The Nortek AWAC is the base of the Nortek vesselmount system. A normal AWAC can be converted into a VM AWAC by purchasing a new firmware. This firmware is unique for each AWAC and must be bought seperately for each unit. The customer can switch between AWAC and VM AWAC themselves. In addition to the firmware, the customer will need to purchase software to run the VM system. This software is called SurveyVM (earlier also sometimes refered to as SurveyP).
To get the system to correct for the boats movement, and to position the value in a sensible place you will need the following:
- To give the current relative to the vessel, you need just the AWAC
- To give the current relative to Earth coordinates (ENU), you will need an external Compass/Gyro with digital output (NMEA) or, if the boat is not magnetic, the internal compass can be used.
- To give meaningful positions on the chart you will need GPS.
- DGPS system can be used
In contrast to a stationary profiler, such vessel mounted system will measure the sum of the vessel velocity (Uv) and the currents (Uc(z)):
UVM_profiler(z) = Uc(z) - Uv , where the use of bold signifies vector quantities.
To calculate the currents, it is necessary to subtract the boat velocity from the measured water velocity. This requires information from the ship heading (gyro) and navigation system (DGPS).