AIS engine feedback

[ChrisE]

I've put an AIS engine on Rival Spirit this year, it interfaces with our Navmaster plotting programme. I said at the time I'd report back, so here's the report.

1. Due to my utter foolishness it took an age to get the thing to display (try clicking the activate button, Chris). Once this hurdle had been overcome, I have to say that I'm impressed.
2. I get a display of all targets with their name, SOG, bearing, whether they are on a collision course and their MMSI number. It aso provides a bearing line so that you instantly work out how much of problem a particular craft will be, All displayed as overlays on the chart.
3. The signal seems to get lost quite frequently but not enough to cause a problem.
4. My conclusion is that it represents a good complement to radar. I especially like the MMSI and name of ship display which means that you can confidently identify and call up a potential troublesome craft.
5. Not much more to say other than it does what it says on the packet.

 

[shmoo]

I installed a NASA AIS transducer running into the thinkpad I use for navigation with SEACLEAR, earlier this year. I cannot praise it too highly. Here is a link to a screenshot of us www.shmoo.demon.co.uk\ais3.htm just east of the "OFF CASQUETS TSS" . We are the purple boat. The small circle in front of us is our projected 10min position, and the dotted lines from the targets are their 10min positions. Just to see the turn indicators pop up is very reassuring. It also does wonders for improving ones distance and speed perception.

We sail out of Orwell/Deben and one (of the several) thing(s) that AIS does that radar doesn't is to "see round corners" to alert us when something big is about to pop out of Felixstowe.

The best 120-odd GBP I can remember spending.

Regards
Peter Wilkinson

 

[ChrisE]

Yes, I forgot about it's ability to look around the corner. We found this v. useful in the fjords some of which twist and turn and contain a fair number of ferries and cruise ships all of which were picked up.

 

[2Tizwoz]

Looks very good - how many vessels are carrying it in your experience ? What size of vessel is not carrying it ?

 

[Amphitrite]

All vessels above 300 tons and all passenger vessels carry it. And also most tugs, pilots, coastguard and SAR vessels have it on board.
I find it particulary useful for collision avoidance - with CPA and tCPA on the screen you do not have to scratch your head for long. And if the danger of a collision exists, you know the name and MMSI of the other ship to call on VHF!

 

[Phoenix of Hamble]

Wonder how long it'll be before the plotters have AIS support... must be a pretty minor software job.....

 

[BlueSkyNick]

Young Mr Parahandy gave me a demo of his system using the same engine - certainly very impressive. However, there seems to be some concern that it uses a fair bit of PC processing power - to the extent that an oldish laptop cannot support chartware and AIS together.

ANybody had a problem with their laptop being too lightweight?

 

[Amphitrite]

If the AIS signal comes from a dedicated AIS receiver such as the NASA Engine (and not from a modified radio scanner and soundcard processing of the signals) the processor load is close to minimal. It should not present a problem to any laptop that can run plotting software....

 

[BlueSkyNick]

Sorry my earlier post was not very clear - I didn't mean the processor specifically, but more the peformance of the computer as a whole. So the RAM maybe an issue too, I don't really know myself.

 

[Phoenix of Hamble]

Its interesting that you say that Nick, as my understanding is the same as Amphitrites... thats the AIS engine does the processing and just passes position, track and identification information via NMEA... that would leave nothing for the laptop to do other than to overlay the information on the chart... it may be that it forces many times more refreshes of the graphics on the laptop, which could hit perfromance pretty hard....

 

[BlueSkyNick]

As I say, I don't really know. Parahandy made a point of saying he had PC problems but I would need him to be more specific and I think he is away at present.

 

[ChrisE]

Like young PH, I have noticed that sometimes the signal disappears which is due, I believe, to processing by the PC of NMEA sentences from the engine. The PC that I use has a 2gHz processor and 1gig of memory.

However, the overall result is a useful addition to navving, how else would you get the MMSI number and identity of an approaching vessel?

 

[BlueSkyNick]

[ QUOTE ]


However, the overall result is a useful addition to navving, how else would you get the MMSI number and identity of an approaching vessel?

[/ QUOTE ]

Not disputing this point Chris - was certainly impressed. Just wandered if PH's PC issue is unique to him (maybe even just an excuse to justify a new one /forums/images/graemlins/smile.gif ) or if others had an issue too.

 

[ChrisE]

Nick, you can never have too big a PC! I'm not convinced that the problem is at the PC end either.

At present I'm not sure whether the loss of signal is due to the AIS engine itself, the PC, or a dodgy GPS signal. The symptoms, which include a loss of fix to the Raymarine chartplotter and radar which are upstream of the AIS engine, indicate a dodgy GPS signal. I wish that I could solve it because it causes a periodic loud, rather annoying bleep, as the signal is first lost then regained.

 

[shmoo]

My elderly IBM thinkpad 600Mhz P3 with 300Mb RAM copes with SEACLEAR free nav software, with two seperate USB/Serial bridges (PC is superslim - so no serial port): one for GPS, and one for AIS; as well as SeaTTY software with audio from SSB into the soundcard for HF Fax from Northwood/DWD. Not to mention use as general laptop. All run at same time. Gives reasonable response. Does not act as if overloaded, or even close. SEACLEAR uses disk rather a lot, but that is a power use issue, not machine loading.

Peter

 

[shmoo]

Re: AIS engine feedback (signal loss)

My take on the occasional signal loss is like this:
a) 9600 baud over VHF is quite an achievment: its going to drop out from time to time.
b) the protocol uses a sort of negotiated contention for slots so each ship grabs a short time slot in which to transmitt. To prevent new ships that have just sailed into the area/switched on from being starved out each currently transmitting ship periodically gives up its slot and finds a new one. (Like musical chairs)
c) I think the underpinning assumption here (that may not yet be picked up by the software/display providers) is that an object with a mass many thousands of tons and moving quite slowly will not stray far the track predicted by simple physics in a few tens of seconds. So if its signal drops out the software could keep displaying, perhaps indicating lower confidence in position (by color change?)

All this with suitable health warning, IMHO and so on.
Regards
Peter

 

[tillergirl]

Where was the Pride of Bilbao going? Isn't she in the wrong lane or an I reading this wrong?

 

[shmoo]

I think Pride of Bilbao is heading for Portsmouth via eastern end of IOW.

She is clear of TSS, as this slightly earlier and smaller scale shot shows. http://www.shmoo.demon.co.uk/ais2.htm

 

[tillergirl]

Thanks, that makes it clear. Good screenshots.