In this Tech Note we are going to cover a key issue that we will encounter for the foreseeable future, that is, analogue systems that have to be connected to NMEA2000 networks.

Typically the best way forward will be to have an all NMEA2000 boat, that will happen eventually in time but currently there are lots of boats that have different systems that are not directly connectable to NMEA2000 and hence are isolated.

That situation makes the customer reluctant to go for a NMEA2000 boat therefore locking ourselves into a catch 22 situation. The number one system in this category is engines and to a lesser extent levels (drink, grey, waste, etc).

Having recognised the need to convert engine data to NMEA2000 first we have to understand how a typical marine engine reads information and displays it. We will cover one by one:

Battery and Alternator voltage: This is measured with a standard moving coil voltmeter. Therefore it is straight forward to do a measurement with a “box” and convert it to NMEA2000.

RPM: This also is easy. Typically there is a W output on the alternator. That output is a sine wave coming from one of the alternator coils, its frequency correlates directly to the RPM of the engine. That correlation is different from engine to engine and is normally expressed in “pulses per revolution” and that number is constant across the range of revolutions. In the rare situation that the alternator does not have this output, we can manage to modify the alternator and add that W output, or as a last resort put a pick up sensor and measure directly from the flywheel the teeth speed.

Those two measurements are easily converted to NMEA2000 through the Albatross ALBA-ENGINE box and just need a few calibration points.

Just one thing more is needed. You need to “instance” your engine, depending on the display and the number of engines you will differentiate your engines through their unique instance ID.

Typically in a single engine situation, instance of the engine is cero. In a two engine boat port engine is zero and starboard engine is one. Further engines are incrementally numbered.

In our next tech note we will cover something a little more complicated but easily achievable with our ALBA-ENGINE. That is, reading all the other parameters of the engine: temperatures, pressures, etc.

This article has been provided by Albatross Monitoring System