Fish finder woes

[Trotter]

I've been getting a lot of false positives with fish finders. In some instances I can see down into the water and clearly see I'm not sitting on top of a school of fish. The one I'm using now is the Garmin Fishfinder 140 and the one previous was the Humminbird 120 (complete crap FYI).

I'm a little perplexed because I know a lot of times these fish finders claim that there's fish below when there isn't. Other strange behaviors include fish that apparently live underground. I want to attribute the falses positives to underwater debris, but sadly I know in a lot of instances that simply isn't the case. The depth I fish is between 10 and 30 feet. The Garmin is supposed to be specialized with shallow water detection.

What gives?

 

[bitterboater]

Re: Fish finder woes

There is likely some electrical interference somewhere. Possibly a poor transducer cable. I have had the same thing from my Lowrance unit, but mine is over 10 yrs old, and hasn't been used or many of those years. I just use mine to give the bottom contours, and weed edges, and I take it from there.

 

[Trotter]

Re: Fish finder woes

I'm not sure about the inteferance. I have mine setup in a Zodiac and the only things I have on/in it is the outboard, battery, trolling motor, and then the fish finder. I turned off the "Fish ID" option and just started looking for arcs. But the same thing happens oddly where it would show a series of arcs, beep, I look down into the water and nothing. The last time I was in 1' of water and the Garmin was showing all of these crazy fish arcs. If anything it should just be flat ground.

 

[Silvertip]

Re: Fish finder woes

If you see an arch (or a fish symbol) you need to think about two things. 1) an arch is plotted as a fish moves into and out of the cone. By the time the locator has drawn the image the fish is no longer straight under the boat which is why you can't see it in otherwise clear water. 2) Setting the "Sensitivity" too high increases the chances for false positives. If you think about the width of a 20 degree cone, you should realize that the deeper the water, the larger the covered area is so the fish will hardly ever be directly under the boat. Try this, just go fishing at a spot that you know has fish -- you know that when you catch a few. Have the sensitivity set at about 50% and work up in 5% increments from there AFTER you start catching fish. You will then learn what sensitivity works best IN THAT particular water. You use different sensitivity settings in different waters.

 

[foodfisher]

Re: Fish finder woes

Moving? Water turbulence at the transducer will give off false readings.

 

[dingbat]

Re: Fish finder woes

There is no such thing as false positive on a sonar device.

A fish finder is nothing more than a sonar device. Its sole purpose is to detect objects that are denser than the surroundings and display a sonar image of the object. The darker the image, the denser the object that reflected the beam .

The returns may have come from fish, leaves, plastic bags, temperature inversions or any number of anomalies. It's up to the operator to interrupt the returns to determine if the object is a fish or not. An experienced operator can tell what species of fish they are looking at.

 

[tarpleyg]

Re: Fish finder woes

There is no such thing as false positive on a sonar device.

A fish finder is nothing more than a sonar device. Its sole purpose is to detect objects that are denser than the surroundings and display a sonar image of the object. The darker the image, the denser the object that reflected the beam .

The returns may have come from fish, leaves, plastic bags, temperature inversions or any number of anomalies. It's up to the operator to interrupt the returns to determine if the object is a fish or not. An experienced operator can tell what species of fish they are looking at.

I think the implied "operator" in this case is the software on the FF unit. Sometimes the "operator" isn't right. I see these symptoms all the time. I have all but given up trying to use it to find fish. I use mine for determining depth and structure and should just turn off the fish ID.

Greg

 

[dingbat]

Re: Fish finder woes

I think the implied "operator" in this case is the software on the FF unit. Sometimes the "operator" isn't right. I see these symptoms all the time. I have all but given up trying to use it to find fish. I use mine for determining depth and structure and should just turn off the fish ID.

Greg

There is nothing wrong wth the software. The implied "operator" is the person operating the unit.

Fish ID is a feature used on most "consumer" units to help educate inexperienced consumers.

Without the ability to understand what you?re seeing on the screen, you might as well buy a simple depth gauge and keep guessing. Even the most expensive commercial sounder are not going to help you until you learn to use it.

 

[fishrdan]

Re: Fish finder woes

Where I fish a sonar will give off a lot of false positives because of air bubbles in the water. I always wondered why I would mark a lot of fish in certain areas and catch nothing,,, until I was out there once when it was dead quite and heard the water snap-crackle-popping. It was air bubbles from an under ground spring or decaying vegetation, surfacing. You could see them if you looked closely.

 

[sschefer]

Re: Fish finder woes

Silvertip gave us an almost text book explanation. All the manufacturer reps would tell you the same thing. The trick is to learn to read the arches. Go to Garmin's website or better yet, go to Lowrances website and run through one of their tutorials. They will show you the difference between a fish arch and a debri or scatter arch. Once you learn to read the arches your luck will improve. Until you do that, all fish finders will seem like garbage to you.

 

[Faztbullet]

Re: Fish finder woes

Order the dvd below and forget eveything you have been told about a sonar/gps unit. My buddy Wilson teaches the pro on how to use a sonar unit. Believe it or not the only part you need to look at is the first 1/4 of display off the side of unit as every thing else shown has already happened. This is how the pro drop shot a worm on top of a fish!!!!!
http://www.itainttv.com/sonar.php

 

[dingbat]

Re: Fish finder woes

Silvertip gave us an almost text book explanation. All the manufacturer reps would tell you the same thing. The trick is to learn to read the arches. Go to Garmin's website or better yet, go to Lowrances website and run through one of their tutorials.

The Lowrance tutorial is misleading. The arches you see on most recreational sounders is a software ?feature?. How else do you explain the 10 foot tall arch on this screen shot?

I particularly like the piles of "brush" fish in the background.

Fish on a Furuno Sounder

Look mom, no arches

 

[sschefer]

Re: Fish finder woes

FB I wasn't going to go there because I didn't think he had it on his finder. I learned how to do that with my 525cdf and never went back. I just bought a Lowrance HDS-8 with the LSS1 for my new boat. I still won't be looking at arches. Structure scan is pretty incredible. I think it beats the Furuno in the same price range.

 

[dingbat]

Re: Fish finder woes

I just bought a Lowrance HDS-8 with the LSS1 for my new boat. I still won't be looking at arches. Structure scan is pretty incredible. I think it beats the Furuno in the same price range.

Sold a Lowrance to get the FCV585. The HDs is nice but not in the same league as the FCV585.

Looked at adding a HDS for structure scan but was steered away by a local installer. Went out with a friend of a friend with Structure scan and was unimpressed. It was speed limited and without heave compensation, it was pretty useless in anything but flat calm seas. Can't see spending that kind of money for something I can only use occasionaly.

 

[ward cleaver]

Re: Fish finder woes

dingbat, would you explain what you mean by an inexperienced operator misinterpreting the display? when it shows a fish icon, it is suppose to be a fish. nothing to interpret there as far as i can tell.