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Old 10-09-2012, 05:34   #1
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Anyone Using an Ultrasonic Log Sensor?

I'm really sick of paddlewheel log sensors. I don't think they're accurate. Besides that, of course, it's a PITA to clean them all the time.

Has anyone used an ultrasonic log sensor, like one of these: Raymarine A102119 Airmar CS4500 Ultrasonic Speed Sensor $650.50 ?

I know a lot of people just say screw it, and use the GPS generated SOG instead, but I sail in strongly tidal waters and really need accurate speed through the water. I'm sick of futzing with my paddlewheel sensor, cleaning it, antifouling, constantly recalibrating it, and STILL not believing in its accuracy
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Old 10-09-2012, 06:16   #2
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Re: Anyone Using an Ultrasonic Log Sensor?

The ultrasonics need to be clean to work also. Get a transducer with a thruhull fitting that has a valve in it. That way it is easy to pull the transducer out of the water after each passage/sail, and return it when needed, without making a mess.

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Old 10-09-2012, 07:13   #3
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Re: Anyone Using an Ultrasonic Log Sensor?

Quote:
Originally Posted by colemj View Post
The ultrasonics need to be clean to work also. Get a transducer with a thruhull fitting that has a valve in it. That way it is easy to pull the transducer out of the water after each passage/sail, and return it when needed, without making a mess.

Mark
I've got that kind of through-hull, but it doesn't work very well -- it's still a messy job with lots of water in the boat.

Besides that, the paddlewheel sensor seems to be wildly inaccurate, even when clean, then the calibration changes literally day by day, as carp starts to build up on it. I just don't like it.

I heard that the ultrasonic sensors are much less subject to being fouled, and are much more accurate. I'm trying to find out whether that's really so.
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Old 11-09-2012, 07:50   #4
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Re: Anyone Using an Ultrasonic Log Sensor?

From the Airmar installation manual:

"Aquatic growth will seriously affect the ultrasonic insert’s performance. Clean the active face with a dull putty knife being careful to avoid scratching the surface".

It can be painted with water-based antifouling, but if you get fouling in your area even with antifouling, you will be cleaning it anyway.

But if it provides more accuracy, it may be worth it for you. We don't see the inaccuracy you experience on our paddlewheel transducer. Also, our thruhull does a decent job of preventing water inflow (water just bubbles over the top when the transducer is out, and simply inserting the blanking plug 1 inch stops it). However, we are a catamaran and our transducer housing is only ~2' underwater. If yours is deeper, the pressure may create more problems.

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Old 12-09-2012, 19:47   #5
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Re: Anyone Using an Ultrasonic Log Sensor?

...and do you need N2K or 0183? I was waiting for the N2K ultrasonic but Airmar apparently shelved the product for the time being so went with paddlewheel.
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Old 12-09-2012, 20:52   #6
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Re: Anyone Using an Ultrasonic Log Sensor?

That's strange, they do seem to have removed references to the output (they used to list both). They now list the output only as "Airmar paddlewheel output". What does that mean? We have an Airmar paddlewheel that outputs N2K...

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Old 12-09-2012, 21:29   #7
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Re: Anyone Using an Ultrasonic Log Sensor?

Here is a thread I started awhile back on this subject.
GPS vs Knot Meter
I will be hauling out within a month and seriously considering removing the knot meter which either is fouled and not working or when it does work, is too inaccurate to be of any use. When I would be going 1 knot on the GPS, it would say 2.2 on the meter and if the GPS said 7.5 knots, the knot meter said 6.5. A GPS does not lie. Every watch should record what is on the GPS log when they come on and leave their watch.
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Old 12-09-2012, 21:48   #8
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Re: Anyone Using an Ultrasonic Log Sensor?

The SOG and STW are often different from each other in currents and with leeway. This is important navigation information.

The mounted position on the boat can be problematic if it is not in clear, attached flow water, is shadowed on one tack by a keel or is taken far off the vertical when heeled.

Our knotmeter reads correctly through all reached speeds and stays calibrated as long as the impeller isn't fouled.

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