The acoustic signature of R/V ATLANTIS was successfully measured during this acoustic test. The levels of the EM 122 were controlled by a combination of flow noise and gondola cavitation. Higher sea state data was also influenced by bubble sweepdown effects.
The general acoustic levels of ATLANTIS with the new gondola mounted EM 122 sonar system were good and should produce excellent bathymetric data results:
- At low speeds (from DIW to 350 RPM), sonar levels were controlled by a combination of sea‐state and local machinery.
- At mid speeds (from 350 to 500 RPM), sonar levels were controlled by hydrodynamic flow noise.
- At high speed (above 500 PRM), sonar levels were controlled by gondola cavitation transients. Eventually, propeller cavitation was dominating sonar levels (above 700 RPM).
- The forward center of the gondola was determined to cavitate at vessel speeds above 500 RPM. It is believed this cavitation is caused by the bracket welded between the gondola and the vessel hull.
- A modest amount of bilge keel cavitation was detected during the acoustic trial when the vessel was rolling in high sea states.
- A series of 4 kHz harmonics with very high levels was detected during the acoustic trial, but were only present for a few minutes and further diagnostics could not reproduce these tones.
- Ship headings into prevailing sea states was determined to cause bubble sweepdown transients.