Author Topic: Can you mount the transducer to shoot through hull?  (Read 9828 times)

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Offline lolar3288

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Can you mount the transducer to shoot through hull?
« on: March 01, 2011, 08:52:26 PM »
My unit is Humminbird 798cx si combo serial # 9022502-0140
Other numbers 407440-1M and N2170

My boat is a Bayliner cruise…32 foot motor yacht series.

The 3288 has inboards, and drive tunnels with the props near the transom.  The rudders are outboard of the transom and the four trim tabs pretty much cover the transom side to side. 

To get a clear sonar shot side to side as well as down the transducer would have to be outboard of the trim tabs.  The only way to do this is to mount a plate on the tab and install the transducer on this plate.

Of course this is not ideal. 

Will being behind the props and well into the prop wash be a problem at low speeds? (I suspect it will probably be a problem at higher speeds but this is not really an issue).

I  there is a shadow area (25 degrees) on the side scan from the horizontal plan so could you shoot through the hull by mounting the transducer in a water or oil bath on the bottom of the hull between the engines and behind the keel? 

ila_renderedila_rendered


Offline RGecy

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Re: Can you mount the transducer to shoot through hull?
« Reply #1 on: March 02, 2011, 01:43:24 AM »
lolar3288,

Welcome to the forum.  I would recommend going to a dual transdcuer setup with the thru hull SI transdcuers.  This will get the transdcuer in front of the prop and elimnate the turbulence issue that you will most definitely have if you mount it on the transom.  Even at low speeds you will not get good readings where the SI beam shoots thru the prop wash.

If you have not opened your transducer yet, you can exchange it thru the Hb transdcuer exchange program.

Hope that helps,

Robert

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Offline lolar3288

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Re: Can you mount the transducer to shoot through hull?
« Reply #2 on: March 02, 2011, 12:49:20 PM »
Thanks for the reply.

Due to the engine placement, short drive shafts and general configuration it would be difficult if not impossible to use two (or even one) threw hull transducer.

THe options I have are to either stick a bracket out behind the trim tab furthest from the prop or shoot through hull just behind the keel in the centre line of the boat.

There is a possibility that  I could also shoot through hull near the bow.  I may even be able to install a through hull transducer there but I have opened the one that came with the unit.

Offline RGecy

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Re: Can you mount the transducer to shoot through hull?
« Reply #3 on: March 02, 2011, 02:26:35 PM »
There are some good images in the Image Gallery and if you search you will alos find a good bit in some of the post related to tunnel drives.

Maybe a dual transducer setup on the transom but out to the sides of each prop may work.

I think jollyroger had a telescoping mount on his to get below the prop turbulence.

Good Luck,

Robert
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Offline lolar3288

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Re: Can you mount the transducer to shoot through hull?
« Reply #4 on: March 07, 2011, 09:11:01 AM »
I had a look at all the setups in the photo gallery.   Some pretty complex systems!

With both props inboard of the transom it's impossible to mount anything at the back that will not be somewhat in prop wash.  How sensitive is side scan to wash? 

At low RPM my large props throw more of a current that a wash.  I have a straight bottom type sonar that is not effected significantly at speed below 1500 rpm and will still find bottom even at higher speeds.

I would like to use the side scan at speeds below 6 knots (1300 rpm) and when fishing (usually only one prop is turning at 1000 rpm or less) which is when side scan is most useful to me.

I’m also making an assumption that the normal down (bottom) tracking will work just like the current unit?

This boat is not a planing hull so there is very little air entrapment under the boat at speeds up to 10 knots (which I seldom do) and at that speed all I would need is simple bottom tracking.

Comments????

Offline sonar2000

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Re: Can you mount the transducer to shoot through hull?
« Reply #5 on: March 07, 2011, 06:38:44 PM »
This is a side image unit  unless you build a towfish.  The side image beam is so wide that it makes prop wash and air cavitation very likely especially at speeds over 8 to 10 mph. It all depends on the vessel type and the location of the transducer.
The tow fish that folks have built helps somewhat, but if you want to use better side scan displays Humminbird should give  us a narrower beam for depths..
Chuck

Offline lolar3288

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Re: Can you mount the transducer to shoot through hull?
« Reply #6 on: March 09, 2011, 06:57:18 PM »
It would be very unlikely that I would be running at 8 to 10 knots and using sidescan.  Just bottom readings.

If  I use the side scan for fishing then I'm running at 2-3 knots.

I wish I had more experience with the side scan transducer. 

I know from experience with standard sonar graphs and lcd units that a transducer mounted in a bath of mineral oil or antifreeze directly to the bottom of the boat so as to shoot through the hull were there is no coring works as well as a transom mounted unit.  I don't know if the side scan transducer would work or why it will not work.

If it is no more susceptible to prop and hull wash than a straight bottom scan unit then it will work on the back of an outboard tab because that’s where the current transducer is mounted.  You just have to play with the gain a bit.

I’m trying to figure out if it just will not work or that  it’s just that no one has tried it?

With the 25 degrees of surface to side scan beam what are the issues with shoot through?

Larry

Offline Humminbird_Greg

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Re: Can you mount the transducer to shoot through hull?
« Reply #7 on: March 11, 2011, 09:46:59 AM »
Larry,
Some of the Marketing guys and one or two Customers have tried the water bath idea with our Si units and had poor results.  The combination of signal strength loss along with the deformation of the beam (if that is the right term) as it passes through the hull make this a bad option.  But feel free to try this and report back to us.  Who knows?  It may work favorably on your boat.

I think that your only option is a Thru-Hull HDSi transducer if you can end up fitting it (or them) in.  If you mount any Si transducer aft of those props the wash from them will show to that side.  Maybe if they were mounted on the outside of the props (those trim tabs are looking good for this…). 

Now the 2D sonar can shoot through the hull and that may be something you want to install in a water or mineral oil bath.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline lolar3288

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Re: Can you mount the transducer to shoot through hull?
« Reply #8 on: March 13, 2011, 05:47:57 PM »
Thank you very much for the reply.

I think I will try a side plate off the outside  port trim tab which is right out of the prop wash and where my current transducer is mounted (I will be removing it).

Worst case is that one side will act up.  I have to make the decision as once the boat is launch anything is there until lift out next winter.  In the down only mode it should be fine.  Also to the left side which is better than no side scan at all.  It will take me a year to learn how to adjust and use the unit anyway.

I will report back on how it works.

Larry


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