Case Studies

Characterizing Vessel Traffic Using the AIS: A Case Study in Florida's Largest Estuary


Tampa Bay, FL, is a large, ecologically rich estuary that hosts one of the largest commercial ports in Florida. Automatic identification system (AIS) records from 2015 to 2017 were used to determine the number, size, speed, type, and transits of vessels in Tampa Bay. The AIS vessel types were grouped into 10 general classes based on function. The cargo and tanker classes had the highest number of unique vessels transiting the estuary. The tug class had the highest number of individual transits, followed by cargo class. The most common vessel lengths were 165–200 m. Typical drafts were 9–11 m, and ship speeds were almost all <10 m/s. Froude numbers calculated from these data indicated that ships were generally underway in displacement mode. Overall, <0.1% of the AIS records reported speeds >10 m/s. These were identified as smaller passenger and recreational vessels operating in planing mode. The AIS navigational status and speed were often inconsistent, therefore, the combination of speed and duration was used to define individual transits. The average tidal dependency (TD) parameter for all vessels transiting into the bay was −0.02, and 0.10 for combined cargo and tanker vessels. Proper evaluation of the TD required inclusion of the phase lag between the entrance position and the tide gauge.