the elevation of the center of the docking skid could be measured. Divers also checked point soundings at critical locations (deepest point of the propellers and rudder posts) on each of the carriers. Time and tide measurements were recorded so that all divermeasured elevations could be corrected for tide and referenced to MLLW. The vessel-based hydrographic survey at Pier 1, Naval Station Newport, was used to develop one-ft. elevation contours in the berths surrounding the pier. The area in red represents the footprints in both berths where the aircraft carriers or their mooring hardware restricted access by the survey vessel. For the restricted-access survey, we attempted to mimic a traditional vessel-based hydrographic survey approach. To do this, we required: (1) accurate horizontal positioning (2) accurate transducer draft (or in this case, vertical positioning) (3) measurement from the transducer to the bottom (4) corrections for sound velocity (5) corrections for tide elevation (6) real-time navigation and tracking to monitor date coverage and density. To this end, we paired the CDL MiniPos aided-inertial navigation system (and the RD Instruments Workhorse Navigator DVL) with a CDL MiniPulse profiling sonar. This satisfied our requirement for accurate horizontal and vertical positioning of a profiling sonar transducer that could make measurements between the transducer and the berth bottom. Tides were recorded relative to MLLW at the nearby NOAA tide station, and sound velocity measurements were taken with the Innerspace 443a sound velocity profiler and used to correct the soundings from the MiniPulse profiler according to sound velocity conditions. The full survey spread was mounted to the instrument skid on the SeaEye Falcon to give us full access to the restricted portions of the berths, and real-time positioning was fed into Hypack so that we could control the survey progress and monitor bottom coverage. Initial deployment of the ROV with the survey spread required the ROV to set in the docking garage for approximately 1 hour prior to the survey activities. This allowed the ring laser gyro time to settle on true north and also provided the INS with a known start location from which all further positions were generated. From the garage, the ROV was directed along pre-planned survey lines under each aircraft carrier with line spacing based on the swath width of the profiling sonar, suitable overlap between lines, and the footprint that was not surveyed during the vessel-based survey. The real-time positioning from the INS, fed topside via the umbilical to to a control computer and imported into Hypack, allowed the ROV pilot to navigate the ROV on each of
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Move The Intrepid
(Photo Credit: Donjon Marine)
While the preceding project was completed for NISMO in April 2006, in early November 2006, the Intrepid Sea, Air, and Space Museum attempted to move the decommissioned aircraft carrier USS Intrepid from her mooring at a pier on the west side of Manhattan, New York City. With VIPs and dignitaries in attendance, the towing contractor cast off all lines and began to pull the Intrepid from her mooring position alongside Pier 86 en route to a planned overhaul period at a shipyard in Bayonne, NJ. After moving 10 to 15 feet from the pier, the Intrepid grounded. Intrepid was placed back into her mooring and dredging was necessary around the carrier in order to free her hull from the mud. One month later (at the next full moon high tide) another attempt was made, successfully, to move Intrepid from her mooring and tow her to a yard in Bayonne where she would go through a complete refurbishment. To our knowledge, the Museum made no attempt to use an ROV fitted with an inertial navigation system to survey under and around the carrier prior to either towing attempt.
Marine Technology Reporter 29
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