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Specifically designed for small professional vessel use (typically 11-20m LOA) the NT921 MKII Autopilot provides a powerful combination of steering system control and interface facilities based on an extremely intelligent Control Unit which is clearly marked and simple to operate.
Accordingly, the NT921 MKII offers Navitron steering expertise in a robust and compact package which includes the following special features:
Straightforward operation is a key feature of the NT921 MKII thus operator controls are kept to a minimum and are clearly identified by control panel markings which are red backlit for night viewing via a variable intensity illumination control.
A conventionally marked Course Selector permits simple course selection which is automatically corrected to maintain the vessel on a specified track when connected to a GPS or Track Plotter programmed with a track based on predetermined waypoints.
In addition to Track data, the NT921 MKII will also accept NMEA heading data directly from GPS compass systems etc. When dual heading inputs are employed (NMEA + mag sensor coil) the priority source is installation programmable with automatic changeover in the event of primary source failure.
Suitable for console or bracket mounting, the NT921 MKII Control Unit is intended for wheelhouse location and is supplied complete with Heading Sensor Coil and Rudder Reference Unit for installation to solenoid hydraulic systems (11-40Vdc/5A max).
High voltage solenoids (110/220Vac/dc) can also be accommodated via the inclusion of an optional Universal Relay Box type NT920URB.
Alternatively analogue signal control of water jets or analogue steering machines requiring -10v/+10v inputs can be configured via the inclusion of a Navitron Analogue Steering Interface (NT990ASI).
| Parameter | Specification |
| Supply Voltage Range | $11\text{V DC}$ to $40\text{V DC}$ (Main power supply with built-in power failure monitoring) |
| Power Consumption | $2.5\text{W}$ @ $24\text{V DC}$ ($8.1\text{W}$ max with full panel illumination) |
| Solenoid Drive Outputs | Solid-state FET switching outputs ($11\text{–}40\text{V DC}$, $5\text{A}$ max continuous rating) |
| Switching Polarity | Selectable Common $+VE$ or $-VE$ |
| Optional Drive Interfaces | Dual solenoid or dual-channel analogue outputs ($\pm 10\text{V DC}$) for independent dual rudder or proportional drive control |
| Display Panel | Servo-driven analogue heading repeater for standby mode, red illuminated control panel, digital heading display, and bargraph rudder angle display |
| Interface Type | Supported Protocol / Signal | Resolution |
| Mag Heading Input 1 | Direct Navitron Sensor Coil (HSC1 or HSC2) mounted to magnetic compass |
$0.25^\circ$ |
| Mag Heading Input 2 | NMEA 0183 ($xxHDM, $xxHDG, $xxHCC, $xxHDT) |
$0.1^\circ$ |
| Track Steering Input | NMEA 0183 ($xxHTC, $xxHSC, $xxAPB) via Plotter / GPS / ECDIS |
— |
| Follow-Up Rate | Minimum $30^\circ/\text{sec}$ for all heading input types | — |
| Output Type | Configurable Formats & Sentences |
| NMEA 0183 Output |
Isolated RS-422 interface • Heading: • Status / VDR: • Selectable Update Rates: $1\text{Hz}$, $10\text{Hz}$, or $20\text{Hz}$ |
| Furuno Format | Selectable $5\text{Hz}$ or $40\text{Hz}$ update rate ($0.166^\circ$ or $0.1^\circ$ resolution, $5\text{V}$/$12\text{V DC}$) |
| Step-by-Step | Selectable $3$, $6$, $12$, or $24$ steps per degree ($5\text{V DC}$ signal amplitude) |
| Navitron Serial Data | Dedicated data line to Navitron digital repeaters / remote displays |
| Parameter | Specification |
| Steering Intelligence | Full P.I.D. steering algorithm with AutoTrim (automatic permanent helm) |
| Steering Modes | AUTO (Heading Hold), STBY (Manual Helm), TRACK (Plotter / Waypoint Steering), DODGE |
| Operator Controls | Rotary Course Setter (Push & Rotate with $+1^\circ/-1^\circ$ fine keys), Yaw, Rudder Mode, Counter Rudder, Rudder Limit, Illumination, and Mode Selectors |
| Automatic Stability | Automatic compensation for rudder speed variations (compatible with two-speed steering systems) |
| Panel Alarms | Power Fail, Off-Course, Steering System Fail, Rudder Limit, Heading Input Fail (includes Alarm Test facility) |
| Rudder Feedback Unit | Heavy-duty potentiometric reference unit (NT920RTU / NT990RTU) |
| Parameter | Specification |
| Control Unit Dimensions | $297\text{ mm (W)} \times 176\text{ mm (H)} \times 110\text{ mm (D)}$ (behind bezel) |
| Weight | Approx. $3.3\text{ kg}$ |
| Operating Temperature | $-20^\circ\text{C}$ to $+60^\circ\text{C}$ |
| Compass Safe Distance | $0.6\text{ m}$ |
| Standard Scope of Supply | NT921 MK2 Control Unit, Mag Heading Sensor Coil, and Rudder Reference Unit |
Manufacturer Part Number: NT921-MK2
Country of Origin: United Kingdom (UK)
MED Approval: Wheelmarked under MED 96/98/EC
Target Vessels: Commercial fishing vessels, workboats, ocean-going tugs, coasters, and motor yachts from 11m to approx. 50m LOA
Standards Compliance: Fully Type Approved to ISO 11674, IMO A.342(IX), and IEC 60945 (Notified Body 0191)
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