JAM

GPS-free navigation with JAM, helping you through waters with intensive GPS-jamming like the Baltic Sea.

JAM utilizes data from the vessel’s log and compass to provide guidance along the planned route. By constantly comparing the ship’s estimated dead reckoning position with GPS signals, JAM alerts you to suspicious GPS behavior and potential jamming.

Based on the estimated position, JAM can transmit virtual GPS data (NMEA RMC) to plotter devices, allowing your ship’s position to be displayed on electronic nautical charts even when GPS is unreliable. JAM also contains an interactive map showing the route with your heading and position plotted in real-time.

What You Need

For using JAM on board:

  • A laptop or a Raspberry Pi (4 or 5 recommended)
  • Your planned route as a GPX file
  • Optional: USB GPS receiver or network GPS connection

Data Input Options

JAM supports three flexible modes for feeding data to the system:

1. Automatic Mode (Recommended)

  • Magnetic compass and log data via NMEA0183
  • Available via UDP network or USB/Serial connection
  • Includes GPS data for monitoring and jamming detection
  • Real-time automatic navigation

2. Manual Steering

  • Enter magnetic heading and speed through water (STW mode)
  • Or enter accumulated log distance only (Log-only mode)
  • Perfect when instrument data is unavailable
  • Large touch-friendly numeric keypad

3. Position Updates

  • Update JAM with ship’s log readings at intervals
  • Virtual position advances along the planned route
  • Displays current location on the virtual map
  • Ideal for periodic position confirmation

Interface Organization

The JAM interface is organized in logical, expandable blocks according to different navigation tasks. Each block can be enlarged for a clearer overview while sailing.

Route & Navigation

  • Current waypoint information
  • Distance and bearing to next waypoint
  • Estimated time of arrival
  • Course-to-steer guidance
  • DR position in decimal or degrees/minutes format
  • GPS position monitoring

Deviation & Trim

  • Magnetic declination for current area
  • Vessel’s magnetic deviation at current heading
  • Automatically updated from the vessel’s deviation curve (use Streamworks MagDev tool or CSV format)
  • Manual trim of deviation
  • Compensation for drift and current
  • Total deviation as sum of all parameters
  • Visual deviation plot across all headings

Speed & Log

  • Trim of STW (Speed Through Water) for current assistance
  • Accumulated distance from STW
  • Accumulated distance from virtual speed (SOG)
  • Real-time speed monitoring

Log/Settings

  • Distance logs (STW and SOG)
  • Trip start options (GPS position or route’s first waypoint)
  • Position format selection (Decimal or DMS)
  • GPS source selection (UDP network or USB/Serial)
  • Serial port and baud rate configuration
  • UDP port settings for receiving and transmitting
  • Auto-start configuration
  • Version information

Virtual Map

  • Interactive route display with all waypoints
  • Ship’s position and heading indicator
  • Real-time DR position updates
  • Zoom and fullscreen controls
  • Touch navigation

Additional Features

GPS Surveillance

  • Continuous comparison of DR vs GPS position
  • Visual warnings for GPS anomalies
  • Position confidence indicators
  • Jamming detection alerts

Manual Steering Panel

  • Dedicated fullscreen interface
  • Two modes: STW+Heading or Log-only
  • Large buttons for easy operation at sea
  • Instant position updates

Web Interface

  • Remote monitoring via web browser
  • Access from any device on the network
  • Real-time navigation data
  • Available on port 8080

Trip Logging

  • Complete navigation records in CSV format
  • Position, heading, speed, and time
  • Resume interrupted trips
  • Historical data analysis

Platform Support

Raspberry Pi (Recommended)

  • Optimized for Raspberry Pi 4 and 5
  • Works with official 7″ touchscreen
  • Supports any HDMI display
  • Pre-compiled binary available (~130 MB)
  • Fast native performance

Desktop Computers

  • Windows 10/11 supported
  • Linux supported

Technical Specifications

NMEA Protocol: 0183 (RMC, VHW sentences)
Update Rate: 1 Hz
GPS Input: UDP network or USB/Serial
GPS Output: NMEA RMC via UDP

Getting Started

  1. Install JAM on your Raspberry Pi or computer
  2. Connect GPS receiver (USB or network)
  3. Load your GPX route file
  4. Configure magnetic declination and deviation
  5. Select GPS source (UDP or USB)
  6. Start navigation and follow course guidance

JAM Navigation – Professional dead reckoning when GPS fails.