Capt. Robert M. Slack

Peer Reviewed

Abstract: A RAPID AND ACCURATE solution to the relative motion triangle is imperative if modern highspeed ships are to operate safely at sea under all conditions. Marine radar of great range, accuracy and flexibility provides early warning of the existence of potential dangers to the new ships, but methods of evaluation of the information provided by radar has not kept place with the advancement of equipment design. The methods commonly taught in the various maritime schools for the solution of the relative motion triangle require transfer of the information provided by the radar to a maneuvering board, conversion of the relative motion line to relative speed and direction, and an ultimate solution for a safe course of action by the maneuvering ship based upon the solution of the speed vector triangle. Since the length of the relative motion line cannot be conveniently measuredo n the radar scope itself, even when a reflection plotter is provided, this procedure cannot be completed on the reflection plotter. The reflection plotter is now the primary method of plotting the relative motion line and due to this inability to solve the problem on the plotter, or to complete the solution on the maneuvering board in the time available, with the methods currently taught ashore, the ship’s officers normally do not carry the solution any further than an extension of the relative motion line to determine the CPA (closespt oint of approach).Changeo of coursei s generallyd decided by estimate-which is another word for guesswork. The use of a distance vector triangle enable the radar navigator to obtain a rapid and accurate solution on the reflection plotter or on the maneuvering board, with the reflection plotter being the preferred method. All calculations are avoided, as the lengths of the vectors for own ship and target’s true course and distance made are based on the time duration of relative movement, and own ship’s distance may be precalculated for various plotting intervals. Since the solution is plotted at the location of the relative motion line, the positions of several ships may be plotted simultaneously, and when a new course or speed to avoid one ship is plotted, the effect of this action on the CPA of all other targets may be determined immediately. Errors and loss of time in reading off and transferring data, are avoided and the solution may be arrived almost instantaneously. The Keystone Method of solving the distance triangle has the advantages of simplicity, clarity, accuracy and speed of solution. No navigator plotting by this method has ever been involved in a collision. The inadequacy of the speed vector triangle system of plotting raises a presumption of unseaworthiness of ships relying on this system where collision results from a failure to plot. When all factors are weighed, it seems abundantly clear that a shit to the distance vector triangle plotting method should be made by the maritime industry.
Published in: NAVIGATION: Journal of the Institute of Navigation, Volume 14, Number 2
Pages: 142 - 149
Cite this article: Slack, Capt. Robert M., "THE KEYSTONE SYSTEM OF ANTI-COLLISION RADAR NAVIGATION", NAVIGATION: Journal of The Institute of Navigation, Vol. 14, No. 2, Summer 1967, pp. 142-149.
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