Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 20-05-2013, 10:37   #406
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,757
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by colemj View Post
Does the plotter accept AIS via N2K? If so, just get an Actisense 0183-N2K converter. They have AIS PGNs on it.

Mark
Yes, but it's not the AIS which is the problem -- that's working fine. It's the DSC position reports which I would like to see on the plotter. So I need to get NMEA data from the radio. It would really be better if the radio was on N2K, but it's not, so I have to get GPS data onto it, and position report data off of it, by NMEA0183.
__________________

__________________
Dockhead is offline   Reply With Quote
Old 20-05-2013, 10:39   #407
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,757
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by Bash View Post
I disagree. There are ultimately only three ways that a commons can be preserved: privatization (at which point the commons ceases to function as a true commons), regulation, adherence to community standards. Evans has appealed to the latter of these remedies. A small but vocal group of correspondents insists that Evans' appeal infringes on their privilege as owners of AIS-equipped yachts. At the shallow end of the pool the argument is being made that since there's no law prohibiting AIS transmission while at dock, it's obscene to suggest that they should stop transmitting as a matter of courtesy. For some reason this becomes an argument about rights, as we have already seen on this thread. The argument is made, "I have a right to transmit at the dock, and ain't nobody gonna tell me not to."

Fine. You kids hang onto your "rights," and let's see how long it takes for regulations to be enacted.
A superb analysis of this thread, which got yanked off track when it became a debate about rights. But I think we've left all that behind us now, right?
__________________

__________________
Dockhead is offline   Reply With Quote
Old 20-05-2013, 10:42   #408
Senior Cruiser
 
colemj's Avatar

Cruisers Forum Supporter

Join Date: Oct 2005
Location: Presently on US East Coast
Boat: Manta 40 "Reach"
Posts: 10,049
Images: 12
Re: Please turn your AIS off when docked/moored/anchored

Didn't you buy the Actisense? It should hook up between your radio and your N2K network and provide 0183 GPS data to your radio and N2K DSC data to your chartplotter.

Mark
__________________
www.svreach.com

You do not need a parachute to skydive. You only need a parachute to skydive twice.
colemj is offline   Reply With Quote
Old 20-05-2013, 10:48   #409
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,757
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by goboatingnow View Post
To address several issues



Well that isnt the COLREGS approach, and AIS always is a "Help". Thats all it is really a, an "aid". It does not substitute for good seamanship.



CLass A can be managed control access and has inbuilt methods to reuse slots etc, or slot accessed can be controlled by a controlling station. Also CLass A has the concept of physical transitional boundaries where automatically Class A changes access methodology ( CLass A has SOTDMA, ITDMA, RATDMA, FATDMA as access methods!), change.

Its also worth noting that the technicals provisions are there for CLass B 'SO' transceivers to also participate in the Self Organised TDMA access methodologies. Im not sure if there are any CLass B 'SO's out there.

Hence Evans , given the nature of CLass B 'CS" ie CSMA-TDMA. IN essence this means that (a) it can only use one slot, (b) it only seeks out a free slot by sensing activity in that slot. (c) the local 'competent' authority can control class B 'CS' in its area of operation , in essence giving higher priority to CLASS A and hence lower to Class B 'CS'.

Furthermore since CLASS B is subservient to class A, in areas of high Class A activity , class B 'CS; is designed to essentially 'fail'


Hence in high density areas several issues can combine to prevent your Class B 'CS' device from transmitting

1. The presence of large number of Class A devices,

2. The presence of large numbers of Class B devices

3. The commands being sent from the base stations. ( including Quiet commands, that essentially shut down Class B, or reduced interval reporting commands )

4. The inherent construction of the Class B protocol, ie a total of only 10 Candidate periods out of the whole available Transmission Interval.


What this means Evans is that CLass B was designed to be overloaded and to in effect stop working. Thats not a fault of the system.

Furthermore, merely reducing the number of class B units transmitting does in fact not guarantee that your class B unit would in fact get through any better. in a large port area, there simply maybe no ( or few) Candidate periods available for CLass B 'CS to transmit in. This is by design.

So to summarise, Class B 'CS' is not designed to work well in areas of high traffic, it is expendable in such situations.

what we need are class B 'SO' sets to arrive!

dave
You say that Class B is "designed to fail" when the system gets overloaded.

According to some reports, this is actually happening in some crowded places. I can report from my own observation that in the Solent, on a nice day, the frequency of updates on Class B sets seems to slow way down -- the AIS symbols jerk across the screen, appearing suddenly in new places. That looks to me like the system is struggling a bit.

All of this seems to contradict the assertion others have made that the system can handle thousands and millions of vessels at one time with no problems of any kind, and is no where near being clogged up. As Dave has said, it doesn't (fortunately!) affect Class A sets, and the system doesn't collapse.

But it does seem to somewhat support the idea that it would be considerate to not take up any slots by switching off your set when parked, bearing in mind, of course, that a stationary boat is not taking up that much space to begin with. But every little bit helps, surely.
__________________
Dockhead is offline   Reply With Quote
Old 20-05-2013, 10:50   #410
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,757
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by colemj View Post
Didn't you buy the Actisense? It should hook up between your radio and your N2K network and provide 0183 GPS data to your radio and N2K DSC data to your chartplotter.

Mark
Thanks -- yes, I will do that if I can't figure out another way.

One option is to pull a cable to the helm and feed the radio data to the cockpit plotter, which has a free port and will bridge the data. I'm trying to decide whether I'm up for the labor or not.
__________________
Dockhead is offline   Reply With Quote
Old 20-05-2013, 10:51   #411
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Please turn your AIS off when docked/moored/anchored

Quote:
A superb analysis of this thread, which got yanked off track when it became a debate about rights. But I think we've left all that behind us now, right?
I see no debate about 'rights' , I see primarily technical people arguing with Evans that the premise upon which he is basing his arguments is flawed and that the main issue is with his setup and use of it ( and generally CLass B).

Most people accept that you should power down the AIS when the boat is on the dock and you have gone home. What Nick and I are arguing is that is irrelevant to the debate as we get increasing higher densities of Class B ( and class A). it matters not what is on and what is off, Evans will see 'his' problem irrespective.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-05-2013, 10:55   #412
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,888
Images: 4
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by Paul Elliott View Post
Good question. I know in Europe the percentage of Class-B is much higher than in the USA, I suppose because it took so long for FCC Class-B approval here. I don't have access to my worldwide AIS data feed at the moment, but I just connected to my San Francisco-area feed, and am collecting AIS targets. After breakfast, I will do a count of A and B stations, and report back. I think San Francisco should be pretty typical, if not over-represented, regarding Class-B. I have no idea how many get turned off when not in use, in San Francisco vs elsewhere. I will filter for zero speed and add that data into my report.

This won't be authoratative, but should be interesting.
Here's the data from a quick look at San Francisco area AIS traffic, collected today around 9:00AM PDT:

This data comes from receivers scattered throughout the Bay area. The coverage area picked up ships as far as 700 nautical miles distant, but by far the vast majority are inside the bay or in the nearby approach lanes.

Total AIS targets: 146. This consisted of:
5 Base Stations
114 Class-A
28 Class-B

Of the Class-B transponders,
3 were moving faster than 1 kt,
6 were between 1 and 0.1 kt,
19 were at 0 kt. It looks like we're leaving them on in the slip.

Of the Class-A transponders,
49 were at 0 kts. By far, most of these had a navstat of "Underway Using Engine"
20 were between 0.1 and 1.0 kt.
46 were going faster than 1 kt. Two of these had a "Moored" navstat, and these were traveling at 15 and 22 kts.

Make of this what you will! If my numbers don't add up, it's either an "off-by-one" counting error, or perhaps a station came or went.
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 20-05-2013, 10:55   #413
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Please turn your AIS off when docked/moored/anchored

Quote:
All of this seems to contradict the assertion others have made that the system can handle thousands and millions of vessels at one time with no problems of any kind, and is no where near being clogged up. As Dave has said, it doesn't (fortunately!) affect Class A sets, and the system doesn't collapse.
I dont see anyone many ascertion of 'millions' of vessels, You must remember that teh system was designed around Class 'A' or more correctly the SOTDMA protocol. ( which goes back to the early days of the Internet and University of Hawaii!!). The reason CLass B took so long to get out as a standard, was to ensure that the class B 'CS' protocol was essentially expendable.

and you know what , were seeing that it is. AIS is working correctly and expunging CLass B transmissions from the system. I mean base stations can actually kill the whole of class B if they want to !!.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-05-2013, 11:08   #414
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,757
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by goboatingnow View Post
I dont see anyone many ascertion of 'millions' of vessels, You must remember that teh system was designed around Class 'A' or more correctly the SOTDMA protocol. ( which goes back to the early days of the Internet and University of Hawaii!!). The reason CLass B took so long to get out as a standard, was to ensure that the class B 'CS' protocol was essentially expendable.

and you know what , were seeing that it is. AIS is working correctly and expunging CLass B transmissions from the system. I mean base stations can actually kill the whole of class B if they want to !!.

Dave
You are not contradicting me.

If Class B is so expendable (and I believe you), then it makes sense to avoid pushing the system to dispensing with Class B sets, if it doesn't interfere with our own safety. Out of courtesy to Class B operators who are on the move and need to be seen. This is a different argument from the one that we should switch off to avoid confusing people by setting off unnecessary alarms.
__________________
Dockhead is offline   Reply With Quote
Old 20-05-2013, 11:11   #415
CF Adviser

Cruisers Forum Supporter

Join Date: Aug 2009
Boat: Custom Van De Stadt 47 Samoa
Posts: 3,755
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by goboatingnow View Post
I see primarily technical people arguing with Evans that the premise upon which he is basing his arguments is flawed and that the main issue is with his setup and use of it ( and generally CLass B).

As you have added in the part in red, then we are in fact agreeing and not disagreeing. For various reasons I am not going to be buying a class A anytime soon, while I might well buy a new class B (in part to get wifi to my ipad - and yes, I know there are other ways to do that).

Most people accept that you should power down the AIS when the boat is on the dock and you have gone home.

Terrific, we are agreeing even more.

What Nick and I are arguing is that is irrelevant to the debate as we get increasing higher densities of Class B ( and class A). it matters not what is on and what is off, Evans will see 'his' problem irrespective.

My focus has been on 'today', rather than on 'the future'.

But even given that, my personal experience with AIS traffic distribution seems to differ from yours. In each of the cases where I have had 'a challenge', I believe it would have gone away entirely if the docked/moored boats had their units switched off. That experience is completely consistent with the inarguable fact that the vast majority of pleasure vessels are docked or moored (and not 'navigating') at any given time, and I expect that will continue into the future.

But neither of us has provided any actual data on this point, so let's see if Paul is able give us some facts to assess this in a currently 'high traffic area', which could also be a 'leading indicator' to the more general future situation.
............
__________________
estarzinger is offline   Reply With Quote
Old 20-05-2013, 11:16   #416
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Out of courtesy to Class B operators who are on the move and need to be seen. This is a different argument from the one that we should switch off to avoid confusing people by setting off unnecessary alarms.
agreed, I dont have any issue nor do I think any have, in generally applying a provision that it is "good practice" to power down your AIS when you are finished with your boat.

However AIS was and is meant for "continuos broadcast" and teh IMO make no distinction in that regard for CLass B. Hence I fully respect any skipper that justifies leaving his on in any circumstances that he ( she) feels its justified. Since I cannot determine what justification is being used, I dont agree with Evans "commons" argument.

In that argument, ( the greater good), Evans used a 'moral ' argument. But (a) the IMO has already taken that decision, your expendable. and (b) who is to determine whether Evans justification versus all those other AIS's ( irrespective of zero knots or otherwise) is superior.

SO I agree with good practice, but I support those that justify it left on ( even though I dont know their justifications) and I conclude that Evans issue is a combination of his kit, his SOP and CLass B in general. We will be seeing alot more of this problem in the future.

DAve
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-05-2013, 11:26   #417
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Please turn your AIS off when docked/moored/anchored

Evans

Total AIS targets: 146. This consisted of:
5 Base Stations
114 Class-A
28 Class-B

Of the Class-B transponders,
3 were moving faster than 1 kt,
6 were between 1 and 0.1 kt,
19 were at 0 kt. It looks like we're leaving them on in the slip.

Of the Class-A transponders,
49 were at 0 kts. By far, most of these had a navstat of "Underway Using Engine"
20 were between 0.1 and 1.0 kt.
46 were going faster than 1 kt. Two of these had a "Moored" navstat, and these were traveling at 15 and 22 kts.


Close to 50% of all CLass A's were transmitting when they needn't,
Close to 67% of all CLass B's were transmitting when they needn't,

In the class B case we really have no clear idea of the mode, so its hard to say why they are transmitting.

Here we see several major AIS issues

(a) Incorrect navigational status of class A, a very very common issue.

(b) Both 'A' and 'B' transmitting when arguably they dont need to.


hence in the area mentioned your ascertain

"That experience is completely consistent with the inarguable fact that the vast majority of pleasure vessels are docked or moored (and not 'navigating') at any given time, and I expect that will continue into the future."

isnt quite correct , teh fact is that 50% of class A vessels take up way way more SOTDMA slots then 67% of CLass B.

The fundemental issue here Evans is that Class B simply hasnt enough bandwidth in the presence of many class 'A" vessels.

Hence my argument could be either (a) ALL vessels should power down their AIS in port , and I suspect port laws will be changed to reflect this in time. and (b) CLass B users will have to accept that AIS for them is an expendable resource that can 'disappear' just when they might want it.


but to summarise

(a) Too many alarms from stationary AIS, == improved filtering and changed SOP

(b) Delayed transmissions from your 'B' unit, suck it up or complainto the IMO about being second class citizens or get a class B 'SO' unit or 'A" unit!!.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-05-2013, 11:35   #418
Moderator
 
Paul Elliott's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 3,888
Images: 4
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by goboatingnow View Post
Total AIS targets: 146. This consisted of:
5 Base Stations
114 Class-A
28 Class-B
[...etc...]
Hey! That's what I said!
__________________
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
www.sailvalis.com
Paul Elliott is offline   Reply With Quote
Old 20-05-2013, 11:38   #419
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by Paul Elliott View Post
Hey! That's what I said!
Yes I know, its obviously a copy of your post ( on the ipad you cant easily selectively quote)

dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-05-2013, 11:38   #420
CF Adviser

Cruisers Forum Supporter

Join Date: Aug 2009
Boat: Custom Van De Stadt 47 Samoa
Posts: 3,755
Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by Paul Elliott View Post
Here's the data from a quick look at San Francisco area AIS traffic, collected today around 9:00AM PDT:

This data comes from receivers scattered throughout the Bay area. The coverage area picked up ships as far as 700 nautical miles distance, but by far the vast majority are inside the bay or in the nearby approach lanes.

Total AIS targets: 146. This consisted of:
5 Base Stations
114 Class-A
28 Class-B

Of the Class-B transponders,
3 were moving faster than 1 kt,
6 were between 1 and 0.1 kt,
19 were at 0 kt. It looks like we're leaving them on in the slip.

Of the Class-A transponders,
49 were at 0 kts. By far, most of these had a navstat of "Underway Using Engine"
20 were between 0.1 and 1.0 kt.
46 were going faster than 1 kt. Two of these had a "Moored" navstat, and these were traveling at 15 and 22 kts.
Thanks! Interesting. It would be interesting to see this at 1pm on a SF Saturday, and in the greater NYC area?

- The vast majority (70-90%) of class B's were 'docked' (I would say that up to .3kts might be docked). And even a large fraction (50%) of the class A's. That's what I would have expected.

- Class B units made up only 20% of the total (and would have made up even less than that of the message count). I am very surprised there were only 28 class B's on in all of SF bay. But perhaps for 9am on a Monday morning that makes sense. And perhaps the SF installers put on/off switches in their black box installations.

Unfortunately I would also not categorize this as 'high traffic'. I am pretty sure I would not have the message failure with this number of vessels that I had by NYC.

So, I would say it does not decide the debate definitively . . .

If we are looking to the future (or apply this data to other areas with already more class B's), and jedi and boater expect increased number of class B's, and we don't expect their fundamental behavior to change much (eg most will still spend most of their time at the dock), then I would suggest this data supports the position that turning off docked class B's would be useful. But that's a number of 'ifs'.

Paul, Thanks very much for doing that.
__________________

__________________
estarzinger is offline   Reply With Quote
Reply

Tags
ais

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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 19:04.


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.