Autotape Offshore Positioning Equipment
Authors: Truelove Hershel 
Published: October 2008

The Cubic Autotape DM-40 is a precision system for electronic positioning by the simultaneous measurement of distances from a vessel or barge to two known points. Both distances to the Responder points are measured automatically and simultaneously once per second. They are displayed numerically on the Interrogator front panel, which is mounted on a ship or aircraft, thus providing its continuous position.

The Autotape System has proven to be a precise means for staking offshore locations, conducting hydrographic surveys and, by using a track plotter, running of route surveys for proposed pipelines or cables. Even though the system is limited to radio line of sight, distances in excess of 100 miles have been measured by employing the 1ine crossing techniques.

For many years offshore surveying was at a virtual standstill as far as progress was concerned. The primary reason for this was not a lack of desire to progress by surveyors and civil engineers themselves, but it was because they were so limited by the instruments at their disposal. As the demands on the surveyor increased, it became evident that, very shortly, he would be unable to accomplish all that he was called upon to do, unless different instruments became available. The breakthrough came with the development of instruments to measure distances and thus position with the precision required in modern day surveying. The first of these instruments was designed to measure a distance quite accurately in a matter of minutes. Even though these instruments relieved the surveyor to a point, they did not satisfy all of his requirements. The surveyor still had a need for an instrument that would allow positioning and navigation completely independent of visual observations. So, it was necessary that such an instrument be able to operate under any weather conditions and still give accuracies commensurate with surveying requirements. The latest and most sophisticated of the positioning instruments satisfied these requiremens; the Autotape DM-40 manufactured by Cubic Corporation of San Diego.

The Autotape is a range-range measuring device; that is, it measures two distances simultaneously. The system operates on the principle that the phase delay of a signal propagated through space is proportional to the distance traveled, and electronically, this phase delay is converted to a distance. The system operates on microwave frequencies and consists of three basic units: an Interrogator, and two Responders each with accompanying antennas. On the face of the Interrogator are what appears to be two large odometers. When operating automatically, the distance in meters from the Interrogator to each of the Responders is measured and displayed once every second. In addition to the basic equipment, there are certain pieces of optional equipment that enhance the Autotape.

There is a printer which provides a permanent record of all readings. Cubic has also developed a track plotter to aid in navigating and, at the present time, is working on a more elaborate plotter system. With this new system, range readings will be fed from the Autotape to a computer which will compute the coordinates of the vessel and plot them.