Pascal wrote:
Ok but am installing an AIS which could overlay the targets on the
radar screen and calculates the CPA/TCPA; this turns the standard Marpa
function of the RADAR almost superfluous?


As long as the other ships have AIS, yes.

Take a look at a picture I took on-board last year.

http://tinyurl.com/hpozz (small)
http://tinyurl.com/ebmda (full size)

Look carefully at the left part, which is chart overlayed with radar,
MARPA and AIS enabled. You'll see that the gray tail behind AIS target
A70 is much more straight than the green tail behind the MARPA target MR8.

Btw, yes the ship represented by A70/MR8 did almost hit MR7. They hadn't
seen each other apparently (this was in THICK fog on the middle of the
North Sea). MR7 did a pretty wild maneuver at about 200 yards from MR8.
Unfortunately I didn't take a screendump of that! I later asked the
skipper of MR8 whether he'd seen or heard anything. He said he had not,
and that he maintained careful radar watch: he checked the screen every
10 minutes but didn't see anything...

--
Kees