Empathy List Archives

RB

ron barr

Mon, Apr 3, 2006 2:27 AM

Referring back to my earlier posts on the Automatic Identification
System, I just got back from the UK and saw a very modestly priced unit
over there offered by NASA Marine Instruments. In fact they have two
versions. What they call their AIS Radar is a stand alone unit which
provides a high contrast backlit display screen of relative ship
positions with radar style rings and adjustable scales. About 6" x4".
This is an NMEA 0183 data stream. Clicking on any ship gives all the AIS
info and of course the targets leave a trail. UK cost retail about $390
ex-VAT. Their other unit is what they call an "engine" - a black box
using NMEA 2000 data stream which you can feed into your laptop plotting
program, or into a plotter that is NMEA 2000 compliant. Comes with
software. About $175 based on the UK price. Both units use regular VHF
antennas and appear to be dual channel 161.975 and 162.025 MHZ. The
competing Milltech Marine unit costs slightly more ($200) and is single
channel I believe. NASA is being handled by Sitex over here and they are
charging too much but will discount. Worth checking out.

Ron Barr
Lady Brookhaven Hatteras LRC 42
Presently lying RI Yacht Club, Narragansett Bay, RI
KB1LFX

Referring back to my earlier posts on the Automatic Identification System, I just got back from the UK and saw a very modestly priced unit over there offered by NASA Marine Instruments. In fact they have two versions. What they call their AIS Radar is a stand alone unit which provides a high contrast backlit display screen of relative ship positions with radar style rings and adjustable scales. About 6" x4". This is an NMEA 0183 data stream. Clicking on any ship gives all the AIS info and of course the targets leave a trail. UK cost retail about $390 ex-VAT. Their other unit is what they call an "engine" - a black box using NMEA 2000 data stream which you can feed into your laptop plotting program, or into a plotter that is NMEA 2000 compliant. Comes with software. About $175 based on the UK price. Both units use regular VHF antennas and appear to be dual channel 161.975 and 162.025 MHZ. The competing Milltech Marine unit costs slightly more ($200) and is single channel I believe. NASA is being handled by Sitex over here and they are charging too much but will discount. Worth checking out. Ron Barr Lady Brookhaven Hatteras LRC 42 Presently lying RI Yacht Club, Narragansett Bay, RI KB1LFX

TD

Trevor Drawbridge

Mon, Apr 3, 2006 8:55 AM

Ron Barr wrote:

Both units use regular VHF
antennas and appear to be dual channel 161.975 and 162.025 MHZ.

I have one of the NASA engines. It is a single channel device. The channel
it is operating on can be selected however by sending it a $PNMLC NMEA
sentence. Although there are an increasing number of charting systems that
support the NMEA standard output that this device produces (in common with
other AIS devices), I have seen no evidence that any of them will enable you
to manually change the channel. Whether they do so of their own volition is
something you need to ask each package provider! The engine also produces
some occasional non-NMEA standard output interspersed with the standard NMEA
sentences. Properly implemented receiving software should reject this but
once again, check the compatibility list to be sure.

Trevor Drawbridge
Samara
44' C-Kip lying York (UK)

Ron Barr wrote: > Both units use regular VHF > antennas and appear to be dual channel 161.975 and 162.025 MHZ. I have one of the NASA engines. It is a single channel device. The channel it is operating on can be selected however by sending it a $PNMLC NMEA sentence. Although there are an increasing number of charting systems that support the NMEA standard output that this device produces (in common with other AIS devices), I have seen no evidence that any of them will enable you to manually change the channel. Whether they do so of their own volition is something you need to ask each package provider! The engine also produces some occasional non-NMEA standard output interspersed with the standard NMEA sentences. Properly implemented receiving software should reject this but once again, check the compatibility list to be sure. Trevor Drawbridge Samara 44' C-Kip lying York (UK)

SD

Steven Dubnoff

Mon, Apr 3, 2006 5:22 PM

Although there are an increasing number of charting systems that
support the NMEA standard output that this device produces (in common with
other AIS devices), I have seen no evidence that any of them will enable you
to manually change the channel.

It is not clear to me why you would want to change the channel. All
information is transmitted on both channels. If you were to change
the channel on a one channel unit you would be likely to miss it,
whereas if you receive constanmtly on a single channel you will
eventually get all of the data that is being transmitted in your vicinity.

Because ship characteristics are only transmitted once every six
minutes, a two channel receiver is desirable, to make sure you get
that in time to do something about it.

Best,

Steve

Steve Dubnoff
1966 Willard Pilothouse
www.mvnereid.com
sdubnoff@circlesys.com

> Although there are an increasing number of charting systems that >support the NMEA standard output that this device produces (in common with >other AIS devices), I have seen no evidence that any of them will enable you >to manually change the channel. It is not clear to me why you would want to change the channel. All information is transmitted on both channels. If you were to change the channel on a one channel unit you would be likely to miss it, whereas if you receive constanmtly on a single channel you will eventually get all of the data that is being transmitted in your vicinity. Because ship characteristics are only transmitted once every six minutes, a two channel receiver is desirable, to make sure you get that in time to do something about it. Best, Steve Steve Dubnoff 1966 Willard Pilothouse www.mvnereid.com sdubnoff@circlesys.com

TD

Trevor Drawbridge

Mon, Apr 3, 2006 10:14 PM

It is not clear to me why you would want to change the channel. All
information is transmitted on both channels. If you were to change the
channel on a one channel unit you would be likely to miss it, whereas if
you receive constanmtly on a single channel you will eventually get all of
the data that is being transmitted in your vicinity.

Because ship characteristics are only transmitted once every six minutes,
a two channel receiver is desirable, to make sure you get that in time to
do something about it.

I guess the function is there in case one of the channels becomes inoperable
for some reason. I assume redundancy is one of the reasons that AIS is a two
channel system. I would have preferred a dual channel device, but the price
of the NASA unit was too tempting!

Trevor Drawbridge
Samara
44' C-Kip lying York (UK)

> It is not clear to me why you would want to change the channel. All > information is transmitted on both channels. If you were to change the > channel on a one channel unit you would be likely to miss it, whereas if > you receive constanmtly on a single channel you will eventually get all of > the data that is being transmitted in your vicinity. > > Because ship characteristics are only transmitted once every six minutes, > a two channel receiver is desirable, to make sure you get that in time to > do something about it. > I guess the function is there in case one of the channels becomes inoperable for some reason. I assume redundancy is one of the reasons that AIS is a two channel system. I would have preferred a dual channel device, but the price of the NASA unit was too tempting! Trevor Drawbridge Samara 44' C-Kip lying York (UK)

WO

william osborne

Mon, Apr 3, 2006 10:50 PM

I have a DF44 with two 300 gallon fuel tanks (port and starboard). I
noticed, for the first time this weekend, that these two talks are connected
via a copper line going directly from there top of one to top of the other.
They are also connected to the fuel manifold by supply lines from the bottom
and by return lines to the tops. They also have vents/overflow lines
directly to the outside. So, why the extra two lines directly connecting the
top of the tanks bypassing the fuel manifold?

Thanks for the help, Bill

I have a DF44 with two 300 gallon fuel tanks (port and starboard). I noticed, for the first time this weekend, that these two talks are connected via a copper line going directly from there top of one to top of the other. They are also connected to the fuel manifold by supply lines from the bottom and by return lines to the tops. They also have vents/overflow lines directly to the outside. So, why the extra two lines directly connecting the top of the tanks bypassing the fuel manifold? Thanks for the help, Bill

RR

Ron Rogers

Mon, Apr 3, 2006 10:51 PM

Perhaps the reason that commercial vessels transmit the same report on two
frequencies is because VHF transmissions of equal strength and proximity can
block each other?

Ron Rogers

Perhaps the reason that commercial vessels transmit the same report on two frequencies is because VHF transmissions of equal strength and proximity can block each other? Ron Rogers

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