MARPA can indicate further information with 2 very different but similar looking vectors : True Vectors and Relative Vectors.
3.
A relative vector of 6 minutes ( RV6 ) would be a line representing the movement of the target for the next 6 minutes.
4.
Finally, human errors such as inaccurate speed inputs and confusion between true and relative vectors add to the limitations of the radar / ARPA suite.
5.
The relative motion of a target can be seen with Relative vectors, these just show the future position of the target on the Radar screen as per Vector Duration, again usually 6 or 3 minutes depending on range in use.
6.
It is essential that users of MARPA do not get confused between RV and TV, especially on Radars that can not display both TV and RV . True vectors allow users to, at a glance, determine the aspect of a target, something that is virtually impossible to do without manually plotting, Relative vectors provide users with, at a glance, information about which vessels pose a collision risk, a RV pointing at the centre of the Radar screen indicates there is a risk of collision.
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