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Using MARPA instead of AIS…

Returning to Brighton from Dieppe recently I realised that the AIS was not working, but had not time to fault trace or fix it so I thought I would revisit using the radar in earnest.

This is crucial given that the Traffic Separation Scheme that separates the Channel into two one way traffic streams for large vessels adds to the excitement for a yacht – as they say a “tortoise crossing the motorway” – gives you some idea of the experience.

DSC01864The rather shaky photo here – sorry but we were bouncing up and down a bit! – and I didn’t want to leave the helm too long just to take a photo! – shows the MARPA targets acquired on the Raymarine (C120 + Raymarine Radome 2kw) – click on the image for a larger view.


Just like the AIS you must take the heading, speed, and collision DSC01865avoidance data with a pinch of salt. I have seen a moored cross channel ferry registering 17kts on the AIS – and so it is here – this screen shot shows variable quality of data eg. was the second vessel in this MARPA list really doing 33kts ! – also the vessels were all clearly on a heading of about 250 degrees magnetic, but the heading data on the display shows the vessels going in all sorts of directions…

The bottom line is that standing in the cockpit with a pair of binoculars and taking bearings was my chosen primary source of data…and although we had bowled long from Dieppe for some 8 hours on a close reach doing 6.5 to 9kts with only the occasional sail trim adjustments… I was forced to reel in the genoa and come to a standstill to let an imposing cargo vessel from Iran thunder past.

Good decision as it turned out since it took a good 10 minutes to cross the wake after it had passed by!.

Track MARPAThis screen shot shows our track as we took avoiding action and then tried to get underway again before the next charging container vessel came barreling down the track.






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