Class B AIS: a big turn-off?
Q
In ‘Cross purpose’ (Letters, PBO September), WW Huybrecht writes that ‘many ships turn off their AIS Class B reception’. Personally, I’d believe such an action to be a breach of COLREGS, which state that every available means should be used to ascertain if a risk of collision exists. However, having just fitted a Class B AIS I had heard rumours of this, and upon searching I came across this, reproduced from the Panbo.com website:
‘A corrected response from Simrad: there are a couple of issues regarding AIS Class B data showing up on Class A vessels. (1) The majority of Class A vessels will have had the AIS fitted before the static data message was defined and will therefore not decode the Class B static data. What typically happens is that people with Class B AIS ask a Class A vessel if they can see them: ‘Can you see ship “XYZ”? The answer is most likely no, since the Class A cannot decode the name of the class B vessel. The vessel will show up as a target showing position, and the MMSI will be available. So if the Class B vessel had asked “can you see vessel 0012345678?” (MMSI number), then they would get a positive answer. (2) Another issue is likely to be down to the Class A vessel’s method of displaying the AIS data either on radar, ECDIS or ECS. These will have filters on to de-clutter the screen, and I believe there are IMO rules on how to filter the Class B information on screen on Class A vessels. The target will be shown on screen as a target but any data will not be shown, eg MMSI, nor any static data (even if the AIS can decode it). The data is likely to be available, but the Class A operator will have to scroll over and/or select the class B target to get to the information.
‘In summary, all Class A and B target positions will show up on both Class A and B AIS devices. However, the static data from Class B may not be decoded by Class A devices. In addition to this, the display may be filtering any Class B information on screen. This can lead to people incorrectly believing that the Class B AIS does not appear on Class A devices.’ STuART CARRuTHERS REPLIES: With the introduction of AIS Class B aimed at the leisure boating market, much has been written and published about its pros and cons. Those who appreciate that you can’t rely on AIS transmissions being received or the correct action taken by any vessel will no doubt find it a very useful aid to navigation. The MCA provides clear operational guidance on the use of AIS at sea. The key point is that collision avoidance must be carried out in strict compliance with the COLREGS. There is no provision in the COLREGS for use of AIS information, so decisions should be taken based primarily on visual and/or radar information.
When AIS was first introduced as a compulsory carriage on certain types of shipping, many ship owners opted for the least-cost AIS installation to meet the requirement. By doing so, many of the benefits offered by graphic display (especially AIS on radar) are not realised with the three-line ‘Minimum Keyboard Display’ (MKD).
Since 1 July 2008, the IMO revised performance standard for radar equipment requires the integration and display of AIS data on all new radar displays. Arguably, AIS targets are now better displayed, and AIS has a greater role in improving navigational integrity and accuracy than was initially envisaged. Anecdotal evidence suggests that many bigger vessels that trade internationally have now converted to equipment capable of displaying AIS data, but – and it’s a big but – a significant number of radars may not have been upgraded, particularly on coastal shipping, and it will be years before AIS data can be used effectively for navigation on many compulsory carriage ships. However, the revised performance standard requiring the integration and display of AIS data on radar displays also includes a requirement to be able to reduce clutter on displays so that detection performance is not adversely affected. As a result, many modern radar displays can filter out AIS Class B signals.
As more leisure boaters invest in low-cost AIS transponders, the problem of Class B clutter on navigation displays for those piloting large vessels is likely to be a distraction. Under such circumstances, filtering of all AIS Class B targets and suppressing alarms might be needed to avoid distracting those on the bridge. The Class B AIS update rate is too slow, and recreational craft often navigate too closely for Class B information to be useful to larger vessels in busy, confined waters.