Author Topic: Transducer Location  (Read 4352 times)

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Offline ak-angler

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Re: Transducer Location
« Reply #25 on: December 17, 2013, 12:53:11 PM »
Well, lets compare apples to apples...

According to what Airmar's own specs mean, any actual difference between their P66 and their P79 is negligible at best, with the P66 having the edge in some categories, and the P79 in others. If their in-hull transducers were "engineered to offset the signal loss from passing through a fiberglass hull", they would either have to have more transmit power, or a more sensitive receiver than their comparable transom-mount model - neither of which are indicated in their spec sheets. So, in my opinion, while the installation may be a bit easier, their recommendation that their in-hull designs would perform better than a comparable transom-mount unit in a shoot-through installation seems like nothing more than marketing hype.

That said, I neither own, nor have actually used either of these transducers - both of which would probably be better than the 'ducers that are typically included in FF packages.
1985 Sea Ranger 17 Skiff Top with 2012 Suzuki DF90A

2007 Cape Cruiser Marinaut 26 with twin 2006 Honda BF90's

Offline Threeweight

Re: Transducer Location
« Reply #26 on: December 17, 2013, 02:09:11 PM »
At a minimum, the P79 set up would be easier to install correctly, with less likelihood of trapping air bubbles in the bedding medium (silicone, epoxy, etc...) than a home-made solution for a skimmer style transducer like the P66.

Former Sea Chaser 17 owner
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Offline StreamFixer

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Re: Transducer Location
« Reply #27 on: December 17, 2013, 02:37:26 PM »
And this we become enthralled with picking the fly doo out of the pepper.   :hoboy:

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Offline ak-angler

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Re: Transducer Location
« Reply #28 on: December 17, 2013, 03:54:09 PM »
And this we become enthralled with picking the fly doo out of the pepper.   :hoboy:

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Offline fishorcrab

Re: Transducer Location
« Reply #29 on: December 17, 2013, 04:41:58 PM »
In a former life, I ran a lab grade sonar thickness instrument in repair of aircraft turbine blades. When there are multiple layers of different materials, you have to compensate for the sound wave velocity in each material. In addition, there must be a good coupling between the transducer and the first layer.  That is why some recommend a pool of oil between the transducer and the fiberglass.  There is good coupling between the fiberglass and water. 

I don't have any idea what effect epoxy or silicon RTV would do to the coupling but I suspect that the resilient silicon might absorb more energy from the sonar pulse than any of the other materials between the transducer and the fish's air bladder. 

I'm inclined to take the mfg's recommendation as bad advice might result in poor sales eventually.

Just my  :twocents:   Free advice is worth twice what it cost.  :whistle:  Jes' saying.

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Offline ak-angler

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Re: Transducer Location
« Reply #30 on: December 17, 2013, 05:45:42 PM »
In a former life, I ran a lab grade sonar thickness instrument in repair of aircraft turbine blades. When there are multiple layers of different materials, you have to compensate for the sound wave velocity in each material. ...
Paul

Just curious... I wonder how much induced error one would expect in 100 feet of water due to the addition of 1/4-inch of fiberglass? We don't exactly need turbine blade type resolution, do we?
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2007 Cape Cruiser Marinaut 26 with twin 2006 Honda BF90's

Offline T-Rex

« Last Edit: December 17, 2013, 10:07:42 PM by Westcoaster »
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Offline ak-angler

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Re: Transducer Location
« Reply #32 on: December 17, 2013, 11:06:55 PM »
Westcoaster - the information at that link indicates that it may be possible to shift a transducer's frequency to partially compensate for signal loss through various thicknesses of fiberglass. But, the data sheet for the P79 I linked to above gives the specifications for that 'ducer operating at the typical 50- and 200-kHz. And, the likely reason for that is... typical consumer fishfinders don't have the capability to shift frequencies. So... like many things in life, the theoretical possibilities are irrelevant due to the inherent limitations of reality.

And, the reality is, that mounting a standard transom-mount transducer in a shoot-through configuration works - and works great - provided there is only fiberglass, and no core, where it's mounted on the hull.

But in the grand scheme of things, where the 'ducer is mounted doesn't really matter that much. Each location has pro's and con's. And, as long as you mount a decent quality transducer in a clean stream of water, and hook it to a decent head unit, you should get a pretty good picture of what's going on under your boat. And, that's really what's important, isn't it? :beerchug:
1985 Sea Ranger 17 Skiff Top with 2012 Suzuki DF90A

2007 Cape Cruiser Marinaut 26 with twin 2006 Honda BF90's

Offline Threeweight

Re: Transducer Location
« Reply #33 on: December 17, 2013, 11:32:16 PM »
I read that document to say any thru-hull transducer will suffer from distortion and a loss of range, it is just less with the big 1 kilowatt shoe boxes, and less if the transducer has the ability to shift frequencies to compensate for the distortion.

A cheap transducer may look like it is performing fine when glued to the hull with silicone, but it is in reality going to suffer some loss of range and detail vs. the same unit mounted to the stern.


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Offline ak-angler

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Re: Transducer Location
« Reply #34 on: December 18, 2013, 12:02:26 AM »
I agree, 3WT. ANY transducer - including those purported to have been designed as shoot-through - will likely lose some resolution. But the transom mounted units have the same specs as the special shoot-through units. So, using a special transducer for a 'shoot-through' install won't provide any added benefit. If you already own a decent transom-mount 'ducer and you want to switch to a shoot-through configuration, you don't need to buy a new one - just use the one you have. But, if you're shopping for a new transducer specifically for an in-hull installation, there's no sense buying a transom mount unit and then adapting it to use as a shoot-through.
1985 Sea Ranger 17 Skiff Top with 2012 Suzuki DF90A

2007 Cape Cruiser Marinaut 26 with twin 2006 Honda BF90's