Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 21-12-2010, 16:57   #1
Registered User

Join Date: Dec 2010
Posts: 4
AIS Collision Warning for Own Boat . . .

Hi,

Have been searching the forum for threads on this topic, but couldn't find one covering it - if I missed, would appreciate if someone pointed me in the right direction.

Am using OpenCPN as additional/back-up navigation system on a netbook, and it has been working beautifully.

Being single-handed sailor, collision alarm capability was one of the main reasons to get AIS: comforting feeling that the system is constantly awake, even if I am not .

Now the problem I have - and this is both with OpenCPN and the additional set-up with chart plotters - is that I keep getting warned for my own boat, basically making the whole collision warning useless.

What I have is a Navico NAIS 300 AIS, combined with Lowrance HDS screens, and AIS input into Netbook with OpenCPN.

All systems show AIS target information well, and system is transmitting own ship AIS info.

Anyone know how to suppress warnings for own ship? Should be simple enough, with mmsi info readily available..

Hope someone can help - am about to start some major crossings, for which a fully working warning system would be very valuable .

Maarten
__________________

__________________
home_maarten is offline   Reply With Quote
Old 21-12-2010, 18:13   #2
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 4,884
home_maarten...

Sounds a bit odd.
Could you describe your hardware and port setup, please?

Thanks
Dave
__________________

__________________
bdbcat is online now   Reply With Quote
Old 22-12-2010, 03:45   #3
Registered User

Join Date: Dec 2010
Posts: 4
Hi Dave,

Thanks for the quick response.
Hardware set-up:
- NAIS 300 AIS transponder
- 2x Lowrance plotters (HDS7M and HDS8M)
- Above connected to a Shipmodul multiplexer, with USB output to HP netbook

The AIS GPS signal is also used by OpenCPN for position information, also coming through the USB output from the multiplexer. All works well (i.e. position, AIS info from other ships etc), except that I cannot use the alarm because it constantly warns me for myself. I agree that i may be the biggest danger to myself, but I already know that .

Would be great if you could help - if you need more data, let me know, but in itself the set-up is fairly straightforward.

Thanks so far!

Maarten
__________________
home_maarten is offline   Reply With Quote
Old 22-12-2010, 05:25   #4
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 4,884
home_maarten....

Thanks for the info.

Could you capture and post a few minutes of the actual NMEA/AIS data stream coming into the PC?

Use Hyperterminal, or something similar....

Thanks
Dave
__________________
bdbcat is online now   Reply With Quote
Old 28-12-2010, 13:22   #5
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 4,884
maarten....

Thanks for the logs.
I see the problem. There are two sources of ownship positioning info: the AIS VDO messages, and the multiplexed GPGLL/GPRMC messages. At any point in time, these two positions will not be exactly the same. In fact, while you are underway, sometimes the VDO position will be exactly one second in front of the GPGLL/RMC position, and on the same course line. You are going to hit yourself, very soon. So sad, we'll miss you....

Clearly a logic bug in opencpn, not seen before. Fix is easy. Look for it in the upcoming 2.3.1 update.

Quick fix for now with 2.3.0: If you can remove the GPGLL/GPRMC messages from the combined stream, the problem should disappear.

Dave
__________________
bdbcat is online now   Reply With Quote
Old 28-12-2010, 14:01   #6
Registered User

Join Date: Dec 2010
Posts: 4
Dave,

Thanks a bunch... Actually have been wrestling with the NMEA sentences to let pass and the ones to filter: seems a lot of duplication, but on the other hand I have learned to be careful, because some instruments (like Navtex) can deal with only certain type of sentences, even if they contain the same info.

In this case this surprises me, because in OpenCPN, you have to indicate from which machine you tke the GPS info - in which I indicated AIS. Guess this is the bug you're referring, to, that in spite of this setting, it takes also position info from other sources?

Being a mechanical engineer (by training anyways, long time ago) this sort of bugs/debugging, apparently without real logic, drives me mad !

I'll give this a try anyway (have some other NMEA issues to fix, nothing to do with OpenCPN) and hope this works.

Thanks again for your time!

Maarten
__________________
home_maarten is offline   Reply With Quote
Old 28-12-2010, 14:04   #7
Registered User

Join Date: Dec 2010
Posts: 4
PS... Would it not be easier to allow entry of own ship mmsi? Every system is bound (and desired) to habe some GPS/position information redundancy, won't it?
__________________
home_maarten is offline   Reply With Quote
Old 28-12-2010, 14:21   #8
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 4,884
maarten....

There are of course lots of ways to fix this problem. Short term, I try to make the smallest possible change to the code, so that we don't need to go through a long Beta test cycle to validate the solution. That is what I have done here.

Longer term, we need to improve our NMEA/AIS data management and routing. There has been some recent discussion of this, and I expect it will come to life on the next Beta cycle.

The AIS issue only arises when the stream includes AIVDO messages .AND. other standard NMEA position messages. We (perhaps foolishly) add ownship to the AIS target list, and there it is just waiting to be a potential target to itself. Needs some more thought....


However, in the general case, if we process multiple positioning sources, there could reasonably be some "jitter" in the displayed ownship position. We need a priority scheme, and steering logic. That will come...

Good luck
Dave
__________________
bdbcat is online now   Reply With Quote
Old 28-12-2010, 16:00   #9
Registered User
 
ozskipper's Avatar

Join Date: Aug 2010
Location: NSW Australia
Boat: Traditional 30
Posts: 1,981
HI guys. After watching this thread I googled and downloaded OpenCPN. Is there a place to download charts as well? I would like to have play with the software and get to know it. Thanks

Cheers
Oz
__________________
ozskipper is offline   Reply With Quote
Old 28-12-2010, 16:32   #10
Registered User
 
ozskipper's Avatar

Join Date: Aug 2010
Location: NSW Australia
Boat: Traditional 30
Posts: 1,981
Also are there any recomendations. Raster vs Vector etc..

Cheers
Oz
__________________
ozskipper is offline   Reply With Quote
Old 28-12-2010, 18:29   #11
Obsfucator, Second Class
 
dacust's Avatar

Cruisers Forum Supporter

Join Date: Feb 2008
Location: Southeast USA.
Boat: 1982 Sea Ray SRV360
Posts: 1,743
Quote:
Originally Posted by ozskipper View Post
HI guys. After watching this thread I googled and downloaded OpenCPN. Is there a place to download charts as well? I would like to have play with the software and get to know it. Thanks

Cheers
Oz
Check the link in my signature. Free charts abound.

Quote:
Originally Posted by ozskipper View Post
Also are there any recomendations. Raster vs Vector etc..

Cheers
Oz
Use both. Learn the limitations and strengths of each.

Here is a start to explain a little about raster vs. vector, but it's about the types of errors, not really about the strength.

Inland Waters Resources - Chart Errors

-dan
__________________

dacust is offline   Reply With Quote
Reply

Tags
ais, collision

Thread Tools
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
Warning! Boat Porn! knottybuoyz Powered Boats 29 20-12-2011 01:22
Can You Get Radar & AIS Overlay on Laptop ? AIS Transceiver Recommendations ? lunasea.ds Marine Electronics 22 27-12-2010 14:06
AIS Shipping Warning holmek Marine Electronics 20 03-05-2010 00:19
Woman killed in boat collision on Lake Washington Dr. Moreau Cruising News & Events 0 28-09-2008 21:10



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 08:08.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.