Water Level Sensor on boat and fuel tanks

I was looking at project using Ultrasonic Sensor for water levels:

Weatherproof Ultrasonic Sensor with Separate Probe Australia (core-electronics.com.au)

My mate wants to keep a check on his boat’s fresh water, (possibly waste water) and diesel fuel tank levels.
Is this suitable for any/all.
Are there better ways?
Also aim to monitor a few other odds and ends around the boat too.
(If it has a fuel gauge can this be used or added?)
[PS safe options]

Cheers Ian

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Hi Ian,

There are a couple of ways of going about this I can think of.
One method would be to use an ultrasonic distance sensor like you have linked to measure the height from the top of the tank with a sensor inside the tank. You can use that distance measurement to extrapolate the volume of fuel left in the tank.

Another method is to measure whether the level is above or below a threshold using a level sensor like this Non-contact Liquid Level Switch. The advantage here is that as long as the tank doesn’t have metallic walls you can measure inside without cutting a hole in it, or having your sensor inside and in contact with the contents.
You wouldn’t be able to know how much volume you have directly, but it would be enough to design a low-fuel alarm or something of that nature.

I’m not sure myself which tanks you would want to measure non-contact, but I imagine things like waste water may corrode your sensor quickly.


Unfortunately I am certain they are all metal tanks and I couldn’t imagine fuel being stored in anything other than metal as it is an ocean going vessel and has a fixed fuel tank.
But I will look into it cheers

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Hi Ian,

For measuring a tank quantity on a boat

You will probably need a stilling tube about whatever device you use in the tank to moderate the content motion from the vessel. This wont completely fix the motion problems but will dampen it a lot.
Mechanical float switches are an established norm for fuel tanks (think cars) and the same can easily be applied to other liquids. There are a number of ways of doing this and there are a number of commercial products to enable this. The momentum of the device you choose may also assist with the motion problem.
If you are programming this yourself you will have to account for the many fluctuations resulting from the tank motion to dampen the extremes. Proprietary systems (think again car fuel tank gauges) have their own ways to smooth this.

If you wish non contact the options are pressure (tank probably too shallow for this to have any useful range), External capacitance (wont work with steel tank -not that great anyway). Ultrasonic or more recently Lidar are other options that will work.
When choosing whatever sensor make sure it is not a cheap “hobby” device. As an example, the well-loved and much programmed HC-SR04s and their various clones are unreliable and very inaccurate in the real world (useless). Choose something like a Maxbotix or similar if going ultrasonic and calibrate it once in position.

Even with the more professional devices I have found period sampling of say 29 samples (odd number) and taking the Mode (not average) of that as the reading also removes the outlier noise for a more reliable indication.
My experience anyway.


Welcome to the forum Richard.
You make an excellent point regarding correcting for the motion of the tank. It would be good to know if a baffle system already exists in some of the tanks and knowing a bit more about the boat itself. I imagine a houseboat and a ski-boat will have a different magnitude of motion to contend with.


I haven’t been back on board yet but is a 50 ft iron cement hull ketch mid pilot clipper. Has been round the globe more than once. His dad built it. I have yet to talk to him about what he still needs.
Looking at setting up a GI for his big iPad to see all info metrics on the boat.
Setting up cameras etc.
I will get back to the forums after I’ve nuted out what he wants and what he has to craft a go between.


Hey Ian,

No worries at all! We’ll jump back on this one again once we have a bit more intel.