Sonar and Rocks - Hard Bottom on a Fish Finder On June 17, 2013
Fish like rocks and one of my favorite fish to catch likes boulders (Smallmouth Bass). After we figure out the fish are relating to boulders, we need to find more spots with rocks and boulders so we have more choices. Maps help because if the best rocks are at 15 feet, we can find 15 foot spots on the maps. You must have high definition map cards (Navionics, LakeMaster and Lowrance Insight Pro/HD) to have accurate 15 foot depth contours. After you find some places to check out with the maps you need to find the rocks with the sonar. Rocks show up as hard bottom with bumps. The bump size depends on the size of the rocks. I use the side scan to find boulders off to the side, regular sonar (2D) and DownScan to find rocks and determine their size. The DownScan shows big rocks as spikes. Fish show up better with DownScan because the cone size is narrower and gives better target separation. This example shows large boulders and a transition to the side of the boat. Lowrance allows me to mark a waypoint on the boulders so I can drive right to them.
I created a waypoint on the boulders and drove over the boulders to get this screenshot.
This screenshot uses the DownScan to show the boulders as spikes and the fish separated from the bottom better than the traditional sonar. The bumps on the traditional sonar are the small boulders and the fish has red instead of yellow. Yellow is the strongest echo return so the boulders give a stronger echo than the fish. The problem is the traditional sonar does not separate the fish from the boulders as well as the DownScan. Notice the cursor above the fish in both views so that I know it is the same fish. The DownScan chart speed is faster than the traditional sonar so it appears less compressed.
I hope you enjoyed and learned from "Sonar and Rocks - Hard Bottom on a Fish Finder."
Now - Go Fishing, The Clock is Ticking
Doc
