AIS becoming “clogged” already?

by Tim on December 27, 2012

The dangers of too much data “cluttering” navigation displays have been discussed at great length all over the maritime blogosphere for several years. Is it really a problem? In crowded commercial ports, it could be.

I operate in Seattle, and yes, the display can be quite well-populated with stationary vessels at any of the commercial Port of Seattle facilities. My solution? I zoom in enough to see the channel, and ignore the rest. Once I get out onto Puget Sound, I zoom out to see the faster traffic a bit further away.

It seems pretty straightforward to me, and it seems to work just fine.

So I was a bit perplexed when I read this announcement from the Port of Seattle. It’s not about “clutter”, though; it’s about “clogging”:

Automatic Identification System Transponder Interference

Attention Vessel Owners

If you have an Automatic Identification System Transponder on your vessel and your vessel is currently at the dock, Puget Sound boaters need your help.  It appears that a large number of vessels at the dock have their transmitters on the underway setting. This is causing interference within the system and affecting the boater’s ability to accurately navigate and detect approaching targets.

According to the Coast Guard,  “Vessels moored (or out of service) are not required to operate their AIS; see our AIS FAQ#6. If they are, they should ensure that their AIS navigation status is accurate. AIS reports once every 3 minutes when its navigation status is set to moored or anchored, vice reporting 5-89 times more if set to underway. This obviously impacts network loading and computer processing…”

As winter weather takes hold with its occasional low visibility, accuracy of your boat’s electronic information becomes critical.  Targets of interest may not show up on the AIS system if it is cluttered with too many contacts reporting that they are underway.

For the safety of all boaters, please double-check the status of your AIS transponder and make sure that you are on the correct setting.  Thanks for your help in keeping the waters of Puget Sound as safe as possible.

If I understand this, the interference discussed here affects the AIS bandwidth-sharing system. Stationary vessels set to underway occupy just as much bandwidth as actual underway vessels, essentially “using up” all the available broadcast pipe so that some vessels’ AIS data can’t be broadcast. Sometimes, the “losers” are vessels that are genuinely underway.

Really? I thought the system’s capacity was large enough to handle even the most crowded commercial ports? Is the problem older AIS gear that doesn’t automatically decrease the number of broadcasts when speed drops below 0.1 knots? Is the problem inexpensive Class-B gear proliferating on smaller vessels not required to carry AIS? Is it something else?

I admit I’m at a loss here. Any ideas?

{ 1 comment… read it below or add one }

Ben Ellison December 29, 2012 at 12:35 am

Hi Tim, A Panbo reader sent me that notice and I too am perplexed. I believe that Class A AIS transponder broadcast rates are based on vessel speed, not the Navigation Status entered by the operator. I’m also dubious about a “clogging” issue. But I’m checking with my sources at USCG…


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