[PUP] AIS Range

[Milt Baker]

Oops, posted this on the T&T Board by mistake . . . let me try again here!


Dave,

With unusual propagation I too have seen AIS signals from vessels up to about 1,000 miles but only once or 
twice.  Using a 6db gain antenna on our Nobeltec receiver, we'll occasionally pick up a signal from a ship at more 
than 25 miles, but that's rare.  Typically, we seem to pick them up at 17-22 miles and by then we can usually see 
the ship on radar as well.   If my experience is anything to go on, expecting 30-30 miles is not reasonable, not 
matter what the coasties say.

Since installing the same Furuno FA-150 unit Phil has (using an antenna comparable to what he has), I am noting 
consistently better range from the Furuno unit than from the Nobeltec one, even with the lesser antenna on the 
Furuno.  I continue to believe it's the combination of antenna and receiver sensitivity that makes the difference.

We also find that often we don't get "complete" information on a ship until he's within about 10-12 miles.  Bigger 
ships (probably higher antenna heights) seem to provide full information sooner.

Practically speaking, we find that 10 to 15 mile notification of a ship "out there" is plenty of time.  Even if he's 
traveling at 25 knots (which is rare, of course), with good bridge management practices on our boat there's lots of 
time to spot him, track him, ID him, and, if necessary, contact him on the radio to negotiate a safe pass.  My rule 
on an open sea, if he's the burdened vessel and the CPA is less than 2 miles, is to ask for "a safe pass of at 2 
point zero miles or greater," and I've never had such a request denied.  If we are the burdened vessel and the 
CPA is less than 2 NM, to clear the air we'll call him and tell him we're altering course (to port/starboard) to give 
him a safe pass of 2 miles or greater.

On another subject, from news reports it looks like el Presidente Chavez is making big changes in 
Venezuela, "nationalizing" the energy and telecom industries and taking the license of the only truly independent 
TV network.  Are you noticing any practical impact on cruisers there or is it business as usual?

Cheers,

--Milt Baker, Nordhavn 47 Bluewater, Fort Lauderdale