Monthly Archives: December 2018

Wilson Lake and what Lies Below

Wilson Lake, Florence, Alabama.

When Wilson Lake was impounded there was a lot of old structures, canal, bridges and other structure let on the lake floor. With the advent of the new sonar technology such as Side Imaging and Down Imaging you can still find a lot of them.

I have both Humminbird Onix and Helix Mega Scan units on my boat. These amazing pieces of technology enable me to see what’s still laying on the ;lake floor to this day almost a 100 years later!

A Little History on the Lake

Wilson Dam spans the Tennessee River between Florence (north) and Muscle Shoals (south), Alabama. It stands at an elevation of 508 feet and crosses the Tennessee on a 20-foot roadway along the top of the dam. Impoundment of the Tennessee River above Wilson Dam has created Wilson Lake, with a maximum width of 1.6 miles and a main shoreline of 154 miles.

Wilson Dam was erected by the Army Corps of Engineers in 1918-25 and turned over to the Tennessee Valley Authority when that agency was established in 1933. Wilson is a concrete gravity-dam on a blue limestone rock foundation. The total length of the structure is 4,535 feet, the height 137 feet, and the maximum width at the base (Including the apron) is 160 feet. The head the water depth on the upper side of the dam is 97.6 feet. There were originally 58 spillway gates in the face of the dam, each capable of discharging 10,000 cubic feet of water per second.

As I scan the lake bottom with my Side Image and Down Image units I’m always looking for objects that are on the lake bottom. If I do manage to find something, if I can I’ll research and see if I can find out what it is and if possible try to find a photo of what the object is or was. In the two photos below I found an old submerged arched bridge crossing a small stream or creek bed. You can clearly see the creek bed in the Side Image photo.

Click on the photo thumbnails to get a larger view.

I found an old submerged mill a couple of years ago that an old time fisherman told me if I had ever looked for it. In the two photos below you can see what the mill looked like before it was torn down and all that was left was the stone work of the mill.

The following photo is an old marina boat cover slips that instead of being torn down was easier to just pull it out into the lake and sink it. The tin metal top and sides are still on the old boat cover slips. I have tried to find a photo of the original one but have not been able to do so.

Tight lines……

Side Imaging Interpretation

In this blog I’ll be discussing Side Imaging Sonar and Down Imaging and do you need it. As I discussed in my earlier blog on Sonar versus Down Imaging was it really needed. From the images I’ll post below we can see that some of the structure is visible in the Sonar and the Down Image views but the problem is where they are located in relation to the boat.

As stated in the earlier blog I will be converting recordings done with my Humminbird Onix 10 SI Touch and my Helix 12 Gen 2 Mega Scan SI units. The software I use to view the recording is ReefMaster Viewer and sometime I will use Deepview FV as well as AutoChart Pro. Three of these are purchased software and the other one is a free software version. You can do a Google search to find out more on these products. As for recording with your Humminbird unit I have a blog discussing this as well just follow this link “Recording”.

The problem with Sonar and Down Imaging while fishing or even scanning the lake bottom with your units. Is to determine where the structure is in relation to your boat. Since we are dealing with a 2 dimensional flat screen and scanning a 3 dimensional world. Since the software on the units is only placing pixel dots on the screen there is no way to show the bottom in a real world display. That is unless we are using Side Imaging.

With Sonar and Down Imaging as we drive over the structure is it under the boat as the display shows? It possibly could be and we can tell this with the Sonar view by looking at the colors displayed on the screen palette. Since on a Sonar transducer set to 200 kHz the cone angle is pointing straight down and for an example shining like a flashlight beam. Take a flashlight and turn it on and point it straight down at the floor. The circle of light you see will represent the transducers cone angle. As you can see the angle is in a circular pattern and any object that enters the cone will be visible. Now lower the flashlight down towards the floor and you will see the circle of light gets smaller. This represents the depth of the water your boat is setting in. With a standard 200 kHz transducer the circle will be 1/3 of the depth of the water, for example in nine feet of water you will only be scanning a three foot circle of the bottom. Now move out into 30 feet of water and now you will be looking at a ten foot circle of the bottom.

With all that being said if your boat is in 9 feet of water and you drive your boat over say a stump, and it shows up on the display screen then that stump is directly under the boat. That is under the transducer where ever it is located.

Now let’s say we dropped a waypoint on that stump and wanted to fish it. As we turn the boat around and go back to the waypoint where is the stump in relation to the boat. Again on the display as we get closer to it it will show up on the display but now is it under the boat or in front, rear or right or left of the boat?

The only true way to know for sure is either with the Side Image or the Humminbird 360* transducer. With the Side Image transducer the problem is we now have to drive past the stump to see it displayed on the unit. But now we will know if the stump is on the right side or the left side of the boat. With the Humminbird 360* transducer we can see the stump without having to even move the boat. If the stump is at a three o’clock position we just cast to the stump at a 90* angle to find the stump.

I hope this explains a little the advantage of the Side Image transducer. Take a look at the images below to see what I am trying to explain. I’ll do a blog on the Humminbird 360* transducer after I get on the water and do some screen shots with it.

Click on the Thumbnails for an Enlarged view of the images.

In this image we can see a stump displayed on the Sonar but only know it is located slightly to the right of the boat by looking at the Side Image view. In this view we see the top is directly under the boat and slightly behind the boat.

In this image there is a creek channel that the boat just passed over but but it did not show up on the Down Image view.

Now let’s look at this gravel point that is off the the right side of the boat. Without the Side Image view we would not even know it was there.Can you see the gravel bar on both sides of the boat in the Down Image view.
See the tree top slightly to the left side but still under the boat?Stump field to the right and a stake-bed to the left not visible on the Down Image view.


Stump field to the right and a stake-bed to the left not visible on the Down Image view.

Sonar Interpretation – Sonar and Down Imaging

I get asked sometimes if Down Image is really worth the extra expense over the regular Sonar  units. I definitely have to say yes but only if you do not know what your looking at with the Sonar unit. I’ve used sonar units since the old flashers and paper graphs from back in the mid to late seventies. One thing for sure is that you want to get one with a GPS so you can return to the structure that you will find with them.

My units are Humminbird Onix 10 SI Touch and Helix 10 DI and a Helix 12 SI. All of these unit have GPS and Sonar built into them. I’ve also used a Garmin unit and Lowrance units with good results.

One thing I must say is that of all the Humminbird units that I have owned, everyone of them has had software issues and several have had to be returned to Humminbird for repairs! I don’t know why they can not get their software right before they release their products. Anytime that they have to release five to ten software updates that tells me they have issue with their software!

All of the images you will see in this article will be from recordings that I have recorded with either my Humminbird Onix or my Helix 12 units and then viewed in ReefMaster Viewer software.

I use the Sonar with the 83/200 kHz transducer settings and my chart speed is normally around 5 or 6 with my boat speed at about 3.5 to 4 mph when I’m doing the recordings.

Look at the images below and you will be able after a lot of time on the water looking at different structures to learn what you are really looking at. In my next blog I’ll show you the Side Images and the Down Images views.

Hope this helps you to learn your units a little better and catch a few more fish.

Click on the image thumbnails for a larger view of the images.