AIS / ARPA Module Documentation



The AIS module is an optional module of ScanNav. When active, it lets you visualize on screen all boats equipped with a transmitter (required above 300 tons), and manage anti-collision alerts. Radar ARPA or MARPA targets are also managed starting from version 10.1 of ScanNav.

AIS targets are represented on screen in a similar way to your own boat, with or without heading line, track, and  corridor proportional to the target's real dimensions. When placing the mouse over an AIS target, a popup window will show all information such as the target's name, size, heading, speed, destination,etc... Options related to the AIS module are grouped in the following 2 locations:

  • "AIS" tab in the "Preferences" (see "Display and alerts" below)
  • and menu "Options" -> "AIS / ARPA":
    • "Show Targets": Lets you globally show/hide the display of AIS targets. Warning: if this option is unchecked, no target will be displayed.
    • "Targets list": To display targets in a list. See appropriate chapter further in this document.
    • "SSN position reports Import" : See appropriate chapter further in this document.
Note: entries of menu "Options -> "AIS/ARPA" are also available dispatched under menus "File" and "View" for historical reasons, so as not to disturb habits. They will be removed from these alternate locations in further releases.
Anti-collision Alerts:

In case of collision risks, an audible alarm is triggered, and a window opens showing all properties of the target, as well as alert conditions (approaching speed, minimum estimated distance (CPA/TCPA), etc...) .
This window can also be opened on demand using the "properties" button in the AIS list view.
AIS Alarm

Display and Alert options
You can tune all display and alert options using the preferences window. To access, use menu "File" ==> "Preferences" and go to the "AIS" tab. 

- "Draw at real size": If this option is checked, targets for which dimensions are known will be displayed at real size when the zoom factor is sufficiently high. 

- The "Security distance" unit can be expressed in "NM" (Nautical miles), "KM" (Kilometers), or "M" (Meters). This unit is also used for the minimum distance to show CPA vectors (see below)

-The MMSI number only needs to be given if you have a transponder on board. The MMSI number entered in this field will be ignored by ScanNav. If you do not enter it, you will have collision alerts with your own boat. If you just have an AIS receiver, you can just leave this field to 0.

-"Erase targets older than" : Targets will disappear from screen if they do not send any information after the given value in seconds. (They will independently also change color after 10 seconds without reception) 

- An alarm will be triggered if the option "Collision alerts" is checked, and if the target's CPA or TCPA are below the given values in "security distance" (for CPA), or "minutes before..." (for TCPA). (here 1 nautical mile for CPA and 30 minutes for TCPA) 
- Alerts may be audible ("Audible alarm") and/or visual ("Show alert box"), and the alert window may stay opened or close after the alert conditions are safe ("Auto close"). On another side, targets in alert condition  are highlighted on screen to distinguish them more easily.
- "Limit alerts to targets with speed higher than": lets you ignore targets that are at mooring or below a given speed (very useful in or near harbors)
- "Delay on validation" lets you ignore alerts from a given target for a given period, once the alert box is validated. (this option can also be changed in the alert box when it appears before closing it).

-The length of the Heading line can be set according to time.  It can also be graduated in time steps as for your own boat (but independent parameters). A corridor with a width proportional to the target's length can also be shown.

- If "Memorize tracks" is checked, all targets positions are logged as tracks for the current session. These tracks will be displayed or not according if you check or not the "Show tracks" option.

- A "Maximum time" value can be set to limit the visible section of the AIS tracks to a given amount of time since the last known position. This will avoid an overloaded display, still keeping the essential information.  The full tracks may be recovered at any time by unchecking the option. 

If "CPA vectors" (Closest Point of Approach) is checked, a vector will be drawn between your own boat and targets to  show the estimated position of both boats at the time where they will be the closest to each other.
You can therefore see on the example at the left, that your own boat (in blue) will pass behind the AIS target. 

To have a lighter display, you can limit the CPA vectors to targets for which CPA is lower to  given distance, by checking "Limit to" option, and entering a distance value (in same unit as "security distance")

"Dead reckoning": When checked, ScanNav will estimate the position of targets that do not emit anymore, according to their last known position/heading/speed. In this case, the target is shown at it's last known position, and a first segment with a dashed line will show the estimated route done since. The estimated position is therefore at the end of the dashed line segment. 

List View
You may view all targets as a text list using menu "Options"->"AIS / ARPA" ->"Targets list" , that will be displayed as follow:

AIS List

  • All available information for each target are displayed as separate columns. 
  • The list has the same general behavior as the objects list view or charts library (ordering, etc...)
  • You may click on the "Columns" button to configure the display (change the ordering, or add/remove columns) 
  • You can sort the list according different criterias by clicking on the columns headers.
  • Targets that are in collision alert will always appear in red and at the top of the list 
  • Selected lines (highlighted in blue when clicking on them) will show up on the chart in a different color to distinguish them (you may use "Ctrl" and "Shift" keys to select several lines)
  • "Center" button will center selected targets on the chart. If several lines are selected, ScanNav will modify the scale so as all selected targets show up on the chart.
  • "Properties" button will open the alert dialog of the corresponding target(s)
  • When option "Filter old targets" is checked, only still visible targets will be displayed in the list (see preference settings above)
  • When right clicking on the map at the position of an AIS target, all targets intersecting this point will be listed at the end of the menu.  Selecting one of these entries in the menu will open the list view with the corresponding entry selected.

ARPA / MARPA support

Starting from version 10.1, the AIS module also lets you monitor Radar with an ARPA or MARPA interface, with equivalent functionality. ARPA/MARPA targets will be distinguished from AIS targets in the list view by their name, starting by "ARPA" and followed by the target number. Supported ARPA sentences are:

  • "TTM" (Tracked Target Message) or "TLL" (Target Latitude and Longitude) : to report radar targets positions
  • "RDS" (RADAR System Data) : to display the Radar cursor on screen

Import of SSN position reports for tracking

  • The AIS module also lets you visualize SSN position reports, used for tracking fishing fleets. Boats are visualized as AIS targets including their tracks. 
  • To import SSN reports, use menu "File" -> "SSN position reports import"


Several connection possibilities exist according to you AIS hardware: 

  1. When possible, plug your GPS to the AIS receiver, then the AIS receiver to your PC with ScanNav. In this case, and if supported by the AIS receiver's possibilities, it will send the GPS positions together with it's own sentences. In this case, you just have to modify the settings in the GPS tab of the ScanNav preferences, to position the speed at 38400bds. although most AIS boxes only retransmit GPS data, a few  also retransmit any  NMEA data received from a multiplexer.
  2. Some AIS hardware also include an integrated GPS (case of most transceivers). In this case, you might not need an additional GPS if the AIS retransmits the GPS info. The configuration is in this case the same as 1 above.
  3. In other cases, you will need to plug your AIS hardware on another independent port. In this case, you need to configure a specific instrument in the "Instruments" tab of preferences. The speed parameter should be positioned to 38400bds. At the opposite of other NMEA instruments that send information continuously, some AIS receivers only send information when a target is in view. This can be interpreted by ScanNav as a low reception alarm. In this case, you should give very high values to "Communication timeout" and "Valid sentence timeout" parameters to avoid raising useless alarms. These timeout values being in seconds, you should enter very high values (for example 3600 for one hour, or 86400 for 24h)