Raymarine’s first Class B AIS unit, the AIS500, is nearly ready to ship. Ben Ellison discusses some of its features over at Panbo; as usual, his report is well worth a look.

But I’ve got something to say about it, too.

Specifically, I want to address my own “pet peeve”: How to get all the data traffic where it needs to go with a C-series multifunction display possessing only one NMEA 0183 port!

This is tricky if you want two-way data traffic with your DSC-capable VHF radio, because those units require 4800-baud (low-speed) NMEA, while AIS (any AIS, including receive-only units, from any manufacturer) requires a 38,400-baud NMEA connection. But you’ve only got one port on the back of your chartplotter, so you’re stuck!

So it would appear.

I’ve got two words for you: Multi. Plexer. Oh wait, that’s one word. Multiplexer. Sorry.

A multiplexer will solve the problem, but I don’t want another box in the limited space aboard my little boat, and I don’t want to spend $300 if I can avoid it. So I’ve made it my goal to make it all work without incorporating a multiplexer.

I’ve written a lot about this over the past couple years. Click here to find some of those posts.

Anyhoo, the manual for the AIS500 makes it explicit that there is some minimal multiplexing built-in:

A multiplexer built into the transceiver manages both 4800 and 38400 baud rates. This feature effectively frees up an NMEA port on your multi-function display (MFD). if only one NMEA0183 port exists on your equipment, the multiplexer eliminates the need for a
separate multiplexer.

Typically the NMEA0183 connections are used as follows:

• The 4800 baud wires connect to the appropriate points on the VHF radio or other NMEA0183 4800 baud input/output device.
• The 38400 baud wires connect to appropriate Raymarine MFDs. The NMEA0183 port on each MFD connected in this manner must be set to 38400 baud.

Nice! This is really a great feature, even though it’s quite limited. It’s going to make life a lot easier for those of us who continue to rely on perfectly reliable but not-quite-state-of-the-art, not-quite-top-of-the-line navigation electronics.

Combined with the built-in antenna splitter, it nearly justifies the Raymarine AIS500’s $1400 price tag, which is $600 more than the Shine Micro AIS-BX unit I’ve been using for the past six months. If the Raymarine unit were discounted to, say, $1100, it would be very competitive, given the features it includes.