In " The Radar Book - Effective Navigation and Collision Avoidance " by
Kevin Monahan, he points out that the compass bearing given by a GPS will be
unstable at low speeds. If you want your radar to show proper compass
bearings and work in the North-up/Course-up modes he says you must connect
to some type of fluxgate or gyro compass. So if you just connect your GPS
NMEA output to your radar it seems you may not get correct heading
information while creeping along at low speed, for example, in fog.

"Gary" wrote in message
...
I saw a few people said something about needing a fluxgate compass. I also
have a Robertson AP3000X autopilot that is connected to a fluxgate
compass.
Am I going to need 3 cables now, or is the GPS most likely connected to
the
fluxgate compass already?


"Gary" wrote in message
. ..
I recently bought a 1995 320 Albemarle Express Fisherman. It has a
Furuno
1830 Radar and a Garmin 220 GPS. In reading through the manuals for
these
pieces of equipment, I have noticed that it's possible to connect a GPS
to
the radar and it will display some nav information on the Radar unit as
well
as having the ability to plot the speed and direction of various targets
on
the radar.

Is this simply a matter of purchasing and attaching some sort of cord
between the units, and if so, where do I get this? I am not sure if they
are fairly universal or do I need to contact one of the vendors for this,
and if so, which one...Furuno or Garmin?

Is there more to it than this? Any idea how much it costs?

Thanks!

Gary

?

On Wed, 27 Oct 2004 18:41:29 GMT, "Gordon Wedman"
wrote:

In " The Radar Book - Effective Navigation and Collision Avoidance " by
Kevin Monahan, he points out that the compass bearing given by a GPS will be
unstable at low speeds. If you want your radar to show proper compass
bearings and work in the North-up/Course-up modes he says you must connect
to some type of fluxgate or gyro compass. So if you just connect your GPS
NMEA output to your radar it seems you may not get correct heading
information while creeping along at low speed, for example, in fog.

"Gary" wrote in message
m...
I saw a few people said something about needing a fluxgate compass. I also
have a Robertson AP3000X autopilot that is connected to a fluxgate
compass.
Am I going to need 3 cables now, or is the GPS most likely connected to
the
fluxgate compass already?


Monahan's book may predate the discontinuance of selective
availability. You have to be going very slowly indeed to make the GPS
track reading less stable than a mag compass nowadays.

It is easy enough to compare on your own boat.





Rodney Myrvaagnes NYC J36 Gjo/a

"Religious wisdom is to wisdom as military music is to music."

In article tZRfd.10435$df2.5362@edtnps89,
"Gordon Wedman" wrote:

In " The Radar Book - Effective Navigation and Collision Avoidance " by
Kevin Monahan, he points out that the compass bearing given by a GPS will be
unstable at low speeds. If you want your radar to show proper compass
bearings and work in the North-up/Course-up modes he says you must connect
to some type of fluxgate or gyro compass. So if you just connect your GPS
NMEA output to your radar it seems you may not get correct heading
information while creeping along at low speed, for example, in fog.

That would very much depend on the GPS, its Position Update Rate, and
internal Math Capabilities. I would suspect that any GPS that updates
faster than every .5 Sec, and has a good floating point processor, would
give good resolution down to at least 2 to 3 knots.

Bruce in alaska
--
add a 2 before @

On Wed, 27 Oct 2004 23:08:51 GMT, Bruce in Alaska
wrote:

That would very much depend on the GPS, its Position Update Rate, and
internal Math Capabilities. I would suspect that any GPS that updates
faster than every .5 Sec, and has a good floating point processor, would
give good resolution down to at least 2 to 3 knots.
=========================================

That is definitely true. With my little hand hand held WAAS unit I
get very good resolution at walking speed, and very rapid update.

would
give good resolution down to at least 2 to 3 knots.

Exactly Kevin Monahan's point. At low speed, creeping through fog, you will
not get a stable heading readout. I have a Garmin 182C plotter with WAAS.
Below 2 knots I start to see the "compass" heading wandering.
Kevin's book is quite recent and takes into account the current situation.
I'm planning on purchasing the Raymarine Seatalk/NMEA conversion box so that
I can feed my Autohelm fluxgate compass heading to my JRC radar. The JRC
has two NMEA inputs, one for GPS and one for Compass. Internal software
selects the Compass heading input over any GPS heading input.
Maybe this isn't necessary a lot of the time but I'd like to be able to rely
on what the radar is showing at all times.

"Bruce in Alaska" wrote in message
...
In article tZRfd.10435$df2.5362@edtnps89,
"Gordon Wedman" wrote:

In " The Radar Book - Effective Navigation and Collision Avoidance " by
Kevin Monahan, he points out that the compass bearing given by a GPS will
be
unstable at low speeds. If you want your radar to show proper compass
bearings and work in the North-up/Course-up modes he says you must
connect
to some type of fluxgate or gyro compass. So if you just connect your
GPS
NMEA output to your radar it seems you may not get correct heading
information while creeping along at low speed, for example, in fog.

That would very much depend on the GPS, its Position Update Rate, and
internal Math Capabilities. I would suspect that any GPS that updates
faster than every .5 Sec, and has a good floating point processor, would
give good resolution down to at least 2 to 3 knots.

Bruce in alaska
--
add a 2 before @

When will GPS compasses come down in price? Just came from the bridge of an APL
container ship where they had two Sperry GPS compasses. They have replaced mech
gyros on many ships and are very accurate and responsive. Cost about $17,000.00
each.

"BOEING377" wrote in message
...
When will GPS compasses come down in price? Just came from the bridge of
an APL
container ship where they had two Sperry GPS compasses. They have replaced
mech
gyros on many ships and are very accurate and responsive. Cost about
$17,000.00
each.

Furuno makes GPS compasses is the $ 5-8K range. A GPS compass is an entirely
different critter from the NMEA compass information provided from a GPS
sensor. A GPS compass is not using the datastream. It is using three
antennas at least and doing carrier signal phase difference measurements. A
proper installation requires a technician who understand radio wave
reflections, and even he may have to reposition the antenna array a few
times for proper results. It is really trial and error at first. I know of
two identical 80 foot Alaska crab fleet boats, where one system works super
and the other is still fighting problems. And, yes, they provide Furuno
AD-10 format compass data to a radar. A diagnostic program may take 12 hours
to run for results.

Doug K7ABX

"Doug" wrote in message
news

"BOEING377" wrote in message
...
When will GPS compasses come down in price? Just came from the bridge of
an APL
container ship where they had two Sperry GPS compasses. They have
replaced
mech
gyros on many ships and are very accurate and responsive. Cost about
$17,000.00
each.

Furuno makes GPS compasses is the $ 5-8K range. A GPS compass is an
entirely
different critter from the NMEA compass information provided from a GPS
sensor. A GPS compass is not using the datastream. It is using three
antennas at least and doing carrier signal phase difference measurements.
A
proper installation requires a technician who understand radio wave
reflections, and even he may have to reposition the antenna array a few
times for proper results. It is really trial and error at first. I know of
two identical 80 foot Alaska crab fleet boats, where one system works
super
and the other is still fighting problems. And, yes, they provide Furuno
AD-10 format compass data to a radar. A diagnostic program may take 12
hours
to run for results.

Doug K7ABX



KVH has one for around $3k. Have not seen it in use.

On 01 Nov 2004 03:52:11 GMT, (BOEING377) wrote:

When will GPS compasses come down in price? Just came from the bridge of an APL
container ship where they had two Sperry GPS compasses. They have replaced mech
gyros on many ships and are very accurate and responsive. Cost about $17,000.00
each.

17000???

How about the CSI-Wireless Vector Lite? We've been using one for over a year
now on oil rigs.

US$3k.

Dave

The email address used for sending these postings is not valid.
All replies to the group please.

JRC also makes a unit. It uses 2 antennae. Costs about $3,000. Read an
interesting article about these on one of the boating websites. The Furuno
unit has 3 antennae and can calculate additional information, for example,
roll period.

"BOEING377" wrote in message
...
When will GPS compasses come down in price? Just came from the bridge of
an APL
container ship where they had two Sperry GPS compasses. They have replaced
mech
gyros on many ships and are very accurate and responsive. Cost about
$17,000.00
each.