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[Leaky Bottom]

Hello
 
What's the best way to measure the RPM of a electric motor in a boat, I can do it with aeroplane motors with a tachometer on the prop but that's not possible on a boat when it's in the water.

[flashtwo]

Hi,

How about these non-contact tachometers.......

http://www.maplin.co.uk/search?text=tachomter&x=0&y=0

or

http://www.rapidonline.com/test-measurement/voltcraft-dt-10l-tachometer-537707

or

http://www.amazon.co.uk/HDE-Handheld-Digital-Tachometer-Contact/dp/B00850ZCRI


Ian

[Leaky Bottom]

Thanks for the links
 
I did realise I was going to need a tachometer but where would I take the readings from? A tachometer won't read from just a plain spinning shaft.

[Big Ada]

Put a bit of sticky tape on it to provide when a turn has been made.

[NFMike]

For an optical tach paint a section of shaft matt black and then paint a longitudinal white stripe over it.

[chuffy]

Most Tachometers that you can buy today come with a short lenth of reflective tape which will last for ages. I cut a little piece about 4mm x 8mm and stick on one blade, mine has remained stuck to the blade for at least two years now. Why reflective?, I don't know but it was supplied with the meter and it works, so good enough for me.


Paul.

[david48]

To refect the light back to the sensor I have a couple that work like that . The none contact type are safer to use
David

[flashtwo]

Hi,

The only problem with the reflective type, is if the optics get dirty. This is not a problem when you're taking the odd reading or the conditions are clean, but, in my application with a steam powered boat, there was a lot of steam and oil about, so I fitted a magnetic (Hall Effect) tachometer, which was immune from the dirt.

Ian

[Subculture]

Cycle computers are cheap (under two quid on ebay e.g. http://tinyurl.com/n54up8r) and can be used to measure RPM.

http://www.reuk.co.uk/Use-a-Cycle-Computer-to-Measure-Turbine-RPM.htm

[mrlownotes]

A tad more ££s but it measures/tracks/logs/stores much more than just RPM.
I use a MicroPower e-logger supplied by RC_LOG.
The Optical RPM sensor and the Micropanel LCD provide Max/Min/Ave for  Amps/Volts/Watts/RPM.
Data is displayed 'live' on the LCD or you can download the data after a run to examine it in detail.
The LCD display is configurable from the PC software.
If you like to know what's going on electrically ...................
http://www.rc-log.co.uk/micropower-e-logger.html?p=1

http://www.rc-log.co.uk/micropower-e-logger.html?p=2

[Subculture]

I use a micro logger. Nice bit of kit, but utter overkill if you only want to measure RPM.