Fred Pot wrote in
ups.com:
On Sep 16, 2:57 pm, Dick Locke wrote:
I'm trying to figure out the best way to install an AIS system in our
cruising sailboat. It's largely used coastally off Mexico with
occasional longer passages of a few hundred miles. Night passages
are common.
Hardware questions:
There seem to be two price points..single channel, serial only for
about $190 from Milltech or dual channel USB capable from Safe
Passage for around $800. I'm thinking single channel is adequate but
I my sole serial port is occupied by the GPS and I've had problems in
the past with the serial/usb adapters. Anyone know of a single
channel USB output receiver?
I have an unused "emergency" VHF antenna on a pole about 12 feet
above the water. I could use that for the AIS or I could use a
splitter on the masthead antenna. I'm not inclined to do anything to
reduce VHF reception. Can someone tell me the formula for VHF "line
of sight" distance?
Software questions
I'm currently using MAptech Offshore Navigator which doesn't have AIS
support. I'd have to upgrade to their newer system or else buy
another. Fugawi seems attractive. I have a whole bunch of Maptech
formatted charts but Fugawi seems to be able to handle these OK.
In either case, I would lose my "tracks" of past passages. Those are
especially handy off the Mexican coast because the charts are hand
drawn in 1888 or so and the shore is a few miles further east than
the charts show...except when it isn't. Finding a way into an
anchorage or around a rock once during daylight gives me a track I
can follow next time. Maptech suggests converting tracks to routes,
but I haven't looked into that yet. Does anyone know how to get the
track files out of Maptech's program? If they have lat longs I might
be able to bring them into the new program.
I also think I could keep the old Maptech program and switch it on
when following a past track is essential. I wonder if I could run
both simultaneously and bring the old program on screen.when I need
it.
Any comments or advice? I'm not at the boat now so can't experiment
very much.
Thanks
Dick Locke
S/V Tanoshii
Full disclosu I have an ax to grind. I am with SeaCAS. We sell
dual- band receivers. Our receivers used to cost about $800 but are
now on sale for $499 and we include a USB power/data cable which makes
connection to a PC or Mac very easy. Also our connectors are
watertight and we offer optional "Direct-Connect" cable for FURUNO and
Raymarine. To circumvent Raymarine's limitation of a single NMEA port
on their C and E series we offer a very capable Multiplexer for $330
(see
http://www.seacas.com/oscomm/product...3&products_id=
47).
I maintain that single band receivers are too slow to be used for
collision avoidance. AIS information is transmitted alternating
between VHF Channel 87B and 88B. Single band recievers receive only
half of the information. Their update rate is twice what it should be.
In a close quarters crossing situation you want the best available
information to help you decide how to get out of a big ship's way. You
may have to wait as long as 12 minutes to find out a ships name so you
can hail it on VHF to make assing arrangements because the name (along
with other statis and voyage information) is sent our every 6 minutes
and it too alternates between 87B and 88B.
Fred Pot
SeaCAS, LLC
I have a single band Miltech receiver and agree that perhaps there's an
issue with not receiving the name of the ship for 12 minutes instead of
6 minutes. But who cares? Course data is transmitted every few
seconds. Until recently we only had radar and never knew the name of
the ship. With AIS we have a much better chance of knowing lots of
details and knowing them well before they get WAY too close. While I'd
love to know the name of the vessel that I'm on a collision course with,
I would much rather know in advance if and when we were going to
collide. I get all of that with single band AIS.
What I really want is a reasonably priced AIS transponder. No offense,
but this is not rocket science. Basically all that you need to do is
transmit position and course information and occasionally your ship
info. I suspect that you'll see reasonably priced units on the market in
a short period of time.
-- Geoff
www.GeoffSchultz.org