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Old 22-08-2019, 16:46   #16
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Re: Probing the Depths of Depth Finders

Mixed water in rivers is not truly mixed though. It is rather layered. And echo is bouncing off the lower layer. Same story at times with water layers at different temperatures.


Test in stable water, if all is fine, then all is fine.


Turbulent underwater flows can fool your instrument too. Funny on a sunny day in home waters but man did I get (----less) scared sailing over top of AUS on a moonless night!



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Old 22-08-2019, 22:41   #17
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Re: Probing the Depths of Depth Finders

I was having similar problems in shallow water (exactly when you want reliable depth information) with my Garmin GPSmap unit. Last year I added a new Garmin unit with CHIRP technology and a CHIRP ClearVu transducer. BINGO. It is a whole new world. Consistent and reliable depth readings in shallow water over all bottom types.
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Old 23-08-2019, 07:09   #18
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Re: Probing the Depths of Depth Finders

The crazy readings in the river are not my worry. It's mixed salt and fresh water and readings are never reliable. I know the river well and can navigate it in fog without any instruments. It's when I'm just on an ordinary shallow channel or anchorage, say eight to sixteen feet, when the GPS depth craps out that spooks me. Yes, I can (and do) use a lead line, but I'd like to see one of my instruments being reliable.

I've moved the GPS transducer and I'll see how that works out. I'll also watch the Humminbird/SR depth finder. That has been reliable in the past. I'm not sure why recently it has been so inaccurate. Soft bottoms?

A new GPS with CHIRP technology would also work well, but that is a multi-hundred dollar investment that isn't absolutely necessary. I'll post back once I've had a chance to use the boat with the re-located transducer.
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Old 24-08-2019, 06:42   #19
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Re: Probing the Depths of Depth Finders

Question: How important is it that a shoot through transducer be aligned with the hull of the boat?
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Old 24-08-2019, 07:29   #20
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Re: Probing the Depths of Depth Finders

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Originally Posted by Homer Shannon View Post
Question: How important is it that a shoot through transducer be aligned with the hull of the boat?
I'm not sure what you mean.? It's all about having a solid interface at any angle. That interface can be mineral oil, silicone, epoxy or etc. The transducer face doesn't have to be parallel to the fiberglass surface, but in reality is far easier to mount that way.
If you mean how important is it that it be aimed directly down on vertical and/or slightly forward, I don't feel it's all that important. But in a perfect world it would be nice. The reality is that mostly the bottoms change gradually and in the case of a rock etc protruding from the bottom, traveling at much speed, a slight angle forward isn't really going to give you much time anyway. You can't stop a boat on a dime.
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Old 24-08-2019, 07:46   #21
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Re: Probing the Depths of Depth Finders

I was thinking of fore and aft. The Garmin installation instructions make no mention of aligning the transducer with the keel of the boat, but I watched a video of a guy installing a shoot through transducer and he mentioned that it need to be carefully aligned. I think the way I had it before, it was more or less athwartships as this allowed it to lay flatter to bottom.
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Old 24-08-2019, 08:32   #22
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Re: Probing the Depths of Depth Finders

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Originally Posted by Homer Shannon View Post
I was thinking of fore and aft. The Garmin installation instructions make no mention of aligning the transducer with the keel of the boat, but I watched a video of a guy installing a shoot through transducer and he mentioned that it need to be carefully aligned. I think the way I had it before, it was more or less athwartships as this allowed it to lay flatter to bottom.
Yeah, I usually just pick a spot NOT on centerline that is as flat as I can get. (There are often thick portions or fillers etc on centerline of many boats.) I most often had two sounders, one forward (but not that far forward to find a flatter spot) which was often at an angle due to hull slope. Then one mid ships on a flatter surface.
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Old 24-08-2019, 08:46   #23
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Re: Probing the Depths of Depth Finders

I just got finished installing a low end Lowrance fishfinder with a shoot through transducer. It worked fine during my test by placing a bag of water between the hull and the transducer. However, it initially wouldn't give a depth or gave me a 300 ft depth in my marina slip after I epoxied it in. I found manually reducing the sensitivity did the trick, it was prob picking up echos from other hulls and the docks.
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Old 25-08-2019, 06:45   #24
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Re: Probing the Depths of Depth Finders

I have 2 thru hulls, they are garmin and apelco bronze, but really they are Airmar. Meaning drill big hole and attach with angled fairing.
The Garmin is a 6 pin, and the Apelco is a 7 pin. Apelco transducer was already in hull when I bought boat, I added the Garmin later.

I figured out the wiring pinout and hooked them into Eagle Fisheasy 320c and 340c color fishfinders, so far they have both worked fine together, each on their side of the hull about 15 feet back from the bow.
Detects no problem shallow or deep.
I even have the speed configured and the temp. The speed had an adjustment in the settings, but temp I had to use an adjustable resistor on the mainboard of the unit.
Bought a 6 pin socket for the garmin and mounted it into the Eagle FishEasy, I had the old Apelco, so salvaged its 7 pin plug and put it into the other FishEasy.

I bought everything used and spent under $150 for all of it.
$25 for a 340C
$60 for Garmin transducer
$40 for 320C
$6 for a 6 pin socket.

I tried the shoot thru hull thing, but honestly was not great, lots of noise.
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