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Who should have AIS?

AIS introduction schedule:

Mandatory carriage requirements are set for all ships of 300 GRT and over engaged on international voyages, and those of 500 GRT and over not on international voyages as well as all passenger vessels irrespective of size.

All ships constructed on or after July 1st, 2002 must be fitted with AIS. Existing ships engaged in international voyages must be fitted with AIS as follows:

  • all passenger ships not later than July 1st, 2003
  • all tankers not later than the first safety equipment survey after July 1st, 2003
  • other vessels of 50,000 GRT and over not later than July 1st, 2004
  • other vessels of 10,000 GRT to 50,000 GRT not later than July 1st, 2005
  • other vessels of 3,000 GRT to 10,000 GRT not later than July 1st, 2006
  • other vessels of 300 GRT to 3000 GRT not later than July 1st, 2007

Existing ships not engaged on international voyages, constructed before July 1st, 2002, must be fitted not later than July 1st, 2008.


AIS broadcast data message – what is in it?

The information that is broadcasted by the AIS unit is sorted into three independent data reports and transmitted at set schedules according to the agreed standards.

Marine traffic is interested in the vessels name, its status according the Rules of the Road, its course and speed, rate of turn (RoT) and what the CPA and TCPA are. This information is packed in the so-called Static and Dynamic data packages, all other data is for the primary use of the maritime authorities.

Static data (update every 6 minutes)
(pre-programmed and does not change)

o Ship’s name and call sign
o IMO number
o Length & beam
o Location of antenna
o Ship’s type

Voyage related data (update every 6 minutes)
(to be inputted every new voyage):

o Draft
o Cargo information
o Destination and ETA
o Other relevant information

Dynamic data (update varies)
(automatically derived from ship’s interfaces):

o Time
o Ship’s position
o Course over ground
o Speed over ground
o Gyro heading and Rate of Turn
o Navigational status (according to Rules of the Road)

The Dynamic reports are updated depending on ship’s speed and status, as follows:

o At anchor 3 minutes
o 0 – 14 knots 10 seconds
o 0 – 14 knots & changing course 3.3 seconds
o 14 – 23 knots 6 seconds
o 14 – 23 knots & changing course 2 seconds
o 23+ knots 2 seconds
o 23+ knots & changing course 2 seconds

The trouble is that that AIS on some commercial vessels I have met at sea are showing “At Anchor” when they are clearly underway and going at a fair rate of knots… this means the so called dynamic data is being refreshed every 3 minutes – more than enough time for a collision event!


SSB On board

Well it seemed like a good idea to get an SSB instead of the dedicated Navtex displays that are on the market…there isn’t much price difference and with an SSB you can receive Weather fax, RTTY and Navtex transmissions anywhere in the world and all for free – no subscriptions required!

DSC00010sThis is the SSB that I installed it is the NASA Target HF3M SSB with dedicated antenna and the audio PC cable to interface with the laptop’s soundcard.

This does cover the spectrum from 30Khz to 30Mhz – so you can listen to AM radio (yes, you would have to be a long way offshore to want to do that !) and also receive the teletext transmissions called RTTY, and also the free Weatherfax




I have found the whole process very fragile however – maybe I just need some more patience to wait for the timed broadcasts and then for the slow acoustic modem speed transmissions – remember 300bd modems?…well this is slowwww….

It is best to do this at anchor or in a marina, so that the signal has a reasonable chance of getting through in a stable fashion.

I keep a folder of frequencies and times of broadcasts handy so that you can set up at the appropriate moment instead of having the laptop on for hours on end. This may be an argument for having the fixed receivers from people like NASA instead of the SSB radio coupled to a a laptop….?


Fitting the RC400

I decided that I would use an RC400 handheld in the cockpit since it DSC00012s would:

a) take less room than any of the smallest C series Raymarine displays
b) Cost a quarter of the price
c) Use Navionics GOLD charts – the same as the C120 chartplotter at the nav table
d) be able to receive and transmit waypoints and tracks using NMEA (or so I hoped)
e) Not be so large or bright that it would interfere with night vision
f) could run off the ships power circuit – saving batteries and the ‘crash’ events that happen when the battery power runs low…(another post later on that one!)

DSC00014sAs it turned out all the above criteria were satisfied except (d). The unit can xmit/rcv NMEA but I have not been able to use that facility since the C120 has only one NMEA port and that is set to 38,400bd so it can receive the AIS data – which only comes at that speed.


I havent been able to work round this yet but I am hopeful that somehow I can use the Brookhouse Mux to recv NMEA waypoint/track data from the C120 at 38,400 and xmit it at 4,800bd – I havent got round to this yet – I am just enjoying the fact that the RC400 works – works off ships power – and fits in really well at the helm without getting in my way.


Connecting AIS – NASA AIS receiver

I used the NASA AIS receiver. It has worked fine and if you look at other posts here you can see some very congested screen shots of AIS data in the English Channel.

I also find that I can ‘see’ AIS transmissions of boats up to 12nm out at sea from inside the marina and inside the port of Newhaven, England.

NASA AISThe NASA device does look a bit cheap and one big complaint is the useless manual and the lack of any form of lights on the device to tell you it has power or is receiving or transmitting anything on the NMEA bus. Very frustrating when you are trying to troubleshoot connections. If you are particularly adept you may want to follow this advice and install your own lights.

But it does work and I have plugged it into the Brookhouse Multiplexer and from there I get two outputs. One is the NMEA 2000 (at 38,400bd) feeding into the C120 chartplotter and the other is the signal on the built in USB bus which feeds straight into a laptop without any tempremental Serial/USB converter in the way. This also means that you can reliably feed two signals into the laptop in parallel running two programs for instance without the data getting corrupted.