Cruisers Forum
 


Join CruisersForum Today

Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 08-09-2019, 04:24   #1
Registered User
 
Karanga's Avatar

Join Date: Jun 2018
Location: NZ/Aus
Boat: Crowther 85 Catamaran
Posts: 136
AIS target more than 2000km away

Recently I was anchored off Hinchinbrook Island on East Coast of Australia, and checking out AIS targets.
I was surprised to be picking up yachts (class B) targets as far away as 750km away.
I scrolled out further, and found targets (class A) at Noumea in New Caledonia, which is more than 2100km away!!
This is VHF only - no internet access.

Is this the effect of sunspot activity?
Or bouncing off satellites?
Or...?

Tim
Click image for larger version

Name:	AIS2000.jpeg
Views:	168
Size:	60.2 KB
ID:	199419
__________________

Karanga is offline   Reply With Quote
Old 08-09-2019, 04:29   #2
Registered User

Join Date: Nov 2013
Location: Nice, France
Boat: Hunter Marine 38
Posts: 856
Re: AIS target more than 2000km away

...... or a repeater installed by the Coast Guard or an passionate amateur .... ?
__________________

sailormed is offline   Reply With Quote
Old 08-09-2019, 04:54   #3
Senior Cruiser
 
StuM's Avatar

Cruisers Forum Supporter

Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPB
Posts: 9,868
Re: AIS target more than 2000km away

Atmospheric conditions.

https://en.wikipedia.org/wiki/Tropos...pheric_ducting


"Tropospheric ducting over water, particularly between California and Hawaii, Brazil and Africa, Australia and New Zealand, Australia and Indonesia, Strait of Florida, and Bahrain and Pakistan, has produced VHF/UHF reception ranging from 1000 to 3,000 miles (1,600 – 4,800 km)."
StuM is online now   Reply With Quote
Old 08-09-2019, 06:01   #4
Registered User

Join Date: Jul 2018
Posts: 182
Re: AIS target more than 2000km away

Most likely troposphere ducting.
__________________
Gary
ohgary is offline   Reply With Quote
Old 08-09-2019, 08:45   #5
Registered User

Join Date: Oct 2016
Location: Carribbean
Boat: Alubat Ovni 435
Posts: 24
Re: AIS target more than 2000km away

You usually get this in High Pressure conditions. I've picked up American FM radio station mid Atlantic on occasions.
gcrothers is offline   Reply With Quote
Old 08-09-2019, 09:03   #6
Registered User

Join Date: Dec 2012
Boat: Jeanneau SO45.2
Posts: 229
Re: AIS target more than 2000km away

it could also be a mis-configured or rogue transponder - the position we see is whatever they report, regardless of where they actually are.
Redline452 is offline   Reply With Quote
Old 08-09-2019, 09:03   #7
Registered User

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 18,507
Re: AIS target more than 2000km away

You are VHF only but the shore station in range can forward AIS messages from anywhere over the net - also data derived from the www component.


AIS is so much more than we initially assume it is. Just think of virtual AIS channel markers - there is none on the water and yet they all pop up on our screens.



Or think of AIS generated mayday message - these can be actually collected by the satellite network.



b.
barnakiel is offline   Reply With Quote
Old 08-09-2019, 10:54   #8
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jan 2017
Posts: 694
Re: AIS target more than 2000km away

Quote:
Originally Posted by ohgary View Post
Most likely troposphere ducting.
Tropospheric ducting is almost always how a VHF will sometimes receive from far away. Last winter a friend was having conversations with another boat across the Sea of Cortez; over 80 miles.

https://en.wikipedia.org/wiki/Tropospheric_propagation
KP44 is offline   Reply With Quote
Old 08-09-2019, 11:06   #9
Registered User

Join Date: Jun 2013
Location: canada
Posts: 2,934
Re: AIS target more than 2000km away

I could pull a boat up beside yours (or 10 mikes away) . And feed fake nmea183 data to a class A ais. And make it show up 2000km away on your screen. Because it’s transmitting within your range you will pick it up and see it’s (fake) data.

But I doubt that is happening if you have multiple boats in big range.
smac999 is offline   Reply With Quote
Old 08-09-2019, 11:11   #10
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 3,555
Images: 7
Re: AIS target more than 2000km away

It's not particularly unusual to pick up Japanese VHF traffic in Perth in Western Australia.
RaymondR is offline   Reply With Quote
Old 08-09-2019, 12:34   #11
Registered User

Join Date: May 2013
Location: Mangareva, French Polynesia
Boat: Heritage West Indies 36
Posts: 750
Re: AIS target more than 2000km away

Some AIS transponders allow the user to manually input or offset the reported position. I've seen fishing boats do this when they want to make it look like they are not where they shouldn't be!
DefinitelyMe is offline   Reply With Quote
Old 08-09-2019, 14:21   #12
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 16,126
Re: AIS target more than 2000km away

These conditions are not all that rare. We often see them here in Oz, and I have been in Noumea and listened to the Tin Can Bay VMR talking on channel 16. Ducting is real and not uncommon... no spoofing of AIS needed to explain the observation.

Jim
__________________
Jim and Ann s/v Insatiable II back in Port Cygnet doin' the isolation tango.
Jim Cate is online now   Reply With Quote
Old 08-09-2019, 14:24   #13
Moderator
 
Jim Cate's Avatar

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 16,126
Re: AIS target more than 2000km away

Quote:
Originally Posted by DefinitelyMe View Post
Some AIS transponders allow the user to manually input or offset the reported position. I've seen fishing boats do this when they want to make it look like they are not where they shouldn't be!
Could you please tell us which ones do allow this? Transponders, IIRC, require an internal GPS receiver to be coupled to the system specifically to eliminate false info from being broadcast.

Jim
__________________
Jim and Ann s/v Insatiable II back in Port Cygnet doin' the isolation tango.
Jim Cate is online now   Reply With Quote
Old 08-09-2019, 14:46   #14
Registered User
 
Diamond Life's Avatar

Join Date: Jun 2017
Location: Esperance, Western Australia
Boat: Expedition 36 Aluminium
Posts: 22
Re: AIS target more than 2000km away

Agree with tropospheric ducting, I have picked up ships several hundred miles south of me on my AIS as they travel around the bottom of Australia. I confirmed their positions later when I was able to access data on MarineTraffic.
Diamond Life is offline   Reply With Quote
Old 09-09-2019, 03:56   #15
Registered User
 
clownfishsydney's Avatar

Join Date: Mar 2014
Location: Sydney, Australia
Boat: Lightwave 38' Catamaran - now sold
Posts: 432
Re: AIS target more than 2000km away

When sailing the GBR in 2015 and 2017 I regularly saw ships on AIS which were thousands of miles away. Not uncommon. Sometimes you will get one that is 8,000 miles away, but when you check you will find that it is 0 degrees lat and long, meaning its GPS has outputted nil location. The real boat is probably close by.
__________________

__________________
Michael
Formerly of Catlypso - Web Site
Lightwave 38' cat
clownfishsydney is offline   Reply With Quote
Reply

Tags
ais

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
GPSD-NG for more than AIS/GPS? muttnik OpenCPN 2 21-08-2014 01:39
Why is an AIS transmitter so much more expensive than a receiver? David Dennis Marine Electronics 36 26-06-2014 09:14
Maxsea 10.3.2.1 does not display AIS Class B target names svBeBe Marine Electronics 7 17-03-2013 08:59
OpenCPN v2.5.0 Unable to Display AIS Target Query Window jsavage Navigation 4 28-11-2011 01:35
AIS Target Mouseover Data idpnd OpenCPN 11 18-06-2010 03:34

Advertise Here


All times are GMT -7. The time now is 18:21.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.