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Tips for using AIS

Here are 10 tips for using AIS on board

 1. Get to know your icons

AIS target icons

The icon displayed on the screen of your chartplotter tells you about the type of AIS target.  Raymarine's latest update gives many more target options than the two above.  A safe target may turn into a dangerous target when the vessel comes within your closest point of approach (CPA) based on it's speed and course.

 

2. Dangerous Vessels

Vessel CPA and TCPA

On most chartplotters you can setup what constitutes a dangerous vessel.  You can configure the Closest Point of Approach (CPA) and the Time to Closest Point of Approach (TCPA) that suits your vessel type and speed.  For example, you may wish to consider any vessel which will come within 0.5NM and with a time of 10mins to be a dangerous vessel.  Any target meeting these criteria will be marked as a dangerous target until it is safe to return to be displayed as a normal target again.

3. Vessel Alarms

Configuration of an alarm that sounds when a AIS target becomes dangerous is a good idea if navigating a channel at night or with poor visibilty, however during busy periods in good weather, this may become annoying with a lot of AIS targets in the area. Being able to turn the alarm on/off easily is a good feature to have available.

4. Radar Overlay

AIS Radar Overlay

AIS is not a replacement for radar, however it certainly helps with identifying targets on the radar screen.  Allowing more information to be known about a target with a simple click.  SOG and COG data available via AIS can confirm the track and speed of a radar target without needing to activate a MARPA target on the radar or watch the screen to keep track of its movement.

5. Extension lines

Ais Vectors

Most chartplotters have the ability to display "extension lines" from an AIS target showing the projected COG of the vessel.  You can configure the time period for the projected course also.  In the example above the plotter may be set to 10mins which shows the projected position of the target in 10mins time. Based on it not changing its course or speed.

6. Silent Mode

AIS Panel switch front

Em-trak Class B transceivers/ transponders come with the facility to be put into "Silent mode" whereby the device then becomes a receiver only for AIS. This can be useful in crowded waterways or if you wish to go incognito for a while.  Picosense have created a stylish AIS transponder silent mode panel switch

7. Linking with a VHF radio

It's possible to link your plotter to a DSC enabled VHF radio so that you may transmit a DSC call straight to a vessel by tapping on it on the screen. NMEA2000 models, like the Em-trak B100 tend to do this seamlessly.  

8. Online AIS

 Marine Traffic Logo

Apps such as Marine Traffic can provide a somewhat false impression.  These take AIS signals received by a range of shore stations, and publish the positions online.  While useful when in range of mobile data services, they are not a substitute for a proper AIS installation on board.  Utilising these online apps does not provide any collision avoidance while on board.  

9. Last position report

Vessel data on OpenCPN

If you are actively watching an AIS target, most plotters will display the time since last transmission.  It is worth monitoring this, as if the time keeps increasing the actual position may be very different.  This is especially critical for fast moving vessels. A lost target icon will appear after a certain time period has passed.

10. Dealing with clutter

AIS clutter

Sometimes things just get very cluttered and on days with good visibility you may wish to disable AIS targets on the screen to assist seeing other data. You may configure it to just show dangerous targets also.  It is also known that the idea that large vessels operating with Class A AIS units filter out class B devices is not true and operators of these larger vessels particularily wish to see small Class B enabled vessels in close range.  

How useful is AIS?

Installing an AIS transceiver/transponder won't act as a complete "ship repellent" and keep big ships away from you - it's still best to stay on your guard. But what it will do is add another level to the other precautions we take - radar reflectors, nav lights etc, - and increase the possibility that you'll be seen.