For Pete's sake! I just want a speed transducer! - Page 2 - SailNet Community
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post #11 of 37 Old 03-26-2018
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Re: For Pete's sake! I just want a speed transducer!

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Originally Posted by Noelex View Post
As Mark has said the Airmar DST800 is the most popular choice. A number of companies sell this transducer such as Simrad:

https://www.simrad-yachting.com/simr...5khz-f57ab51d/

Garmin also produce an adaptor that converts some standard transucers into one that will transmit NMEA2000 messages. I think they sell the black box with or without the transducer

https://buy.garmin.com/en-US/US/p/26510
Yes, I have the DST800 myself. Works fine. I get depth, speed, and temp on the NMEA 2000 network.

I wouldn't bother searching out an ST800, why not have the depth as well? Even if you already have depth, a backup would not hurt.

Please note that it's available in NMEA 0183, and NMEA 2000 versions. Obviously, you want the latter.

The ST 800 is available in analogue, and NMEA 2000 versions.

Bristol 31.1, San Francisco Bay

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post #12 of 37 Old 03-26-2018
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Re: For Pete's sake! I just want a speed transducer!

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Still really frustrating. The only place I've found online that sells the Airmar st800 is here:
http://www.imarineusa.com/AirmarST80...iABEgJOp_D_BwE

However, even though colemj's link claims it's an NMEA2000 device. That vendor claims it has spade connectors for Raymarine gauges. I suppose it's possible that I could just replace the end of the wire with an NMEA2000 connector and it would work?
See above. That one is the analog version.

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post #13 of 37 Old 03-26-2018
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Re: For Pete's sake! I just want a speed transducer!

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Originally Posted by Jeff_H View Post
Knotmeter transducers do not send NMEA information. They either send an electrical pulse or voltage reading. The Display head or 'black box' takes that pulse frequency or voltage, crunches the numbers and converts that to useful data such as a read out on an instrument or a NMEA sentence. Some of the newer systems use a 'smart transducer' but those do not work with older equipment.

Since different manufacturers, or even different models of equipment from the same manufacturer use different transducers which produce different pulse rates or voltages, its extremely difficult to find alternate transducers for any given display head, even if you do know the transducer manufacturer.

One of the things which has happened with great frequency is that the design of transducers has changed over time. Manufacturers claim that these changes have resulted in more reliability or better functionality. So with every new upgrade to the display heads, the transducers seem to change as well. But with each change, the transducer in your hull and possibly thru-hull in your boat, will no longer be correct for the replacement black box or display head.

My best suggestion would be to start with the company that made your display head. Find out what the input characteristics need to be to work properly with by your instruments. Failing that, find out the specific model number for the transducer that was used by your display. Once you have that information, Airmar (or who ever made your transducer) should be able to tell you whether they have other transducers with the output characteristics of the specific transducer that you are replacing.

Jeff
The OP stated that he needs NMEA2000 output, which the Airmar smart transducers produce directly from the unit. No black box required - the physical connector from the transducer is a standard canbus cable and connector.

Pretty much all equipment sold today is standard NMEA2000, and all the transducers are the same. Transducer differences are in housing size, type, and desired frequency, but the work with all equipment. An exception is Raymarine, which uses non-standard connectors and separate black boxes. Just stay away from Raymarine, and all is good.

Display heads are no longer dedicated to the depth transducer. Most now are multi-function displays that simply read network data.

Different transducer pulse rates are standardized and exist for depth resolutions. One has a choice of frequencies when choosing a transducer, and some are dual frequency. Again, this will all be readable by any current MFD display.

Mark

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Re: For Pete's sake! I just want a speed transducer!

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Originally Posted by Noelex View Post
As Mark has said the Airmar DST800 is the most popular choice. A number of companies sell this transducer such as Simrad:

https://www.simrad-yachting.com/simr...5khz-f57ab51d/

Garmin also produce an adaptor that converts some standard transucers into one that will transmit NMEA2000 messages. I think they sell the black box with or without the transducer

https://buy.garmin.com/en-US/US/p/26510
Actually, I pointed out the ST800 or ST850, not the DST models. These are only speed and temp - no depth. While it seems to be a good thing to also get depth with the DST models, they have a poor reputation for early failure. Also, they do not come in tilted element versions to accommodate deadrise if that is important.

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Re: For Pete's sake! I just want a speed transducer!

Airman does make a speed sensor that comes with a MMEA 2000 output direct form the sensor. I had one but I replaced the paddle wheel sensor with a CS4500 ultra sonic which has NMEA output. no more cleaning of the paddle wheel. always reads correctly. Call Gemeco they are very helpful

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Re: For Pete's sake! I just want a speed transducer!

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Originally Posted by BillMoran View Post
What I'm looking for is a thru-hull speed transducer that will send data onto an NMEA 2000 network so all my instruments can use it. Preferably it would 1.25" diameter to fit in the hole from the old (no longer functioning) device.

On the surface, if anyone can point me to a model that fits that need, I'd be eternally grateful.

On a deeper level, I'm wondering if it's just me, or is it insanely difficult to find information about this stuff? Looking at the advertisements, they say nothing about mounting dimensions or even the data technology in use. Especially with the data technology, it's frequently some proprietary protocol that may or may not be NMEA 2000 compatible.

Maybe I'm just impatient or really bad at research ... but it feels like I spend an inordinate amount of time trying to find out important bits of information about the equipment I'm considering buying. Is it just me?
Rest assured it is not just you - I went through the same process a month ago. I had a failed speed transducer (an old Stowe) and wanted to replace it with an N2K unit. Ultimately I went an Airmar ST800 unit, but even the options here are confusing. You have the ST800 and the ST850. The difference between the two being that the ST800 has a flapper valve built into the thru-hull, while the 850 I believe has an additional sleeve with the valve. I honestly couldn't tell the benefits of either one, so I just tossed a coin and went for the ST800.
However, each version has a choice of thru-hull materials - plastic or bronze for the ST800, plastic, bronze, or SS for the ST800. Just to add further confusion, Airmar produces branded versions with different connectors. The model number of the one I have is ST800PV-N2 - this is the plain (unbranded) Airmar plastic housing N2K version with a standard N2K connector - plugs straight into my N2K network and was picked up automatically by my chart-plotter, no fiddling needed.

Note that all versions require a 2" hole, so you will need to enlarge the old thru-hull. I just drilled out the old one - nice and simple even for a newbie like me. At least I think so - I'll let you know if she sinks when she's dunked in a week!
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Re: For Pete's sake! I just want a speed transducer!

Maybe I missed it but haven't seen what to me is the most obvious, easy solution.

If you get a transducer that plugs into whatever MFD or plotter you use AND that display is connected to the NMEA2000 network then all other devices on the network will have access to the data from the transducer.
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Re: For Pete's sake! I just want a speed transducer!

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Maybe I missed it but haven't seen what to me is the most obvious, easy solution.

If you get a transducer that plugs into whatever MFD or plotter you use AND that display is connected to the NMEA2000 network then all other devices on the network will have access to the data from the transducer.
I'm not ware of any chartplotters that will transmit data on to the network like this. Generally you have N2K enabled devices such as depth/speed transducers, air temperature/pressure sensors, wind instruments, etc, which connect to the NMEA2000 network and transmit data. Then you have other N2K enabled devices such as chartplotters or data display units that connect to the network and read data from it to display.

For what it's worth, I'm a new to this N2K network, but I like it. I installed a N2K network running from the V berth to the cockpit. Both my depth and speed transducers were defunct, so I replaced them both with Airmar units. These are very low power devices and plug straight into the network in the V berth - no additional power leads or transducer boxes. The chartplotter automatically picks up the data - it was literally plug and play. I also added air temperature/humidity and pressure sensors, and again these just plug into the network and are picked up in the environmental data display on the chartplotter. All these devices (chartplotter excluded) use less than half an amp, but the real benefit to me was being able to throw out a whole load of old wiring and transducer black boxes.
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Re: For Pete's sake! I just want a speed transducer!

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Originally Posted by peterlsmith View Post
I'm not ware of any chartplotters that will transmit data on to the network like this. Generally you have N2K enabled devices such as depth/speed transducers, air temperature/pressure sensors, wind instruments, etc, which connect to the NMEA2000 network and transmit data. Then you have other N2K enabled devices such as chartplotters or data display units that connect to the network and read data from it to display.

For what it's worth, I'm a new to this N2K network, but I like it. I installed a N2K network running from the V berth to the cockpit. Both my depth and speed transducers were defunct, so I replaced them both with Airmar units. These are very low power devices and plug straight into the network in the V berth - no additional power leads or transducer boxes. The chartplotter automatically picks up the data - it was literally plug and play. I also added air temperature/humidity and pressure sensors, and again these just plug into the network and are picked up in the environmental data display on the chartplotter. All these devices (chartplotter excluded) use less than half an amp, but the real benefit to me was being able to throw out a whole load of old wiring and transducer black boxes.
I'm pretty new to N2K myself but am learning. Here's what I have installed.

Garmin 740s plotter (upgrading to a 942sx), Simrad AP including rudder angle sensor, compass, brain and controller and my old Raymarine Seatalk Bidata40 speed and depth.

I installed a Raymarine box that converts Seatalk to SeatalkNG which is N2K compatible except for the plugs so add an adapter cable. Now my Garmin plotter gets heading info from the Simrad AP compass. I can set a waypoint on the Garmin and the Simrad will steer to it. The Garmin shows speed and depth from the Raymarine and the Simrad AP also sees the Raymarine speed.

So as far as I can tell, anything on an N2K network is available to anything else on the same network.

Last edited by skipmac; 03-26-2018 at 05:39 PM.
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post #20 of 37 Old 03-26-2018
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Re: For Pete's sake! I just want a speed transducer!

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Originally Posted by peterlsmith View Post
Rest assured it is not just you - I went through the same process a month ago. I had a failed speed transducer (an old Stowe) and wanted to replace it with an N2K unit. Ultimately I went an Airmar ST800 unit, but even the options here are confusing. You have the ST800 and the ST850. The difference between the two being that the ST800 has a flapper valve built into the thru-hull, while the 850 I believe has an additional sleeve with the valve. I honestly couldn't tell the benefits of either one, so I just tossed a coin and went for the ST800.
However, each version has a choice of thru-hull materials - plastic or bronze for the ST800, plastic, bronze, or SS for the ST800. Just to add further confusion, Airmar produces branded versions with different connectors. The model number of the one I have is ST800PV-N2 - this is the plain (unbranded) Airmar plastic housing N2K version with a standard N2K connector - plugs straight into my N2K network and was picked up automatically by my chart-plotter, no fiddling needed.

Note that all versions require a 2" hole, so you will need to enlarge the old thru-hull. I just drilled out the old one - nice and simple even for a newbie like me. At least I think so - I'll let you know if she sinks when she's dunked in a week!
The only difference between the ST800 and ST850 is the size - the ST800 is a little longer. There are two of them because there were two historic sizes of housings, so they have one for each size. Then, like you point out, you can get each with plastic, SS, or bronze housings, etc.

As to whether the thruhull needs to be drilled larger, that depends on what you are replacing. Reasonably old Airmar transducers have use the 2" thruhull size for at least 20yrs, and probably longer. If replacing an old Data Marine or similar, then those were different sizes.

Mark

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