April 1977 - Maritime Reporter and Engineering News

Raytheon Company Introduces A Dual-Axis Doppler Speed Log

For increased safety of navigation, Raytheon Company's Submarine Signal Division has introduced a dual-axis doppler speed log that uses bottom reflected sound to provide continuous and simultaneous display of speed along and across a ship's course.

The new system is already on order for six ships.

Manufactured by the division's Maritime Systems Department, Portsmouth, R.I., the Raytheon doppler sonar navigator (model DSN-400) tracks the bottom to depths of 1,000 feet, using acoustic beams directed ahead, astern, and to each side of the vessel.

In water depths over 1,000 feet, the system automatically shifts from bottom-tracking to watermass-tracking. The calculations of speed and distance run along and across course are based on differences in frequency between the transmitted signals and their return echoes caused by the motion of the ship. Depth indication to 1,000 feet is also a standard feature of the DSN-400.

The DSN-400 speed log is of particular value for piloting in shallow water, mooring, and approaching a berth. At depths less than 250 feet and speeds less than 10 knots, it indicates speed in hundredths of a knot, with display accuracy to within 0.02 to 0.04 knot. For bottom-tracking beyond 250 feet at any speed, display is in tenths of a knot, accurate to 0.1 knot.

In either "mooring" or "normal" modes of bottom-tracking, the system's indication of distance run is correct to within one-half of 1 percent of true distance covered over the bottom.

Water depth can be displayed in meters, feet, or fathoms, with an accuracy of plus or minus 1 percent of indicated depth. An adjustable shallow-water depth alarm warns when depth is less than a preset value.

DSN-400 data is processed for digital display on an easily read 14-inch by 18-inch bridge display/ control unit and for input to radars and other shipboard electronic equipment. Weatherproof digital and analog repeater displays are also manufactured for use in exposed locations.

The system has been successfully tested aboard a large tanker and a high-speed ro/ro trailership for extended periods of both bottom- and watermass-tracking in the North and South Atlantic Oceans, the Persian Gulf, and Mediterranean Sea.

Additional information on the DSN-400 may be obtained from Robert A. Sleiertin, Raytheon Maritime Systems, Box 860, Portsmouth, R.I. 02871.

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