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[aprssig] Marine tracking

Ray McKnight shortsheep at worldnet.att.net
Thu Mar 24 07:41:39 UTC 2005


I think a bit of clarification is needed here.

AIS was developed to satisfy the requirements of 33CFR161,
Which details the need for vessels operating in specified ports and
waterways within the US, to provide movement reports to the USCG.
Particularly in ports with a VTS/VTC (Vessel Traffic Center) or VMC (Vessel
Movement Center), AIS satisfies the reporting requirements and may alleviate
the need to provide traditional "sailing plans".  Ports in which the USCG
does operate a VTS requires a vessel over a specified length (I have to look
but I think it's 36 ft) to maintain contact with the VTS when in it's
operational boundaries, and accept direction regarding it's intended
movements.  These directions may dictate the vessels course, speed,
separation from regulated navigational areas such as Navy bases or sensitive
industrial areas, and even the times that the vessel may be permitted to
move.  Vessels equipped with AIS are still under the direction of the VTS,
but AIS assists the VTS operators to more easily identify and track the
movements as compared to traditional methods such as radar and long range
cameras.  Since 9/11, vessel movements have been tightly regulated in the
"interest of national security and port safety".  Vessels are still required
to submit advanced arrival notices prior to entry into the port even when
equipped with AIS.

Not all US ports have AIS implemented, for instance the busy port of San
Francisco is still in the development and testing phase.  This is not due to
lack of transponders for the vessels, but lack of shore-based systems at the
VTS's.  Most USCG vessels still do not have GMDSS installed yet either.

Since this is mainly a USCG initiative, you are not likely ever to expect to
gain access to the data they collect.  They won't provide a port on a server
for us to garner the AIS data stream they receive and archive.  AIS is not
necessarily going to be implemented throughout much of the rest of the world
either.  It isn't a SOLAS requirement, at least not yet, it's not "offshore"
or global, or satellite based, so strictly local "port-centric".

Hope this clarifies things a bit.
"U.S. Coast Guard:  212 Years of Tradition, Unmarred by Progress"


-----Original Message-----
From: aprssig-bounces at lists.tapr.org [mailto:aprssig-bounces at lists.tapr.org]
On Behalf Of WB4GQK at aol.com
Sent: Wednesday, March 23, 2005 17:25
To: aprssig at lists.tapr.org
Subject: RE:[aprssig] Marine tracking

Hi Scott and all,

The marine "tracking" system is actually called AIS for Automatic 
Identification System. Now it's true that the marine DSC for Digital
Selective Calling 
does provide GPS coordinates of the vessel that's doing the calling. If the 
vessel being called has their VHF or HF rig turned on then it will
automatically 
identify itself to acknowledge that it's being called and will in turn
transmit 
it's GPS position. At the same time it will provide a loud alarm to the 
vessel's crew that they are being called.  In the radio's TFT monitor there
will be 
displayed the name of the calling vessel and it's GPS location. There is 
nothing plotted anywhere. Obviously if you are called on marine VHF the
calling 
vessel will be within 30 miles of your location.

The HF DSC is one more big problem. Theoretically it should operate just
like 
the VHF system does, however the big catch is if both vessels have their HF 
rigs turned on to the same marine BAND, such as the 8 mHz calling frequency 
then the system works. But if the calling vessel is set on the 4 MHz band
and the 
called vessel is tuned to the 12MHz band then they don't make a connection. 
Now the GMDSS tries to get around this problem by using the ALE Automatic
Link 
Establishment software that controls the HF marine SSB rig. There is
actually 
a second receiving antenna and PC receiver that scans all the marine bands
and 
when an emergency Mayday is transmitted all DSC equipped HF SSBs will 
automatically switch to the emergency channel and display the stricken
vessel's GPS 
coordinates. Commercial vessels are being required to install this GMDSS 
software/hardware system. It's about a $1400 setup PLUS the cost of a marine
SSB 
radio with DSC capability. Private boat owners like myself, don't want to
fool 
with the added expense plus another antenna. My SSB does have DSC
capability.

With all of the above equipment all you have is position information and no 
tracking. Now the AIS operation does provide full tracking identical to
APRS, 
on marine navigation displays. There are at least a dozen manufacture's that

build AIS systems. It is composed of a completely separate VHF TX/RX along
with 
a separate antenna, that operates on marine VHF channels 87A and 87B only! 
161.975 MHz and 162.025 MHz. And there's no voice capability. These units
will 
display vessel icons such as tankers, container ships, tugs, sailboats
whatever, 
and it will provide course, speed and on the big commercial systems the
ships 
navigator can display his INTENDED TRACK! The cheapest one of these systems
I 
have found run $2000 plus the integration into your particular navigation 
software display system!

I have a jury rig operation where I pull only the LAT LON data fields from 
the AIS frequency transmissions and then using the mouse on my navigation
screen 
I match the position info and click to drop a marker. A minute or so later
do 
it again and get a line which displays the vessel's course and rough speed. 
Considering I have a vessel's position, track and some idea of his speed
while 
he is still some 25 miles away it sure beats a small boat radar!

73 de Jim

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