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Old 06-06-2019, 01:03 PM   #1
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Old speed wheel or new transducer?

Having recently completed an electronics retrofit on my Nordic 26, I've one last item that needs addressing - speed through water. GPS speed (SOG) is all I have currently.

I'm guessing I have several options, including the following - perhaps more:

- Replace the basic thru hull Airmar B117 transducer with something new that gives water speed. Airmar suggested the DST800, available in bronze/N2K for plug&play compatibility.

- Keep the B117 and utilize the existing speed wheel, assuming it is functional and compatible.

- Replace the existing speed wheel if it's not compatible. I'm guessing this might be the least favorable solution, as the DST800 w/N2K is not terribly expensive. If I'm dealing with replacing a thru hull component anyway, it seems to make sense to go with the new transducer.

MFD is a Simrad NSS evo2, but I really don't need all the fancy sounder technology it supports. Accurate depth is adequate, so if I can retain the perfectly functional B117 and existing speed wheel that would be great.

Here's a pic of the speed wheel - I've no idea what make/model it is, there are no markings on it I can see. Perhaps these are somewhat generic. The harness consists of four wires (red, green, white, black) plus shielding - also shown below.

Appreciate any insight and/or advice - thanks!



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Old 06-06-2019, 02:21 PM   #2
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I once went from a Simrad speed instrument with an Airmar paddle wheel sensor to a Raymarine speed instrument and the existing Airmar worked fine with the Raymarine instrument.


But I understand that that doesn't always work.


Try it.


Is the new modern speed transducer solid state with no moving parts. That would be a big plus.


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Old 06-06-2019, 02:30 PM   #3
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IMO paddle wheels suck. Thatís 1960ís technology. But is there any particular reason why you need to know something other than SOG that your GPS reports?
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Old 06-06-2019, 02:57 PM   #4
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Originally Posted by makobuilders View Post
IMO paddle wheels suck. Thatís 1960ís technology. But is there any particular reason why you need to know something other than SOG that your GPS reports?

Yes.

We have relatively large tide changes and due to the geography of our cruising grounds lots of current. SOG doesnít tell us how the boat is performing.

I donít have any water speed indicator on my current boat. After years of sailboats, I really miss it. My depth transducer is actually a depth/speed transducer (I didnít realize until a week ago). I am going to see what it takes to get a boat speed readout.
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Old 06-06-2019, 03:10 PM   #5
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But I understand that that doesn't always work.


Try it.
I would...but I've zero idea how to wire it up, or if I even have everything necessary. Don't know if there's typically some sort of interface box for the wheel, whether it just sends NMEA 0183 - and if so, what wires do what.

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Is the new modern speed transducer solid state with no moving parts. That would be a big plus.
Looks like it, but I'm not certain. However, since posting the note above - I've seen a few less than glowing reviews here on the DST800, both in terms of reliability and accuracy.
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Old 06-06-2019, 03:19 PM   #6
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IMO paddle wheels suck. Thatís 1960ís technology. But is there any particular reason why you need to know something other than SOG that your GPS reports?
Yeah...not a fan of the tech either, but if it's there and free - I'd like to have it for the same reasons Dave mentioned.

Also, I'm considering installing a Floscan FloNET setup to tie into the NSS. Would be nice to be able to view water speed and accurate fuel flow side-by-side so I can better understand what's most efficient, and what penalties exist when I decide to throttle up.
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Old 06-06-2019, 03:51 PM   #7
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I had very poor reliability and performance from the DST800. It might be my review that you read elsewhere. I had two fail in 4 years, including one after only a few months. Repair under warranty would have required a haul out, or showering my ER with salt water. I just abandoned the device and made a note to not buy one again.

Temp failed on both of mine. Only the second one had speed (paddle wheel), but it consistently read about 50% high, and there was no way to adjust any offset, including using the Airmar tools that I bought.

Overall I have had excellent performance from Airmar products, but the DST800 really sucks. Research on cruisersforum too and you will find others with problems.
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Old 06-06-2019, 03:58 PM   #8
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Well, I more carefully read your first post and am confused. The Airmar B117 which you say is what you have now, is a depth only transducer. The Airmar DST800 Triducer you might replace it with is a multifunction speed, depth and temperature transducer. It has a paddle.


So I assume that you want to display the through the water speed on your new Simrad MFD. I am quite certain that your existing transducer whether it is depth or speed won't work as it is an old one that transmits pulses not data.


So ask Simrad what speed transducer will work with their MFD.


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Old 06-06-2019, 04:04 PM   #9
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Yup - yours was one of the reviews. Considering myself adequately warned. Last thing I would want is to yank my rock-solid B117 for something inferior.

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Only the second one had speed (paddle wheel), but it consistently read about 50% high, and there was no way to adjust any offset, including using the Airmar tools that I bought.
It seems in general, most water speed indicators have accuracy issues. What I can't seem to get a good handle on, is if that's reported speed or consistency/repeatability. Or perhaps both.

Truthfully, if the reported speed is a tad off - no big deal, as my speed variance is minimal and I could adjust that offset in my head. Of more concern is if I can trust it gives the same number, every time for a given RPM.
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Old 06-06-2019, 04:13 PM   #10
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Well, I more carefully read your first post and am confused. The Airmar B117 which you say is what you have now, is a depth only transducer.
Correct.

If my original post wasn't clear, I also have a standalone thru hull paddle wheel. Completely separate from the B117 transducer. Unknown make/model, unknown wiring, unknown functionality. It was disconnected when I purchased the boat several years back, but if I can easily tie it in to the Simrad MFD and see if/how well it works - I'd like to try that first.

If that's not possible, I'll move on to other options. I only mentioned the B117 and DST800 , as one possible solution to getting water speed is to replace my B117 with a multi-function unit.
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Old 06-06-2019, 04:21 PM   #11
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Yup - yours was one of the reviews. Considering myself adequately warned. Last thing I would want is to yank my rock-solid B117 for something inferior.







It seems in general, most water speed indicators have accuracy issues. What I can't seem to get a good handle on, is if that's reported speed or consistency/repeatability. Or perhaps both.



Truthfully, if the reported speed is a tad off - no big deal, as my speed variance is minimal and I could adjust that offset in my head. Of more concern is if I can trust it gives the same number, every time for a given RPM.


My experience with STW was a sample size of one, and it wasnít working, but..... Iíd say it was consistent in the reported speed. Just way, way off. Like reporting 12kt when I was doing 8, and on a boat that isnít capable of 12 Kts under any circumstances. If it were off a little I would probably have done your mental adjusts too. And then the temp crapped again....
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