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What type of transducer?

Old 04-19-2004, 12:14 AM
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Default What type of transducer?

Hello all,

I just registered to the site though I have cruised a bit doing research on fishfinders. I am leaning strongly toward getting the Furuno 582L fish finder but I am a bit confused about which type of transducer to get. I have an '89 23' wellcraft coastal with a newer 225 outboard. I fish Long Island Sound and surroundings almost all of the time (300 ft and less), but plan to do a few trips to deeper water. I am replacing an old Alpeco Transom mount system that came with the boat. Is there a significant advantage to the thru hull vs the transom mount? I have heard that getting the transducer away from the propeller and water turbulance off the end of the boat gives better readings at speed. I don't mind doing the extra work to install if it gives better performance, but if it's real close......
Also I have seen a couple of posts suggesting to get the 1 KW transducer even though the unit will only drive at 600W. Does anyone know why? Better definition? Bigger crystal?
From what I have read on this site there are a lot knowlegable members here and I would like to hear any advice you can offer.

Thanks,
Tony R
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Old 04-19-2004, 10:27 AM
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Default RE: What type of transducer?

Hi ,
It sounds like you only have a single motor ,if so a transom mount will work fine. I would lean towards the B260 in hull
because it will enable you to upgrade at a latter date to a more powerful echo sounder. But if you use the B260 make shore to fit the fast fairing.

regards

rushman
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Old 04-19-2004, 01:11 PM
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Default RE: What type of transducer?

Thanks Rushman. You are correct it is a single outboard. Will the narrower cone angle on the B260 limit it's effectiveness in shallower water? Does this unit give better performance as far as definition of the target? Where is the best place to mount, on the centerline or off to one side?
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Old 04-20-2004, 11:45 PM
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Default RE: What type of transducer?

Tony I just bought a B-260 and High Speed fairing block for it. This thing is HUGE!

http://www.classicmako.com/projects/xshark/bw24.htm
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Old 04-21-2004, 12:36 AM
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Default RE: What type of transducer?

Holy cow warthog5 that is quite a project you have going! Looks like you have it set up pretty nice. I just bought the fairing block on e-bay for about $130 because it was about double that retail. I was pretty POed about getting bent over for that cheap hunk of plastic, but I had no idea it was so big. Do you think I am going about this backward by buying the fairing before the transducer before the fishfinder? I am commited now. I am going to try to get to your page 1 of your project so I don't feel so bad mucking 4200 all over my hull. Thanks for the info.
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Old 04-21-2004, 04:11 AM
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Default RE: What type of transducer?

Tony R

Point 1, No
Point 2, yes.

I do not know this model of wellcraft, we have just installed this setup on a 33 inboard which has tunnels over the prop shafts.It is mounted approx 15ft back from the transom and works very well.

Do you have the removable fish boxes that give access to the hull. I would try to mount outside of the centre line.

with no water pickups close by, which can generate noise. you could place in a plastic bag and cover with water, then just move it around inside the hull for best results. then install it in that position.

regards rushman
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Old 04-22-2004, 01:03 AM
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Default RE: What type of transducer?

Thanks for the reply again Rushman. The B260 is a thru-hull installation (M260 is the in-hull) so the transducer will be mounted under the boat with a fairing. I was not sure if there was an optimal spot to mount to avoid turbulance and get the best performance. I will also need to stay out of the way of the trailer rollers when I pull in the fall. My access is somewhat limited to within a few feet of the transom. Is it better to stay as far from the engine as possible? Is the centerline the best spot, or off to one side?

The 230 Coastal is a walk-around cuddy.

Thanks again for the info.

Tony
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Old 04-22-2004, 08:52 AM
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Default RE: What type of transducer?

Tony R. - Your question about the 600w rated transducer versus the 1kw rated transducer is a good one. The 600 watt rated transducer has a single ceramic element that resonates in the thickness mode at 200kHz and a radial mode at 50kHz. This single ceramic solution has reasonable transmit sensitivity (dB of sound per volt of input) 155dB at 50kHz and 164dB at 200kHz. The 1kw transducer is a completely different animal - it uses a separate 50kHz seven-element array and a dedicated 200kHz ceramic. Therefore, for the 1kw transducer, the sensitivity at 50kHz is 162dB and at 200kHz the sensitivity is 169dB. This means that at equal power input you will get much more sound energy into the water with the 1kw rated transducer. (Remember that sound intensity is measured on a log scale so a few dB greater means several times the energy output.) Another benefit is that the 1kw transducer (specifically the 260 family) has less ringing than the 600w rated transducer - meaning that the pulse is much "sharper" which results in better target discrimination. Hope this helps. E Fitz.
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Old 04-23-2004, 05:51 PM
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Default RE: What type of transducer?

Thanks E Fitz,

Sounds like you are either associated with Airmar or have done some reading of their technical bulletins. I just finished looking at their "Sensor design fundamentals" paper and I am impressed by the amount of information. How about this one: How do the various OEM manufacturers match the impedance of the various transducers available for their units? Are the transducers themselves tuned to have the same impedance? Do the units somehow self adjust to each transducer, or do the OEMs just produce an impedance which best fits the average of the compatible transducers? Part 2 of this question would be whether it would be good to try to match up the impedance of individual transducers with the individual driver (ie tune each installation)? I saw some information on the B260 where the FOM with a transformer is 5 db higher at 200 kHz. I am assuming the transformer was used to tune the impedance.

Thanks again for the Info,
Tony
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Old 04-26-2004, 11:06 AM
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Default RE: What type of transducer?

Tony R - Have to admit that everthing I know about transducers comes from either transducer / echosounder training seminars (with Peter B. and Jen), from reading the sensor design fundamentals you mention, attending trade shows, and from used college texts. I honestly do not know the answer some of your questions but I'll assume that most echosouders are somewhat impedance tolerant (for example, will perform well as long as the impedance is between 200 and 450 ohms.) Some transducers may have internal transformers for correct impedance matching but I think this is the exception and not the rule - probably more expensive transducer models are built this way.

To boost the transmit sensitivity (add dBs) for a given transducer you would have to add a transformer that lowers the impedance of the transducer. This gain can be easily calculated by taking the log (base 10) of the square root of the ratio of the impedances, then multiply by 20. That said, if you have a transducer with 370 ohm impedance and transform that to 50 ohm impedance the transmit dB gain is 8.7dB. ('Course the sounder would have to be tolerant of the low 50 ohm load,...) This boost in transmit sensitivity should have a corresponding boost in insertion loss (figure of merit) as figure of merit is a composite of the transmit and receive sensitivity curves. E. Fitz.


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