Trials and tribulations with AIS

[ParaHandy]

erm .... why do none of the Wightlink ferries out of Portsmouth transmit AIS signals? they're (well) over the 300 tonne minimum and carry passengers (mandatory for passenger vessels to transmit AIS according to MCA MSN 1780). what's more curious is that none of these vessels seem to have MMSI numbers so presumably don't have DSC radios so if CG cease to listen on CH 16 .....

I was rather hoping to "see" these b*ggers when foggy as they're less predictable than t'others particularly when they cross into the swashway ....

and AIS transmits at 162 +/-0.025 mhz and most standard vhf aerials are tuned to 156mhz so is is it essential to fit an AIS tuned aerial or is this just a ruse for the aerial manufacturers benefit? I ask this after trundling round and finding reception "patchy" .... (with NASA AIS engine)

 

[boatmike]

Not entirely sure Para but I think AIS is only compulsory for vessels on international voyages (Don't think the I.O.W. counts)

 

[Peppermint]

Re: Now this is a can of worms

500 tonnes if not engaged on international voyages.

A bit of info here http://www.imo.org/home.asp.

I still maintain that unless every moving thing has AIS transponders it's just a dog that doesn't bark.

 

[milltech]

Advice by AIS users welcome

I have offered software users a free link to my AIS Engine page to recomend their choice of software. I've got three from the US so far.

Whilst these software options may also be used in the UK, I'd quite like to hear which of the commonly used UK charting software progs include AIS compatibility, (that is AIS compatibility with the Nasa AIS engine). This is as an aid to prospective purchasers since the UK is still my target market for everything.

 

[milltech]

[ QUOTE ]

and AIS transmits at 162 +/-0.025 MHz and most standard vhf aerials are tuned to MHz so is is it essential to fit an AIS tuned aerial or is this just a ruse for the aerial manufacturers benefit? I ask this after trundling round and finding reception "patchy" .... (with NASA AIS engine)

[/ QUOTE ]

The VTronix specialist AIS-MAST antenna will retail at £49.95. I have not been able to convince myself it would be worth stocking in support of a relatively inexpensive AIS receiver, especially since I think Nasa say the antenna shouldn't be next door to the VHF antenna, and with a masthead option this is unlikely to be avoidable.

That's not to say it wouldn't make an improvement, I'm not qualified to comment. I did suggest to Nasa they might like to package a suitable antenna like they do for Navtex and Weatherman, but it didn't seem as if my suggestion was greeted with the grovelling approbation I felt it deserved!

 

[david_bagshaw]

Re: Advice by AIS users welcome

Charting compatibility & ais Sea clear seaclear free

& shiplotter a few dollars after free trial not particularly a nav prog though, more a display of ais info

 

[plombier]

I was told on my recent cross-Solent trips on the bridges of both the W/L car ferry & the FastCat that the company have, as yet, not decided to fork out the £3.5k cost per ship for the installation of the AIS system. /forums/images/graemlins/frown.gif

 

[ParaHandy]

MSN 1780 is here.

I've snipped two bits off:
In practice, this [EU Directive] results in the dates for fitting AIS to ships on domestic voyages being brought forward from the SOLAS date of 1 July 2008. It further results in the size of cargo ships on domestic voyages required to fit AIS being reduced from the SOLAS 500 gross tonnage to 300 gross tonnage. It also extends the carriage requirement to include High Speed Craft.
and
It should be noted that AIS is now an immediate carriage requirement for passenger ships [if engaged in domestic trade] of 300 gross tonnage or more of Class IIA, III, IV, VI, VIA and Classes A, B, C, and D. The MCA will contact the owners of such vessels to discuss implementation arrangements.

Typical MCA confusion imho .. it still doesn't explain the missing MMSI numbers though.

 

[ChrisE]

Re: Advice by AIS users welcome

Navmaster does, I've just upgraded mine to support the AIS engine.

 

[ParaHandy]

Re: Advice by AIS users welcome

software was SeaClear plus some raster charts got from elsewhere and it all works rather well for an initial test - except for IoW ferries but that's another story! it does pick up both pilot vessels (Haslar & Hampshire) who are also v. unpredictable in fog and extremely difficult to see on radar ...

 

[graham]

As the AIS transmitters can be switched off at any time by the ships officers it can never be fully relied on even for large ships.

 

[milltech]

Re: Just sent you a pm. n.m.

..

 

[Oldhand]

I use a standard masthead type VHF antenna and from home (4 miles inland with an antenna height about 17m above mean sea level) typically receive and decode ships at a range of 40nm. My record is 102.3nm on a great declining anticyclonic conditions day. This is obtained using a communications receiver scanning between the 2 frequencies and not a dedicated AIS receiver/engine.

I would conclude a standard Marine VHF antenna should be more than adequate for onboard use where I suspect one only needs an AIS range of about 12nm.

 

[Birdseye]

Apparently, whilst AIS is mandatory for SOLAS vessels above a certain size (and certainly including your ferries), it doent have to be turned on. And in certain areas it is often kept off for security against terrorism - like the Red Sea. Whether that is the case here, I do not know. Maybe it is off so that officials cant as easily monitor boats doing what they shouldnt! After all, how many lorry drivers would leave their tachos on if they didnt have to?

An aerial that is tuned to the wavelength of the signal you want to receive is good - but the tuning of the aerial is nothing like so important in receive situations as it is in transmit. But VHF is "line of sight" (for these purposes) so having an aerial on the pushpit wont be good.

 

[Oldhand]

<An aerial that is tuned to the wavelength of the signal you want to receive is good - but the tuning of the aerial is nothing like so important in receive situations as it is in transmit. But VHF is "line of sight" (for these purposes) so having an aerial on the pushpit wont be good. >

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From my trials you can't be too sloppy with the antenna you use if you want satisfactory AIS decoding. The 28 odd millisecond GMSK modulated data burst that is an AIS message transmission requires good and undistorted reception to be decoded correctly. The antenna height requirement depends wholly on the range you wish to receive AIS messages at. I wouldn't have thought that most pleasure boat installations need more than 12nm, i.e similar to the radar range one probably uses in open water.

 

[gniersma]

Are there are already VHF manufactors, which deliver there normal VHF set with AIS signal output via NMEA. Like they can delvier DSC messages.
So one tuner for AIS, one for DSC and one for the other voice channels

 

[ytd]

if you use the same aerial, won't the AIS receiver be fried as soon as you hit the transmit button on the VHF? lot's of unplugging or an antenna switch. The separate aerial doesn't look to bad.

 

[milltech]

The Nasa instructions say your AIS antenna should be a metre away from the VHF one.