AIS Class B: Newbie

[keithwins]

I'm new to all this, but helping some friends think about an around-the-world 1-2 year trip in a couple years. They just bought their boat.

They believe they should get AIS, which I surmise (39' sloop) would be a class B. Here's what I THINK I understand: class B is still not part of the formal USCG AIS standard, so maybe things could change, but in any case there's no reason to get SAIS (satellite link) or Class A if all they're trying to do is not get run over, and in general they might want to hold off until the last minute since equipment is still changing rapidly right now (and maybe a bit high-priced): a couple years from now might offer better equipment/better deals.

Differences of opinion? Other thoughts? Thanks! I could be totally off, school me!

[Paul Elliott]

Class-B transponders have been FCC-approved for several years now, and the prices have already dropped significantly from their initial release. The AIS standard definitely includes Class-B. Class-A has some advantages (higher power and typically faster update rates), but Class-A also cost more and burn more power than Class-B units.

There are some very nice Class-B units out there (look at Vesper and others). Garmin, Raymarine, and others also make good Class-B transponders that integrate well with their chartplotters.

I think for a "normal" sail or powerboat a Class-B transponder is a great choice. The prices are competitive and reasonable. All considered, I don't personally think that Class-A provides enough of an advantage over Class-B to warrant the extra cost, power, or integration difficulties.

[keithwins]

Thanks Paul, very helpful. I'm just learning about nema2000, which I guess is the current ship electronics bus standard. It's there anything else on the horizon, or is that it? Maybe that should be a new thread

[MarkJ]

Keith,

I think AIS is the most significant advancement in marine safety since GPS and chart plotters. For anyone doing a cricumnavigation is is an absolute as far as I am concerned.

[VirtualVagabond]

Originally Posted by keithwins

I'm new to all this, but helping some friends think about an around-the-world 1-2 year trip in a couple years. They just bought their boat.

They believe they should get AIS, which I surmise (39' sloop) would be a class B. Here's what I THINK I understand: class B is still not part of the formal USCG AIS standard, so maybe things could change, but in any case there's no reason to get SAIS (satellite link) or Class A if all they're trying to do is not get run over, and in general they might want to hold off until the last minute since equipment is still changing rapidly right now (and maybe a bit high-priced): a couple years from now might offer better equipment/better deals.

Differences of opinion? Other thoughts? Thanks! I could be totally off, school me!

Welcome to CF.

A lot depends on what kind of sailing they're going to be doing between now and when they set off. Poodling around in an area with no commercial vessels makes AIS pretty pointless.

Once they get to serious passagemaking it's shortsighted to consider getting a receive only setup when for just a couple of hundred bucks more you can be transmitting too and enjoying a huge extra layer of safety.

I haven't come across any leisure craft with class A, only commercial vessels. Class B is what you see coming up on the screen even for $20 million superyachts with fulltime crews.
We've used our little $500 em-trak plugged into a laptop from Chesapeake to Bermuda, to St Martin, to Panama.

Would not dream of being without it now.

Vic

[goboatingnow]

Just be clear , if you mention class A or B , you are talking about AIS transceivers not receivers. There is no such thing as a A or B receiver.


And OP , in electronics never wait for what might co,e around the corner , buy what you need now, the " corner " in electronics always recedes
Dave

[VirtualVagabond]

Originally Posted by MarkJ

Keith,

I think AIS is the most significant advancement in marine safety since GPS and chart plotters. For anyone doing a cricumnavigation is is an absolute as far as I am concerned.

+1

Mark has some great screen shots that convinced us to buy.

[barnakiel]

I think buy gadgets just prior (say 1 year) to departing. Things change, gadgets develop, prices drop. Cash can earn interest.

b.

[fairbank56]

Originally Posted by VirtualVagabond

I haven't come across any leisure craft with class A, only commercial vessels. Class B is what you see coming up on the screen even for $20 million superyachts with fulltime crews.

I see pleasure craft with class A frequently around the Annapolis (Chesapeake Bay) area. Seeing two of them right now, one is just a 22 footer, the other 108'.

Eric

[VirtualVagabond]

Originally Posted by fairbank56

I see pleasure craft with class A frequently around the Annapolis (Chesapeake Bay) area. Seeing two of them right now, one is just a 22 footer, the other 108'.

Eric

That's interesting. I wonder why a 22ft pleasure craft would feel the need to go to class A?

[Bash]

Originally Posted by keithwins

they might want to hold off until the last minute since equipment is still changing rapidly right now (and maybe a bit high-priced): a couple years from now might offer better equipment/better deals.

Smart cruisers don't hold off on navigational equipment until the last minute. Navigational gear is worthless until you know how how to use it.

If you wait until the first time you're fogged in to turn on your radar, you're screwed. And if you wait until the first leg of your circumnavigation to install your AIS....

[Paul Elliott]

Originally Posted by Bash

Smart cruisers don't hold off on navigational equipment until the last minute. Navigational gear is worthless until you know how how to use it.

If you wait until the first time you're fogged in to turn on your radar, you're screwed. And if you wait until the first leg of your circumnavigation to install your AIS....

This is wise advice. You need to learn how to effectively use your nav tools, and AIS is no exception.

I too have seen some pleasure craft in the U.S.A. with Class-A, and while some of these are perhaps installed because of the advantages of Class-A (minor, in my opinion), many of these Class-A installations are there because FCC approval of Class-B was delayed for so long.

An AIS receive-only unit is extremely useful, but if I had the option I would install a transponder. A modern receive-only unit will pick up signals from both Class-A and Class-B transponders. Unless you get something like the integrated Vesper units, you still need to connect your receiver or transponder to a chartplotter, or computer.

NMEA-2000 is indeed the latest marine interface standard, but there are still probably more AIS transponders using the older, and perfectly functional, NMEA-0183. Get whichever interface works best with the rest of your nav equipment. NMEA-2000 is the future, but NMEA-0183 isn't going away anytime soon. I think eventually Ethernet, or something like it, will be the next interface, but waiting for the next generation is usually a big mistake. There's *always* a next generation on the horizon!

[goboatingnow]

A modern receive-only unit will pick up signals from both Class-A and Class-B transponders

this is getting the status of an Internet myth, ALL AIS units picked up both A and B transmissions, there were issues with the static data part of class B on early merchant ship class A units.

In the leisure market , every thing sold for a long long time can receive all transmissions.

NMEA-2000 is indeed the latest marine interface standard, but there are still probably more AIS transponders using the older, and perfectly functional, NMEA-0183. Get whichever interface works best with the rest of your nav equipment. NMEA-2000 is the future, but NMEA-0183 isn't going away anytime soon. I think eventually Ethernet, or something like it, will be the next interface, but waiting for the next generation is usually a big mistake. There's *always* a next generation on the horizon!

Wifi or ethernet will never take over from N2K, more likely some of the WPAN systems might in future. Too much pain has been gone through to back out of N2K now.

Anyway for interoperability its data protocols that are important , rather then transmission media, and the N2K PGN methodology will predominate in that regard.

If at all possible implement the solution using N2K, 0183 was never desigend for this type of data or datarates and its a kluge with AIS, that only got life because of teh delay by NMEA in sorting out N2K PGNS.

Dave

[Paul Elliott]

Originally Posted by goboatingnow

this is getting the status of an Internet myth, ALL AIS units picked up both A and B transmissions, there were issues with the static data part of class B on early merchant ship class A units.

In the leisure market , every thing sold for a long long time can receive all transmissions.

Show me where what I said was incorrect. By the way, there are people out there still using the old Nasa black-box receivers that don't even decode Class-B dynamic data. Most of these have been replaced though. As you say, all Class-A transponders ever installed on ships decoded at least the dynamic Class-B messages, it was the static data (vessel name, etc) that wasn't decoded due to changes in the message specifications.

Wifi or ethernet will never take over from N2K, more likely some of the WPAN systems might in future. Too much pain has been gone through to back out of N2K now.

NMEA is currently developing protocols for ethernet transport of N2K. I think we're both right.

Anyway for interoperability its data protocols that are important , rather then transmission media, and the N2K PGN methodology will predominate in that regard.

If at all possible implement the solution using N2K, 0183 was never desigend for this type of data or datarates and its a kluge with AIS, that only got life because of teh delay by NMEA in sorting out N2K PGNS.

The NMEA-0183 high-speed spec is just fine for AIS. The maximum data rate of the AIS channel is under half of the 38.4kbit/s capacity of high-speed 0183. I agree that in a new installation N2K is probably the way to go, but if for some reason you want to install a transponder and use NMEA-0183, it should work just as well. If your navsystem includes a "legacy" chartplotter that uses 0183, then that's what you have to use for the AIS connection.

[japarker11]

NB,

The Class A vs B is all about the relative speed of the two vessels, if you are the smaller boat. Vessels moving at less than 10 knots need only the 2.5 Watt broadcast signal to jolt the Class A equipped vessel doing +20 knots to initiate bridge to bridge com and enact course modifications in plenty of time. Our ComNav Class B with rail mount antenna can reliably pick up Class A's in the 12 to 18 nm range. And, our little 2.5 Watt signal easily gets out 8 nm to receiving antennas 30 to 40 feet off the water.

I can see situations involving two +20 knot vessels that would need the extra room allowed by two 25W Class A transponders.

No need to wait on this stuff, it is here, now:

• It is much more intuitive than radar
• Takes less power
• Bridge to Bridge com is quicker, more concise, no more stumbling on hailing channel especially if the big guy is monitoring VTS channels.
• And, talking to several of the freighters' bridges, most are leaving the transponders energized while offshore.

As for NMEA 2k vs 0183, simpler the better. We initially were running on the 2k buss, but I was constantly overriding the collision alarm - we were colliding with ourselves. Runs fine on the 0183.


Funny how things evolve? DSC and NMSI showed up in the mid 90's. No one knew what to do with the stuff. Then 9-11 happens and we figure out how to shoe horn AIS into this standard and out pops something better than radar!


John
S/V Odyssey - Nordic 44

Originally Posted by keithwins

I'm new to all this, but helping some friends think about an around-the-world 1-2 year trip in a couple years. They just bought their boat.

They believe they should get AIS, which I surmise (39' sloop) would be a class B. Here's what I THINK I understand: class B is still not part of the formal USCG AIS standard, so maybe things could change, but in any case there's no reason to get SAIS (satellite link) or Class A if all they're trying to do is not get run over, and in general they might want to hold off until the last minute since equipment is still changing rapidly right now (and maybe a bit high-priced): a couple years from now might offer better equipment/better deals.

Differences of opinion? Other thoughts? Thanks! I could be totally off, school me!