miércoles, 4 de junio de 2008


Nowadays to a safe navigation every vessel should include in their equipment an Automatic Radar Plotting Aid (ARPA) system,but to manage that kind of system you must refresh your knowledge about some theorical topics

  • Whether danger of collision exist
  • Calculate CPA,TCPA and relative motion lines

Possible error sources in manual plotting

  • Error in bearing
  • Error in range
  • Error in time between plots
  • Low relative speed
  • Error in own ship speed
  • Error in own sip heading
  • Error due own ship manouvering


1. IN TRUE MOTION: True combination of true motion and speed. True direction of motion of a target expressed as an angular displacement of north.

2.IN RELATIVE MOTION: The direction of a motion of a target, relative to own ship position expressed as an angular displacemen from north.

The Plotting process include:

DETECTION: recognition of presence that a target.

SELECTION: choose of a target

TRAKING: the computer process of observing the sequential changes in the position of a target, in order to stablish its motion.

Fuente: Modulo de Introduccion al ARPA publicado por SEAGULL and MACROMEDIA