Boat Fuel Management

Some years ago I bought an old boat with very basic instruments on the console. The fuel gauge was so unstable during cruising that I barely distinguished between full and half tank. Then suddently the gauge and fuel level sensor stopped working and it was impossible to replace.

Fuel management is one of the most important task on a motor boat.

Dispite several devices available on the market, I decided to build a small counter of fuel liters through an Arduino UNO, an aliexpress flow meter and a LCD display.

The upgrade from a simple counter to an econometer was very fast. The device became a fuel level gauge and econometer, able to measure liters/hour while setting throttle, pitch and trim to minimize the fuel consumption over the boat speed.

https://youtu.be/C1YyB6J1ifk?si=Lk5zJDjZH8jAOd7q

Since I was quite satisfied with the result, I decided to upgrade the system to include a touchscreen, a GPS, trim sensor, throttle position, and boat pitch...

https://youtube.com/shorts/D3eOutZOpVg?si=kltiyWjdtAzZNvPb

https://youtu.be/0HsfpaqQn2M?si=f-0DaIC1zfwzFmbv

After first trials I recognized that backlighting of 200/300 nit of my Nextion display was not the best during sunny days on an open boat, so I start playing with a bluetooth connection to the smartphone that tipically have 1000/1300nit display. Under Android the scenario changed completely with the possibility to calculate distances, waypoints on a map, record and recall data... It was funny to develop my first app.

https://youtube.com/shorts/z2h2maR6PME?si=WNOqkWI0LZ1tgqIq

ITEM Qty Description Link

1 1 Upper Housing https://www.printables.com/model/1887225-upper-and-lower-housing-for-fuel-flow-sensor

2 1 Lower Housing https://www.printables.com/model/1887225-upper-and-lower-housing-for-fuel-flow-sensor

9 1 Turbine https://www.printables.com/model/1887225-upper-and-lower-housing-for-fuel-flow-sensor

3 2 Brass fitting M8x1 x 8mm https://s.click.aliexpress.com/e/_c33wHbVV

4 1 Cable terminal ---

5 1 3A MINI DC-DC STEP DOWN CONVERTER VOLT REGULATOR 5V-23V TO 3.3V 6V 9V 12V

6 1 A3144 Hall Switch Effect Sensor

7 1 Microcontroller ESP32-S3

8 1 Small magnets Diam 2mm x 1mm h

10 2 O-ring OD:10.5mm, sez: 2mm

11 1 8x1,5mm Cylindrical Pin 304 Stainless Steel https://s.click.aliexpress.com/e/_c37zlBhz

The key element of the system is the flow sensor. There are several type of flow sensor on the market depending on the liquid and flow rate. To select the sensor, you need to know the engine's maximum consumption in liters per hour. Pressure drop should be between 0.05 and 0,1 bar.

The sensor here described is tested between 1.8 liter/h up to 30 liter/h with max pressure drop of 0,08 bar. 30 liter/h is enough for my small Evinrude eTEC 90HP. The range should be extended by replacing or removing the nozzle inside additionally I'm quite sure that this design is scalable.

After few calibration tests I've detected a very nice linear behaviour that makes the software conversion within pulse/min to liter/min very easy.

Of course the sensor can be used for other application, old cars, motorbikes ect.

The sensor shall have different outputs dipending on the system on board. During my first trials the output was a square signal but can be easily convertend in:

1. Bluetooth
2. Serial TTL, I2C, SPI
3. NMEA2000
4. Analogic signal 0 - 12V
5. Square signal (in this case MCU is not needed)

I have two fuel tanks on the boat for a total of 110 liter. They are connected by a pipe in the bottom. Only one of them is equipped with a standard 5 holes SAE flange for a mechanical sensor; unfortunately, the sensor cannot be removed without destroy the boat.

Seeking a non-invasive alternative, I opted for an ultrasonic sensor.

Initial attempts were unsuccessful, as fuel droplets would settle on the sensor and interfere with its operation. To resolve this, I installed the sensor inside a 5 cm tube, which protects it from fuel splashes. Everything works fine, except when the tank is nearly full or nearly empty. In these conditions, the rolling of the boat causes the sensor to enter its "blind zone" (less than 3 cm from the top of the tank), or it ends up measuring the full height of the tank because the fuel has shifted to the other side due to the boat's roll.

Due to the installation of my tank I can easily lift the tank and place 2 cells underneath. I've already tested a Film Pressure Sensor on another application that should suit for the scope. It's rated 100gr to 150kg ... few euro and delivery in a couple of week. Let's see

The first version of the display was printed in PLA; as a result, minor deformations caused by the sun compromised its watertight seal. I therefore need to reprint it, improving both the seal and the ease of assembly.