the Autopilot to be interfaced to a range of proprietary Decca, Loran or GPS receivers provided the latter are equipped to transmit Cross Track Error (CTE) in NMEA 0180 or 0183 serial data format. When the appropriate coordinates have been entered into the proprietary receiver and a track (rhumbline) to desired waypoint established, any departure data (right or left of rhumbline) is received on the NMEA CTE input terminals of the Autopilot via the GPS receiver or Track Plotter. The CTE data received is processed within the Autopilot and applied (after computation) as a heading offset resulting in automatic correction of CTE to maintain the vessel on the specified track. This process enables the Autopilot to correct errors in direction over the ground in addition to errors in direction through the water.

Heading Set

Heading Set and required track

Uncorrected direction over the ground due to uncorrected drift

Corrected direction over the ground by measurement and correction of Cross Track Error (CTE)

Set

Set

CTE

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function (Continued). The Track computer within the Autopilot continuously inspects the direction (Left or Right of required Track) and the distance (0.01 to 9.99 nautical miles from required Track) based on the CTE data received and automatically orders heading corrections in a series of 3° steps. N.B. The frequency of automatic heading correction (course change) is dependent on the Track operating level selected (LO or HI) and each level is programmable (Autopilot Set Up mode) to provide optimum correction intervals as follows: Track Operating Mode Set Up Programme N° Correction Interval (Secs)

LO 01 02 03 180 150 120

04 90

05 60

06 50

07 40

HI 08 30

09 20

10 15

As a general rule, the more frequent the correction (HI mode) the higher the TRACK steering resolution. However, too frequent a correction in the case of long distance open sea navigation or applied to very slow vessels will produce an unnecessarily large number of heading adjustments. Conversely, a high speed craft covering significant distances in short periods of time will benefit from a shorter correction interval. The factory default settings are 08 (HI) and 05 (LO) but can be reprogrammed by reference to ‘Optimising the Track Function Parameters’. Provided the Track function is switched ON (LO or HI) the Autopilot will respond to correct any CTE by initially ordering a 3° heading offset (Course change) towards the desired track. Unless subsequent CTE data received confirms that the vessel is closing to the track, further 3° heading changes will then be automatically ordered until the vessel is parallel. Once determined as parallel to track, a further 5° or 10° heading change will be ordered to close to the track. N.B. This is referred to as the Closing Angle (CA) and can be programmed for 5° or 10° via the Autopilot Set Up mode. When the vessel has obtained the specified track, further heading corrections will be automatically reduced to as little as 0.3° to maintain the vessel smoothly on track.

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function (Continued). Track Mode Status Information. When the TRACK function is operational (LO or HI) the Autopilot ACTUAL HEADING display is interrupted at 15 second intervals to display current CTE and current angle of automatic heading offset applied by the Autopilot to restore or maintain the vessel on track. Track data appearing (every 15 secs) is confirmed by illumination of the TRACK DATA LED adjacent to the display window. i.e.

CTE

means

0.02r

Cross Track Error 0.02nm right of track

Followed by and

HC

09.0L

Heading Correction of 9° to Port (Left)

Track Mode Alarms. In the event of NMEA data failure (CTE data) when the TRACK function is engaged, visual and audible alarms are automatically initiated. The ACTUAL HEADING window will display the message ‘0180’ or ‘0183 DATA FAIL’ and the failure message and accompanying audible alarm will only be cancelled by switching the TRACK function OFF as confirmed by the TRACK ‘OFF’ LED. For safety reasons, automatic heading corrections to restore the vessel to track are limited to 3° steps in addition to which, the maximum cumulative angle of change (over several correction intervals as tabulated) is limited to 30°. If the 30° maximum offset is attained, the audible alarm will ‘bleep’ in time with a flashing TRACK RESET LED and the ACTUAL HEADING window will display the message HC30 (Heading Correction 30°) Since a cumulative 30° heading offset is significant, watchkeeping intervention is now invited to assess current navigating conditions (original heading specified, vessel speed and drift etc). If automatic correction (Track function) is to be continued, operation of the TRACK ON/OFF key will cancel the RESET alarm and a new series of correction intervals will commence (Periodic 3° step changes to a cumulative maximum of 30°). N.B. Operation of the ON/OFF (TRACK) key to RESET or switch OFF the track function will automatically result in immediate realignment of the Course Selector (Heading Setter) card with current vessel heading. This ensures that the vessel will continue to steer the current heading despite the sudden removal of any automatic heading offset caused by TRACK function RESET or disengagement.

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function (Continued). Engaging the Track Function. The TRACK function is only available when the Autopilot is engaged (MODE switch set to ‘ON’ or ‘REMOTE’ position). Independent ON/OFF (TRACK) key operation is always required to engage the track mode which is never automatically initiated by the Autopilot MODE switch. Disengagement of the Autopilot (MODE switch to STANDBY or OFF) will automatically switch off the TRACK function and any subsequent reengagement of the Autopilot will require independent ON/OFF (TRACK) key operation to reinstate the Track mode. The operational status of the TRACK function is clearly defined at all times by the illumination state of 4 LED’s adjacent to the ON/OFF (TRACK) key which responds to single press operation as follows: -

Track ON/OFF key

LED Illuminated ‘OFF’

Press 1

‘LO’

Press 2

‘HI’

Press 3

‘OFF’

Track mode Operational Status Track function disengaged Track LO mode active Track HI mode active Track function disengaged

Reset - Operation of the ON/OFF key to cancel a flashing RESET LED will restore the TRACK mode status to the LO or HI condition which existed immediately prior to the RESET request.

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function (Continued). Operational Assessment of the Track Function. The vessel should be underway steering on Autopilot with adequate sea space to accommodate heading changes associated with a safe and realistic track. Accordingly, the appropriate track data must be available to the Autopilot from the GPS or Track Plotter system. (i)

Operate the ON/OFF (TRACK) key to initiate the LO mode confirmed by illumination of the LO LED.

N.B. If an audible alarm immediately (or at any time during Track mode operation) sounds accompanied by a display message of 0180/0183 DATA FAIL, no CTE data (or invalid data) is being received by the Autopilot from the GPS/Track Plotter. (ii)

In the event of DATA FAIL alarm, use the ON/OFF (TRACK) key to disengage the track mode confirmed by illumination of the TRACK ‘OFF’ LED.

(iii)

Provided valid track data is available to the Autopilot, CTE data and resultant track correction measures will be displayed at 15 second intervals in the ACTUAL HEADING window coincidental with illumination of the TRACK DATA LED.

(iv)

An initial heading change of 3° may be observed followed by further 3° changes (if appropriate) and a 5° or 10° change to finally close the vessel to the specified track until the track is attained and held.

(v)

If the correction process is too slow or too fast: -

Too Fast - Increase the correction interval via the Autopilot Set Up mode (Refer to Optimising the Track Function Parameters Table A). Too Slow – Operate the ON/OFF (TRACK) key to select the HI mode. (Optimise the HI mode correction interval if necessary as above). (vi)

In the event of maximum cumulative heading correction (30°) occurring during the correction process, the RESET alarm will automatically be initiated: Operate the ON/OFF (TRACK) key to cancel the alarm and automatically recommence the correction process confirmed by illumination of the LO or HI LED as applicable.

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function (Continued). Sea Trial Simulation of Drift Correction. Any track specified from the vessels current position to a realistically distant waypoint, combined with an Autopilot heading intentionally set to steer the vessel 10-15° Port or Stbd of the correct heading to the target waypoint, will be interpreted by the TRACK function as drift induced. As a result, the Autopilot heading steered will be progressively updated for automatic correction to the specified track en route to the target waypoint. In controlled trial conditions as described, the correction characteristics and attendant HI/LO correction intervals are more easily assessed and optimised. Distant Waypoint

Distant Waypoint

Specified Track

Specified Track

Closing Angle (5 or 10°)

10-15°

Parallel to Track

Uncorrected result due to Intentional 10-15° error (Heading to WP versus Autopilot heading Set)

CTE due to incorrect Hdg Set

CTE corrected result despite intentional error. Current Position

Current Position

NT921G AUTOPILOT OPERATING MANUAL 2.29 The Track (RadioNav Interface) Function (Continued). Optimising the TRACK Function Parameters. Three parameters can be programmed in the Autopilot Set Up mode: 1. NMEA data type – 0180 or 0183 (will be 0183 in virtually all cases). 2. LO/HI Correction Interval – 01 to 05 (LO mode) 06-10 (HI mode): Track Operating Mode Set Up Programme N° Correction Interval (Secs)

LO 01 02 03 180 150 120

04 90

05 60

06 50

07 40

HI 08 30

09 20

10 15

Table A. 3. Closing Angle – 5° or 10° change from parallel to track closure. To inspect and/or optimise current Track parameters: (i)

Switch the Autopilot MODE switch to STANDBY. (Vessel now under manual steering control).

(ii)

Enter the Set Up mode. (Simultaneous 5 second operation of TEST and CANCEL keys until confirmed by ‘SET UP’ display).

(iii)

Press the TEST key to display HI.xx. (Where xx is the number corresponding to the correction interval in Table A).

(iv)

Use the SET or ZERO keys to alter the number as required.

(v)

When the required number is displayed, use the TEST key to display LO.xx. (Where xx is the number corresponding to the correction interval in Table A).

(vi)

Use the SET or ZERO keys to display the number required followed by TEST key operation to display 0180 or 0183.

(vii)

Use the SET or ZERO keys to select 0180 or 0183 as required followed by TEST key operation to display CA xx. (Where xx is the 5° or 10° Closing Angle)

(viii)

Use the SET or ZERO keys to select 5° or 10° as required.

(ix)

Exit the Set Up mode by simultaneous 5 second operation of the TEST and CANCEL keys until confirmed by normal ships head display.

(x)

The Autopilot can now be re-engaged (MODE switch from STANDBY to On) followed (if required) by Track mode re-engagement (TRACK ON/OFF key operation) confirmed by LO or HI LED illumination as selected.

NT921G AUTOPILOT OPERATING MANUAL 2.30 Alarm Test Key and Cancel Key Functions. The TEST and CANCEL keys provide various single and t functions as follows: TEST (Single Operation)

In normal Autopilot steering mode, interrupts heading display to show current heading reference (com, gyro, NMEA etc) followed by ROT control status.

TEST (5 second Operation)

Initiates sequential test of all audible alarms and alarm LED’s.

CANCEL (Single Operation)

Silences (mutes) any current alarm for a predetermined period (programmable in Set Up mode) from 10 to 60 seconds. (Off Heading Alarm – see section 2.26) (All other Alarms – section 3.27 in Installation and Technical Manual).

CANCEL (5 second Operation) Permanently mutes all audible alarms confirmed by illumination of LED. N.B. 5 second operation to mute the POWER FAIL alarm consistent with Autopilot internal battery failure automatically initiates boost charge for predetermined factory set period. TEST + CANCEL (5 second Simultaneous Operation)

Enters the Autopilot Set Up mode confirmed by ‘Set Up’ message in the ACTUAL HEADING window.

TEST (Single Operation in Set Up mode)

Steps forward through the Set Up parameters.

CANCEL (Single Operation In Set Up mode)

Steps backwards through the Set Up parameters.

TEST + CANCEL (5 second Operation in Set Up mode)

Exits Set Up mode confirmed by normal ships head display in ACTUAL HEADING window.

NT921G AUTOPILOT OPERATING MANUAL 2.31 NT920NFU (Navitron Non Follow Up Power Steer & Dodge Control). The NT920NFU is a dual function device, which enables temporary (DODGE) and permanent (POWER STEER) heading changes to be ordered at locations remote from the Autopilot Control Unit. N.B. Type Approved Autopilot systems equipped with facilities of this kind are required to exercise unconditional main station control of all such remote inputs. Accordingly, the NT920NFU is only enabled when the Autopilot Control Unit MODE switch is set to REMOTE and regardless of the NT920NFU mode selected (DODGE or POWER STEER) movement of the Autopilot Control Unit MODE switch from the REMOTE position will immediately disable the remote station(s). The Dodge Function Provided the Autopilot mode switch is set to REMOTE, the NT920NFU will respond to DODGE switch selection confirmed by illumination of the DODGE READY LED on the NT920NFU control . The Autopilot will continue to steer the vessel normally in the DODGE READY state unless the NT920NFU Jog lever is moved from the sprung to centre position. Movement of the Jog lever to the Left (Port) or Right (Stbd) will produce corresponding rudder movement to a preset maximum angle (installation adjustable within the NT920NFU) which will override Autopilot heading control of the vessel. The resultant change in vessel heading will continue (due to the fixed angle of rudder applied) until the Jog lever is returned to the central position at which time the Autopilot will immediately resume control and return the vessel to the original heading. The Power Steer Function Provided the Autopilot Mode switch is set to REMOTE, the NT920NFU will respond to NFU switch selection confirmed by illumination of the POWER STEER LED on the NT920NFU control . In the POWER STEER state the Autopilot will immediately assume a standby condition such that the Autopilot Course Setter Card will ‘track’ any movement of ship’s head resulting from Power Steer instruction received from the NT920NFU (i.e. the Autopilot is effectively disengaged in favour of Non Follow Up Power Steer Control). N.B. Confirmation of the Autopilot remote standby condition is signalled by illumination of the REMOTE LED on the Autopilot Control Unit and is accompanied by an audible bleep at regular 10 second intervals.

NT921G AUTOPILOT OPERATING MANUAL 2.31 NT920NFU (Navitron Non Follow Up Power Steer – & Dodge Control) Continued. Subsequent movement of the NT920NFU Jog lever to the Right (Stbd) or Left (Port) will produce corresponding rudder movement to hard over rudder if the Jog lever is held right or left of the central position for a prolonged period. Shorter-term operation and release of the Jog lever will produce smaller angles of applied rudder. In all cases, the angle of rudder attained at the point of Jog lever release to centre will be adopted and held pending further Jog lever operation. When the vessel is power steered to a new heading, the Autopilot Course Setter Card will track ship’s head. When the required heading is attained and the NT920NFU switch is set to DODGE or OFF, the Autopilot will immediately resume control and maintain the vessel on the new (current) heading.

NT921G AUTOPILOT OPERATING MANUAL Section 3: Display Messages, Alarms and Status Indicators (LED’s).

3.1

Displays at Power Up (Self Test).

3.2

Failure Messages at Power Up (Self Test Failure).

3.3

Operational Display Messages.

3.4

Alarm Display Messages.

3.5

Alarm LED’s.

3.6

Operational Status LED’s.

NT921G AUTOPILOT OPERATING MANUAL Section 3: Display Messages, Alarms and Status Indicators (LED’s). The Autopilot system is comprehensively equipped with alarm mechanisms that continuously monitor the operational integrity of a wide range of functions from heading input data to steering gear response. These are brought to the attention of the watch by audible and visual means as follows: 3.1

3.2

3.3

Display at Power Up. (i)

8.8..8.8

-

Actual LCD display segment test.

(ii)

SELF tESt

-

Autopilot Self Test and Course Setter Card Alignment.

(iii)

x.x

-

Software version number.

Possible Failure Messages at Power Up. (i)

----

-

Autopilot attempting to read programmed Set Up data.

(ii)

dEF dAtA

-

Failure to load Set Up data. Factory default settings loaded instead (Section 3.33 of Installation and Technical Manual).

(iii)

CS FAIL

-

Course Setter mechanism failure indicated (No movement or Course Setter Card detected).

(iv)

ALgn FAIL -

Failure to align Course Setter Card (electronic alignment process suspect).

Operational Display Messages. (i)

CtE x..xx L/r HC xx.x L/r

Cross Track Error Automatic Heading Correction

(ii)

HSC1 or HSC2

Mag Sensor Coil signal

(iii)

Hdnn

HDM (NMEA) sentence

(iv)

HCC

HCC (NMEA) sentence

(v)

Hdt

HDT (NMEA) sentence

(vi)

Hdg

HDG (NMEA) sentence

(vii)

Sync

1:1 Gyro signal

(viii)

ROT XX.X or OFF ROT control status initiated by test key operation.

(ix)

SEt UP

Every 15 seconds in TRACK mode.

Heading source confirmation followed by rate of turn limit programmed in Set Up parameters initiated by TEST key operation.

Autopilot Set Up mode entry confirmation.

NT921G AUTOPILOT OPERATING MANUAL 3.4

Alarm Display Messages. (Accompanied by audible alarms when the Autopilot is engaged). (i)

S HI FAIL

Signal level from Mag Com too high.

(ii)

S LO FAIL

Signal level from Mag Com too low.

(iii)

S PHS FAIL

Com cable connections or HSC suspect.

(iv)

Gyro HI FAIL

Signal level from Gyro too high.

(v)

Gyro LO FAIL

Signal level from Gyro too low.

(vi)

Gyro PHS FAIL

Gyro cable connections or Synchro suspect.

(vii)

0183/0 dAtA FAIL No valid CTE GPS/TrackPlotter.

(viii)

OHA Hdg FAIL

Heading signal failure to Off Heading Alarm.

(ix)

HC:30

Maximum (30°) heading correction in TRACK mode.

(x)

no dAtA

No 0183 heading data and 0183 set as priority heading data.

(xi)

rru FAIL

Rudder Reference Unit failure indicated.

(xii)

HSC FAIL

An unreasonable rate of change of heading has been detected from the HSC (heading sensor coil). The HSC sensor has been inhibited and will not be re-enabled until the Autopilot MODE switch is set to STANDBY. Check the connections and cable to the HSC (Terminals 3 to 8).

(xiii)

SYNC FAIL

An unreasonable rate of change of heading has been detected from the gyro. The gyro sensor has been inhibited and will not be reenabled until the Autopilot MODE switch is set to STANDBY. Check the connections and cable to the 1:1 synchro (Terminals 27 to 31).

(xiv)

HDT FAIL

An unreasonable rate of change of heading has been detected in the HDT (NMEA 0183) heading data. The HDT sentence has been inhibited and will not be re-enabled until the Autopilot MODE switch is set to STANDBY. Check proprietary heading source.

data

received

from

NT921G AUTOPILOT OPERATING MANUAL

3.5

(xv)

HDG FAIL

An unreasonable rate of change of heading has been detected in the HDG (NMEA 0183) heading data. The HDG sentence has been inhibited and will not be re-enabled until the Autopilot MODE switch is set to STANDBY. Check proprietary heading source.

(xvi)

HCC FAIL

An unreasonable rate of change of heading has been detected in the HCC (NMEA 0183) heading data. The HCC sentence has been inhibited and will not be re-enabled until the Autopilot MODE switch is set to STANDBY. Check proprietary heading source.

(xvii) HDnn FAIL

An unreasonable rate of change of heading has been detected in the HDM (NMEA 0183) heading data. The HDM sentence has been inhibited and will not be re-enabled until the Autopilot MODE switch is set to STANDBY. Check proprietary heading source.

(xviii) 3.5 rEF FAIL

The 3.5v reference voltage is outside the tolerance band. Check HSC and 1:1 synchro connections.

(xix)

The internal 2.5v reference voltage is out of tolerance. Seek service advice.

2.5 rEF FAIL

Alarm LED’s. (Accompanied by audible alarms unless alarms muted). (i)

O POWER FAIL Internal battery (discharged) or external (Continuous alarm) (ships) power supply failure.

(ii)

O POWER FAIL (Pulsed Alarm)

(iii)

O STEERING FAIL Steering gear not responding to Autopilot demands.

(iv)

O RUDDER LIMIT Maximum specified angle of rudder or rate of turn attained.

(v)

O RESET (Pulsed alarm)

Internal battery open circuit

Maximum (30°) heading correction in TRACK mode.

NT921G AUTOPILOT OPERATING MANUAL 3.6

Operational Status LED’s. (i)

O MANUAL

Autopilot in STANDBY mode (manual steering required).

(ii)

O AUTO

Autopilot engaged (ON).

(iii)

O REMOTE

Remote Station demand forcing Autopilot to track vessel. (Manual Steering or Remote Power steer in progress).

(iv)

O MAG

Current ACTUAL HEADING displayed is MAG heading.

(v)

O TRUE

Current ACTUAL HEADING displayed is True heading.

(vi)

O TRACK DATA

Current ACTUAL HEADING display showing Track data.

(vii)

O RUDDER LIMIT Rudder Limit control is switched off (no limit). OFF

(viii)

O TRIM OFF

Automatic Trim function is switched OFF.

(ix)

O OFF HDG ALARM

Specified maximum degrees off course attained.

(x)

O OFF (TRACK)

Track function switched OFF.

(xi)

O LO (TRACK)

Track function operational in LO mode.

(xii)

O HI (TRACK)

Track function operational in HI mode.

(xiii)

O ON (AUTOPILOT MODE SWITCH)

Autopilot engaged.

(xiv)

O ON – Pulsed LED (AUTOPILOT Autopilot internal computer fail. MODE SWITCH)

(xv)

O

ALARMS

All audible alarms muted (OFF).