Cathode-ray tube displays for fish detection on trawlers

Current echo-sounder recorder and cathode-ray tube display techniques are reviewed and their shortcomings stated. An improved cathode-ray tube display is described in which the seabed echo always occurs in the same position on the screen irrespective of changes in range due to the contour of the seabed or vertical motion of the trawler. A magnetic recording drum with out-of-contact heads stores the echoes from the range adjacent to the seabed and enables them to be displayed repeatedly during each sounding period.