Sailboat Monitor

NavCal has a preliminary design for an inexpensive, monohull sailboat monitor. It would monitor older sailboats with analog gauges as shown. American sensors have a resistance of 30 to 240 ohms and gauges typically have a resistance of about 100 ohms. As you can see in the drawing below, if we attach a wire to the sensor, we can sense the gauge reading.

Gauge monitor
Analogue gauge monitor

We can count RPMs and with a Hall Effect sensor in the negative house battery bank lead we can measure amp hours in and out to sense the house battery state of charge.

We are in the preliminary development strage and welcome all input to

This monitor is designed to work with U S 100 ohm gauges that are well chacterized and their curves can be fitted with fairly simple equations. European gauges, like VDO, are typically 180 ohms and their values are much more difficult to fit.


The current design will monitor:

  • Water temparature
  • Oil pressure
  • Engine battery voltage
  • House battery voltage
  • House battert current in and out (Amp Hours)
Typical diesel sailboat gauges wiring


  • Oil swith
  • Bilge pump switch
  • Running lights
  • Anchor light

It will have a GPS receiver for time and other data.