A Vessel Position Monitoring System


The Onacom Vessel Postion System, onaVPS, is a vessel position reference system tailor-made for offshore floating vessels by Onacom.

onaVPS combines high performance GNSS sensors and the onaGPS software suite to provide reliable and accurate position monitoring for various offshore and oil production vessels like FPSOs, Oil Storage Vessels, Semi-submersibles and FSUs.

Features and Benefits
  • Real-time data acquisition
  • Alarm limits
  • High reliability
  • Snail trail
  • Up to 5-year movement history
  • Multiple client connections
  • Clean graphical user interface
  • Open protocols: NMEA-0183, Gill ASCII, TSS1, TSS3, OMC-2900
  • Custom NMEA sentences
  • WGS-84 to local/custom UTM conversion
  • Customise to vessel's requirements
  • Vendor neutral
Observator Instruments SMC Teledyne TSS Trimble Gill

  • Vessel Position Monitoring
  • Vessel Position Reference
  • Anchor-chain Integrity Monitoring
  • Weather Information System
  • Data Server
  • Absolute, Differential and Relative Position Reference

More on Features and Benefits

onaVPS is a GPS-based system. It uses data from high perfomance GPS sensors on a vessel to monitor the position of the vessel relative to its (the vessels's) mooring centre. The vessel's position can be monitored to a 20cm accuracy: depending on the quality of the GPS sensor. The position accuracy can greately improve with differential correction, DGPS; satellite-based correction, SBAS; and other high precision commercial correction services.

For GPS sensors that support RTK accuracy, postion accuracy of 10cm horizontal and 2cm vertical can be achieved.

DGPS v GPS data

Alarm zones

Vessel Position Monitoring Operations

When the onaVPS is depolyed as a vessel postion monitoring system, the system monitors the movement of the vessel relative to its mooring centre.

If the vessel moves into the alarm zones, audible alarms are sounded to alert the control room operators. The system also provides an alarm panel on the graphical user interface. The system can also be configured to alarm on several events.

In the vessel postion monitoring mode, onaVPS doubles as a Vessel Anchor-chain Integrity Monitoring System.

The onaVPS operations follow simple steps:

  1. Acquire good GPS position data.
  2. Integrity check the position data.
  3. Compute vessels position relative to the mooring centre and offsets from the GPS antennae locations.
  4. Convert GPS position data to local/custom UTM: Eastings and Northings.
  5. If the vessel has moved into the alarm zones, sound alerts.
  6. Archive position data: UTM, GPS and weather data.
  7. Display snail trails of up to last 2 hours movements.
  8. Communicate with other systems to exchange data.

onaVPS Software Specification
Data Input/Output
Message formats NMEA-0183, Gill ASCII, TSS1, TSS3, OMC-2900
Gill ASCII FormatsMode 1 - ASCII, UV, Continuous; Mode 2 - ASCII, Polar, Continuous
TSS Formats TSS1 Format, TSS3 Format
Modbus Protocols Modbus ASCII/RTU/TCP
Other Protocols NTP, SMTP, SNMP, SSH, UDP

*onaVPS NMEA-0183 supports various NMEA sentences: it is flexible and can be updated to support new NMEA sentences.

onaVPS Hardware Specification*
onaVPS Hardware* Based on Amplicon Impact-R 1000LP. See Amplicon for more information.
Processor Intel Atom N270 1.6GHz
Memory 1GB fitted (max 2GB)
Chipset Intel 945GSE + ICH7M
LAN 2x Gb Realtek with Wake-on-LAN
USB 6 ports (2 front & 2 rear)
Internal interfaces SATA, CompactFlash
Serial Ports 1x R-232/422/485, 5x RS-232 ports. Expandable via network serial port servers.
System expansion 1x PCI slot (190mm length)
Chassis Heavy-duty cold-rolled electroplated steel
Dimensions 483 x 43 x 220mm (W x H x D). 1U
Weight 4kg
Power supply Industrial 250W ATX power supply.
Autoswitching 100 to 240Vac.
Power requirement Typically between 30~40W (excluding PCI card)
Certification CE for EMC and safety standards
Operating temperature0 to +45 °C
Hardware Monitor Monitors CPU temperature, system temperature, voltage and fan speed

GPS Receiver/Compass Specification*
onaVPS GPS Hardware* GPS Receiver/Compass hardware is Trimble SPS361. See Trimble for more information.
Satellite system GPS
Signal with GA530 antenna L1/L2 GPS, MSK Beacon, SBAS, and OmniSTAR
Dimensions L x W x D 24 cm (9.4 in) x 12 cm (4.7 in) x 5 cm (1.9 in)
DGPS Position Accuracy**
Correction type DGPS RTCM 2.x
Correction source DGPS Base via radio or Internet
Horizontal accuracy(mm+ppm) ± 250+1 RMS
Vertical accuracy(mm+ppm) ± 500+1 RMS
Position Accuracy***
Horizontal accuracy Typically <1 m (3.3 ft)
Vertical accuracy Typically <1 m (3.3 ft)

** Accuracy and reliability may be subject to anomalies such as multipath, obstructions, satellite geometry, and atmospheric conditions.
*** Depends on SBAS system performance.

All specifications provided are current at the time of publication. However, because of the Onacom policy of continual product improvement, we reserve the right to make changes at anytime without notice.



Gill ASCII is a communications driver for transmitting and receiving Gill Anemometer Digital Serial Output traffic. Gill Anemometers are produced by Gill Instruments Limited. The anemometers output digital serial data in various formats. Onacom's Gill ASCII support the following formats:

Mode 1 - ASCII, UV, Continuous
Mode 2 - ASCII, Polar, Continuous

The Global Positioning System - is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. The system provides critical capabilities to military, civil and commercial users around the world. It is maintained by the United States government and is freely accessible to anyone with a GPS receiver. [GPS]

National Marine Electronics Association. NMEA-0183 defines the standard for interfacing marine electronic devices such as echo sounder, sonars, anemometer, gyrocompass, autopilot, GPS receivers and many other types of instruments. This standard defines a number of 'strings' or 'sentences' referred to as NMEA sentences that contain navigational details such as positions, current time and so on.

onacom's NMEA-0183 supports various NMEA sentences: it is flexible and can be updated to support new NMEA sentences.

Observator Instruments

OMC-2900 is a communications driver for transmitting and receiving OMC-2900 messages. OMC-2900 messages are used by various instruments manufactured by Observator Instruments to send and receive weather data.

Real-Time Kinematic - A real-time differential GPS method that uses carrier phase measurements to achieve high accuracy.

Satellite-Based Augmentation System. SBAS is a differential GPS method tha uses wide area networks of reference stations. Corrections and additional information are broadcast using geostationary satellites. Various SBAS implemetations include: WAAS, EGNOS, MSAS, SDCM, GAGAN and so on [SBAS].

Teledyne TSS

TSS is a communications driver for transmitting and receiving DMS Series XX (Dynamic Motion Sensor) Digital Data Output traffic. The DMS Series XX is a small portable sensor for measuring the vertical displacement and attitude of a vessel when no stationary reference is available. The device is produced by Teledyne TSS Ltd. The sensor output digital serial data in various formats. Onacom's TSS support the following formats:

TSS1 Format
TSS3 Format

World Geodetic System 1984. The World Geodetic System (WGS) is a standard for use in cartography, geodesy, and navigation. All GPS coordinates are based on the WGS-84 datum surface. The WGS-84 datum is based on the ellipsoid of the same name.

Universal Transverse Mercator - a projected coordinate system that uses a 2-dimensional Cartesian coordinate system to give locations on the surface of the Earth. UTM only represents the horizontal position. [UTM]

[GPS] Wikipedia
[SBAS] Wikipedia
[UTM] Wikipedia

How to Order

We supply onaVPS directly to our customers. Please contact us with your requirements.

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