Category: NMEA 2000, 0183 & Signal K

Panbo reader Laurence Woodward built his own 40′ catamaran in Devon, England, and he’d like to use Garmin GMI 10 color N2K instrument displays at both helms.  However, his mast rotates and therefore he needs some sort of sensor to keep track of that rotation, which must then be applied to the apparent wind data coming from his masthead vane (or ultrasonic).  I doubt that Garmin will develop its own rotation sensor because there aren’t that many rotating masts out there, but then again maybe just a software tweak to their existing rudder angle adaptor might be all it takes.  Or perhaps there’s another way?  Let’s discuss…

I think you’re going to be amazed at how many NMEA 2000 sensors and displays Jeremy Anwyl has managed to install on his lovely sloop Tranquilidad, but probably not surprised that they haven’t all played together perfectly.  In fact, when I wrote the first entry on N2K bridges I joked that Jeremy’s soon-to-come guest entry on the subject might be sub-titled “One brave man’s experiment with a CANbus bridge, and the issues that drove him to it!”  The publishing delay is entirely the fault of your easily distracted editor, but the good news is that Tranquiladad did some cruising over the holidays and Jeremy has more testing results he can add to the comments that will no doubt follow his initial bridge experimentations…

So what the dickens is a NMEA 2000 bridge and why would you want one?  Well, I think the answers are complicated enough, and important enough, that they deserve two entries.  Mystic Valley Communications, the small company that produced the prototype above, describes its bridge as an “intelligent connection between two electrically isolated NMEA 2000 networks that copies transmitted data between the two networks.” Obviously, then, this is another way to deal with the backbone power issues discussed here in the past; with a bridge you can have two N2K networks that act as one in terms of data but are independent in terms of supplying power to devices, and in terms of a power failure.  But the Mystic Valley brochure (unfortunately not online yet) goes on to claim that the bridge can also be used to increase the number of devices and drop lengths beyond what’s allowed for a single backbone.  How is that possible?…

What this screen means:  Since Gizmo’s current NMEA 2000 network has more than one sensor able to supply the types of data listed above, the Garmin 5212 gives me a choice of which source to use, and in each case I’ve chosen data that originated from Raymarine SeaTalk sensors and instrument displays, but was converted to SeaTalkNG (aka NMEA 2000) by Ray’s much-discussed-on-Panbo ST-to-STng Converter.  Not only does the Garmin perceive all that converted SeaTalk data as valid NMEA 2000 PGNs, but it all looks decent when displayed, and I’ve done similarly successful testing on the Simrad NSE, Lowrance HDS, and Furuno NN3D MFD.  So, despite Ray’s caution against using the converter on a standard N2K backbone, a whole passel of ST40 instruments are feeding Gizmo’s network, and getting power off it.  And maybe that’s all you need to know, though I did get into some nitty gritty detail…