Craig,

At the cost of AIS today, it's probably not worth intentionally buying an AIS receiver.  A few years ago, AIS was a new toy that allowed the wealthy to show off their wealth.  Now, it's mainly a way to keep up with the Jones'.

Usefulness?  True usefulness?  I would guess 95% of the true usefulness comes from the receiver function, not the transponder function.  So all those guys out there with transponders, turn the transmitters "off" when not in actual use.

Firstly, throughout the mid-Atlantic and Gulf Coasts, it's still a huge minority of pleasure craft that actually carry a transponder, so at best, it's only occasionally helpful.  And, it's also true that many commercial vessels are not required to carry and do not carry AIS.  I actually think Norfolk is worse than NY for nav safety issues.  But in NY and Norfolk (and Charleston, Savannah River, St. John River, Brunswick, etc) many smaller work boats do not carry AIS.  In NYC, there are hundreds of water taxis that move fast and don't carry AIS.  The Staten Island Ferry doesn't carry; some of the Seastreak boats don't carry.  Many smaller tugs don't carry.  The military has AIS aboard, but they don't transmit.  Many Pilot boats working busy seaports don't carry.  USCG "cutters" don't transmit.  Many, many CoE vessels don't transmit.  Some dredge equipment transmits, some does not.  In construction areas, many workboats do not.  Anyway, at best, usefulness in busy harbors is limited.  And, potentially distracting.  The proximity alarms are useless because there are so many false targets that proximity alarms never stop sounding.  Distracting, because you're much better off with eyes out the window rather than fixed on a glass screen.

Someone recently told me that lobstermen in Maine carry AIS.  Is that true?  It wasn't my experience on our last trip downeast, in 2012.

Being from Camden, you'll understand my next point.  More sailboats in Maine have AIS than in other parts of the US generally.  Somehow, sailboats in Maine have the battery power to install AIS transceivers, but they don't have the brains to answer up on the VHF when you call the to arrange safe passing.  Like sailboats in the Annapolis region of the Chesapeake Bay, they are selfish and rude about AIS use and seamanship in general.  Someone recently defended that as being because VHF radios on sailboats are installed below deck.  Well, duh!  If you don't operate from a position in the hole, why install the radio in the hole?  And if AIS is such a good safety tool, what's wrong with having a handheld VHF in the cockpit to supplement AIS safety?  Duh!  It's just arrogance on the part of sailors, and in the sailing community in general.  So IN MY OPINION, you're better off with an old-fashioned fog horn.

Receiver vs transponder: there are more and more "Virtual ATONs" appearing on the water these days.  Mostly in busy sea lanes where large vessels operate.  "Virtual" because there is no physical ATON in the water, but on the chart plotter, the virtual marker appears plain as day.  That's an AIS target.  You do not need an AIS transponder to see those virtual ATONs.  All that's needed is a receiver.

There are places and times when AIS transponders are helpful.  I put that in five categories:

1. Operations in reduced visibility
2. Night operations
3. Offshore operations
4. Operations on the Great Inland Rivers
5. Vessel not under command

In these five categories, AIS transponders are actually a marginal safety adjunct.  However, even on the rivers, an AIS receiver is plenty adequate.  Tows are not required to call pleasure craft.  Some do, largely because those captains don't trust us pleasure boat "skippers."  To them, we are not "captains."  However, the truth is, it's up to us to stay out of their way, so with a receiver, you can see them and CALL THEM by name to arrange safe passage.

For most pleasure craft, the above five cases account for about 1% of the time we all spend aboard, and most of that is in reduced visibility.  So I'm back to, 95% of the actual usefulness of AIS can be had with an AIS receiver, and a receiver DOES NOT create VHF airways pollution with unnecessary and distracting traffic.

And in the "outback," AIS can actually be a security threat.  People will anchor on the Inland Rivers and leave AIS on over night to let tows know they're there.  If they're anchored safely, of course, that's not necessary, but they think it's a good idea.  Of course, the AIS also tells anyone with a cell phone where that boat is, and that it's probably alone out there.  Someone with nefarious intent could be attracted to that boat, as a moth to a candle.

If you, personally, are thinking about buying a transceiver, buy a unit that is rated at "Class B+," not the older technology "Class B" units.  The "Class B" units do have technology limitations, especially so in areas where there are lots of AIS units blasting away from boats that are slipped/anchored/moored.  "Class B" AIS uses CSTDMA, "Class B+" uses SOTDMA.  SOTDMA is much more reliable.  I have an article on my website that explains the AIS VDL (VHF Data Link) and time slot assignment.  If interested, here's that link: https://gilwellbear.wordpress.com/category/boat-technical-topics/equipment-topics/ais/ https://gilwellbear.wordpress.com/category/boat-technical-topics/equipment-topics/ais/

When I write this kind of review of AIS, I always get a chorus of people who tell anecdotal stories about how AIS "saved their bacon."  All of those stories are probably true.  And all of them are definitely anecdotal.  If those boats had not had AIS, those captains would have developed other good seamanship techniques to have avoided those same "near catastrophes."  Anyway, AIS transponders are just like any other tool.  Use right in th right circumstances, they are good.  Used wrongly, they create confusion, annoyance and doubt as to their reliability.

The key point in Bob's note, in my opinion, is how many people abuse AIS by leaving it on all the time.  If there was somehow a way to mitigate that arrogance, selfishness and stupidity, the promise of AIS would be more realizable.

JUST MY OPINION.  And, you did ask...

And yes, this message is too big for the T&T list.  I couldn't sleep.  Sorry, Bob.

Jim

Peg and Jim Healy, living aboard Sanctuary
http://gilwellbear.wordpress.com http://gilwellbear.wordpress.com/
Monk 36 Hull #132
MMSI #367042570
AGLCA #3767
MTOA #3436

My first mate has reminded me of a useful time to have AIS.  It was before
we upgraded MARY KATHRYN's electronics (rather than buy a new car, which
was comparably priced!).

We were entering Absecon Inlet on the Jersey Coast to visit Atlantic City
on our way to New England.  We had left Cape May in patchy fog which was
forecast to burn off.  Well, it did not.  Arriving at Absecon, it was pea
soup.  To make things fun, a dredge with a long slurry pipe was in the
inlet.

There were a number of radar targets, fishing boats probably, but it was
difficult to pick out the dredge for sure.  I called the dredge for
instructions and his first question was whether I had AIS.

If he knew which boat was mine through AIS, he could direct me around the
dredge and the pipe...and I could see where he was.  Yes, AIS would
have been useful then!

Stay safe!
Bob

Robert Calhoun Smith, Jr.
M/V MARY KATHRYN (on the hard this winter)
Hatteras 58 LRC      Annapolis, Maryland
Annapolis Yacht Club    Hatteras LRC Club
Marine Trawler Owners Assoc.  #4861