An electronic device used by commercial fishermen to measure and locate the position of a trawl was recovered recently from the sea floor off South Africa. The so-called Trawl Height Sensor, which measures the opening of a trawl’s net and emits both radio and acoustic signals, was recovered in 1,500 feet of water by a fishing vessel trawling for hake.
The device was returned to the manufacturer, Simrad, a Norwegian electronics company, for identification. "We cleaned it up, put the sensor on a charge, and after two hours the unit came back to life," said Mike Hillers, Fisheries Product Manager for Simrad’s Seattle office. The device was determined to have been lost by a trawler in 1994. The sensor was returned to service and is presently serving the South African trawler Berbena.
A trawl height sensor sends a split-beam acoustic signal to the vessel’s GPS system for location of the headrope of the trawl. It also simultaneously measures the angle and depth of the opening of the net between the headrope and footrope.