Purchased a 185 for my carbon unit and see I have high chirp, 200 hrz, and custom 150 to 250 or something like that, sorry not by the boat, anyway I troll for trout and fish for sturgeon and am wondering the best setting to find the sturgeon that are stuck to the bottom in 50 to 100 feet. Also when I am in a custom setting or in the 200 is it just the non chirp. Thank you
Whenever you look for fish close to bottom (or structure) it will usually be the frequanzy with the narrowest coneangle that gives the best results (and that is the highest frequenzy). When looking for pelagic fish in those depths use chirp.
If in doubt, take a look at this screenshot:
Last edited by Team Colibri; 09-03-2019 at 05:55 AM.
TC.... Are you saying that when using the TM185HW in single frequency mode that the cone angle does indeed change and the constant 25 degree is available only in high chirp?
The constant conangle is not that constant, even in chirp. ;)
For 175/185/165HW it is true that the coneangle varies less then what it does on the other chirp-transducers. Here is TM165HW:
As you can see it varies less than one would expect but it does have variations. Here is TM185HW:
tm185hw.PNG
I'm aware there are lobes on the pattern which prevents "perfect" cone.
But...
Got me how to read those charts. On the 185 charts I'm seeing -3db @200KHz where the first dotted line is with -5db the first solid line - coming from the top or 0db. Then I see where the -3db line intersects the degree mark, which looks to be 15 degrees. Ahhhh... hahhh.... think I figured it out. 15 degrees to each side is in fact 30 degrees. Well whad'a'ya' know. Old dog... new trick... will wonders never cease?
;)
Thank you for the information. What would be the purpose of setting my own custom frequency? I think I can go between 150 and 250. Is there a good read on this a old farmer can understand.
This:Originally Posted by The gman
Ok I have done searches, etc on finding sturgeon and looked at your Instagram post and understand that but your chart shows 235 kHz at 26 and am wondering if chirp is a narrower cone angle so I find them on the bottom or will they most likely look like a bump or rock. On side scan I know smaller fish are grains of rice but it seems that sturgeon are very translucent with my 3D if that is what I am seeing. Have been told being as sturgeon don’t have swim bladders sonar doesn’t reflect like on normal fish. Any help will be great
Sturgeon do have swim bladders. Sometimes you will see them leaping out of the water or just coming to the surface and gulping air to fill it. I was always told it is the swim bladder that is producing the echo from a fish but I have started to doubt that. First, sound doesn't propagate well in air, so you would think the bladder would be less reflective. Second, as frequencies get higher and better shots show up especially of downscan images, we are seeing entire fish outlines including fins. I think the sound can actually bounce back from anything that is denser than the water.
NoCAL
2004TR-21X/2015 250 ProXS
2B112175
So you peaked my curiosity. I found the density of water. Started looking for the density of fish.... Ran across "Tom" from the "Department of Physics" University of Illinois at Urbana - Champaign. Now... understand that this conversation dates back to 2011 when the world was still fresh and science was still evolving... I'll give him credit - he got close.
Q & A: Density of a fish
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Most recent answer: 01/25/2011
Q:What is the approximate density of a fish, compared with the density of the water in which it swims?
- Mary
Austin Tx
A:Hi Mary,
A fish should have a very similar density to the water it swims in. Archimedes' principle states that the buoyant force on an object is equal to the weight of the water it displaces. The total vertical force on a fish is that of gravity, the buoyant force, and any reaction force generated by swimming ("dynamical buoyancy"). If the fish were much denser than water (or saltwater, as the case may be), the weight of the displaced water would be much less than the fish's weight, and the fish would sink. If the fish were much less dense, then the fish would float to the surface. To keep at a desired depth, perhaps with a little help from swimming, the fish should be about as dense as the water it swims in.
Many fish have a swim bladder (also called a "gas bladder") which fills with a gas (usually oxygen) and which helps regulate the fish's average density. The rest of the fish then is a bit denser on average than water.
When a fish dies, bacteria decompose it and generate gasses as byproducts, which often swell the gut. The dead fish then floats to the surface, belly up.
Tom
(published on 10/22/2007)
1. Keep in mind that 185HW and 165HW sort of "breaks the pattern" when it comes to the rule of thumb for coneangle and frequenzy. Don`t ask me how they did that, I have no idea. :) Usually when the frequenzy increases, the conenagle decreases and vice versa. So when a transducer is using 83 kHz, the coneangle is a lot wider than when the same transducer uses 200 kHz. This is also true when chirping, if we look at TM150M the conenagle increases when the frequenzy decreases.
That means that when chirping (using the full frequenzy-spectrum) the effective conenagle is the largest as the lowest frequenzy is used in the chirp-sweep and that has the largest conenagle. You will have a narrower coneangle in fixed frequenzy with the same transducer, using one of the high single-frequenzies then you would have using chirp. But 185HW and 165HW are exeptions from that, as seen in the diagrams from Airmar. I have never seen a full list of frequenzy vs coneagle for 185/165HW, so I don`t know which single frequenzy in the available spectrum that has the narrowest coneangle for those transducers.
Moral: If you are looking for fish close to bottom/ structure, get a transducer where you know the coneangle at a given frequenzy. Not the HW-models but typically the B75 or B175/TM185 versions in H or M (depending on typical depth) Then use that transducer in fixed frequenzy at the highest possible frequenzy that still gives a good return.
2. Not sure what you mean by 3D, so I`ll cover both options.
The 3D-image with Structurescan 3D is not suitable for looking for single fish, the resolution is not there for such use.
3D as in Sidescan/ Downscan is good for looking for single fish.
Yes, fish show up as small grains, due to the narrow strobe-like cone of scanning sonar. Yes, the swimbladder makes up a big part of what we usually see as fish on our sonar, but you can still see fish that do not have swimbladders. It will just be less defined, more "blurry". I have never fished for sturgeon, but I would imagine the main issue with them is that they lay close to bottom so seperation is key.
Last edited by Team Colibri; 09-11-2019 at 06:35 AM. Reason: typos
someone ask Tom how Airmar is pulling off those cone angles
Thank you for the insight. I got a good deal on the 185 so I am happy with it.
As far as side scan I should of been more clear I is the 3 d box for down and side
and have seen blurry returns I assume are sturgeon as the shadow is big and the
image is somewhat like when they blur out faces. Still learning but really appreciate
all your input. Garry
I prefer 220 kHz fixed frequency for B175H-W (same element as TM185H-W) at 100' and less.
Scuirus would you be so kind as to elaborate on what 220 is better at or why you use 220. Haven’t tried that many different setting yet.
I've had B175H-W for more than 5 years. I've used more or less any single frequency from 150 to 250kHz including of course CHIRP. Until the frequencies from 211 to 250 kHz became available with NOS56 released early 2017 I preferred 200kHz or High CHIRP. I've found 220 kHz to be a sweet spot when it comes to target separation and sensitivity. When looking at the B175H-W performance graphs 220 kHz is the highest frequency with full sensitivity, at higher frequencies the sensitivity drops slightly. With the external S5100 sonar module 250kHz is giving the best resolution and performance in shallow waters, but with integrated sonar or SonarHub I prefer 220 kHz both for shallow waters and up to 100-150'. The reason for the difference between the very expensive S5100 sonar and the integrated sonar modules is the quality of the filters. The resolution in High CHIRP has improved the last couple of years and is a good alternative except when it's 15-20' or less where fixed frequencies are better.
Thank you for the information. You are a lot more in tune with this than myself but with info like that I hope to get better.
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