Coast Guard Warns About Accuracy Of AIS Data

The Eighth Coast Guard District Investigations Office issued a Marine Safety Alert (04-20) May 13 urging operators of towing vessels to take steps to ensure vessels are transmitting accurate information over the Automatic Identification System (AIS).

“Accurate broadcasts don’t happen automatically,” the Marine Safety Alert cautioned.

The warning comes as part of a not-yet-complete investigation into a January 26 collision between two towing vessels at Twentysix Mile Point on the Lower Mississippi River near Destrehan, La. (WJ, February 3) Just before dawn that day, the mv. Cooperative Spirit with a tow of 40 barges was headed upriver near the east bank at Mile 123, while the mv. RC Creppel was downbound with a pair of barges loaded with sulfuric acid, when the two tows collided.

The impact damaged one of the RC Creppel’s barges, resulting in the release of sulfuric acid vapor into the air. The RC Creppel sank rapidly. Of the four crew members on board the vessel, one was rescued by a Good Samaritan vessel, while the other three were never found.

While conducting an investigation into the collision, Coast Guard officials identified inconsistencies with AIS data broadcast from the two vessels involved.

“Neither vessel was broadcasting the total length overall of their tow to other AIS users,” the Marine Safety Alert said. “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.”

Though not named, the first vessel, based on those details, is the RC Creppel. Likewise, the Cooperative Spirit, identified as the “second vessel,” also was broadcasting incorrect AIS data.

“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,” the alert said. “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.”

Though the investigation is ongoing, Coast Guard investigators said the notice should “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.”

The Marine Safety Alert goes on to outline how to meet the AIS broadcast requirements outlined in 33 CFR 164.46. Operators may also access the Coast Guard Navigation Center’s AIS Encoding Guide online at

“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,” the alert concludes.

The issue isn’t new on the nation’s inland waterways. According to a July 3, 2018, blog titled “Is your Automated Identification System ready for Subchapter M?” and posted to the Coast Guard Maritime Commons site, more than half of towing vessels at that time—just weeks before Subchapter M went into effect—were transmitting inaccurate AIS data.

“During the month of June 2018, over 50 percent of towing vessels operating in U.S. waters transmitted incorrect AIS data,” Lt. David Turay, with the Navigation Center at the time, wrote, “and an alarming number of these vessels did not accurately report their dimensions or broadcast a properly assigned MMSI number.”

The recently published Marine Safety Alert does not go so far as to assert that the incorrect AIS data broadcast from the RC Creppel and Cooperative Spirit on the morning of January 26 caused the collision. But it also makes clear that, particularly in dynamic river conditions, “accurate AIS data entry and display is essential to safe navigation.” AIS is only one of many tools that provide mariners with “a clear picture of potential upcoming vessel passing situations, especially on waterways with bends, bridges or other visual obstructions,” the alert said.