Joe Bazin, Topeka, Kansas: "In re-reading your April 2006 'Factoring Ping Speed' article I came up with a question: As I understand it, some pros think constantly pinging will drive walleyes away from the area. If this were true, would it make sense to reduce 'ping speed' to minimum on the unit mounted on the trolling motor, especially when vertically jigging for crappie or walleye? In 'hovering mode', like over a brushpile, the minimum ping speed will still give an accurate picture, right? Thanks."
The idea of sonar scaring fish has been around a long time. The actual frequency of sonar is above what most fish can detect. The number of vibrations or cycles per second that occur is called frequency and is measured as a Hertz -- a Hertz being one vibration per second. A 200 kHz transducer would vibrate at 200,000 cycles per second or at 200,000 Hertz. Most fish only detect frequencies less than 1 kHz or 1000 Hertz. Human hearing is typically in the range from 10 Hz to 20 kHz. However, the clicking sound, caused by an energy burst in the transducer, is audible to the human ear but not to a fish. This clicking sound may be what some people refer to as "fish scaring noise." I haven't come across any study that shows that the transducer clicking or pinging scares fish, but maybe there is some research that suggests otherwise.
In a "hovering mode" a slower ping rate is okay. However, if you want fish detection at higher boat speeds, a higher ping speed is necessary.
I'd Like To Mount A Second Unit
Glenn Schramm, Jackson, Michigan: "I'd like to mount a second Lowrance unit in my 17-foot Lund Mr. Pike. At the helm I have a LMS339c with the transducer mounted on the transom. I'd like to mount my old unit (M68C) in the front. What suggestions do you have? I have a Minn Kota 70 24-volt powerdrive trolling motor mounted on the front."
The setup that you're proposing should work quite well, however, there will be some interference issues between the two units. In shallow water, to about 20 feet, interference should be minimal. In deeper water, you'll see more interference on the screen, and you may also see an occasional false reading with depth if both units are on at the same time. There are several things you can do to minimize the problem. One of them is to set different ping speeds on each locator when you're fishing. Ping speed is one of your menu functions. For instance you may set the bow mount unit at 75% and the transom unit at 50%. These numbers are just examples, you will have to experiment to see what combination best reduces interference. At trolling speeds it's not necessary to have high ping speeds.
The other option you have is the dual-frequency on the LMS-339. When you get into deeper water you could switch the LMS-339 to 50 kHz. This should also reduce interference when both sonar units are running at the same time. Keep in mind that the lower 50 kHz frequency isn't as effective in shallow water as the higher 200 kHz frequency. You may not get much of an image inside of 15 feet and you'll also have poorer target separation with the lower frequency. For deep-water fishing, the lower frequency is good, and it also makes it easier to track downrigger weights.
Deep-Cycle Battery That Won't Freeze?
Ron Dye, Forsyth, Montana: "I saw on TV that there's a new deep-cycle battery that doesn't have any liquid and thus will not freeze. Do you know who manufactures it? Thank you."
I checked with the In-Fisherman TV show, and they don't recall anything recently about a new battery. There's a relatively new battery out there called the Optima, which can be mounted upside down, or any other way. In general, deep cycle batteries with liquid should not freeze in the winter. Most boats, mine included, are stored outside or in unheated buildings in Minnesota. I haven't had any problems with the battery after storage.
Here are two things will help your battery get through a cold winter in storage: First make sure the battery is fully charged before it's stored and second, disconnect the battery from the wiring harness in the boat to eliminate any chance of a slow discharge.
An excellent fisherman in his own right, Bill Diedrich's real expertise is with the understanding and use of fishing electronics. His strength is the ability to communicate the operations and applications of Sonar (fish locators) and GPS (Global Positioning System) to his audience. He combines his multi-spieces fishing experiences with his math and physics background to help both the novice and tournament angler to better understand outdoor applications of electronics.
Bill is a frequent speaker at Boating, Camping, and Fishing Shows throughout the Midwest.
