ultrasonic speed *and* ultrasonic depth

[Olsonist]

Airmar makes the CS4500 which is an ultrasonic speed transducer. It uses a frequency of 4.5 MHz. They also make the B22 which is an ultrasonic depth transducer. It uses a frequency of 200 kHz (or 235 kHz).

Can these be used together or would there be any interference issues? Also, why doesn't/wouldn't anyone make a combined ultrasonic speed/depth transducer?

[chabrenas]

Well, if Airmar doesn't make a combined unit, Nexus does:
triducer (http://www.nexusmarine.se/templates/Products____31.aspx?epslanguage=EN&productId={06F87E83-CC75-44E8-9532-7C742578544C})

[masalai]

chabrenas, to me looks like speed/distance is still the old "paddlewheel" which is a mechanical means of measuring water velocity. there have been a few ultrasonic or other sonic transducers but laminar flow and other near hull influences in the water turbulence impact on accuracy as they rely on small particles of air bubbles in the water to get a return from, whereas depth reflects off passing fish (air bladders) and bottom surfaces for depth and nature of the bottom. - - The forward looking sonar may work of solids in shallow water.

Most seem to rely on GPS data for speed/distance over "land" and discounting tide and current flows unless one is happy with a "paddlewheel" device.... Cross frequency interference should not be an issue as some depth transducers boast of dual frequency operation (50hz and 200hz I think - though I have not looked into this aspect at all...) At 4.5 Mhz it seems they are targeting small objects in the water and if the range for the targets is a meter or so could give reasonable results but still susceptible to the rise and fall of the boat in the water giving false speed/distance readings so the electronics would need to have some averaging system as well...

[marshmat]

Hi Olsonist,

It looks like there are a few companies selling "triducer" units that provide speed, depth and temperature from a single housing, but all of the ones I've seen use a paddlewheel for speed.

I very much doubt you'd encounter interference issues between a 4.5 MHz transducer and a 200 kHz unit on the same boat. Piezo transducers tend to have a fairly narrow resonance and, in general, do not respond strongly to frequencies well above or below that resonance. A doubling or halving of frequency typically cuts the sensitivity of a piezo transducer by 30 dB or more, unless it is specifically designed to be a broad-band type.

[Olsonist]

Ok, I have pored over the Airmar website and talked to their reps and Gemeco. First, Airmar is the de Beers of transducers. They pretty much have a benevolent monopoly in the transducer market so much so that a lot of manufacturers refer to one of them as an XXX Airmar transducer.

What I'd like is an NMEA 2000 depth sounder and an NMEA 2000 ultrasonic speedo and that's it. No paddlewheel for me, thank you. While Airmar does make the ($80) D800 depth sounder there isn't an NMEA 2000 version just now. Instead you have to spend $248 from Defender to get the DT800. Next, Airmar doesn't manufacture an NMEA 2000 ultrasonic speedo right now. The CS4500 is the closest approximation. You have to look at the product web page (http://airmartechnology.com/airmar2005/ex20/RMProducts/ElectCat.asp?ProdID=68&Man=All&PageNo=131) to get an idea and then carefully look at the cross refererence (http://airmartechnology.com/XRefDisplay.asp?From=Interface&Model=CS4500) to get an idea of what's available in what housing/deadrise and what interface.

So for my boat for right now I'm forking out for the DT800 and also putting a through hull blank in place for a future NMEA 2000 ultrasonic speedo. I'm pretty sure that at some point in the near future there will be an NMEA 2000 ultrasonic speedo. I'll wait.

I should also say that the Airmar reps were very insistent on the sounders not being referred to as ultrasonic, and yes, they're right. It is enough to just call them depth sounders.

[masalai]

Get a cheap GPS for speed/log/trip and position and look over the side for depth (if it is dark blue you are OK) Garmin 60 is cheap and chartless but a good backup if your chart plotter & radar fail from whatever or flat batteries as it will work on 2 x AA rechargable for a while so just keep some rechargables ready or use 12v battery otherwise - You will then have good backup and redundancy covered and no paddlewheel and just as accurate....

as I said earlier the technology has been around for a good 20 years and not adopted so must be issues - go the gps route and accept good redundancy and one less hole in the boat.... My boat will have NO HOLES below the waterline....

[Olsonist]

Well, there is the P79 with is N2K depth only for about $100. But it is in-hull transducer which wouldn't work for the class rules of my boat.