Scroll Speed - Sonar Imaging
Written by Adam Broughton.
The scroll speed setting on most sonar units controls the speed of BOTH the 2D sonar and sonar imaging screens. However, each has totally different use on the water. So depending on which you're using (2D or imaging), you'll need to set your scroll speed accordingly.
Here is what you need to know about setting scroll speed on the sonar imaging screens:
Imagine if you took your control head and pointed the display toward the sky. You want to set your scroll speed to match the rate at which the boat is passing though the environment. So imagine the little boat on the display is your boat, and the "stuff" on the screen is passing by at the same rate that you are actually, physically passing through it. These illustrations should help...
Case 1: You got it right.
The boat speed and scroll speed are matched nicely.
Imagine a square house foundation on the bottom of the lake. In theory, when your boat speed and scroll speed are set properly, you will get a perfect square shown on your display.
Case 2: Boat speed too slow or scroll speed too fast.
In this case the image is stretched vertically.
Your boat is too slow, the sonar pings the foundation too long, and you paint too much of it on the screen.
Similarly, if your scroll speed is too fast, you'll get the same result: the image is stretched vertically. The image is literally rolling down the screen faster than the boat is moving, giving you a distorted image.
Case 3: Boat too fast or scroll speed too slow.
In this case, the boat zips past the target and you get an image that is squished vertically.
Similarly, if your scroll speed is creeping along slowly, you aren't putting enough information on the screen to keep up with the boat. Again the image is distorted, but squished instead of stretched.
Obviously, you won't have perfectly square house foundations all over the lake to help set your scroll speed --it is a "feel" or "judgment call" that you need to develop on the water. Look at your display. If images are smeared vertically, you're either going too slow or your scroll speed is too fast. Similarly, if you are getting a lot of wide, short images then you're either going too fast or your scroll speed is too slow. Adjust one or the other (or both) until you get a good picture.
Also, keep the imaging quality in perspective. Ultimately, you're only looking for "things" to which fish relate. Don't get wrapped around the axle about not being able to see the texture in the bark of that tree down there. Just find the tree and fish it!