Best sonar for viewing the bottom in a silty river?

Kushtaka

I am looking for a sonar that I can get a look at the bottom on a river that is completely occluded by glacial silt, large, and swift.

This is a research application, not a CDory, but I thought I might be able to get some good ideas here.

The transducers will be mounted to a removable rig that places the transducer under the center of a fishwheel (think aluminum pontoons with 3-4 spinning Ferris wheel like baskets. As they spin they catch fish that are deposited in livewells for the science, then released.

Current technique includes a probe of the bottom with a piece of rebar. It has not been completely effective, and has cost us some data.

Most boat sonars work okay when stationary relative to the bottom, and that will be the case here. Most lose the bottom at speed in this river, but we don't need to worry about that.

I am interested in fine scale bottom topography, ability to be rigged for portable deployment, removal, flexibility for use on different platforms with different transducers. A simpler user interface, rugged construction (we will ruggedize anything we use with a pelican case mounting, etc). A good realtime image and detailed depth data for a 10'x10' area. We fish these wheels so that they are pretty close to the bottom (where the fish are) so one little rock sticking up can ruin everything. Depths of concern aren't great, only 8-10' or so.

I appreciate your learned insights.

thataway · Posted: Sat Dec 21, 2013 7:14 pm Post subject:

I would be considering CHIRP --garmin might be the best way to go right now. This recent blog by Bill Bishop suggests that CHIRP can be a real boon in shallow water--and perhaps that with silt and turbidity:
http://themarineinstallersrant.blogspot.com/2012/05/shallow-water-chirping.html

Down scan is great , and would seem ideal for your use.--but I suspect that the image would be "clouded" with the silt.

Another resource would be the Hummingbird forum, since they have had the technology the longest--and may have more experience with the turbidity.

Sea Angel · Posted: Sat Dec 21, 2013 7:44 pm Post subject:

Not sure how the new Raymarine fish finder would work, but the demo in WM was impressive last week with its refined detail.

Art

Kushtaka · Posted: Mon Dec 23, 2013 12:56 pm Post subject:

Have a model number for that raymarine?

I should also note that GPS and chart plotting are not at all necessary, although if the right sonar package came with a GPS/plotter, it wouldn't bother me.

reelchef · Posted: Mon Dec 23, 2013 1:59 pm Post subject:

I beleive Art is referring to the Raymarine Dragonfly. CHIRP technology without the big price tag; The gold package loaded with all of US coastal, lakes and rivers can be had for under $700. It has a 5.7 inch display, and a locking gimbal mount. THe only potential problem I could for see with this unit is the size of the transducer- it is freaking huge!!!! I would recommend the sliding transducer mount to preserve it from the trailer, or shallow river. I am getting ready to take the plunge on this unit as well. Thumbs Up

Kushtaka · Posted: Mon Dec 23, 2013 2:32 pm Post subject:

The dragonfly came to my mind first, however I wouldn't exactly call the unit "new" as he did. Made me think there was maybe an upgrade.

It would fit the bill.

Transducer is no problem. It's going to be mounted to a removable piece of aluminum box tubing that will be mounted and removed as needed. In fact, the unit will not be permanently mounted to the fishwheel in any manner.

thataway · Posted: Mon Dec 23, 2013 4:43 pm Post subject:

Before investing in any of the Chirp/down scan technology, you want to contact the engineers at the company you are considering, and ask if they have done, or will do a series of studies in silt laden water. The issue is how much the silt can be filtered out, or how much it will interfere with the clarity of the image. Often images which are seen on brochures and the internet are not representative of the actual images you may get in the circumstances you are using the instrument...

thataway · Posted: Mon Dec 23, 2013 5:04 pm Post subject:

Just for comparison--here is a "good" Garmin 547xs depth sounder image (has chart plotter as well).

Wonder what it would be like with heavy silt?

Kushtaka · Posted: Mon Dec 23, 2013 5:20 pm Post subject:

I doubt I'll try to get any manufacturers to do a test. There aren't a whole lot of places with water like this.

Even if they did silt tests, it would likely be less silty than our water. BUT, the silt may be a bit of a red herring, or at least, the challenges that the silt present may be offset by the fact that the platform is relatively stationary relative to the bottom. We have used handheld depth sounders but we really need an image.

I think the dragonfly model may be a pretty good bet, and it's one I was considering. One thing I like about the downscan/sidescan tech is the ability to head downriver to the mouth and cruise the same silty water looking for derelict fishing gear to remove.

Anyway, thanks for the input. More is always good!

thataway · Posted: Mon Dec 23, 2013 5:56 pm Post subject:

You won't know, if engineering will do tests, unless you ask. Form a relationship with the department, and most likely they will accommodate you. PM sent.

Kushtaka · Posted: Tue Dec 24, 2013 2:01 pm Post subject:

It's true, I shouldn't dismiss so quickly. I've had some frustrations. I like Gamrin gear, but In the way far North on the Arctic Ocean there is a lot of bad map data. Landing strips are mapped on the wrong islands, towns in the wrong places, etc.

We sent them good data for their next update, no cost, just as interested users of their gear who would benefit from better map accuracy. It would have cost them hundreds of thousands of dollars to go out and get these data themselves.

However, we were repeatedly told that we must be mistaken and that their maps are checked carefully for accuracy. It was infuriating, and made me sour on reaching out for any special favors.

But, I suppose the time has come to bury the hatchet and give it another shot. Thanks for the encouragement.

tpbrady · Posted: Tue Dec 24, 2013 3:12 pm Post subject:

Kushtaka,

I share your frustration with charts and software. I can't the number of times, I have boated through islands and driven my truck down the Turnagain Arm. There's not much difference between the Copper River and chocolate milk made with 3 or 4 times as much powdered mix as necessary.

Lowrance has some fairly inexpensive down scan sonars available that have some good reviews (http://www.panbo.com/archives/2013/12/lowrance_elite-4_hdi_a_whole_lot_of_tech_for_a_little_dough.html). For the money, they might be worth a test. I have used their down scan in clear water and resolved cables, logs, and rocks on the bottom that would cause a problem anchoring. I would say working with the gain should help get through the silt in the water without completely washing out the display.

Tom

Kushtaka · Posted: Tue Dec 24, 2013 4:28 pm Post subject:

My experience with sonar in silty water is that it has to do with power and getting your gain right. But you need decent power. Even to look down only about 10' or so (my application), more power is better, despite the common use of power to get readings at greater depth.

But sonar works just fine in silt. In fact, our colleagues at Fish and Game use sonar to count salmon coming up the river, because they can't see the fish in the water without it. Granted, they have a very sophisticated array, but the concept remains.

I honestly have given up on running sonar on my boats in that mess. One need keep both eyes on the water surface and the deep water will reveal itself. Pinning your eyes to a digital readout constantly switching between 1 and 2 (and only telling you the depth of the water you just passed) while going 30mph in a debris strewn remote braided river is asking for trouble.

When forward looking sonar gets good in shallow applications, I'll start thinking about it again.

What I'm gathering from this survey is that there are a few different units I might consider, but that downscan and sidescan should be on my list.

Is there a particular transducer (airmar is all I use) that might be better for this application? It might be worthwhile to test a couple of these units with a standard transducer for a true comparison. I'll probably actually mount it on a model boat and would rather not have to swap out transducers to test different units.

Thoughts?

thataway · Posted: Tue Dec 24, 2013 7:32 pm Post subject:

If you are using Chrip or down scan, you have to use the very specific transducer made for that unit. Yes, most of them are made by Airmar.

The one thing to look at is the service. Reading the forums about service may be misleading since you head of the complaints--rather than those that don't have complaints. Many of the complaints are about soft grades upgrades as well as interfacing the various units, rather than the specific units such as the Elite series of Lowrance.