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Old 04-10-2014, 19:50   #1
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Anchor chain counter app

Hi everyone,

I am currently working on an anchor chain counter app for smart phones. It works by analyzing the sound patten produced by the anchor chain.
But to make it work reliable I need quite a few samples from different boats to optimize the algorithm.
I was wondering if some of the sailors is this forum could record the sound of there anchor chain while anchoring and send it to me via email? During the recording the microphone should roughly point in the direction of the bow roller .
I would also need the approximated length of chain deployed as well as type of boat and chain used.
It would be great if you guys could help me out.

Cheers,
Bernd
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Old 04-10-2014, 20:06   #2
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Re: Anchor chain counter app

This is not likely to work with much accuracy. Consider dropping the anchor and the chain is falling very fast, at various depths. The boat speed also matters.
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Old 04-10-2014, 20:24   #3
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Re: Anchor chain counter app

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Originally Posted by boat_alexandra View Post
This is not likely to work with much accuracy. Consider dropping the anchor and the chain is falling very fast, at various depths. The boat speed also matters.
I think it's possible. The "rattle" of the chain going down is actually a clang sound for every second link of chain as it bangs on the roller. I think you could get a decent idea. Not so good for rope rode, though!
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Old 04-10-2014, 20:30   #4
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Re: Anchor chain counter app

This is really an early April Fools joke, isn't it? Please tell me it is....
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Old 04-10-2014, 20:34   #5
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Re: Anchor chain counter app

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This is not likely to work with much accuracy. Consider dropping the anchor and the chain is falling very fast, at various depths. The boat speed also matters.
I currently calculate the chain dropping speed every second this should account for variations in dropping speed. Therefor, this is not a major issue. But to account for things like wind noise people talking and the different characteristics of boat types and hull materials is a problem. My tests so far had an accuracy of roughly 10%.
I also experimented with different methods like spectral decomposition or graphical analysis of the signal. The Spectral decomposition seemed promising but I am not happy with the reliability. Therefor, I am considering to use artefical neural networks but in order to do this I need a large set of training data which is the reason I need more recordings form a diversity of boats.

Cheers,
Bernd
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Old 04-10-2014, 20:37   #6
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Re: Anchor chain counter app

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This is really an early April Fools joke, isn't it? Please tell me it is....
No it is not an early April fools joke..
I am working on this for quite a while but it is much more complex then it sounds.
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Old 04-10-2014, 20:39   #7
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Re: Anchor chain counter app

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I think it's possible. The "rattle" of the chain going down is actually a clang sound for every second link of chain as it bangs on the roller. I think you could get a decent idea. Not so good for rope rode, though!
Spot on!!
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Old 04-10-2014, 20:52   #8
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Re: Anchor chain counter app

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Originally Posted by Bernd_ View Post
I currently calculate the chain dropping speed every second this should account for variations in dropping speed. Therefor, this is not a major issue. But to account for things like wind noise people talking and the different characteristics of boat types and hull materials is a problem. My tests so far had an accuracy of roughly 10%.
I also experimented with different methods like spectral decomposition or graphical analysis of the signal. The Spectral decomposition seemed promising but I am not happy with the reliability. Therefor, I am considering to use artefical neural networks but in order to do this I need a large set of training data which is the reason I need more recordings form a diversity of boats.

Cheers,
Bernd
Interesting. The frequency will change with speed, so you need to be clever about spectral analysis. I would think that you could do an FFT and then look for the peak (since wind, voices, etc will be a broad spectrum but the chain rattle is more consistent). The peak frequency would give the speed the chain is going out.

You know roughly what frequencies to look at from a practical standpoint, so you can limit the bandwidth to speed up calculation.

10% accuracy is actually pretty good. Anchoring isn't so precise! You should think about the user interface. The user should, of course, input the chain size up front, but also the height of the bow roller above the water. Then, right before heading up to the bow to drop, the user should enter the water depth and the expected maximum tidal increase (if you were really clever you could have the app know the tide information, but that might be a bit much).

The app could then calculate the chain out and give a real-time reading of scope. You could colour code the scope to be red below 3, turn yellow, then green at 5.

Great idea, I think. If you can get it to work in real conditions!
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Old 04-10-2014, 21:03   #9
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Re: Anchor chain counter app

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Interesting. The frequency will change with speed, so you need to be clever about spectral analysis. I would think that you could do an FFT and then look for the peak (since wind, voices, etc will be a broad spectrum but the chain rattle is more consistent). The peak frequency would give the speed the chain is going out.

You know roughly what frequencies to look at from a practical standpoint, so you can limit the bandwidth to speed up calculation.

10% accuracy is actually pretty good. Anchoring isn't so precise! You should think about the user interface. The user should, of course, input the chain size up front, but also the height of the bow roller above the water. Then, right before heading up to the bow to drop, the user should enter the water depth and the expected maximum tidal increase (if you were really clever you could have the app know the tide information, but that might be a bit much).

The app could then calculate the chain out and give a real-time reading of scope. You could colour code the scope to be red below 3, turn yellow, then green at 5.

Great idea, I think. If you can get it to work in real conditions!
I did use an FFT and a peak detection within a frequency range. But it is not always giving back the correct frequency. This is due to the high amplitude of the noise and other sounds from for example the anchor winch which often has a similar frequency range.
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Old 04-10-2014, 22:42   #10
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Re: Anchor chain counter app

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I did use an FFT and a peak detection within a frequency range. But it is not always giving back the correct frequency. This is due to the high amplitude of the noise and other sounds from for example the anchor winch which often has a similar frequency range.
That's kind of surprising. Have you run the windlass on its own and had a look at the spectrum? Then run some chain over the roller by hand and looked at the spectrum? There may be something about the signature you could pick up. Getting tricky if they're both in the same frequency range, though. Especially since you need it to be a general app, not just tuned to a boat.

Personally, I prefer to let the chain out by hand.
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Old 05-10-2014, 00:55   #11
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Re: Anchor chain counter app

Thanks for all the great comments.
But dose someone have the opportunity to record a sample for me? That would be a great help!

Cheers,
Bernd
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