"Geoff Schultz" wrote in message
6...
"Paul" wrote in
:


"Jim" wrote in message
. ..
Paul wrote:
Has anyone seen a ship position as reported by AIS being off by over
one nautical mile?

snip
Any thoughts?

Thanks,
Paul

This is really off the wall but is there a possibility that the datum
being used was that far off? Isn't the LAT/LON calculated for the chart
datum?
Jim

I don't think so, since the chart datum isn't an issue unless the
positions are being shown on a chart (whereas my display is similar to a
radar screen). Even so, my boat's position relative to the ship's
position should be displayed correctly regardless of any datum
discrepancies. What I've got is a situation where a ship that is
physically to the north of me is transmitting a latitude that is to the
south of me.

I'm not completely ruling out cockpit error or bad code on my part, but
I can't find it and the raw data seems to exonerate me. If anyone wants
to help figure it out, here is the minimum NMEA data capture that shows
the situation. The first line is my position, and the second is the AIS
message from the ship:

$M2RMC,225040,A,4038.518,N,15149.375,W,5.6,072.5,0 40806,014.5,E,D*6
!AIVDM,1,1,,A,15@HsT001wE8wopG@0K5:3=N0@L6,0*6

The "$M2" has been substituted to indicate which multiplexer port the
data came from.
My position is 40.642433 deg (N), -151.820917 deg (W)
The reported ship position is 40.630167 deg (N), -151.822000 deg (W)
The range and bearing to the ship are 0.7NM, 183.8 deg true

Trust me, the ship was actually to the north. I have photos!

-Paul

I really don't know much about AIS data and how often ships report, but do
other reports from that ship show it moving in a reasonable manner?

-- Geoff

Since this was a "ships passing in the afternoon" situation, I only had the
the one encounter with them. It looked like their reported longitude was
more or less correct -- their position was moving from west to east in a way
that matched what I was seeing with my eyes. It was just that the latitude
was consistently off by perhaps a minute.

Someone has mentioned (on the Panbo blog) that they saw a ship in San
Francisco reporting her position as being in the middle of Treasure Island
(a small island in the bay), so perhaps this problem isn't unprecedented. I
still have no idea what could be causing this error, other than an
un-reported GPS failure causing the position reporting to be running in
dead-reckoning mode. That would be two unrelated failures, or a failure and
a design flaw. In any case, I'm definitely going to keep using my eyeball
to verify what the AIS reports.

-Paul

"Larry" wrote in message
...
"Paul" wrote in
:

At the moment I am using a second bluetooth channel to connect
the AIS receiver to the PocketPC, but I hope that I with the upgrade I
can run everything through the MiniPlex.



Oh, oh....WARNING WARNING....HE'S BYPASSING NMEA ALTOGETHER!

Next thing you know he'll insist all instruments in the whole boat be
Bluetooth....negating needing multiplexers or even wires to make it all
talk to each other!

What a pleasure THAT will be to install! I'm all for it!

I can hear it in the Bluetooth headset telling the helmsman, "Come left to
course 085. May I energize the autopilot for you? Say 'yes' or 'no'."

"Radar, how far is that ship just off the port bow?"...."Eight point four
nautical miles. I'm tracking it for collision avoidance, sir. Please
slack the sheet on the Genoa. I'm detecting it stalling at this relative
wind setting, slowing us down."

No knobs at all at the helm. You just tell it what you want through your
Bluetooth headset.....(c;


Well, technically I was still using NMEA -- the BT connection was just
substituting for the serial cable.

I agree with the sentiment though, NMEA 0183 is old and slow. I would
prefer WiFi. BT networking is pretty primitive and the port-count
limitations on most devices make a it difficult to create a flexible
multiport system. BT still has the power advantage though, and I hate
wasting Amp-Hours (thus the Pocket PC for my logging application instead of
an always-on laptop).

-Paul

RW Salnick wrote in news:ed2bcl$aiu$1
@gnus01.u.washington.edu:

I think you may want to go a little farther than depending on WEP for
protecting your network... Netstumbler requires about 1 minute's worth
of traffic to break a WEP key.

bob



Not a problem. We're dealing with sailor-bankers, sailor-lawyers, sailor-
just-plain-rich-people.....not intensive hackers with banks of computers
and millions of lines of code experience. From my experiences helping them
getting their VHF antenna to radiate, reliably, and some of the other
situations they've asked me to help with, there's no danger at all.

If they can't figure out how to hook up the new starting battery to a
Yanmar, there's little danger they're going to break the WEP code in the
wireless lan any time soon....(c;

Some of the lawyers can't load a flashlight. I've never figured out why
society allows lawyers to make so MUCH money with so little brains. How
stupid.

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

"Meindert Sprang" wrote in
:

450mA at 3.3V

450ma x 3.3V = 1.485w at 13V = .114A x 24 = 2.74AH which isn't much a
significant part of a small 330AH house battery, even smaller on the two
banks of beasts we drag around in the stern. 2.7AH a day isn't much of
an issue, is it? The stern running light uses 10-20 times that much
overnight.

PLEASE tell me you're getting the 3.3V from a highly efficient tiny
switching supply....not some 7800 series analog heat sink heater
regulator....please? 450ma x 13V off an analog regulator = 5.85w or
10.8AH/day....not so good....not a catastrophy, but not so good. My
friend Dan's Hatteras 56 got 12VDC to run the toys from the 32VDC train
engine power that ran the 8V92TA beasts-in-the-bilge. Most of the power
went up in smoke because they had 3 HUGE heatsinked analog regulators
wasting the 20 volt difference between the systems, heat created in
hundreds of watts. Of course, with power to burn on this oil burner, it
wasn't much of an issue, but seemed an awful waste as the main salon's
air conditioner had to pull this heat out of the cabin, wasting more
power from the two gensets. Me? I used to tell the pump boys at the
diesel dock to "fill 'er up and don't forgit ta wash the windshields"
(5). It wasn't my money, after all...(c;

We quibble about the tiniest things.....

When I used to work for the Federal government, we had a saying that went
something like:

"In any meeting, the amount of time spent on any line item was
proportional to the inverse square of its cost."

A $2 whazzit took hours to fight over. The $480,000 diggit took 10
minutes, mostly in motions to pass it. I never saw 'em buy something
over $1M, but that might have happened during one of my yawns and I
missed it.

If 2.74 AH/day is too much of a strain on the system, should we REALLY
sail it out of the harbor in the first place??



--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

"Paul" wrote in
:

I agree with the sentiment though, NMEA 0183 is old and slow. I would
prefer WiFi. BT networking is pretty primitive and the port-count
limitations on most devices make a it difficult to create a flexible
multiport system. BT still has the power advantage though, and I hate
wasting Amp-Hours (thus the Pocket PC for my logging application
instead of an always-on laptop).



Wifi Ethernet transceivers are so cheap there's 4 of them coming out built
right into tiny telephone handsets to hook Skype-in-EEPROM directly to the
router, eliminating running Skype on desktop or laptop completely. I bet a
fully Ethernet-compliant chipset and radio transceiver now costs OEMs less
than $20, maybe even less than $10. Amazing what Asians can do with slave
labor.

The Chinese company making Ipods for Apple was investigated for child labor
abuses. The investigators didn't find anything wrong. They were paying
the help nearly $100/month for six, twelve-hour days a week.

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.

Larry wrote:
"Meindert Sprang" wrote in
:

450mA at 3.3V

450ma x 3.3V = 1.485w at 13V = .114A x 24 = 2.74AH which isn't much a
significant part of a small 330AH house battery, even smaller on the two
banks of beasts we drag around in the stern. 2.7AH a day isn't much of
an issue, is it?


It wouldn't if it were the only WiFi network hw on the boat;
unfortunately one is not very much use :-) by definition you need two.

The power draw starts to add up if you are going to replace all
NMEA/Seatalk/whatever-bus drivers with WiFi. 3 sensors, 6 displays, 1 PC
adds up to 27 Ah... that's no longer neglible.

--
Kees

"Larry" wrote in message
...
"Meindert Sprang" wrote in
:

450mA at 3.3V

450ma x 3.3V = 1.485w at 13V = .114A x 24 = 2.74AH which isn't much a
significant part of a small 330AH house battery, even smaller on the two
banks of beasts we drag around in the stern. 2.7AH a day isn't much of
an issue, is it? The stern running light uses 10-20 times that much
overnight.

Ahem, does a PDA or laptop have a 330Ah battery?
The average battery life of a PDA (Paul said he uses one) halves if you
enable its Wifi. Not so for BT.

PLEASE tell me you're getting the 3.3V from a highly efficient tiny
switching supply

I am, don't worry :-)

Meindert

"Larry" wrote in message
...
Wifi Ethernet transceivers are so cheap there's 4 of them coming out built
right into tiny telephone handsets to hook Skype-in-EEPROM directly to the
router, eliminating running Skype on desktop or laptop completely. I bet
a
fully Ethernet-compliant chipset and radio transceiver now costs OEMs less
than $20, maybe even less than $10. Amazing what Asians can do with slave
labor.

The only problem is that Wifi is only cheap if you buy 100k chipsets or
more. Most, if not all Wifi chip vendors won't talk to you or send you a
datasheet if you don't sign a contract first for at least 100k units. So for
low volume applications, Wifi is very expensive. The Wifi modules I use cost
around $100 each, even in 100's.

Meindert

Meindert Sprang wrote:
"Larry" wrote in message
...
Wifi Ethernet transceivers are so cheap there's 4 of them coming out built
right into tiny telephone handsets to hook Skype-in-EEPROM directly to the
router, eliminating running Skype on desktop or laptop completely. I bet
a
fully Ethernet-compliant chipset and radio transceiver now costs OEMs less
than $20, maybe even less than $10. Amazing what Asians can do with slave
labor.

The only problem is that Wifi is only cheap if you buy 100k chipsets or
more. Most, if not all Wifi chip vendors won't talk to you or send you a
datasheet if you don't sign a contract first for at least 100k units. So for
low volume applications, Wifi is very expensive. The Wifi modules I use cost
around $100 each, even in 100's.

Meindert



Meindert,

I assume you use these modules in your non-marine products right?

To me having a WiFi multiplexer doesn't make sense, as there is no
"serial profile" defined on top of Ethernet, by my understanding. Even
if there were in my opinion it would more sense to have an (wired)
Ethernet version of your multiplexer instead? A lot of people
considering this type installation might already have a PC/access point
installed, and it would mean higher reliability for users willing to run
wires. People that really want wireless you can sell a $50 access point
to... Ethernet modules are surely a lot less expensive?

The new integrated systems (Furuno, Raymarine, Garmin) also use wired
ethernet, so the infrastructure is getting installed already.

What we need now is a standard for transmitting NMEA and NMEA-2000
(like) data over Ethernet/UDP. Guess that won't happen for a while...

--
Kees

If they can't figure out how to hook up the new starting battery to a
Yanmar, there's little danger they're going to break the WEP code in the
wireless lan any time soon....(c;

No, but someone onshore near their boat certainly can. Use WPA and you're
done.

Some of the lawyers can't load a flashlight. I've never figured out why
society allows lawyers to make so MUCH money with so little brains. How
stupid.

You've obviously never needed effective legal service. But hey, play dumb
until you do, then $350/hour to keep you out of prison will seem CHEAP.