Hi John,
My primary navigation system is now a built-in OpenCPN system.
I have Class-A AIS. Class-A is the commercial standard that transmits and receives "full strength" for big boats. If you want Class-A AIS, I think the one I installed is great and at a great price point. West Marine actually seems to have the best price around ($749):
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https://www.westmarine.com/buy/em-trak-marine-electronics--a100-ais-class-a-transceiver--12333944
A Class-B transponder is the version for recreational boats. It allows you to "see and be seen", but you can be seen from less of a distance because it transmits with less power. (but you can receive from the same distance). I had Class-B built into a back-up chart plotter on my last boat, and it also supplied my two primary chart plotters with the data. My two primary plotters were PC based, in many ways like OpenCPN, but were a product from Maptech. The plotter/AIS device I had was this one:
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https://www.ebay.com/i/282384162118?chn=ps
Back to my present setup, I actually have 3 AIS devices. Each of my two radios has class-C (receive-only) AIS. Each can display the data on a small screen, but I don't find that super helpful. Regardless, each supplies AIS data to the boat's network. OpenCPN does a really nice job displaying the contacts as well as clicking on them for details, guard zones, etc. You'll like it (I think).
Then, I have the Em-Trek A100 Class-A AIS transciever (as described above), which is independent. It also has a small screen, which I don't find particularly useful. But, again, it supplies AIS data to the network for the chart plotters.
My system is crazy redundant. It doesn't need to be. It is somewhat silly. A single one of the radios could have supplied AIS to both OpenCPN systems. The same is true of the A100 device. In fact, having all three complicated my set-up a little bit because I had to set up the NMEA bridge to ignore all but one of them just to avoid wasting network and buffer capacity, which could have caused things to be dropped if it got too congested.
I don't use VHF splitters. Insted, I just use separate antennas. The antennas are cheaper than the splitters, have no loss, and can be backups for my radios. For the little bit of time it takes to run an extra cable, I think it is well worth the better performance, additional redundancy, and money saved. Just my opinion.
So, regardless of my own setup, my real thinking is this:
-- Class-C AIS built into radios is a nice "pre packaged" solution that can supply your OpenCPN system with AIS and GPS data with very little effort and at a very modest cost, especially if you are upgrading VHF radios, anyway.
-- For most folks doing coastal cruising, Class-B AIS is actually my recommendation. It'll let you see everyone and let everyone near enough to care see you. And, it does this without annoying boats farther away cluttering their screens with AIS contacts they don't care about. There are just a ton of recreational boaters and terminals are really crowded with contacts as is. Class-A AIS probably won't help, but may annoy people. Some units, but not all, allow the output power to be reduced.
-- If you really are going farther out, class-A AIS is really great because you can stay trackable to friends and family and other boats for longer.
-- Please don't forget that antenna height is everything. A ton of power won't help with an antenna mounted low, because the horizon will eat it. So, like VHF radio, the upshot is that a really powerful transmitter isn't likely to reach as far as one might expect if the boat isn't very tall or the antenna isn't very high up. This line of site calculator (
https://www.everythingrf.com/rf-calculators/line-of-sight-calculator) is fun to illustrate the idea -- but remember the height of the other radio matters, too.
I hope this helps. Have fun!