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RPM from exhaust sound

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Windy09/11/2012 10:11:19
892 forum posts
190 photos

I am trying to find a Rev Counter that uses the exhaust notes from your engine.

I understand you can use the sound card on a computer with a suitable program and microphone.

I know some years ago somebody compared Bob Kirtleys hydroplane rpm to mine using sound and there was a few 100rpm difference between the boats.

I would like to know if a sound recording off a video could be used?

The rev range would be about 9000rpm to 12000rpm.

How do you compensate for Doppler effect as the hydroplane runs in circle?

If so how to set up **LINK**

Can a hand held Sound RPM Meter be bought at a reasonable price and who supplies them?

It would be useful to work out how efficient the propeller design is, as I know the time and distance.

Any help welcome.


DerryUK09/11/2012 10:36:41
125 forum posts

Windy the author of the program in the link gives his email address have you asked him about the Doppler?

JasonB09/11/2012 10:37:48
23039 forum posts
2769 photos
1 articles

Links to a free download in this thread, not tried it.Just needs a mic and a PC or laptop


Google Audio Tachometer and there is a lot more



Edited By JasonB on 09/11/2012 10:38:12

Andrew Johnston09/11/2012 11:23:14
6668 forum posts
701 photos
Posted by Windy on 09/11/2012 10:11:19:

How do you compensate for Doppler effect as the hydroplane runs in circle?

To a first approximation average over an integral number of circles.



Simon036209/11/2012 14:14:41
219 forum posts
77 photos

If you have an iPhone (and probably Android smart phones as well) there is an app for doing this - search for "engine rpm" in the iTunes app store.

You may also be able to use an app that I have installed on my iPhone called "Vibration" that uses the internal sensors to carry out a frequency spectrum analysis. I have used it to determine the care engine RPM by looking for the frequency peaks around the expected speed.


Steamshy09/11/2012 19:17:13
38 forum posts
2 photos

Hi Windy, To work our propellor effeciency you would first have to know you engine thrust horsepower ( horse power ) then simply divide that by the shaft horse power to find the propellor efficiency. Shaft horse power is the actual power deliviered to the propellor, Which would exclude any auxiliaries, PTO`s etc.


Stub Mandrel10/11/2012 20:48:40
4315 forum posts
291 photos
1 articles

Hi Windy,

I assume it's you who's chasing the UK speed record?


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