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How to measure the speed of a moving boat acurrately?

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soon1401

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Boat Speed Meter

Anybody have the information on how to measure the speed of a moving boat acurrately? I have some information on the control circuit but having trouble finding the right speed transducer which will not come in contact with the sea level. Any idea what kind of sensor can measure boat speed without touching the water?
 

Re: Boat Speed Meter

Try to look into data sheets of certain types of GPS devices.
integrated Garmin GPS sensor that provides precise speed, distance
You can reed it directly from their LCD screens or get it in the ASCII format from the RS-232 (TX only) interface.
 

Re: Boat Speed Meter

it's quite expensif if using GPS , may be some body have another idea about measuring the speed of boat and i have the same project for controlling the speed of boat, how about using digital compass we measure the distance and time neded for such distance then we measure the speed ?
any body could help me
 

Boat Speed Meter

maybe a radar + filtering with dsp
just an idea ...
 

Re: Boat Speed Meter

How about using windspeed. You can use an ultrasonic sensor to measure windspeed and factor in the idle wind speed. I think EPE magazine did an article some time back I will see If I can find it and upload.
 

Boat Speed Meter

Measuring wind speed to measure the speed of the boat is not a good idea as the ideal wind speed(when the boat stands still) also addes or subtracts the original speed due to boat. there is a way i think it will be usefull, you can use the technique used in optical mouse to find the speed of the boat or by using accelerometer.

Regards,
Puvi
 

Re: Boat Speed Meter

puviarasu said:
you can use the technique used in optical mouse to find the speed of the boat or by using accelerometer.
no there is no accelerometer in an optical mouse but a small CCD sensor

maybe you can use pitot tube like planes with accurate pressure sensor and microcontroller, have a look at
https://www.grc.nasa.gov/WWW/K-12/airplane/pitot.html
 

Re: Boat Speed Meter

Looking to the formula from above link seems that you need a lot of pressure to get some speed indication. What about when the boat will have 10 km/hour?
I think Pitot tube on a boat is a joke.
 

Re: Boat Speed Meter

Aircraft use a Venturi tube which is a hollow cylinder with variable inside diameter. The pressure difference between two diameters is used to compute the air speed. One problem with using this on a water craft is the coating of animal life which will form on the inside and change the readings.
 

Re: Boat Speed Meter

If you are operating in sea water, there is a proven method. Naval vessels use a detector called a Rodmeter.

The rodmeter is a coil inside a waterproof sheath. On the surface of the sheath are two contact buttons. A constant magnetic field is established by the coil.

- As the vessel moves through the water, the conductor (seawater) is cutting through the magnetic field generated by the coil.
- A conductor moving in a magnetic field generates a potential difference between the two ends of the conductor.
- The induced voltage appears across the two contact buttons on the outside of the rodmeter sheath.
- Measurement and display circuitry converts the voltage to speed units.

There are many variations of rodmeter. Some are shaped like small wing shaped antennas that stick out from the boat or ship hull. Some are mounted flush with the hull.

There is another, more sophisticated, method that also can be used with great accuracy in any type of water. You can mount an ultrasonic transducer on both the front and back of the boat. You pulse the front transducer, and measure the time to detect the pulse in the rear transducer. The time required for the ultrasound pulse to reach the rear transducer through water will be a fuction of the speed of the boat. This method of speed measurement is generally accurate to within 0.1knot.
 

Re: Boat Speed Meter

Hi you
I think that Pitot tube is OK.
But This's easily: Use GPS.
data Field RMC in GPS return speed 0 to 300 mile/hour. Not Sensor or Pilot tube
 

Re: Boat Speed Meter

vfone said:
Looking to the formula from above link seems that you need a lot of pressure to get some speed indication. What about when the boat will have 10 km/hour?
I think Pitot tube on a boat is a joke.
you can find (not a joke) low cost differential pressure sensor with 0.1 Pa resolution.
but as i said myself this was just an idea. GSM is a better solution.
 

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