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Definitely One for PBraffitt

Old 12-24-2003, 05:11 AM
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Default Definitely One for PBraffitt

Now that you've surfaced, I guess we will all deluge you with our transducer questions. Here's mine: I am trying to figure out whether I would see a significant and worthwhile performance gain from mountiing an M256 in hull to use with my Furuno BBFF1 Navnet in lieu of the current B744V. The hull is pretty thick (Regulator 32) and the current through-hull is mounted very cleanly on the keel in a pocket and reads fine even at 25+ knots. My primary use is relatively shallow water from 25-300 feet, lots of bottom structure and bait to find.
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Old 12-24-2003, 07:12 AM
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Default Definitely One for PBraffitt

I think it’s best that I explain the differences between the two models and let you decide which will suit your fishing style the best. The B744V offers depth, speed and temperature output. It will only handle 600 watts of input power, which is more than acceptable for your application. The 50kHz beam width is 45 degrees and the 200kHz is 12 degrees. The wide beams are an asset in shallower water but won’t display structure as clearly or detailed as a narrow beam will. The B744V transducer has a “Q” of 28 and 31 (at 50 and 200). I have attached an article that was published in our newsletter a while back and should explain “Q”.

The 256 series is manufactured using four of the same elements used in the above B744V, but all four ceramic elements are wired together so they act as one large element. This gives the 256 series 16 times the sensitivity of a single ceramic model such as the B744V, and the ability to handle 1000 watts of input power. The beam at 50kHz is 14 x 23 degrees, and 3 x 5 degrees at 200kHz. Both beams are elliptical since the four elements form a football shaped pattern. The “Q” factor are 21 and 30 (50/200).

Basically the 256 series will give you more detail of fine structure due to its narrower beams. It will show much more detail of suspended targets such as bait schools and fish close to the bottom, where the single element model will tend to “blend” targets together or into the bottom image. The 256 will also allow you to output 1000 watts, which won’t really help you in the shallow environment. The B744V will give you a broader view of what is around the boat due to its wider beams, but you won’t be able to tell you where they are any better than the B256.

If you don't mind a narrower beam than the 256 you may want to consider the 260 series. They are very serious performers with \"Q\" factors of 8 and 10 (50 and 200) and beam widths of 19 degrees at 50 and 6 degrees at 200. The detail on the screen would be awesome, but you would spend more time trolling due to the narow beams.


The \"Quality\" Factor:
Measuring the Sharpness of a Transducer's Response

We all know the term horsepower as a measure of engine performance, stereo output is measured in decibels, and knot expresses boat speed. But what term is used to describe the performance of a transducer? It’s Quality Factor or Q. More specifically, Q measures the sharpness of a transducer’s response. A transducer with a low Q will allow a sounder to display sharp images.

To understand Q, you must understand a little about how transducers work. When an electrical pulse from an echosounder is applied to a transducer, the element inside begins to vibrate. This vibration sends sound waves through the water under the boat. This is much like the vibration of a bell after it is struck.

You know that a bell continues to ring for a time. Likewise a transducer will continue to vibrate after an electrical pulse has been applied. This phenomenon is known as ringing and is indirectly measured by Q. Unfortunately while a transducer is ringing, it cannot receive a clear echo. Thus ringing reduces the clarity of images on an echosounder screen. And it keeps a transducer from \"seeing\" in very shallow water.

It is important that the element inside a transducer stop ringing as quickly as possible. In other words, the goal of a good transducer is a sharp sound wave that stops quickly followed by \"listening\" for an echo. We say such a transducer has low ringing. Ringing cannot be totally eliminated, but with the proper engineering it can be greatly reduced. Airmar designs its transducers to dampen vibration quickly.

The lower the Q, the less ringing a transducer displays. Factors range between 1 and 40. A Q factor of 10 or less is considered low. Compared to our competitors' transducers operating at the same frequency, Airmar transducers have a lower Q, thus less ringing. All things being equal, a sounder coupled with an Airmar transducer will display sharper images.

Happy Holidays!!

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA
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Old 12-24-2003, 08:46 AM
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Default Definitely One for PBraffitt

Thanks so much. You are really providing a great service. I also have a B744V and a Furuno and had exactly the same question as Saltdog.

If I am doing my math correctly, in 30 feet of water the B744 will see a swath about 7 feet wide (assuming the boat is moving), while the M260 would see about half that and the M256 slightly less. Not sure that matters a whole lot.

Since you didn't mention it, I am assuming your comments about better definition take into consideration going from through hull to shoot through. Is there a the hull thickness where losses become an issue?

Finally, one more question: could I get a Y adapter that would let me use my B744 for temperature and an M260 for depth, or would have I have to get a new temperature sensor? I don't care about the speed paddlewheel, it's almost worthless.
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Old 12-24-2003, 10:41 AM
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Default Definitely One for PBraffitt

Your calculations are very close and yes, even shooting through a glass hull up to 3/4 inches thick you would see a big improvement with the M256, but even more with the M260.

How about a switch that you could leave the speed temp connected at all times and toggle between the B744V depth and the M256/M260 depth? You would have to do a little custom wiring, but it would give you a great option.

I'm leaving for the holiday break so everyone please have a safe and happy holiday.

Peter Braffitt
Business Development Manager
AIRMAR Technology Corp.
Milford, NH USA
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