Author Topic: Does side imaging see fish swimming at the surface?  (Read 330 times)

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Offline trout

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Does side imaging see fish swimming at the surface?
« on: May 24, 2019, 09:18:43 PM »
I have my Humminbird Helix 10 G3N SI transducer mounted on the bottom of my Hobie kayak. It is below the hull so that there is no hull obstruction to the left and right.

I was in a narrow canal (80ft width, 4-5ft depth) the other day with more than 50 good sized mullet (12" or so) swimming at the surface (the very top). I could visibly see them with my eyes but they weren't showing up on the screen. The dock pilings and shoreline were showing up perfectly clear.

I had the range set to 40' each side, and the sensitivity I changed from between 10-20 and I adjusted the contrast after each sensitivity change so that the dock pilings in the canal weren't washed out. I tried both 455 and Mega+ and no matter what still couldn't see the mullet on the screen.

So my question: is side imaging not able to see anything "above" the depth that the transducer is at? I know the angle is supposed to be 86 degrees, but even if it was 90 the mullet would still not show up right? A blindspot basically for surface water out to the side and up.

The side imaging worked fine in both 455 and Mega+ for finding schools of fish on the bottom out in the channel.

If you Google Image Search "Hobie Guardian" you can see an example of my transducer install.
« Last Edit: May 24, 2019, 09:22:13 PM by trout »


Offline rnvinc

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Re: Does side imaging see fish swimming at the surface?
« Reply #1 on: May 25, 2019, 09:01:05 PM »
The 455kHz SI frequency is more likely to show targets at the surface than the 800kHz or the 1200  ...



We should note that even tho the 455kHz beam does reach all the way to the water's surface - the sound pulse strength is getting weaker as it travels away from the Main Axis of the SI beam form = less sound pulse strength = less sound reflected from targets = less data to display  ...



So larger (or more reflective targets) would more likely reflect enough of the weaker part of the sound pulse to actually display  ...

Rickie

« Last Edit: May 25, 2019, 09:02:51 PM by rnvinc »

Offline trout

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Re: Does side imaging see fish swimming at the surface?
« Reply #2 on: May 25, 2019, 10:09:20 PM »
With my transducer being under the kayak hull in the middle (total hull width there 34"), do you think part of the surface is being blocked when using 455 kHz?

I was messing around with it earlier and couldn't see a floating branch that was like 3ft long or my sandals with either 455 or MEGA, 30-40' range each side.

I see every dock piling no matter what sens/contrast or frequency.
« Last Edit: May 25, 2019, 10:12:08 PM by trout »

Offline rnvinc

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Re: Does side imaging see fish swimming at the surface?
« Reply #3 on: May 26, 2019, 09:59:58 PM »
Is it possible to remove the xducer from hull and temporarily mount it to something that yet it down a few more inches into the water to determine if the hull is blocking some of the beam  ...??

Rickie

Offline trout

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Re: Does side imaging see fish swimming at the surface?
« Reply #4 on: May 26, 2019, 10:38:20 PM »
I'm doing that later this week with a transducer arm mount off the side of the kayak. I'll update the thread.

Offline trout

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Re: Does side imaging see fish swimming at the surface?
« Reply #5 on: May 29, 2019, 01:37:34 PM »
So I moved the transducer to the back of the kayak on a RAM transducer arm so that there is no hull above it, very shallow maybe 2" from the surface. I can now see the mullet, the bottom of floating boat hulls, and floating docks that I couldn't see before. Tested with 455 and MEGA+, all 3 looked better with MEGA+.

On the way back to the ramp I put the transducer way deeper about equivalent to how deep it was under the hull (but still on the back of the kayak on the arm with nothing above it). I could still see the bottom of floating boat hulls and floating docks that I couldn't see before. Wasn't any mullet around anymore to verify that I could still see them.

It seems like when the transducer is mounted under a boat/kayak that the hull blocks part of the upwards SI beam even if there is full 180 degree clearance.
« Last Edit: May 29, 2019, 01:40:43 PM by trout »

Offline rnvinc

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Re: Does side imaging see fish swimming at the surface?
« Reply #6 on: May 30, 2019, 08:01:57 AM »
Thanks for the update  ...

This info can help future similar questions  ...

Rickie

Offline bhgammon

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Re: Does side imaging see fish swimming at the surface?
« Reply #7 on: June 02, 2019, 11:50:02 AM »
I have A H 10 like  yours and I see fish and even trash on the surface. Play with your settings and see if you can improve on your problem.

BG-


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