Hydro Acoustic Position Reference

A cost effective and highly accurate position reference system for a Dynamic Positioning System DP1, DP2 and DP3


The Mega-Guard Hydro Acoustic Position Reference (HPR) is applied as a cost effective and highly accurate position reference system for a Dynamic Positioning System DP1, DP2 and DP3. The position of the seabed  USBL Transponders are used as reference points for the ship mounted USBL Transceiver. The USBL Transceiver is connected to the HPR Workstation through Ethernet connection. The MRU-INS, gyro and optional  DGPS are connected as well to the HPR Workstation. The HPR Workstation accurately calculates the relative position of the vessel taking into account the data as received from the USBL Transceiver, MRU-INS, gyro and  optional DGPS. The USBL Transponder contains a release mechanism with floating collar for recovery of the transponder from the seabed.

The Mega-Guard Hydro Acoustic Position Reference consists of the following components:

  • HPR Workstation providing a user friendly man-machine interface
  • USBL Transceiver with a 5000 meter range
  • USBL Transponders for 4000 meter water depths.
  • Motion Reference Unit
  • Control Cabinet

The USBL Transceiver can be mounted in two different ways:

  • Hull mounted with gate valve and deployment machine
  • Pole mounted with over-the-side pole

Accuracy Hydro Acoustic Position Reference

  • Beam angle repeatability : 0.12 degrees
  • Slant range accuracy : 0.01 meter

Accuracy specified at 1500 meter range and water depth (0 degrees beam angle) and no influence from roll / pitch / yaw of ship and no influence from sound velocity variation.

HPR Workstation

  • Mega-Guard Workstation: Marine PC, 19~22” TFT and Trackball.
  • Ethernet link to USBL Transceiver.
  • NMEA inputs: Gyro, Motion Reference Unit with optional INS and DGPS.
  • NMEA output: position data connected to DP system through Ethernet or serial link.
  • Dead reckoning with position improvement through MRU-INS (option)

USBL Transceiver specification

  • Transceiver operating beam width: +/- 90 degrees (omni-directional)
  • Transceiver frequency: 12 to 24kHz
  • Angle measurement: 3D measurement arrangement with 5 antenna's
  • Interrogation rate: 0.6 to 6.6 seconds depending on operating depth
  • Supports up to 128 transponders
  • Optional: accoustic modem data link

USBL Transponder specification

  • 4000 meter water depth
  • Omni-directional
  • Aluminium housing with polyurethane coating
  • Equipped with sleep mode for long term deployment
  • Equipped with long life rechargable battery pack:
    • 0.5 million replies at 5000 meter range
    • 10 million replies up to 1000 meter range
  • Equipped with release mechanism and floating collar
  • Optional: pressure, tilt and temperature sensors.

Motion Reference Unit

  • Pitch and roll accuracy : <0.03 degrees
  • Minimum update rate : 10 times per second

Control Cabinet

  • Bulkhead mounted cabinet size: H=1000, W=600, D=400mm
  • Operator Panel for deployment machine mounted in front door.
  • Power supply: 230VAC – 1250W

Gate valve and deployment machine

  • Gate Valve size: 8” (type approved)
  • Depth below hull when down: 1 or 2 meter
  • Maximum vessel speed: 7 knots
  • Optional: Operator Panel on bridge



  • Deployment pole (supplied by customer) height: up to 15 meter.
  • Minimum depth below hull 1 meter.

Sales and service

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Contact information

Praxis Automation Technology
Zijldijk 24A,
2352 AB Leiderdorp
The Netherlands

+31 (0)71 5255 353

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