Hi I am thinking about a depth alarm in the hydrofoil. The idea is to trigger a beep sound if it is to shallow below the foil wing.
This would be nice if you are riding water with shallow parts.
The biggest problem would be to find a sensor that does the depth measurement in real time and with speed.
I have bought a cheap fish finder that’s on its way but changes are big this is not going to work.
What I would like to know, what are your thoughts on a depth alarm is of any use? Do you know others that are working on this?
I like the idea. I ran into a rock once and broke off the mast. Not sure any sensor would have been able to warn me in time here though, it would need to be forward facing and looking ahead quite a bit.
I would recommend using ultrasound waves as the work underwater. The sensor would be mounted on the bottom of the mast and angled slightly towards the front. Here is the youtube video i found: https://www.youtube.com/watch?v=wb0sTy_26XM
I dont get it. U install perfect sensor, then what? 
Like Nanning said, you’d trigger a warning chime if it is a certain depth or less below/in front of the foil wing.
Yeah but, u dont know where shallow is only regarding the sound, u would need “mapped area” in front. Potential problem would also be a fish or seaweed or simmilar. I wouldnt actually know what to do if i hear shallow water beep.
Presumably if these micro sized echo / depth sensors’ fidelity improves over time, all it would tell you is you are travelling towards a shallow area or hard obstruction that has suddenly appeared some defined distance ahead of your foil, or you are in a shallow area already - both of which could be presumably set to your personal preference by some adjustable depth choice set in your app / firmware.
As far as knowing what to do if you hear a shallow water beep, up to you I guess 
Heed the warning chime or ignore it at your peril.
I believe sophisticated sensors can distinguish the continuous echo return of a seabed, versus a transient fish or piece of seaweed, but I could be wrong. I leave it to the experts who know a lot more than I do.
This same problem presented itself in the Vendee Globe last year when Hugo Boss struck an object (probably a submerged 40ft / 30,000lb shipping container) at 24 knots, tearing off its starboard foil. Same problem, but obviously the closing speeds and kinetic energy in an IMOCA racing yacht are much higher.
So, yes it’s not a new problem, and one assumes Hugo Boss and others are trying to solve it on a platform that has a lot more space to implement a solution, and a lot more money to throw at the problem. Since the consequences are a lot higher.
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Yeah it makes big sense. I just guessed we cant do much if we hear beep. We could zigzag around and hope we dont hit something. I have mostly deep and cristal clear sea here so i find it a bit odd to not see the shallows but thats not the case everywhere. Especially on some local muddy lakes. Its a big problem on unknown underwater terrain
I want to elaborate a little more on the purpose. I want to go foiling in not to deep water with tide and slowly emerging sandbanks. It would give me peace of mind if I knew the water depth and when I should be cautious. I think it would extent my possibilities. The alarm for a certain set depth is the simplest approach but ideal would be to also have a visible display with the current depth.
For measuring the water depth sonars, ultrasonic sensors are used.
There are two types of ultrasonic sensors, for air and for water, they use different wave lengths. The sensors for use in air are cheap and easy to find and even waterproof if you take a parking sensor, but of no use under water. I think the YouTube link from Rinzler is pointing to a sensor like this.
The only cheap sonar I found is the fish finder. The fish finder is able to detect the bottom and distinguish it from fish and weed.
I will try to connect the sensor to Arduino and hopefully get some sensible readings. My hopes are not to high because I can’t find someone else who has done the same. On the other hand, connecting an ultrasonic air sensor with Arduino is easy for 2 euro you can buy this sensor. Perhaps I could somehow combine this sensor with the fish finder sensor and make it talk to Arduino.
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