Class B AIS

[a64pilot]

Does an AIS have to be pre-programmed with vessel name, discrete number etc?
I'm about to order it, but think I have to have my vessels MMSI number and what other data?

[CAELESTIS]

The Vesper 850 only uses 3w as a stand alone unit. I would routinely see over 40nm (antenna height is about 70ft) offshore. If that is further than you want to see, then change the range setting. It also works great as an anchor alarm while using very little power.

[transmitterdan]

Originally Posted by a64pilot

Does an AIS have to be pre-programmed with vessel name, discrete number etc?
I'm about to order it, but think I have to have my vessels MMSI number and what other data?

In the US you have to give all details to the seller so they can program MMSI and other details. Other countries have different rules.

[a64pilot]

What I thought, details are MMSI and vessel name? anything else?

[Paul L]

Originally Posted by colemj

I don't understand that logic. Are you suggesting that Class B is designed for surface-level mounting only and that putting it any higher is outside its design specs (and a societally bad thing to do)? Why not put it below decks where it would have even shorter range and one could feel even better about oneself in not being a "congester"? Or get a receive-only unit?

I think the design spec for Class B took range into account using power and transmission interval - not antenna height. I don't think anyone views having a class-B antenna 50-60' above water is a bad thing - technically or socially.

40nm is an extreme range for sure, but how about 20nm? 10nm? More important is the transmission range - the people I have talked with that removed their stern mount for a masthead mount were claiming 3-4nm max transmission that improved to 8-10nm. That is significant to me.

However, like you, I don't have any problem with the antenna mounted anywhere. I was just pointing out some of the trade-offs (and implying which way we went in deciding).

Mark

Of course I didn't say Class B was designed for surface mount antennas. I said that it was designed for low-power and low congestion. If you want your signal to be seen at 20 miles, then Class A AIS is specifically designed for this.

While 40nm is an extreme example, I see 20 mile away Class A's with my lower antenna. So that is the comparison.

I just don't understand the hype about having to have your Class B xmit go as far as possible, as if you will surely die if it doesn't. Putting on a Class B AIS xmiter that broadcasts 3-5miles is way better than what you had before you had AIS. That covers the 95%. Now if you want to get anal and work on the next 5% to 2% mprpovement-- have at it. If you want to finish the job, get a Class A xmitter.

If all the Class B vessels had 20 mile xmits, the screens of a lot of ships displays would be unnecessarily crowded - maybe even to the point of loosing some of the safety that you gained by putting on an AIS xmiter in the first place.

[MarkJ]

Originally Posted by a64pilot

What I thought, details are MMSI and vessel name? anything else?

Just your shoe size, neck measuremnt... Hang on! With the MMSI they have everything else! All the other information can be put in by the user and changed

[continuouswave]

Originally Posted by Dockhead

AIS is digital with robust error correction.

AIS transmissions are one-way broadcast transmissions. Please explain how there is error correction.

[monte]

I programmed the Raymarine unit myself with MMSI, vessel name, length, width, gps offset. It depends where you buy it if the regulations state they have to be pre programmed or not. Don't mess up the MMSI though because I think you just get one chance then it's back to Raymarine to reset it. The rest of the info can be changed with a mini USB cable and pro2ais software which you will want anyway.

[El Pinguino]

Knowing at what distance you can 'see' transmissions is the easy bit. I know that with my taffrail mounted dedicated ant and a Class B unit I can receive class A transmissions ( on a regular basis ) at about 12/15 miles..... normally seen on AIS before they are sighted visually. I have the occasional one at 50 or 60 miles and also receive transmissions from behind quite high ground. There should be no difference in reception performance between Class A and B receivers, it would all be down to height of the antenna.

Knowing how far your class B transmission is going is a bit trickier.

Here is a thought... go to marinetraffic.com and select a receiving station such as this one
Details for AIS station Strait of Juan de Fuca - AIS Marine Traffic
then sniff out class B transmissions and see what ranges the shore station is receiving them. As most of these shore stations will have some altitude the distance will reflect the effectiveness of the transmit power... not the yacht's antenna height.

[El Pinguino]

Or even easier... go to Marinetraffic.com and have a look at the Auckland area. The shore stations are at Torbay ( near Gulf Harbour),St Heliers (close east of the city) and Maraetai so any Class B you can 'see' is being received by one of those three.

[maine50]

Milltec Marine is currently selling the vesper 850 (transmitter & receive on independent display w/ anchor alarm, can feed plotter also) for $763. This is a short time discount due to boat show">Annapolis Boat Show Special.

[Cuttyhunk]

Just as several others have said, get the XB-8000 and the Vesper splitter. A truly great addition to our boat. We have old Raytheon equipment, plus a very small 5" Lowrance chartplotter for now. I'm not ready to upgrade that stuff yet. So for now, I use the Watchmate app and whatever i-device I feel like using -- the xb-8000 can have up to 5 devices connected. I usually have my phone and ipad on it, and my spouse also connects to it to make sure I'm not doing anything dangerous ;-). AIS is truly a wonderful thing. Ships "see" me.

[El Pinguino]

Here are the results of my little bit of research...
The northern most boat, Laissez-faire, is about 14 miles from St Heliers - the monitoring station for the three Class B boats to the north and east ....
The most westerly one, Equilibrium , is being monitored by Torbay.
St Heliers is at the bottom of the shot.... Rangitoto island is between the yachts and the shore station.

Sort of scotches the idea that Class B can only be received out to 5 miles.

[Dockhead]

Originally Posted by continuouswave

AIS transmissions are one-way broadcast transmissions. Please explain how there is error correction.

You are right, and I stand corrected. There is no error correction in our AIS systems. Thanks for clearing this up.

I'm not sure where I got that idea, except that it is often discussed in connection with space-borne AIS systems.

It is not strictly true, however, that AIS transmissions are "one-way broadcast transmission" only. Various aspects of the system involve two-way communication. AIS stations can interrogate one another, and base stations can order mobile stations to change frequencies or timing.

[colemj]

Originally Posted by Dockhead

You are right, and I stand corrected. There is no error correction in our AIS systems.

But you did have a valid point about the digital aspect of AIS - no doubt there is signal processing and filtering going on in the receiving end that increases the S/N more so than is done on the voice end.

Mark