Originally Posted by delmarrey
Radar has become even less useful now that AIS is available.
Absolutely, possitively NOT, especially without some strong caveats. At least up here in Maine
AIS is NOT ready for prime time replacement of radar. IMHO AIS is a literally waste of money
on this coast, at this point, unless you want and need to track the handful of commercial
ships that move through very predictable passages, many of which can be avoided.
I have AIS and it is also NOT always real time, especially with pleasure craft of which perhaps 95% of the vessels on this coast do not TX AIS.. Out of 1200 boats in our mooring
field I have seen TWO pleasure craft that TX AIS. Saw four more throughout the entire sailing season sub 40 feet, this is by far the largest boat population on the Maine
coast. Counted about 10-20 LARGE mega-yachts with it but that is all in an entire six months.
Roughly 95% of the boats we encounter along the Maine coast are NOT displaying AIS, and neither are we with the Matrix 2100 so we are more part of the problem, rather than solution at this point.
When we do get a recreational vessel on AIS the system can be very SLOW to update the TX ships ACTUAL location. I have actually taken photos of my screen, see below, showing the vessel off my beam when the vessel TXng is now actually off my bow and already well passed me.
In real fog this is an UNSAFE feel good device that could potentially cause real harm if not used in conjunction with radar as a supplement or very carefully tracked during the refresh blips. In order to make the most efficient use of the AIS bandwidth available, vessels that are at anchor
or moving slowly are set to TX on a less frequent basis than those that are moving faster. The AIS refresh rate can range from as long as 3 minutes to as fast as 2 seconds for a fast moving vessel. The big problem is that not all boats are supplying SOG/STW info and you can be often guessing at the refresh rate. AIS class A boats are more accurate relative to what they are doing and tend to give the most information.
AIS, at least at this point, I feel needs to be used with respect if using them in an area that gets fog and with the understanding that only some commercial
vessels (not commercial ships) and a small handful of pleasure vessels use and TX AIS. I have yet to see a commercial lobsterman who is TXing AIS and we have LOTS of those up here.
These photos should give you an idea of how inaccurate, compared to radar, AIS can be. We were doing 6 - 6.2 under sail and that boat was moving slightly faster than us but not TXng SOG. Look at my position on the chart at .3 nm range compared to the AIS vessel in red. If this was in fog, and your only device for collision
avoidance was AIS, this could be very dangerous if you had not been tracking it for a while or they made a sudden course change. This was in bright sun so no danger
and I only wish I had been spinning my dome. I moved less than .1 of a nautical mile when the AIS boat went from photo
position #1 to position #2 in a split second refresh rate. Not cool if in pea soup and this is why I don't feel AIS is ready for a prime time "replacement" of radar at this point.
Sorry for the blurry photo