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Old 06-14-2003, 10:04 AM
Boatnut Boatnut is offline
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Join Date: Oct 1999
Location: Delaware, Ohio, USA.
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Default viewing thermocline on sonar

I mostly fish a deep (270'), clear lake in south central Kentucky. I know the lake develops a thermocline in the warmer months and that a lot of fish hang out just above it. What's the best way to get the thermocline to show up on my sonar (X-15MT)?? I've only had a few trips with this unit and it's been in "auto" mode most of the time, but the thermocline doesn't show up. Do i need to run in manual and adjust the sensitivity?
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Old 06-14-2003, 10:11 AM
Boatnut Boatnut is offline
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Join Date: Oct 1999
Location: Delaware, Ohio, USA.
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Default RE: viewing thermocline on sonar

I may have found answer to my own question at http://www.fishingenet.com/Features/vgthermo.html
any other comments welcome though!
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Old 06-14-2003, 01:19 PM
retire55 retire55 is offline
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Location: Ottawa,Ontario, Canada
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Default RE: viewing thermocline on sonar


Thanks for the reference to the article about thermoclines. I have a Lowrance X-85 sonar unit and I have no difficulty seeing thermoclines in automatic mode. I'm sure you just have to optimize your sensitivity settings in order for you to see thermoclines.

My X-85 shows the thermocline demarcation more clearly than figure 2 in the article for a Lowrance X-75. In a couple of weeks, we leave on our annual walleye fishing trip. During the day, we usually fish for lake trout. The lake is deep and last Jul I was seeing the thermocline very clearly at at about 90 feet in about 120 feet of water.

REW, a regular poster to walleyecentral.com has previously provided steps to take to optimize your sonar unit on this board. I have copied his steps here because I can not find the reference.

From REW

About three different things to do to set up depthfinder for the best results.

After trying these things in manual mode - and becoming familiar with the results, you can modify these suggestions to go into a modified auto mode for final on the water use, with excellent results.

1. First find the general water depth over which you are travling.

2. Remember, that any water that is less than about 15 feet will almost never show fish on the graph. The boat and spooking factor is simply too great for fish to stay in the shadow of the boat at depths much shallower than about 15 feet. Once in a while, if you are traveling at a pretty good rate of speed, you might see a fish more shallow, simply because they can't quickly move out of the boats path.

3. Lets say that you are in 15 feet of water.

4. Now, take the depth finder and first insure that all filters are turned off. Many depth finders have surface filters, have rfi filters, have clarifier filters etc. Turn them all off. All of these filters, use a computer interpretation of what should be filtered or what should not be filtered. Use your mind to do the filtering - at least initilally, and become what really needs to be filtered from your display.

5. Now, turn the settings to manual, and the scroll rate to the highest speed.

6. Now, turn the depth setting to a range, which will cover a bit more than double the bottom depth - in other words for a 15 foot bottom depth, at least a 40 or 50 foot range.

7. Now, with the boat sitting still, turn the gain of the depth finder up, until you first see the true bottom at 15 feet, and then see a 2nd bottom reflection at 30 feet. Take note of this gain setting. This is the gain setting that you will want to run the depth finder for this bottom type and depth. At this setting, you will be getting maximum information from your depth finder, with respect to the surface and the initial bottom reading of 15 feet.

8. Now, without changing the gain of the depth finder tun the range to a lower setting like 25 or 30 feet for the given 15 foot lake bottom. Obvioulsy the 2nd bottom will disappear, because it is off scale, but you will be receiving maximum information, with respect to the surface and the 15 foot depth.

9. Again, with the boat standing still, preferably on a calm day, and the motor and all other electronics turned off - take a 1/16th or 1/32 oz jig or split shot, and lower it slowly along side the transducer and lower it slowly to the bottom.

10. The test for your depth finder is your ability to follow this very small piece of lead, all the way from about 2 feet under the depth finder, all the way to the bottom of the lake. It should show up as a line, with a falling angle to the line, which will correspond to the rate at which you drop the jig. At any point, in the jigs descent, if you freeze the drop - the depth finder should simply display a solid black horizontal line moving quickly across the screen.

11. Now, as your jig nears the bottom of the lake, you might lose track of the jig, or it might blur into the bottom reading. If you are on a relatively hard bottom, this bluring, it the distance, above the bottom, where you will be able to reliably mark fish. You might find this distance to be as much as 2 feet or as little as two or three inches. It is quite possible, that if you look very closely, and if you are on a farily hard bottom, you might see a slight thickning of the bottom reading when your jig is only about 2 inches above the bottom. If so, this is the true indication - of where fish can be sensed.

12. Following these tests, you know the best that the depth finder can deliver. Now, you need to test a real world.

13. Turn on all of the other posslible electronics in the boat. Turn on the vhf radio, turn on the trolling motor, turn on the am radio, turn on the fm radio, turn on the gps, turn on the kicker, turn on the big motor. At each of these points, use the lift drop method on the jig, to insure that you can still sense the clear changes in the jigs positon. As long as you can still sense the jigs changes, you will be fine.

14. It is quite likely however, that you might find that turning on one of the other electrical items in the boat - could seriously affect the clear display on your depth finder. Armed with the knowledge of what causes the interference, you can began testing filters.

16. Now, with the knowledge, of how a jig should look, and what effects if any - the other items cause on the display, you can now turn on and off the various filters on the depth finder, to see what, if any effect these have on the display. Now integrate this information into either using thse filters, set in the correct method, to resolve problemes caused by some of the other interfering items in the boat.

17. Finally, when you have learned all of these things and their interaction, you can then duplicate the great action that your unit is capable of displaying, in the auto mode. Turn the unit to auto mode, and do the necessary tweaks in the auto mode, as explained in your users manual to duplicate the display that you found to work so well in the manual diaplay.

Good luck and enjoy a great product.

Take care
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