Cross Channel AIS, part 2
Panbo friend John C. came back from more sailing aboard Solent Blue to discover that his overview photo of English Channel AIS traffic had stirred up quite a conversation. So he adds this:
The original photo was intended to show the number of AIS targets received from a 22 metre aerial whilst sailing across some busy shipping lanes. I don't routinely operate the equipment on 48 mile range other than to get a quick view of what is coming my way. Actually I do have some other photos taken in the same few minutes which depict a more normal operating practice at least for me.
Image 4828 {above} was taken about 4 minutes earlier, and shows the same shipping. The range is 6 miles, and the trend lines both for my yacht and the AIS targets is 6 minutes long. The target to the NW at 19.8 kts was the "threat" - I found that the CPA calculations from the E80 based on AIS were much more accurate that I get off MARPA. Indeed I did pass about 1/2 a mile astern of her, the Al Motanabbi a 925 feet long conta
iner ship. The visibility was about a mile and I just saw her in the mist. I never made a visual contact with any of the other ships.
One point to note is how the E80 displays the CPA - notice how there is no clue as to where the CPA will be. Compare that to the other image taken about 90 minutes earlier and showing a MARPA CPA with a nice graphic showing where the CPA will be (red lines). {The CAPN is also a good example — ed}. One hopes Raymarine will consider making their AIS and MARPA graphics similar.
Here is a radar question for your team! When I am travelling north, my radar alignment is 0 degrees, i.e. it lines up with the chart without correction. When I face south, I need a 5.5 degree shift to make things line up with the chart - this happens for isolated targets like bouys and for block targets like harbour walls. Is there a correction setting for this?
Thanks, John, and go “Team”!
Have you verified the accuracy of your heading sensor (fluxgate compass, gyro compass, etc.) when on both headings?