Si Pictures

[Moveon]

Note the stream or roadbed that crosses the SI picture from left to right. It's the darker area that's visible from the brighter parts parts of the picture.

Areas that reflect the sound waves better will have a brighter return on the screen. Areas that absorb the sound waves will appear darker in color.

Objects that stick up off the bottom will cast shadowns on the side opposite of where the sound waves are coming from. Just like a flash light beam on a tree will cast a shallow on the other side of the tree.

Fish suspended in the water column will also cast shadows. The distance from the fish to the shadow can help you tell how far off the bottom the fish is suspended. The higher in the water column the farther the shadow will be from the fish. Fish will appear as tiny white dots in the water column and their shadows will show up on the brighter parts of the bottom some distance to the side of the center line. The center line in the pictures represents the path of the boat/sonar/transducer. The top is the recent sonar pings or images and the bottom is the history. The farther down the page the further back in history the recording was made on the screen. Old sonar pictures will drop off the bottom of the screen as the new data appears at the top of the screen. Everything to the right of the center line will be what was shown on the right side of the boat's path. And vise versa for the left side. The humminbird can show one sides data or the others side only or both sides like in this picture.

[Bandit1]

I'm confused. How come in the bottom left of the picture it says 5.4 ft. but in the upper portion it says 7.1 ft.? Which one of these numbers is the actual depth? What is the other number for?

Thank you,

Jason

[Moveon]

OK that's an easy question to answer. The depth is 7.1 ft deep from the transdcuer to the lake bottom at that point in time. Remember that the top of the screen is the most recent sonar reading results. So at that time it's 7.1 ft deep.

Now for the tricky part. With the Humminbird units you can travel back in time so to speak. At any time there is a something on the screen I (the user or operator) can stop the display from scrolling and put a mark on the screen using the four way button. When I push the four way button a "CURSOR" will appear on the screen and the screen will stop scrolling. Then I can use the up/down or left/right arrows on the 4 way button to move the Cursor over anything on the screen. At that point I pushed the "MARK" button and took a Snap shot of the screen and the humminbird stored a way point position for the point where the cursor was located on the screen. But it calculates where that would be in relation to where the boat was at that time. So the Boat is at the top of the screen and the data on the top will show how far the boat is from the cursors location.

In this case the cursor is over to the right side of the boat's line of travel and so many feet over to the rightt. Remember that the distance shown from the center and the left or right side of the screen can be changed by the user using the menus on the Hummibird Unit. I can change the distance shown on the screen from 1 ft to 240 ft or something like that. If I decrease the distance shown I get better Resolution on the screen. And things may look bigger. But if I expand the distance, Increase distance, shown on the screen, I can see more of the lake bottom. But when I increase the disance shown things will look smaller on the screen when I do that. There are only so many pixels on the screen to use to show things on the screen. Pixels are constant. But the size of the pixels can be changed I guess. Not sure exactly how it's done but when you change the scale the things on the screen will changes size.

Note: Depth readings are taken from the Transducers 200 KHz frequenty sound waves that shoot straight down from the bottom of the transducer. There are several different crystals inside these Humminbird SI transdcuers and some shoot sound waves in very thin slices out the right and left to do the SI portion of the screen. In this case that's the picture I showed above. But the depth and other screens (SWitch fire Screen views) use either the 200 KHz frequency crystals or the 84 KHz Frequency Crystals. The latter has a wider cone than the former. So it will show more fish symbol and arches as it sees more in the water column.



So the Cursor is 4 ft from the center line of the boat's travel path. Or is could be that at the point where the cursor is located it's 4 ft deep. I just noticed that on the lower left side it shows the depth to be 5 ft something. so that's got to be the depth of the boats position when I took the snap shot and marked this waypoint.

The unit can calculate how far the cursor is from the boat's different positions as it uses trigonometry (surveyors math) to figure the angles and distances from point a to any other point. We have a right triangle where the sonar beams (sound waves) hit the bottom right under the transducer. These sonar waves are sent out every few milliseconds. So there can be 100 pings a second at times. And sound travels faster in water than in air. So it travels very fast to the bottom and returns in just a few milliseconds. This is called the Pulse Lenght. Since the left and right parts of the screen are measured from the center of the screen. We can form a right triangle at the bottom of the lake right under the boat at any time. This can be Side A. Side B can be calculated from the point where side A hit the lake bottom to where the cursor is positioned on the screen. This all has to assume that the bottom is flat though. A sloping bottom will cause errors in the calculations so the numbers on side B's length may not be accurate. Any using Trig you can calculate the Hypotenous on the right triangle using the Pathagrium Theroum. So now we know the angle between side A and B as 90 deg. The lenght of side A (depth below the point at any point on the center line) and the lenght of side B. From where line A touches the bottom and where the cursor is placed on the screen.

Remember that the longitude and latitude at the cursor's positon is figured out and recorded too.

I'm confused. How come in the bottom left of the picture it says 5.4 ft. but in the upper portion it says 7.1 ft.? Which one of these numbers is the actual depth? What is the other number for?

Thank you,

Jason

[Moveon]

Let me try to simplify my answer.

The top row of numbers are the distance and depth at the cursor location. ie the distance of the cursor from the boat's location at the time the snap shot picture was taken. The cross with the circle around it is the cursor. The top middle of the SI picture is the boat's current location.

The depth reading on the Bottom Left column numbers are the depth at the boat's current location when the snap shot was taken.

Hope this clears this up for you. It can be confusing until it's explained how these things work. It's not rocket science but it's close.

I'm still learning and need to read the manual again just to keep it all straight in my head.

I'm confused. How come in the bottom left of the picture it says 5.4 ft. but in the upper portion it says 7.1 ft.? Which one of these numbers is the actual depth? What is the other number for?

Thank you,

Jason

[Bandit1]

I'm really glad you simplified your answer. I was more confused after I read the first post with the answer than I was before. The first post made me wonder if I really wanted one of these units or not. LOL.

Thank you for responding. (especially the second response) LOL

Jason

[Moveon]

Your welcome. I know I can get pretty detailed and deep. That's why I posted the simplified version.

Bottom line is that these things really do show you what the bottom of the lake looks like. They are not that difficult to use once you work with them a lot.

And there are many web sites and forums that have people that can help everyone learn to use these sonar units. There are a lot of pictures posted that show things like fish or sunken boats in the lake.

I make a recording the other day and today spent some time looking at it on my computer. I saw some fish suspended in the water column. I could see the bright white dots which are the fish and then I also saw their shadows some distance away from the actual fish school. It was as if my transducer was a flash light beam and the fish cast a shadow on the bottom of the lake. The farther the shadows are away from the object the higher in the water column the fish are. Fish right next to the lake bottom will have a shadow right next to the fish. But fish that are suspend up off the bottom have their shadow some distance away from them. And large schools of fish that are bunched tightly together casts a lot of shadows on the lake bottom.

Plus there are many videos on U Tube that show how to use the Humminbird and the Lowrance Units.

I'm really glad you simplified your answer. I was more confused after I read the first post with the answer than I was before. The first post made me wonder if I really wanted one of these units or not. LOL.

Thank you for responding. (especially the second response) LOL

Jason