On the west coast of Mexico, on the way into port a barge hit a high spot and sustained considerable damage. The high spot had to be located and identified before the arrival of the next barge in 5 days. Side-scan sonar images located a possible target in the approach channel. The target proved to be a large boulder, possibly off the breakwater, A DGPS system was used to geo reference the boulder to sub-metre accuracy. Using the profiling sonar a 3D image of the rock was produced and used for insurance purposes.