Depth Sensor/Sounder for Mini Boat

Hey everyone,

I hope I've got the right forum here, please feel free to let me know if not!

I'm currently working on a small boat project and need a way to detect when the water is getting shallow. It doesn't need to be too accurate I'd simply like to be able to tell when it's less than about a metre deep.

I've attempted to use one of these but it doesn't work underwater at all: 1pcs Waterproof Ultrasonic Module Distance Measuring Sensor for Arduino TE501 for sale online | eBay

From what I've read this is to be expected as the frequencies of air and water sounders are pretty different, even when catering for the speed difference of sound.

Another suggestion that I've come across is to use an NMEA compatible fish finder. Has anyone had any experience with integrating with these or able to suggest one that would work (preferably something fairly cheap)?

I was looking at these but not too sure if I'd be able to hook into it at all: Lucky FF717 100ft Fishfinder Portable Sonar Fish Finders Depth Echo Sounder for Fishing PK FF1108 FF718# A5|fishfinder portable|sonar fish finderportable sonar - AliExpress

I'm also open to any other suggestions that anyone may have.

Thanks for your help!

Ultrasound modules meant for use in air indeed don't work for water. It's to do with the impedance difference. Water is a very different medium than air (much higher density) so needs a different transducer.

It's an interesting problem - not many suitable transducers out there. This one came up on this forum a few years ago and may do the job. Fish finders are another option indeed.

Yes, the acoustic impedance of water is 3500 times higher than that of air, which means a transducer
for one is hopeless for the other!

It looks like the Chinese are starting to mass produce less expensive underwater ultrasonic transducers. There are several interesting offers on Alibaba, but you have to inquire about the details.

For example, this one is available for as little as $30 in unit quantities.

Or aliexpress, Marca sorte Inventor Dos Peixes Sonar Portátil Fish Finder Profundidade Sonar Sounder Alarme Carpa Pesca À Prova D' Água 100 M 328 Pés 1108|fish finder depth sonar|depth sonarfish finder portable - AliExpress
Of course whether its any good is another matter...

Thanks for the replies everyone, sorry about the delay in getting back to you. If anyone has had any luck hooking any of those up I’d be pretty keen on hearing about it?

If anyone has had any luck hooking any of those up

An Arduino can't be used directly with an ultrasonic transducer. You will need some electronics between them, and so far for underwater technology, all the available options are pretty expensive.