The Mysteries of NMEA 0183

We ordered a new battery charger and GPS chartplotter when we were at the Southampton Boatshow. What we had onboard worked but the old GPS chartplotter wasn't modern enough to show AIS data. We'd tried using a notebook to display this whilst we were away in France but notebooks are not really designed to be used at sea and need to be secured. We found it frustrating to set it up and wanted something more robust that would monitor for potential conflicting traffic all of the time.

The new battery charger is only a little bit more powerful than the last one but it has three big advantages.

Firstly, it knows the right voltages and charge rates to deal with our modern AGM batteries. Having fitted new AGM batteries we don't want to risk any damage to them from by being charged at the wrong voltages.

Secondly, the charger can be fitted with a battery temperature sensor (still to be delivered) so that it adjusts the charging voltages to compensate for hot climates. Ideal given that we plan to sail in hotter climates.

Thirdly, the new charger works with US and European mains voltages and frequencies so Blue Velvet is now equipped for worldwide travel.

Fitting the new charger went very smoothly. It is effectively a very updated version of the old charger and, happily, all of the existing wiring reached. To install it we just needed to drill a couple of fixing holes and solder on and connect some different terminals. Integrating the new GPS plotter was more complex.

With its two configurable NMEA 0183 comms channels I had hoped to save myself the hassle and expense of having to fit a new NMEA2000 data network to link the plotter and the AIS. So, before cutting any panels, we connected up the wiring and ran a series of tests. The problem is that the NMEA 0183 network only likes to have one thing 'talking' on each comms channel whilst everything else listens. With a GPS aerial, an AIS, a plotter and a network of wind, speed and depth sensors all wanting to 'talk' there is plenty of scope for interference.

The other minor problem for us is that we want to use our existing GPS aerial mounted on the pushpit. The new plotter does have its own internal GPS aerial but that does not get such a good signal as the one mounted outside (probably because we have lined the deckhead with heat reflective metal insulation sheets). After several hours of trying out all of the options we concluded that the only way to get a really stable GPS signal around the network, without any interference, was to dedicate one of the plotter comms channels to the outside GPS aerial. That meant no free NMEA 0183 comms channel to configure for the higher data-rate AIS. Blue Velvet will therefore need to have an NMEA 2000 network added so that the AIS can talk to the GPS plotter. At least that will configure her for the future as any new equipment is likely to be able to plug into the more capable NMEA 2000 network.