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Old 13-02-2013, 15:10   #1
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Airmar Ultrasonic Speed Transducer?

I have just about despaired of the the DST900 Airmar ultrasonic speed and depth transducer to be shipping before I splash my boat, with a complete N2K electronics refit.

I really need precise Speed Through The Water data in order for my B&G Zeus plotters to do their leeway and drift/set calculations well. And anyway, we all need better STW data then we get from these stupid paddlewheels which clog up with marine growth 5 minutes after docking on every passage.

So what shall I do? There is the old reliable CS4500 ultrasonic transducer which Airmar has produced for some time already. N2what? It doesn't produce any kind of NMEA data; just 2000 pulses per nautical mile, sent in -- get this -- "Airmar Paddlewheel Format" (FFS!). I have sold my old Raytheon log, so I guess I will have to buy some kind of box to translate that Paddlewheel Format (!) into something intelligible by modern networks.

Or I could just buy an NMEA2000 DST transducer and use that temporarily until Airmar finally ship that DST900.

What do you guys think?
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Old 13-02-2013, 15:53   #2
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Re: Airmar Ultrasonic Speed Transducer?

Looks like I could buy a Ray ST60+ tridata instrument, connect both my old depth display to it as well as the CS4500 speed transducer, then connect the NMEA0183 output to the NMEA0183 input in one of my Zeus MFD's, and I should be in business. Hate to bastardize the N2K network like that, but might be the most elegant way to have ultrasonic speed data on the network.
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Old 13-02-2013, 23:48   #3
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Re: Airmar Ultrasonic Speed Transducer?

Or the Actisense DST2 module. Outputs NMEA0183, but my MFDs accept such data and bridge it onto the N2k network. The Actisense module allows calibration of the ultrasonic transducer. Sounds like the way to go.
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Old 14-02-2013, 01:41   #4
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Re: Airmar Ultrasonic Speed Transducer?

Or maybe most elegant of all:

"The Smart™ DT800 Depth and Temperature transducers can accept input from a separate analog speed sensor. Speed signals are obtained in analog format and sent to the Smart™ Sensor where they are converted to digital data. With this approach, only one cable is routed to the display, simplifying installation. Airmar has added more functionality while eliminating the need for an NMEA combiner."

I guess that's the ticket if you can properly calibrate the ultrasonic speed sensor via the N2K connection of the depth sensor. The lack of responses here make me think no one has tried this, so I guess a call to Airmar tech support is in order. I'll let you all know what they say, in case someone is considering a similar installation.
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Old 14-02-2013, 06:35   #5
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Re: Airmar Ultrasonic Speed Transducer?

We haven't experienced any problems with our Airmar N2K paddlewheel sensor and it remains quite accurate. The thruhull for it contains a valve which shuts off the majority of the water flow when the transducer is removed. After a passage, we simply pull the transducer and put in the blank plug. Takes 10 seconds and no mess. Reverse procedure when getting underway again.

No growth and accurate readings.

Mark
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Old 14-02-2013, 07:07   #6
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Re: Airmar Ultrasonic Speed Transducer?

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Originally Posted by colemj View Post
We haven't experienced any problems with our Airmar N2K paddlewheel sensor and it remains quite accurate. The thruhull for it contains a valve which shuts off the majority of the water flow when the transducer is removed. After a passage, we simply pull the transducer and put in the blank plug. Takes 10 seconds and no mess. Reverse procedure when getting underway again.

No growth and accurate readings.

Mark
I think that's the same transducer 99% of cruisers everwhere use, AFAIK. I have had trouble getting mine out so I usually wait until a liftout -- I lift and scrub every 2 months or so in the summer. If I had mastered getting the thing out so that I could keep it out when I'm off the boat I would of course have had better results with it.

But paddlewheel transducers are inherently inaccurate for different reasons -- for one thing, they measure the speed of the boundary layer (the ultrasonic transducers measure particles going by some distance away -- beyond the boundary layer), secondly they are very sensitive to any kind of fouling and read differently day by day as you cruise. Lastly, they are very inaccurate at low speeds.

I think it's not just a caprice that I want really accurate STW data. This data is so important for understanding so many things going on while you're sailing -- sailing performance, true wind, and now, with my new Zeus system, drift and set calculated dynamically.

So I am gladly investing some money into this!

My last question is whether the unit can be conveniently calibrated if I hook it up through a DT800 smart depth transducer. I will call Airmar tech support when it's morning there.

Other options I've discovered so far are:

1. Hook it up through a Raymarine ST60+ dedicated log or ST60+ tridata, then bridge to the N2K network with a Seatalk to N2K adapter or Seatalk to NMEA0183 adapter via one of the Zeuses. Shame I just sold my old ST60 log, which could have been used for this purpose; albeit I would have lost a hole for an instrument on the scuttle.

2. Hook it up through a Raymarine ST50i tridata display. This will also connect directly to my old depth transducer, and will bridge both that and the ultrasonic speed transducer directly to N2K. I like this.

3. Hook it up through an Actisense DST2 module, then pipe the resulting NMEA0183 data to one of my Zeuses, which will bridge it onto the N2K network. This will also allow me to save some money by using the old depth transducer.

4. Hook it up through one of those very cool Raymarine ITC-5 transducer adapters, which will allow me to use my old depth transducer as well.

So I have five apparently viable options. The two I think I like best are (a) using the Airmar DT800 to bridge the speed data; and (b) using the Ray ST50i Tridata. I think the Tridata will even bridge my backup wind data (I am leaving my old wind transducer at the masthead), so I will have both streams of wind data on the network. Cool! Cost-wise there's not much to choose between these variants -- cheapest is probably the surprisingly economical ITC-5.
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Old 14-02-2013, 07:35   #7
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Re: Airmar Ultrasonic Speed Transducer?

I'm with Mark and think you should go with the N2K tri-ducer until the 900 or similar comes on the market. I'm pretty convinced that it will fit the same thru-hull fitting.

Removing the transducer to put in the plug while in the water should not give you any trouble. Make sure to put some Superlube on the O-rings when fitting it.

When clean, the accuracy is within the limits you need I think.

cheers,
Nick.
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Old 14-02-2013, 07:39   #8
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Re: Airmar Ultrasonic Speed Transducer?

This guy built a circuit board to convert the data: DMI
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Old 14-02-2013, 07:47   #9
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Re: Airmar Ultrasonic Speed Transducer?

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Originally Posted by s/v Jedi View Post
I'm with Mark and think you should go with the N2K tri-ducer until the 900 or similar comes on the market. I'm pretty convinced that it will fit the same thru-hull fitting.

Removing the transducer to put in the plug while in the water should not give you any trouble. Make sure to put some Superlube on the O-rings when fitting it.

When clean, the accuracy is within the limits you need I think.

cheers,
Nick.
Yes, they're all the same through hulls, so that would work.

The DST900 will be much cheaper than the CS4500, and I won't need any interfaces or converters of any kind.

But I'm not sure it's going to be better. It's a different technology (electromagnetic instead of ultrasonic) and has a much smaller sensor. Apparently Airmar themselves advise that the combined depth sensor is worse because of the smaller sensor area.

I think at least two of these variants are pretty elegant and I don't think I really mind spending a few hundred dollars extra to have it now and have the best possible sensors.

Or do you think that conversion of the data is risky -- will be more failure prone -- or might degrade the quality of the data?
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Old 27-08-2016, 12:09   #10
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Re: Airmar Ultrasonic Speed Transducer?

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Originally Posted by Dockhead View Post
Yes, they're all the same through hulls, so that would work.

The DST900 will be much cheaper than the CS4500, and I won't need any interfaces or converters of any kind.

I think at least two of these variants are pretty elegant and I don't think I really mind spending a few hundred dollars extra to have it now and have the best possible sensors.

Or do you think that conversion of the data is risky -- will be more failure prone -- or might degrade the quality of the data?
Sorry to resurrect such an old thread but........

What was the outcome? I'd like to get an NMEA 2k log that doesn't require the services of a full time impeller cleaner...... Curious to know what you decided.
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Old 28-08-2016, 12:24   #11
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Re: Airmar Ultrasonic Speed Transducer?

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Sorry to resurrect such an old thread but........

What was the outcome? I'd like to get an NMEA 2k log that doesn't require the services of a full time impeller cleaner...... Curious to know what you decided.
Yes, I've been using the CS4500 now for thousands of miles and more than three years.

It's good, but not quite as good as I hoped. Some notes:

1. It's much less sensitive to fouling than paddlewheel logs. Huge plus.

2. It seems to be very accurate most of the time. Plus.

3. It gets confused sometimes and gives a radically wrong reading, then you can see it "hunting" for the right speed, going up and down. Minus.
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Old 28-08-2016, 13:48   #12
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Re: Airmar Ultrasonic Speed Transducer?

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Yes, I've been using the CS4500 now for thousands of miles and more than three years.

It's good, but not quite as good as I hoped. Some notes:
So if you could spend the money again what would you buy?
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Old 28-08-2016, 15:36   #13
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Re: Airmar Ultrasonic Speed Transducer?

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So if you could spend the money again what would you buy?
I dunno. I'd check to see if something better has been produced.

I'd weigh whether I had that much money to blow on the log.

But in any case I think a normal paddlewheel log is ok. They foul very quickly but it's easy to jerk them out to clean them (or jerk them out and leave them out when the boat's not being used).
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Old 28-08-2016, 17:01   #14
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Re: Airmar Ultrasonic Speed Transducer?

I had problems with the DST850 because the yard did not install it properly. The valve was not set down to engage the o rings into the grooves and so it didn't work... water flowed in like crazy. They left off the screw nut as well... So the paddle wheel was not down the the water. I found that out from the diver and then "reinstalled" the valve and the paddle wheel. Now it works.

However it IS only a few seconds and pehaps a few cups of water... to take it out and insert the plug... But my unit is installed under part of the settee with perhaps 12 or more things stored in it... so I have to remove the cushions. the lift off plywood, the 12 items, then the lift out floor they are on to get to the DST850.

YES if you leave the paddle wheel in place it will foul way too quickly. I am thinking when the boat is out to move it to CL forward of the keel where all I would have to do is lift up a cabin sole section.

There is no way around the fouling issue.... frequent cleaning if left in... or frequent remove and insert and left out most of the time.

My B&G Hornet can calibrate to .00 places and dampen as well. Excellent for sail trim and sensing current.
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