Anglers can change chart speed to faster, slower or factory setting.
Changing Chart Speed for Better Sonar Imaging
by Brad Wiegmann
Faster is not always better when it comes to chart speed.
Fish finders collect data and display it on a screen, with the exception of live-imaging sonar. The imaging scrolls from right to left. Everything you are seeing is the history of what was in the cone under or on the side of the boat, depending on the sonar view.
Chart speed can be adjusted to improve the image you are seeing on your fish finder. It’s important to realize that adjusting chart speed doesn’t change the short bursts of electrical energy known as pings. The image you are seeing on the factory setting are good for most anglers, however, by tweaking the chart speed, you can have perfect imaging.
A general rule of thumb for anglers setting chart speed is to match the speed of the boat to the number setting. For example, if the boat is going 3 mph, the chart speed should be set to 3. Going just one number lower than the boat’s speed typically results in the highest resolution of imaging, and going one or two numbers higher will stretch out the fish echoes or may separate them.
Traditional sonar, side imaging and down imaging with chart speeds too fast will result in imaging with elongated returns and loss of resolution. A good example of this is fish arches in traditional sonar that are longer in length and skinny, or, by going too fast, two separate schools of gamefish become one school.
Another example is submerged tree limbs going too fast will not have a sharp image of the branch or gamefish suspended in or around the branches.
A chart speed too slow will shrink the data, overlaying echoes on top of each other, which results in a blurred imaging in side imaging or down imaging, making cover, structure, baitfish or gamefish unidentifiable. Traditional sonar imaging will continue to scroll, but the image of a gamefish, baitfish, structure or cover will be behind the transducer’s cone.
Most touch-screen fish finders allow an angler to scroll back to see recent prior imaging or to mark a waypoint. When exiting the scrolling history or waypoint tool panel, the fish finder will return scrolling at the prior chart speed.
One mode that is not affected by chart speed is mapping or charting mode on some fish finders. The mapping/charting moves according to boat speed.
