AIS..how accurate is yours???

[AedanC]

It's rare for cruisers to have class A AIS but I do know of one that does.

[barnakiel]

Originally Posted by TheThunderbird

IS it really necessary to have a transreceiver?

What is REALLY necessary is decided by:

- the regulations of your country, and then:
- by your equipment preferences.

Regulations are fixed but preferences are subjective.

Navigare necesse est, vivere non necesse.

b.

[Bleemus]

Originally Posted by El Pinguino

Well, some people believe in sky fairies but if my position as transmitted by my AIS was jumping around like a one legged tap-dancer when tied up I would not simply be assuming that all was well at sea.... I'd be anchoring somewhere for a day or two and making quite sure it wasn't doing it when away from any external strucures likely to cause multipathing.

A random marina this morning (Aucklamd).... looked at the track of four yachts...this was the fourth one. The other three were steady as a rock despite being in the same environment.

Walk over and ask them why they keep their AIS antenna below decks.

Originally Posted by rgleason

http://www.cruisersforum.com/forums/....php?p=2242522

[Paul L]

Originally Posted by TheThunderbird

A bit out of topic, but.... :-)

Do any cruisers use CLASS A AIS !?
IS it really necessary to have a transreceiver? I think that its usefulness rests with the TX section 80% of cases, the 20% being on the RX side.

Do you agree?

There are a few usually larger cruising boats with class A units.

I disagree with your percentages. I am most interested in getting AIS info that I will deal with to avoid collisions. When I had only RX AIS I found it very useful and cost-effective addition to the boat. Now that RX/TX units are so much less I have a TX unit.

[jeffrobbins]

Originally Posted by Bleemus

Walk over and ask them why they keep their AIS antenna below decks.

Yeah, I agree that could be the problem. If their AIS shows them the DOP/PDOP or HDOP that would also be good to have a look at. However, it could be that the GPS within their AIS has poor static characteristics as was mentioned in an earlier post about SRT units so if the above isn't the case, then how about taking the boat out and capturing a track from the AIS unit's GPS and see if there are any crazy outlying positions? A simple practical test might at least reveal if anything looks wildly out of whack.

[barnakiel]

Originally Posted by Bleemus

Walk over and ask them why they keep their AIS antenna below decks.

gps antenna ...

b.

[El Pinguino]

Originally Posted by Bleemus

Walk over and ask them why they keep their AIS antenna below decks.

It would be a rather long walk even in my Jesus boots .... I was doing the monitoring via MarineTraffic.

Moving right along... a bit off topic...
This is what I was getting yesterday.... the rings are 6 miles so furthest targets all about 18 miles.All are Class A, no distant B s received although I had one class B over land at about 3 miles the previous day from the same location.
Boat pretty much surrounded by hilly ground, TX/RX AIS ant on the taffrail maybe 2 metres above the water, all targets being received over terra ( see 2nd photo)rather than directo over the sea, no special propagation likely, its not the NE monsoon in the Arabian Sea.

AIS is an AMEC unit.... GPS input is a simple AMEC puck stuck inside a cabin window which yields quite steady positions as observed on Marine Traffic... ie... far less than a boat length.

[Bleemus]

Originally Posted by barnakiel

gps antenna ...

b.

I was thinking of the only AIS unit I have used (Vesper) and it has its own antenna for its built in GPS.

[barnakiel]

Originally Posted by Bleemus

I was thinking of the only AIS unit I have used (Vesper) and it has its own antenna for its built in GPS.

Off course. I was just driving the screw for the sake of some less experienced readers in the thread.

I would guess Vesper is using a very recent chipset and these have little if any challenge working well 'indoors'. So wherever you place the antenna, this unit may work fine (off course, not on a boat with five decks, bridgedecks and flybridges over the ais unit and its gps antena).

Older, units (e.g. Simrad AI50) have older chipset that could have problem down below BUT their antenna is off course an external unit. Should one place this gps antenna down below, errr ..... I do not know.

My wild guess is very fee owners would install an external antenna inside, which would be a mistake, imho. But sure given the number of ais transponders now in use, there will be a couple of odd balls.

b.