Despite the magic of today’s Automatic Identification Systems (AIS), which allows ships and sailors to share important vessel and navigational information instantaneously via a VHF link, it is vulnerable to user error. Recently, a tragic incident involving two commercial tow boats on the Mississippi River exposed one of the these vulnerabilities—as described in the U.S. Coast Guard Safety Alert 04-20 issued by the Coast Guard’s Inspections and Compliance Directorate earlier this year.
Although this accident involved a tow boats pushing another boat, the circumstances could easily apply to the dreaded long tow like the one I had a near brush with off the coast of Venezuela during the pre-AIS days. In that case, the tow and the barge were so far apart they appeared to be separate vessels, a conclusion that could have had disastrous consequences.
In a long tow, a long, partially submerged cable separates the the tow boat and its tow. Should a long tow be mistakenly identified as two vessels, or simply one smaller vessel, real trouble would ensue. This is one more good reason to be thoroughly familiar with the habits of commercial ships and the relevant day shapes and lights (COLREGS) designating their type and activities—even in the age of AIS. Luckily in my case, the tow vessel carried the appropriate lights and I was able to discern them with enough time to change course.
Today, there are cheat sheets, flash cards, and apps that you can use to help identify lights and shapes, but keep in mind that the farther you go into international waters, the less compliance you will find. Even in the U.S. small fishing vessels often carry no lights at all, so a lookout is always needed. There are a variety of aids that can help identify lights and shapes, but some (like phone apps) can spoil the night vision of the person on watch. As we saw in our recent study, it can take several precious minutes for your eyes to recover from exposure to even the ordinary red-shaded nav station light. (All the more reason to commit these to memory.) If anyone has used an app or other aid to identifying lights and day shapes, please share them in the comments or by email.
What follows is an excerpt of the Coast Guard Safety Alert 04-20. It important that mariners do not rely solely on our republished account, but also read the Coast Guard’s full account here.
A recent collision on the Mississippi River serves as an important reminder that accurate AIS data entry and display is essential to safe navigation as one of the many important tools used in providing vessel operators with a clear picture of potential upcoming vessel passing situations, especially on waterways with bends, bridges, or other visual obstructions. Although the investigation into this casualty is not yet complete, the following information is provided to alert owners and operators of the hazards created by inaccurate AIS data, and prompt them to review and update their procedures to prevent similar casualties from occurring.
Before sunrise, two towing vessels were approaching a bend on the Mississippi River. Neither vessel was broadcasting the total length overall of their tow to other AIS users. The first vessel’s AIS broadcast showed its length at 72 feet, but the overall length of the vessel and its two-barge tow was 672 feet. The second vessel’s AIS broadcast showed the length at 200 feet, but the overall length of the vessel and its 40-barge tow was 1,600 feet. Without the information regarding the total length of the other vessel and its tow, the operators did not have a full understanding of the pending passing situation. As the vessels rounded the bend and completed their turns, they collided, causing the down bound towing vessel to capsize and sink with several fatalities.
The AIS is a valuable tool, which broadcasts critical vessel information to other vessels on the waterways. However, proper function of the AIS is dependent on accurate vessel data entry, including entering the proper ship type code and the full length of a vessel and its tow. The accurate display of a vessel’s full length becomes particularly important in situations that prevent vessels from seeing each other until they are in very close proximity. The AIS carriage and operating requirements are found in Title 33 Code of Federal Regulations 164.46, which includes a requirement for the accurate input and upkeep of all AIS data fields.
The Coast Guard Navigation Center has produced the AIS Encoding Guide, which provides instructions on how to populate all data fields in AIS, including steps to report the total length of the vessel and the vessel’s tow. Given the wide variety of sizes and lengths of tows, and the heavy density of these types of vessels traveling on the country’s marine transportation system, accurate AIS input is vital to an operator’s ability to make informed navigational decisions.
(Editor’s note: The Coast Guard’s encoding guide is aimed primarily at Class A AIS used by commercial vessels. The coding for Class B AIS commonly used by recreational vessels may not have all the designations. Follow the user’s guide or contact the manufacturer for instructions on inputting your vessel information.)
For more information on setting up and using your AIS, see your manufacturer’s literature as well as the Coast Guard’s Navigation Center, which covers the technology in great detail. Mariners should also be sure to read Practical Sailor’s detailed report on AIS interference to ensure that their system is not subject to the interference that has plagued other sailboats. I discussed the events that prompted that report on AIS interference in a previous blog post on AIS. Practical Sailor has tested a wide range of AIS systems and related equipment. Here is a link to many of those past Practical Sailor reports on AIS.
If you’ve had experiences with mistaken identities using AIS, we’d be interested in hearing them. You can leave comments below, or write to me at email@example.com.