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Transmit Magnetic Heading from a ship’s Magnetic Compass to a remote Heading Repeater Display over a digital NMEA 0183 connection.

  • Description

    Magnetic to Digital Overview

    Increasingly, Maritime Authorities are accepting the use of Transmitting Heading Device (THD) Systems on board vessels. Marine Data offers two types of THD system:

    • A system which senses the angular position of a ship’s magnetic compass card; this is known as a Transmitting Magnetic Compass System (TMC). This type of system provides a digital heading from an existing host magnetic compass installation in its binnacle; it detects the position of the moving compass card
    • A system which directly senses the Earth’s magnetic field; this is known as an Electro-Magnetic Compass System (EMC). This type of system provides a digital heading directly from the Earth’s magnetic field; it does not require a host magnetic compass; it has no moving parts

    The MD71TMC Transmitting Magnetic Compass System

    Instead of using inflexible and bulky optical apparatus (reflectors, periscopes etc.) to view the magnetic compass, electronic remote displays may be used in the form of a Compass Repeater. The Marine Data MD71TMC is a Transmitting Magnetic Compass (TMC) System which detects and transmits the ship’s Compass Heading over a NMEA 0183 digital connection to one or more Compass Heading Repeaters at any convenient location on a vessel.

    The Marine Data MD71TMC is a Transmitting Magnetic Compass (TMC) System which uses the latest technology to accurately process and convert the ship’s magnetic compass heading to NMEA 0183 heading data with unparalleled accuracy. TMC systems from Marine Data are simple and intuitive to use with quick and easy installation and on-board calibration.

    Special Features

    • Automatic calibration of the Magnetic Sensor Coil with host ship’s magnetic compass by turning the ship through 390°
    • Intuitive menu-driven installer assistance when mounting the Sensor Coil to the ship’s host magnetic compass
    • Dual power supply inputs
    • Bright OLED display provides good clarity with high contrast and wide viewing angles
    • Output: 2x NMEA 0183 data channels


    • Provides a digital NMEA heading output to drive a Heading Repeater (or other devices) at a convenient location
    • An elegant alternative to using an optical reflector in a ship’s magnetic compass installation

    Parts Included in this TMC System

    • MD52A/B – Compass sensor
    • MD97CSP – Compass sensor processor
    • MD71THD – Control and Display unit; provides 2x digital NMEA 0183 outputs; applies Magnetic Corrections to digital NMEA outputs; displays the heading**
    • 10 m D-type 9-way interconnect cable (CAN Bus)
    • 2.5 m D-type 15-way data cable for supplying system power and carrying 2x NMEA 0183 data channel outputs

    Required Option: Compass Sensor Mount

    • Optional Sensor Mount MD54 or MD58 – this is not included as standard because it depends on the type of host magnetic compass. Since there are many different manufacturers of magnetic compass,  please let Marine Data know the type of Magnetic Compass you will be fitting to so we can determine the correct sensor mount.

    Products for expanding the TMC System

    • Dedicated Heading Repeater(s)
    • MD96JB/8 Junction Box which can be used to supply system power and act as a breakout box for 2x NMEA 0183 data channels (2 in; 2 out)
    • MD94DDU NMEA 0183 Data Distribution Unit which can be used to supply system power and act as a breakout box for up to 9x NMEA 0183 data channels (2 in; 9 out)
    • MD71TB Trunnion Bracket – a versatile mount for the MD71THD Head Unit

    Related Products

    • MD97TMC – Standard Transmitting Magnetic Compass System
    • MD71EMC – Electro-magnetic Compass System

    **The MD71THD Control and Display Unit is capable of displaying the heading in numeric form as a basic heading repeater (compass repeater). However, we always recommend using a dedicated Marine Data Heading Repeater suitable for the precise purpose to which it will be put (a repeater for steering the vessel; a repeater taking bearings; a repeater to be mounted on the bridge wing, etc. See the full range here)

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