Understanding Your Sonar when Trolling

[Trophy Taker]

We all know the typical view of our transducer is downward in the shape of a cone. So depending on your transducer view (angle in degrees) and the depth your fishing you get a wider view the deeper you go. This problem is more pronounced in the spring when the fish are usually in shallow water, say for example 10-15 feet deep. Your sonar field of view (cone diameter) in shallow water is relatively small and in essence you don’t see all the fish in the general vicinity of your bait. This phenomenon will often times prematurely cause an angler to relocate to another spot in an effort to “see more fish”. When using sonar with a downward looking only transducer often times trolling anglers see fish and mistakenly assume they are trolling through these fish. Unfortunately logical human interpretation of what we are seeing is actually flawed logic because of the transducer cone angle and the sonar display unit interpretation of the transducer data. Just because we can see our downrigger ball running “through” the fish on the display (pic-1) doesn’t mean we are necessarily running our ball/lure within striking distance of those fish.

If you want to calculate your cone diameter you first need to know what your transducer angle is, this can be found either on your manufactures web site or is sometimes published in the user’s manual. (pic-2)

This is the formula:

1/2 cone angle x 3.14 (which is pi) ÷ 180 = t (which is tangent)
t x depth x 2 = cone diameter in feet.

Say for example I have a 20 degree transducer. 1/2 of 20 degrees is 10 degrees

So I enter 10 into my calculator multiply 10 by 3.14 then divide my answer by 180 this gives me the tangent. In this example = .174

Now let’s say we are trolling in 40 feet of water. I now take .174 multiply it by my depth (40 feet) then multiply that answer by 2. This results in a cone diameter at 40 feet of 13.92 feet.

That isn’t a very wide view all things considered.

Have you ever been trolling and found that one downrigger/rod seems to get more hits than the other? You put the same lure/bait set up on both rods, the same set back yet despite your best efforts you just can’t seem to get a consistent number of hits on both rods. Let me offer this explanation as something to consider. Using the example above of trolling in 40 feet of water it’s highly likely if only one rod is striking that you are actually catching the very outside edge of a school of fish (pic-3).

Remedy: Troll back through the same area but on your next pass move more to the right or left by 14 feet and see if this changes that hit ratio.

 

[HiTechKoke]

This is a great post and is making me think about looking into a wider cone option for my pure 200Khz transducer. One thing to be aware of in the past at least for those that have the Lowrance combo 50/200Khz transducers is the cone angle on the 200Khz portion is 40% less, 12 degrees, versus 20 degrees for a pure 200Khz transducer. This would narrow that cone diameter even smaller when using the 200Khz side of a 50/200Khz. I've seen the new 83Khz transducer in action on another boat and it was very clean. in the signal and distinguishing fish.

The open question for it is how effective and deep will the 83Khz be reliable to mark fish as they keep saying it is for shallower scenarios, less than 60 feet, from what I have read. Ideally if you have an 83 / 200 it is a good combo. With such a wide cone I wish Lowrance would come up with a way to distinguish the fish left or right of the cone. Older Humminbird Matrix 3D units do this in that mode but are not really reliable for finding fish in my experience.

Kevin

 

[Propnut69]

TT,thanks for the info on a very confusing subject. I never knew about the formula to figure the width of the cone angle at any given point,til now.thumbsup I copied and printed out the formula,and will now keep a copy in my tackle box. What you say about not seeing fish at a shallow depth ,say the top 15 ft of the water column is so true.I can't count the times that I have been catching fish,without seeing then, when fishing shallow. I know that these fish are coming in behind the boat,out of the transducer cone,because it not wide enough at shallow depths. Like you say moving over 14 ft one way or the other ,may make the difference between fishing and catching.

 

[SilverBullets]

Great post Trophy Taker! I have a Humminbird 777c2 with the QuadraBeam Plus Transducer. It says it's able to provide 90 degrees of coverage by two 35 degree (455kHz) side locating beams and the option of either useing the 60 degree (83kHz) or 20 degree (200kHz) beam down the middle (or the 20 and 60 degree beams can be used simultaneously.) These beams overlap each other to achieve the 90 degree coverage (to the side's.) It works well to help locate fish when their spread out, and to show what side is holding more fish.thumbsup

 

[Bduck]

For the past couple of weeks, I have been working with Trophy Taker on troubleshooting my Lowrance X100C sonar. For some reason I quit picking up fish signals where as it always worked great in the past. My xducer is the 200khz. I also realize that shallower the water column that I won't see that many fish. However, there are the deep creatures down there and I should have been marking some of them. Nothing. TT advised me something went wrong with my xducer and I now have another one installed awaiting for the next trip out. My many thanks to Thomas for all your help. I'm ready to get back to business. Like HT says, this a great post.

 

[Propnut69]

Bduck sorry to hear about your ducer problems,but I can relate. The ducer on my x-135 went south on me a couple weeks ago.I t just quit showing any bottom ,and was showing depths anywhere from 60 ft to 1100 ft.. I ordered a new one from bass pro ,and now I' am back to fishing . My other ducer I sent back to Lowrance,as it was still under warranty,but they told me it would be 3-4 weeks turnaround time. so when I get it back I will now have a spare.

 

[Bduck]

I'm wandering if there is a power spike causing these xducers to go south. Thinking it may need a diode installed to prevent these power surges or spikes. Don't know if it would interfere with the sonars performance.

 

[SilverBullets]

I've experienced and have read other's reports of the depth readings going crazy early in the season on some of our local high lakes. You can be in say 200 feet of water, and the depth reading shows 70', then back to 200'. It seems to not be a problem when in shallow water. From what other's have mentioned, it might be due to the lake stratifying during the turnover, and the sonar is having trouble reading through that layer. Adjusting the sensitivity has helped. Also, on one particular lake the finder works well except for a couple areas where the screen becomes cluttered. It goes away quick right after you pass over the area. I think this is due to underground springs. Has anyone else encountered these problems? At first we thought it was the ducer causing this and sent it back for an upgraded model...same thing happening with it. So far this year it's been working great except for the cluttered screen in just 2 particular areas of the lake.

 

[SuperD]

I've caught WAY more fish on a graph that didn't show any fish than the number of times I've drug my offerings through black balls of fish and gotten nothing. I don't get too hung up about it. If we start fishing where we expect the fish to be, we will either catch fish and continue to fish there or move off until we start getting bit. I am admittedly a low end power user on my sonar and really tend to use it more for a "where is the bottom" unit. And I think I put as many fish in the box as the next guy.

 

[Trophy Taker]

Silver Bullets,

It’s not uncommon to loose bottom when trolling near structure as at the Gorge we often experienced this when fishing near rock cliff walls. One of the reasons you’ll loose it for a bit is a product of your “ping speed setting” being turned up to high. When your sonar emits pings through the water column, based on the time it was sent and the time it returns as well as the strength of the return it will show you the bottom. However; when trolling near structure sometimes your “ping” is distorted, split or absorbed based on structure composition and can cause a reduction in the number of pings received versus those that were sent out. You can limit how often this occurs by turning your ping speed setting down. When your skipping across the water a higher ping speed is better as the bottom is constantly changing, however when your trolling its better to turn your ping speed down to avoid false readings.

 

[HiTechKoke]

On the 100% scale of ping speed where do you like to leave yours at normally Trophy Taker? I pretty much max out the ping and chart speed but a lot of the lakes it not about structure as much as it is open water.

 

[Trophy Taker]

My Ping settings

I leave the chart speed at 100%. I'm kinda a math geek so I have a chart with both my 50khz & 200khz cone angles calculated all the way down to 200'. So if I am trolling close enough to the wall, that the wall is within my cone I turn the ping speed down to 25%. However; if the wall is outside of the cone angle but still near structure and the bottom appears to be jagged indicative of sharp rocks I turn it down to 50%. But I always run it 100% when over open water.

 

[3RivrFishr]

I have the same humminbird as Silver Bullets. LOVE that quadra beam. Huge coverage area. I'm still getting used to the wide side function and trying to interperet the returns I get in that mode but with the split screen in with quadra beam showing on top and wide side on the bottom I can see a ton of area. Problem with going that wide is that I'm never sure exactly where everything is in relation to my S turning course changes. I know that the 83kHz returns are in blue and the 200kHz are in red but Im still not sure what that all means in relation to space and time. Gotta do some more tinkerin...

I usually dont have a problem losing the bottom while koke fishing. The reservoir that I fish is really freakin deep. I just dont care about structure 400 feet below me so I usually tune the sonar to show 10 to 100 feet of the water column and the wide side 160 feet. Occasionally the bottom shows up when I troll over points and into bays.

I have gotten funky depth readings before. Never sure if its a wall of plankton, some wierd thermal thing as Silver Bullets suspects or the loch ness monster. Usually when that happens I get scattered clutter showing on the screen as well.

Super D, my dad is like you when it comes to a sonar unit. I bought my HB777C2 a couple years ago because the old bottomline greyscale just wasnt cuttin it any more. It had vertical lines on the display and every air bubble or piece of bark tripped the fish alarm. It was a little on the simplistic side. On our last trip I had the sonar tuned up well and it was marking fish. Not the goofy symbols that the old man likes but real returns. Blips, arches and lines. After explaining what all that was dad says you should've left the old one in here. It was simple. UGH! So anyway, later on I actually trolled through some fish then said, Okay get ready as I reached for the portside rod. One half second before I touched it a fish hit it. Grinning I said, I think this fish finder works pretty good dont you? nananana Granted it was W.A.L and it will never happen again but I think it sold him on the advanced technology. Also, I have it plugged into my GPS. A few days ago we were struggling to find fish. When we finally got one on I marked it. Ended up with doubles right there so after landing both and rebaiting I headed right back through the spot. Right when the arrival alarm went off two rods went off as well. I smiled at the old man and said "aint technology great?" I'm not saying everyone needs a high tech sonar to catch fish but for a hack like me its an advantage that I need.

 

[SilverBullets]

On the Humminbird unit I have an adjustment for chart speed, but don't see a ping speed adjustment. This might be the problem, as I've read that the Humminbird brand in particular gets alot of these false bottom readings. The sensitivity setting did have an effect though, and after adjustment have rarely had the problem since. Would algae blooms cause this, to where the unit has trouble getting an accurate depth reading with too high of a sensitivity setting?

 

[SuperD]

I like some aspects of the technology. The 10" color screen is very nice. thumbsup

 

[redmanjr1]

One thing I'm not sure of is transducer alignment (in two ways). First, how deep below the water line can it be mounted and still be effective? I'm on a pontoon boat and my mounting options are slim (although I may be able to build a bracket that could accommodate relocation if absolutely necessary). Second, what is the best angle for the transducer? Horizontal with the water line or angled toward the bottom below the aft of the boat (or somewhere between)?

3RivrFishr, good post. Curious about your pics. Is that Dworshak I'm looking at? If so, how's the fishing? It's been 4 years since I've been up that way for fishing.

Thanks,
Bob

 

[redmanjr1]

One thing I'm not sure of is transducer alignment (in two ways). First, how deep below the water line can it be mounted and still be effective? I'm on a pontoon boat and my mounting options are slim (although I may be able to build a bracket that could accommodate relocation if absolutely necessary). Second, what is the best angle for the transducer? Horizontal with the water line or angled toward the bottom below the aft of the boat (or somewhere between)?

3RivrFishr, good post. Curious about your pics. Is that Dworshak I'm looking at? If so, how's the fishing? It's been 4 years since I've been up that way for fishing.

Thanks,
Bob

Guys,
Just saw another post that helps me on the above question. I'll repost at http://www.kokaneefishingforum.com/fishing-forums/showthread.php?t=2058

Thanks,
Bob

 

[Code4]

Since it sounds as though many of you have Lowarance sonars I need help. I have an X96 that I purchased new last spring. I used it twice with no problems before my boat motor died. It sat all summer and after a motor replacement this winter I took the boat back out on the Gorge. I immediately started having problems with the sonar not reading bottom accurately when trolling and even sitting still. In water over 80' is looses bottom and also does not seem to be showing anything but bigger targets when it is working properly or when I am in really shollow water (20'). I have checked the transducer, cleaned it and it has never moved from it's, what I think is correct location. I have ran the wiring away from all other electronics and moved the finder up on my dash rather than the back of the boat. New boat batteries, new connections, no broken wires but it just seems to not have enough power to hit bottom. The only way it will half way work is to change the setting to manual, set the bottom depth to around 125' and at least it shows a weak bottom so I know approximately what the depth is. As soon as I get in water around 50' or less it seems to work fine, except for not showing fishes! (Kind of important). Anyone have suggestions?

 

[SuperD]

Use a multi meter to check power at the back of the unit.

 

[Code4]

Use a multi meter to check power at the back of the unit.

SuperD,

Would that be to the power line going into the back of the fish finder? What reading should the meter be at, max power output or something different. Getting really frustrated with this and of course it is past the one year warranty but I think it should work for more than three trips! Any thought that it could be the transducer?
Thanks.