One of the very first Class B AIS transponder prototypes -- the Shine Micro RadarPlus -- was a standalone design, and it seemed to make a lot of sense (though for some reason it never came to market).  It's a little surprising then that EMA's new BlueAIS is the first truly available standalone Class B, to my knowledge.  Everything is in that 8-inch square waterproof box, and its single cable -- which carries power, RS232 and 422 data feeds, and even "silent mode" switching to a little breakout box (with LED indicators) below -- can be had in lengths up to 300 feet.  The configuration purportedly performs very well and, because EMA already has a lot of experience with similar standalone marine communications designs, there are numerous mounting options now and interesting possibilities to come...

If you poke around the EMA BlueTraker site, you'll see that they've been building various vessel monitoring and tracking systems for some time, and they all use a similar standalone design.  Hence there are mounts for towers, masts, rails, and cabin tops.  I'd also guess that they have the waterproofing and cabling well figured out.  And the illustration below suggests how well a small AIS antenna can perform when the coax cable and splitter are eliminated (though the signal losses may be somewhat exaggerated?).
   EMA's Business Development Manager, Chris Eckersley, recently told me that BlueAIS will hopefully get FCC approval soon, and it should sell for about $900

here in the U.S. (and he is looking for distributors).  He also said that EMA is working on a low cost, completely self-contained vessel security system that has mesh broadcasting abilities, and that the BlueTraker
-- which uses an Iridium SBD modem -- is the only one approved
for use in high latitudes.  In fact, he noted that the miniaturization of those modems and of Class B AIS transponders (2nd gen SRT photos coming soon) mean that future models of the BlueAIS will have some novel capabilities.  Combine that tease with what's happening in the sat phone world and there's little doubt that things are going to get interesting.