Over the past 13 years, the use of 3-dimensionalforward-looking sonar (3D FLS) for real-time navigation has been adopted globally by a growing number of vessel operators. More recently, FarSounder started collecting bathymetric data using 3D FLS sonars in Forward Looking Multi-beam (FLMB) mode. Before exploring all of the possible applications of collecting bathymetric data on vessels with an installed 3D FLS navigation system, the accuracy and limitations of this data should first be understood. In this paper, results from two small surveys using a FarSounder 3D FLS in FLMB mode are presented and analyzed. The survey depths are corrected for tide height and compared to NOAA survey data. The average absolute error in depth is found to be 6.6 and 2.2% in the Patience Island and Newport Bridge survey area, respectively. Further, the average survey swath width is computed from the data recorded as ~9 water depths at ~6
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