Recovery of unattached offshore facilities or missing equipments is a challenging activity. Generally speaking, this activity involves a comprehensive procedure which includes: target characterization, searching, detection, verification, locating, reacquisition and salvage. Among them, target searching and detection are the most critical components of the whole procedure. The purpose of this investigation was dedicated in discussing the efficiency by the application of side-scan sonar, magnetometer and sub-bottom profiler simultaneously in searching, detecting, identifying and locating underwater stationary targets. Procedures of this research include:
1. Discussing the capabilities of instruments and verification cruises on target.
2. Discussing the salvage activity we conducted off Kaohsiung harbor on a depleted
anchor.
3. Estimating the practicability of the methodology.
According to the characteristics of these apparatus, the water depth, collected by echo sounder, is capable of expressing the relief of the seabed. Seabed sonographs, recorded by side-scan sonar, show that it is feasible to detect, verify and locate targets on the seabed. Sub-bottom profiler provides the sub-surface sedimentary information which can be used to detect buried targets. Magnetometer can detect environmental magnetic intensities, which can locate and determine the size of ferrous targets.
Two depleted anchors were recorded off Kaohsiung harbor on the navigation chart. A recovery plan was then arranged which included 4 phases: collection of anchor characteristics, initial field survey and target detection, target verification and locating, target recovery. The underwater searching equipment employed in this activity include: side-scan sonar, sub-bottom profiler, magnetometer, echo sounder, underwater positioning system (include GPS), remotely operated vehicle (ROV) and professional divers. The offshore working platform used in this activity was R/V Ocean Research#3.
Results of the initial search phase by side-scan sonar indicated there was only one potential target in the searching area. Follow up verification cruises confirmed acoustically that the target was an anchor with a piece of chain clogged on a block. The results of this investigation included the information such as the dimensions and the location of the anchor. Furthermore, the reason which caused the anchor being abandoned on the seafloor was derived. For underwater ferrous targets, such as anchor and chain cable, all of the aforementioned apparatus, have good potential for their detection and verification. It can be concluded that, applying these apparatus simultaneously can more effectively conduct searching, detecting, identifying and locating underwater stationary targets than by the application of a single instrument such as side-scan sonar system.
Optical verifications of this target by ROV were attempted, nevertheless, were not success due to the difficulties in maneuvering OR#3 into proper position. An attempt to recovery this target by divers was arranged. But due to bad weather and rough sea state, the divers were not even allowed to dive.
However, according to the experiences collected, a target reacquisition and recovery facility was built to fulfill the necessity of guiding divers to the target and lift it.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0726106-131547 |
| Date | 26 July 2006 |
| Creators | Tsai, Ying-guan |
| Contributors | none, none, Wen-miin Tian, none |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0726106-131547 |
| Rights | unrestricted, Copyright information available at source archive |
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