Monday, August 17, 2015

Where is everybody?

AIS really is a wonderful thing.  With it, equipped ships periodically broadcast over VHF a digital burst of information including such things as their name, their heading, their speed, and a lot of other things.  All large ships are required to have AIS transceivers aboard, and many smaller ships and pleasure craft have them as well.

AIS does not replace RADAR; instead, it augments it, telling you not only what a ship has done, but what it is doing right now.  And it allows you to "see" ships that are not visible to RADAR due to terrain or even distance, as long as they are in VHF range.

And beyond this, NOAA has begun deploying both AIS-equipped aids to navigation, as well as "virtual" aids to navigation.  The latter are shore-based transmitters that broadcast a location and type as an aid to navigation in the proper place.  If you go there, you'll find nothing at all, but it will show on your AIS display.

So you know that Eolian had to have an AIS receiver.  I managed to get one in a trade for an old cell phone:

It's a tiny little thing

Temporary hookup; the "antenna" is just a length of coax
Even with virtually no antenna, this little gizmo was picking up nearby boats:

Eolian is the boat at the bottom of the display surrounded by the red circle - the guard zone I have set.  If a boat enters the guard zone, or will enter it in the next three minutes, the chartplotter issues an alarm.

So now I need to climb the mizzen mast and attach the coax to the abandoned VHF antenna up there - I knew it would prove useful some day...



SV Pelagia said...

We love AIS, but have learned that we can't "trust" it. That is, just because no "targets" appear it doesn't mean they are not out there. Obvious candidates for boats without AIS are other pleasurecraft (sailboats, powerboats and especially sport fishers), but the not-obvious ones surprised us:

- large (even 80-100 ft) USA fishing vessels off the WA/OR coast rarely had AIS

- middle of the night visit by Mexican Navy as we did a night passage San Diego to Ensenada (didn't show up on radar either... a real stealth boat)

- all panga fishers in Mexico

- most commercial fishwrs in BC (not necessarily large vessels)

Further, we've learned thatjust because a vessel has AIS doesn't mean they are paying attention to it (or, at least, taking any action). Then, especially relevant to sailboats under sail, there are those vessels whose AIS indicates they are towing but aren't.

So one has to be careful.

Robert Salnick said...

Pelagia -
Absolutely one has to be careful. But one more source of information is always a good thing!


Howard Tucker said...

Avoiding ferries in the fog and constantly broadcasting your position provides for a margin of safety in an emergency.

John Miller said...

I have AIS on my VHF Radio, using NMEA 2000 to display on my chart plotter. VERY cool! Now I gotta get an AIS Transmitter so that I can be seen!!! You can NEVER have too many tools! arrr, arrr, ARRRR! (as Tim the Toolman would say..)

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