Chesapeake Instrument Corporation project TOAD: principles and applications of Towflex hydrophones

• Published in: IEEE journal of oceanic engineering 2004-04, Vol.29 (2), p.388-406
• Main Authors: Fitzgerald, J.W., Doolittle, R.D., Greenwell, R.F.
• Format: Article
• Language: English
• Subjects: Acoustic noise; Amphibia; Hydrodynamics; Hydrophones; Instruments; Knots; Marine; Marine vehicles; Noise; Noise cancellation; Noise level; Noise levels; Reduction; Ships; Sonar; Sonar applications; Sonar equipment; Submarines; Tuna; Underwater acoustics; Underwater vehicles; Vibration
• ISSN: 0364-9059; 1558-1691
• DOI: 10.1109/JOE.2004.829793

The principles of a new method for reduction of self-noise in sonar systems are presented, together with corroborative experimental data taken from both surface ships and submarines. The technique is one of towing or streaming one or more hydrophones, called Towflex Hydrophones. The self-noise reduction observed in such Towflex units is due to several contributing factors. In the first place, the many structure-borne vibration paths feeding energy into the hydrophones are virtually eliminated, except for the cable itself. Because of the flexible construction, the transmission of cable vibration, in turn, is also reduced substantially since the fluid-filled flexible tubing discourages transmission of vibrations to the hydrophone elements. Moreover, the hydrodynamic flow around the hydrophones is at all times nearly axisymmetric and the hydrophones stream stably at speeds up to 30 knots with a minimum of flow noise. Additionally, the sensitive elements in Towflex hydrophones are so designed as to respond only to acoustic pressure and to cancel vibration and acceleration inputs. The net result is a hydrophone array system of remarkably low self-noise. In tests of Towflex units streaming from the sail of the submarine ALBACORE noise reductions of as much as 20 to 40 dB were observed when compared to the hull-mounted unit of conventional design located below the Towflex unit. The levels observed with the Towflex hydrophone on ALBACORE are 2 to 12 dB lower than those measured by USNUSL for the BQR-2 installations on other submarines, depending on operating conditions. This difference represents a detection range improvement of as much as a factor of four. When towed as little as 200 yards astern of the converted seaplane tender J. WILLARD GIBBS, noise levels approximately 10dB above sea-state 1 ambient and some 20 dB below the ship noise level expected for a omni-directional hydrophone were found, because of pattern discrimination against the noise from the towing vessel. There is reason to expect that these low self-noise figures may extend 20 knots or above. Towflex hydrophones are simple, inexpensive and suitable for many ASW applications including helicopter sonars, surface ship sonars, and submarine sonars. Both passive and active continuously scanning systems are feasible. The optimum design parameters for such systems using Towflex hydrophones have yet to be determined.