Collision Avoidance : AIS vs. ARPA


The Incident

On 11 January 2014, the MV Rickmers Dubai collided with the towing vessel Kingston and crane barge Walcon Wizard in the Dover Strait.  This case highlights some of the issues of using shipborne Automatic Identification Systems (AIS) for collision avoidance versus use of Automatic Radar Plotting Aids (ARPA) combined with AIS information.  While there are numerous issues relating to Bridge Resource Management (BRM) on both vessels, we will concentrate on the aforementioned AIS vs. ARPA issue.

Just before 0200 on a clear night, Rickmers Dubai, a multi-purpose cargo vessel was overtaking the towing vessel Kingston, towing the crane barge Walcon Wizard.   The deck watch officer on Rickmers Dubai failed to recognize the overtaking situation until Kingston was close aboard and also failed to recognize that Kingston was towing a barge ~250 meters astern.  Altering course to overtake Kingston  on her port side, Rickmers Dubai collided (unknowingly!) with the tow and then snagged the tow wire, towing Kingston astern until the tow line released.  Amazingly, there were no injuries or fatalities!

“Relied solely on AIS information displayed on the ECDIS as an aid to collision avoidance.”

UK MAIB Report No. 29/2014

Kingston was not required to have, nor was outfitted with a transmitting AIS unit.  Kingston did however have a ECS (Electronic Charting System) provided by the vessel captain that displayed AIS contacts in the area.  Kingston’s radars did not have ARPA capabilities.  Rickmers Dubai was a paperless vessel, being outfitted with ECDIS units which had AIS contacts overlaid on the chart display.  All three of Rickmers Dubai’s radars were full ARPA units.  Unfortunately, neither vessel made effective use of their radars to further their situational awareness “bubble” and relied solely on AIS to determine risk of collision.  This perceived “one stop” shopping for information directly contributed to the incident.

What do COLREGS say?

It would be difficult to argue that either vessel, but Rickmers Dubai in particular, were maintaining a proper lookout.  The watch officer on the overtaking multi-purpose vessel used only one of at least three means available to him.  AIS, ARPA and a visual lookout might have allowed him a greater awareness of traffic and the overall situation.  As Kingston did not have AIS transmitting, they would have had to been detected visually or by radar – neither of which were used.  Additionally, a visual scan might have shown it to be a tug and tow ahead (hey, what are those lights?) and consulting the radar would have shown two distinct contacts until they were one nautical mile ahead.


Rule 5 – Look-out “Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions to make a full appraisal of the situation and risk of collision.”


Another tool that would have expanded Rickmers Dubai’s situational awareness might have been the VHF radio.  As both vessels were transiting a heavily trafficked area, securité calls would not have been out of the range of reason for either vessel, but particularly for a tug and tow operating at a low-speed.  Additionally, Kingston had a known navigation defect in that her restricted in ability to maneuver (RAM) lights were not working – a very good reason to make frequent securité calls.  Certainly, traffic reports from the Channel Navigation Information Services (CNIS) contained information on traffic of which to be concerned.  Granted, the last traffic report had been over two hours prior. Even still, it would have been valid information for a watch turnover, making the oncoming watch aware of future hazards.

AIS Limitations and Guidance

Updated guidance on the use of AIS was promulgated by the International Maritime Organization (IMO) in Resolution A.1106(29).  One of the main issues when considering AIS as a source of information is that it merely displays the information supplied by the target vessel.  These inputs are susceptible to all the errors possible in computer systems, but could be boiled down to the basic, “Junk in, junk out.”  In other words if any of the inputs are incorrect or corrupted, then that’s what you are getting.  Compare this to the information from an ARPA or your eyes that is independently generated.  While those systems are liable to their own perceptions and issues, they are wholly self-supported.


40 The potential of AIS as an assistance for anti-collision device is recognized and AIS may be recommended as such a device in due time.

41 Nevertheless, AIS information may merely be used to assist in collision avoidance decision-making. When using the AIS in the ship-to-ship mode for anti-collision purposes, the following cautionary points should be borne in mind:

.1 AIS is an additional source of navigational information. It does not replace, but supports, navigational systems such as radar target-tracking and VTS; and

.2 the use of AIS does not negate the responsibility of the OOW to comply at all times with the Collision Regulations, particularly rule 7 when determining whether risk of collisions exists.

IMO Res. A.1106(29)

Possibly the most critical piece of information for the watch on Rickmers Dubai and many other deck watch officers out there is 41.1 above.  This guidance from the IMO specifically states that AIS does not replace, but simply supports the information acquired from the radar/ARPA.  Unfortunately, it is being observed more and more frequently that AIS is being used as the primary and, sometimes, the only source of information for collision avoidance.

Data Segregation

Why would we want to segregate data?  Heck, what does that even mean?  When we start using information from multiple sensors (i.e. AIS and ARPA), understanding the limitations of the different sensors as well as the sources of information become important.  Therefore, the segregating (to separate or set apart from others or from the main body or of data becomes critical.

Again, why?  Take for example the ability to place AIS data on your ARPA display – when you do so and you select a particular contact to view its information, from where does that information come?  You might be surprised to learn that even if the contact has been acquired on your ARPA system, the information displayed may be from the AIS.  This may (or may not be) indicated by an additional symbol or icon on the data page.  And the information displayed may (or may not be)  significantly different from reality – remember, AIS has many limitations.  As does ARPA.

How do we segregate this data?  Well, one option might be to NOT overlay the AIS data on the ARPA on a continuous basis.  Turning this data on or off to check the ARPA information might be preferable.  Another option might be to keep the radar (ARPA) data on the radar and the AIS data on the ECDIS.  While this requires visually correlating the data between both units, it does create a situation where “never the tween shall meet” for this critical information.

Best Practices / Guidance

  1. Know the source of your information, especially if there are multiple sources possible.  Examples of this are AIS overlays on the ARPA or ARPA contact overlays on the ECDIS.  Different manufacturers have different displays – know your equipment!

  2. Standardize how you set up the equipment and make it work for you.  In the end, IT IS YOUR WATCH and your responsibility.  Make sure you have the tools necessary and use them!
  3. Understand what the ARPA display and the AIS can provide and what they cannot provide – they cannot tell you that there is no risk of collision.

  4. Do not rely upon one aid to navigation; use the ARPA in conjunction with visual bearings, and any other means, to establish if a risk of collision exists. If there is any doubt, such risk shall be deemed to exist and appropriate action must be taken which is in accordance with the COLREGS.

  5. Many tools are great when used properly – examples are AIS and VHF.  They can add tremendously to your situational awareness (i.e. knowing and understanding what is going on around you) if used properly and judiciously.  Unfortunately, when over-relied on or used in lieu of official methods (ARPA/COLREGS), they can be disastrous.

AIS, ARPA and ECDIS are just tools to be used when we are on the bridge of a ship.  They represent the science of watchstanding, navigation and collision avoidance.  The way that we meld these information resources with our training and experience to create the masterpiece that is our safe and successful watch is the art.

Let’s be safe out there.

Additional Reading and Links

MAIB – Rickmers Dubai and Kingston/Walcon Wizard Tow – Collision – January 2014


Bridge Watchkeeping and Collision Avoidance – Japan P&I Club


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