Multibeam towfish for the Klein 5000 side scan sonar resting on deck in its cradle. The unit is approximately 2 meters (long) by 0.2 meters (diameter) and weighs 70 kg (155 lb). The towfish uses 5 beams each on its port and starboard sides to map the seafloor using high frequency (455 kHz) sound pulses. This system is designed so that each swath of sound energy overlaps with the adjacent swaths giving 100% coverage of the seafloor, even at relatively high tow speeds.
The large yellow “wing” above the towfish helps the unit dive toward the seafloor as the ship moves forward. As part of the Next Generation Tools project, procedures were developed for safely launching, towing and retrieving the valuable towfish from a commerical fishing vessel. The towfish was launched over the stern of the F/V Ocean Explorer by “tight-lining” the device between the towing winch, mounted overhead, and a small, multipurpose winch mounted nearby. A boat hook was used to hold the unit forward until the winch hook was removed, and then to reduce swinging as the towfish was lowered into the water. Launching and retrieval of the towfish required three people. During deployment and turning operations, the helmsman was careful that neither the towfish nor it's cable was drawn into the ship’s propeller. This procedure was successfully used over a wide range of conditions, including wind speeds greater than 25 knots! Image courtesy of Next Generation Tools 2001, NOAA-OER.
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