What is a data repeater, and why is it needed. Well, the smart-aleck answer might be; because there was space at the helm for one...
A data repeater is simply a device that displays certain data from the network. The Garmin GMI-10 is a very nice data repeater as it can seamlessly and simultaneously connect to both NMEA-0183 and NMEA-2000 networks. The Garmin display is also a multi-function display, and can display several different screens, some with gauges, and some with digital data. The display can be customized with up to 4 different parameters per screen as well.
So why is this needed if the chartplotter can display the data? Simply because the chartplotter display gets very busy, very fast. By off-loading data to the Garmin display, the chartplotter can be used to display a different data set. For example, depth data is available on the chartplotter, and is available two ways; either by a full-screen display (which limits other displayed data, such as radar), or a small digital readout, which can be hard to see. If we display the depth on the Garmin display, it can be displayed in much larger numbers, making this reading easier to see, and leave the chartplotter to display other data.
In a nutshell, it just provides a higher degree of flexibility to the Navigation system.
Well, we are at the point-of-no-return, and have cut out the dash for the display. Investment in a good drill, such as a Milwaukee "Hole Shooter" and high-quality holesaw is essential, and should be considered if you are prone to drilling holes - especially big holes - in your boat.
The Garmin GMI-10 has two cables. A combo cable for power and NMEA-0183, and one for NMEA-2000. Note however that the GMI-10 cannot translate between networks. For instance, if a packet arrives on the NMEA-0183 port, it cannot be translated into a NMEA-2000 packet and transmitted. The display is simply a display.
A student of NMEA-2000 may discern that power is available from the NMEA-2000 network itself, so why is power also required by the unit. Some display units simply use the power connection for the NMEA-2000 network to detect that there is an active network.
The GMI-10's NMEA-0183 DATA IN is connected to the output of the Brookhouse AIS-C multiplexer's "Talker" port as shown in the drawing shown below. Recall that up to 4 "Listeners" can be connected to one talker, the other listerner being the input of the VHF DSC Radio. The GMI-10s DATA OUT is left unconnected. This port would only be needed if the GMI-10 were to control a NMEA-1083 device such as Garmin's GPS 17 antenna/receiver.
To fully understand this concept, you may wish to review my technology paper on NMEA-0183 NMEA-0183 Concepts as well as the Brookhouse/AIS step of this project.
This handy little RayMarine R55006 splicing box was used to interconnect the two talker devices on the output side of the Brookhouse multiplexer.
Connection to the NMEA-2000 network backbone is done with a Tee, just like any other NMEA-2000 device.
The screen shown here is one of many available on the unit, and is one of the more attractive screens. The data being displayed is positioning data from the on-board KVH 1000 Fluxgate compass.
The GMI-10 has standard displays, such as Compass, boat speed, depth, and others, as well as allow the programming of up to 4 settings of your choice on any one screen.
One nice aspect of modern nav electronics is they can be kept up to date with firmware updates which often add functionality, and the GMI-10 is no exception. However, the GMI-10 can only be programmed with a Garmin brand Chartplotter. As I do not have one, my only choice is to sent the unit to Garmin for an update. This is one area of incompatibility that still exists in the NMEA-2000 environment.
Our navigation project has now grown to the configuration shown below.
RayMarine R55006 Junction Box