Channel Clearance Surveys - Texas Ingleside, Texas

The purpose of these surveys was to provide accurate clearance knowledge for tow-outs of deep sea oil platforms. This survey was conducted three times, for two separate clients. In question was whether the Corpus Christi Channel was large enough to handle two very large custom oil platforms. In one case, the shoulders of the channel were thought to be too narrow, and in the other, the draft of the rig was possibly too deep. In each case, precise channel morphology was required for 3D modeling of the tow-outs to see if the rigs could physically fit down the channel. In addition, sidescan sonar provided information on debris, which would be hazardous to rig navigation.

The survey was completed using two variations of survey systems. The M/V Royal Fish completed the survey with a Reson 8101 multibeam and EdgeTech DF-1000 sidescan, and the M/V Bella Marie completed the same survey using the Reson 8124 multibeam and DF-1000. C-NAV RTG GPS was used for horizontal positioning, and in both cases, tides from NOAA stations Aransas Pass and Ingleside were used to interpolate tidal data across the survey area for vertical datum. Multibeam line spacing varied with the water depth to ensure 150% coverage of both multibeam and sidescan.

We processed the collected data using CARIS and QPS QINSy. The deliverables for the project were paper and digital charts used in real-time 3D models to assist in the tow-outs of large over-sized oil platforms.

Approximately 117 nautical miles of multibeam bathymetry and 60 nautical miles of sidescan were collected to ensure full-bottom coverage for the 17 nautical mile long channel.

Tasks for these channel surveys included:

• Applying water level, vessel motion, and velocity of sound correctors to determine the true depths;
• Marking and correlating sonar targets;
• Compiling reports, final smooth sheets, sidescan mosaics, magnetic contours and digital data; and
• Creating 3D models of the sea floor for integration into a full rig tow-out time series model.

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