Paddlewheel Speed Sensor

Electrical and electronic topics for small boats
pcrussell50
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Paddlewheel Speed Sensor

Postby pcrussell50 » Sat Jul 27, 2019 6:33 pm

I have an old but almost never used Lowrance basic SONAR. Depth and water temperature were what I use it for.

There is an input for a paddlewheel speed sensor, which I bought off eBay.

Are paddlewheel speed sensors only for trolling speed?

Or are they good up to 55-MPH?

Race-grade precision not needed.

-Peter

jimh
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Re: Paddlewheel Speed Sensor

Postby jimh » Sun Jul 28, 2019 9:07 am

A paddlewheel speed sensor should work well at moderate on-plane boat speeds. I don’t know if they work at 55-MPH because I never had a boat that would go that fast. As I recall, they work fine at 25-MPH.

Jefecinco
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Re: Paddlewheel Speed Sensor

Postby Jefecinco » Sun Jul 28, 2019 11:11 am

We have had [a paddlewheel speed sensor] with our Mercury SmartCraft system for about nine years. Ours can be "Field Calibrated" for accuracy. We have done this by comparing our GPS "Speed Over the Ground" or SOG reading to the paddle wheel "Speed Over the Water" reading or SOW reading. Because the SOW and SOG are often not the same due to current or wind conditions we chose a calm day at slack tide to do the calibration. Although it was probably not needed we checked the speeds at 90 degrees difference in heading around the compass points.

We were impressed by the uncalibrated similarities between the readings. We made our best guess and adjusted the SOW to match the SOG speed at cruising speed or around 3500 RPM. We have found the SOW speeds to be accurate to within an MPH or two across the speed range. Our Montauk has never reached 55-MPH but we have no reason to believe it would be any less accurate at that speed.

Before common usage of GPS I believe Chapmans recommended using shoreline points a known distance apart to determine the accuracy of pitot or paddle wheel speedometers.
Butch

pcrussell50
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Re: Paddlewheel Speed Sensor

Postby pcrussell50 » Sun Jul 28, 2019 11:34 am

Great info, guys. Thank you.

As you may have guessed by now, the boat in question is NOT a Boston Whaler boat. My Montauk (actually it's 1998 Alert 17) cannot go 55mph either. Nor can my 13 Sport.

A couple more questions:

The boat in question has only very rudimentary systems, only a tachometer, in point of fact. With this SONAR device, besides depth sounding, I can get it to display a voltage, speed, water temperature, and distance traveled—all data I enjoy observing. It is our family recreation boat, a speedy bow rider that looks like a bass boat except with seats instead of casting decks and live wells.

Is depth sounding the primary power consumer in these devices?

What might the current draw be with the SONAR function ON, versus SONAR function OFF?

-Peter

Jefecinco
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Re: Paddlewheel Speed Sensor

Postby Jefecinco » Mon Jul 29, 2019 9:59 am

I don't know the answer but will speculate that the sounder transducer draws more power than any other device. If you turn it off it will decrease battery drain. I base this on the recommendation of transducer manufacturers to turn off the depth sounder/fish finder when a multifunction display is turned on when a boat is out of the water. Otherwise the transducer can overheat to the point of damage.
Butch

pcrussell50
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Re: Paddlewheel Speed Sensor

Postby pcrussell50 » Mon Jul 29, 2019 11:09 am

Thanks Butch. That’s what I gathered. I found an online manual for it and I think the (basic skimmer style) transducer draws 200W RMS, (peaks are higher of course). Definitely worth paying attention to, when you’re out all day on a one-battery boat, and don’t have a dedicated house battery that is separate from the starting battery.

-Peter