Fishing with lights!! Help

[boat49]

I need some help!! After about a year, I finally made it to the lake to fish after dark WITH my light!! I set up at one of my usual spots, the fishfinder, that my buddy swears is just a video game!!, was showing fish from top to bottom. After the sun went down I got out the light to give it a try. I set it behind the boat next to the motor so it wouldnt float around alot. After about 30 minutes or so I happened to look at the fishfinder and remarked,"Well, we have managed to scare every fish away!!". There were no fish showing on the finder. As we loaded to leave I unhooked the light, put it up and as I was getting ready to start the boat I glanced at the fishfinder and low and behold.....fish top to bottom!! I am wondering why this would be. I'm sure the fish didnt really leave. Could it be the heat from the light made it impossible for the transducer to detect the fish?? Someone, please educate me on these things.

[skiptomylu]

First (IMHO) you would be better if the light was turned on before dark. If you turn it on after dark it will move the fish away, but they will return once they get use to it and soon you will probably start to see bait fish show up and soon many will be around.

The activity should really start to pick up sometime around 10:00-12:00 with more and more activity.

You have to give it some time.

[Moose1am]

Heat from the light will not have very much effect on the sound waves. Colder water is denser than warmer water but not that much. I doubt if the heat from the lights will have heated the water that much to effect the sound waves.

Depth finders work by sending a sound signal (Wave) of different frequencies out of the transducer (Crystal) and then measuring or timing the return echos. The sound is sent downwards and bounces off the bottom and back up. The same transducer that sends the waves out will also receive the waves and convert those sound waves into a small current. The time to reach the bottom and to return back up to the transducer (receiver) is calculated by the depth finder (display unit computer chips) and then displayed as the depth of the bottom. Hard bottoms such as rocks will reflect a lot more of the sound waves back up to the transducer. Soft mucky bottoms will ABSORB the sound waves and not reflect them back up as well.

The deeper the water the longer it takes for the sound waves to travel down and to bounce back up.

Anything suspended in the water that is in the path of the sound waves will also reflect the sound waves back up. So fish will show up on the display and the display will show the depth of the fish.

But there is an area directly under the transducer that shows the bottom. If you were to drop a plumb weight directly under the transducer with the boat sitting in one place and then mark that spot on the bottom you would have the center point of the cone of influence of the sound waves. Take a stake and drive it into that point on the bottom and then take a string and tie it to the stake. Now let out enough string to represent about 1/3 of the depth of this spot in the lake. Now draw a circle around the stake using the proper lenght of string to form the circle. If you are in 30 ft of water the circles diameter will be 10ft. In 100ft of water the circle will be approx 33ft in diameter. The area of the bottom that shows up on the depth finder increase with depth and with the signal strenght. Like wise in 10ft of water you will only see about a 3ft diameter circle of the bottom. The cone will be about 20 deg. Fish swimming at the surface would have to swim right under the transducer before you would see them.

Bottom line is that you are only looking at a very small area of the bottom of the lake

Another way to describe this is to take a flash light and shine it down into crystal clear water. The part of the lake that the flash light illuminates would represent the cone of influence. Fish outside the beam of light would not be seen. This is simlar to the sound waves being focus toward the bottom simular to the way the flash light focues the light beam. The crystal inside the transducer is made to focus the sound wave into a beam of sound and directed toward the bottom. This is why the setup of the transducer is key to getting a good signal reading.

Any fish outside the cone of influence will not show up on the depth finders screen. A fish could be three feet away from this area and not show up. But if the fish were to swim into the cone of sound then he would show up. Or if the boat were to move over to the fish then the fish would show up as long as the fish remained inside the cone of influence of the sound waves.

Also the fish must refect the sound waves back up. Smaller fish have less mass and will refect less sound waves back up to the transducer.

Only in the deep ocean will the water density provide a thermocline that can stop the sound waves from penetrating below the thermocline. This is how modern nuclear attack submarines hide from the sonar of surface ships. But I am talking about the ocean here and very deep water. Remember that sonar waves have to be very strong to reach into very deep water. Some of the subs and surface ships have such powerful sonar units that it can damage the ears of porposies and whales.

But our fishing sonars are not that powerful and will only reach bottom in shallow fresh water lakes.

This should help you understand why you see the fish sometimes and not at other times. In a matter of seconds the fish can swim out of the area and back into the area. And it sounds like you are talking about a school of fish. They may have moved only a few feet and dissappeared off the sonar screen.

I need some help!! After about a year, I finally made it to the lake to fish after dark WITH my light!! I set up at one of my usual spots, the fishfinder, that my buddy swears is just a video game!!, was showing fish from top to bottom. After the sun went down I got out the light to give it a try. I set it behind the boat next to the motor so it wouldnt float around alot. After about 30 minutes or so I happened to look at the fishfinder and remarked,"Well, we have managed to scare every fish away!!". There were no fish showing on the finder. As we loaded to leave I unhooked the light, put it up and as I was getting ready to start the boat I glanced at the fishfinder and low and behold.....fish top to bottom!! I am wondering why this would be. I'm sure the fish didnt really leave. Could it be the heat from the light made it impossible for the transducer to detect the fish?? Someone, please educate me on these things.

[Meat on the Table]

Moose, I studied all this in college, and passed with an A, but you just explained this better than any professor I ever had. If it is not to personal, what do you do for a living, my guess is a physicist, or college professor, or you stayed in a Holiday INN express last night. LOL

[Moose1am]

I am an Environmental Scientist who still enjoys fishing. I went into the Enviromental field to try to help clean up the waters where I fish.

Today one of my goals has been accomplished. ALCOA announced today that they are spending 400 million dollars to install new air pollution controls on their plant here in Newburgh, IN. This will help clean the air of 98% of the sulfur dioxide emissions and 98 % of the Hydrochloric Acid emissions as well. And the new pollution control equipment will reduce their mercury emissions by 60% which is great news. Not only that but it will put hundreds of construction guys to work during the construction phase. The unit is scheduled to be completed by 2010. Work is to start Immediately. They broke ground today.

This is the best news that I have heard in the last 30 years. Finally we will be able to reduce the amount of smog in this area and beyound.

And ALCOA will be hiring 25 new employees to run the new equipment.

I must say that I really am happy to hear this new and ALCOA should be congratulated in leading the way to cleaner air for us all.

The emission from the power plants in this area travel many miles from here.

Also the Cinergy plant in Gibson County IN will have thier power plant fully controled with scrubbers in a few more years. This power plant is one of the largest coal fired power plants in the WORLD. They use 300 coal cars of coal every day. I think that each coal car can carry 100 tons of bitumous coal. That is a lot of coal being burned in Gibson County. With the addition of the new scrubbers the emissions of Sulfur Dioxide will be reduce by 95% or better.

We can all begin to breath easier in the future thanks to these guys making the commitment to clean up their air emissions.

I work in the Environmental field. I specialized in Air Pollution and Water Pollution control.

[boat49]

Thanks for all the info!!! That was alot more than I expected. I had always thought heat was involved, but if I read it right it's sound waves and timing ? Thanks again and happy fishing.

[Meat on the Table]

Moose, In the late seventies, in between college stints, I worked construction on the coal scrubber addition at Paradise Steam Plant in Drakesboro, Ky.. We were about a year from completion on a five year job, and the government shut the job down in order to attempt to balance the budget. Well, a balanced budget is very much needed, and a noble cause, but not at the expense of the water we drink and the air we breathe. Too many times it seems our government sacrifices the future of our young ones for the MONEY!!!! You have a noble calling and I am proud there are watchdogs like you in our country!!