Bĝrge Wedel Müller wrote:
I've heard you had a discussion about AIS for leisure crafts (eg sailboat),
so I have just started "listening" to this news group.
Could you "kick-start" me on the subject?
Good timing. I just installed a Nasa Marine "AIS Radar" on Voyager this
week (see
http://www.nasamarine.com/). I don't think they're available
in the States but was in England on business so picked it up there.
Price was 230 pounds, including VAT.
It takes 12 volts, a VHF antenna, and NMEA from the GPS in, and plots
on a radar-like screen the position of all vessels transmitting AIS.
The rule is that all ships over 300 GRT must have AIS.
On Voyager we sail very short-handed so a watch is always a headache. I
have an old Combi Watchman radar detector, but have found that over
half the ships we encounter at sea do not have their sets on (you can
see their antennas not rotating). We use radar sometimes with an alarm
set, but that sucks an awful lot of power. And, it can't tell the
difference between a ship and a squall, and too often there's rain
squalls everywhere, making the alarm feature problematic.
Here in Baltimore harbor the AIS immediately found and plotted two
dozen ships. You can toggle to a specific ship and it shows the
vessel's position, name, MMSI, course, speed and status. The alarm,
when enabled, beeps loudly when there's a ship within a user-specified
range of the yacht.
The gear works great. My biggest complaint: it uses a brain-dead PIC
micro without enough memory to remember all of the info about the ships
it tracks. So when you toggle to a new ship there's a delay - sometimes
a couple of minutes - while it waits for an AIS transmission from the
ship.
The device is rated at 80 milliamps draw, though I measured 130ma.
Still, that's nothing. I'm anxious to try it at sea.
It does need its own VHF antenna - the higher the better the range.
Voyager is a ketch so the antenna lives atop the mizzen.
AIS appears to be a real boon for short-handed watchkeeping.
Jack
www.ganssle.com/jack