The concept of a point-of-possible-collision (PPC) and its associated predicted-area-of-danger (PAD) make it possible to analyse and compare various collision-avoidance situations and systems. For example, the effects of using different speed references in collision-avoidance manoeuvre planning is analysed. Possible references include speed through the water, speed over the ground and single-axis speed over the ground. It is shown that speed through the water is the appropriate reference for avoiding collision on the high seas since it will produce a correct measure of the target-aspect information that is essential in determining legal collision avoidance manoeuvres. Estimates of passing distance and time to CPA are not dependent upon the speed reference since these are based solely upon relative motion radar data. There are situations, e.g. where a shear line exists between ocean currents of different speeds, for which no single speed reference can deliver the total collision avoidance information. Collision avoidance in channels and restricted waters may sometimes use speed-over-the-ground to advantage. Under these conditions, target aspect is not of paramount importance. But, here again, speed-through-the-water will be required if correct target aspect is to be determined during the collision avoidance manoeuvre planning. Paradoxically, harbour-control radars can easily determine when ships will be meeting or overtaking near land-referenced obstacles, but harbour control cannot give correct manoeuvring advice without compensating for the effects of current. The PPC/PAD concept is also useful in analysing and comparing high- and low-speed navigation. The different types of decision involved in planned and emergency manoeuvres are compared. Converging traffic is easily analysed and the experience of ferries crossing the English Channel at right angles to the dominant traffic patterns is discussed. A formula is presented for estimating the cost of delayed progress when the collision-avoidance system does not present adequate information regarding the locations of PADs in cross-channel traffic.

  • Availability:
  • Supplemental Notes:
    • Paper presented at the International Congress of the Institutes of Navigation held at the University of Sussex, England, from 10 to 14 September. The Congress was sponsored by the Institutes of Navigation in Australia, France, the Federal Republic of Germany, Italy, Japan, the United Kingdom and the United States of America.
  • Corporate Authors:

    Royal Institute of Navigation

    Royal Geographical Society, 1 Kensington Gore
    London SW7,   England 

    Royal Institute of Navigation

    1 Kensington Gore
    London,   England 
  • Authors:
    • Riggs, R F
    • O'Sullivan, J P
  • Publication Date: 1979-9

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Filing Info

  • Accession Number: 00303238
  • Record Type: Publication
  • Report/Paper Numbers: Conf Paper
  • Files: TRIS
  • Created Date: Jan 15 1980 12:00AM