transducer questions

[DesolateGreg]

Hi Everyone,
When I purchased my center console it had two transducers on it. They are both hooked to a 12" Simrad NSS evo3 screen. So channel 1 / channel 2 input.
I have been using the boat for about a year now and getting pretty comfortable with the electronics. I just want to make sure I'm getting the most out of my set up. I was in a friends boat one day going over some deep water ( couple thousand feet) and I had noticed his Simrad was reading the depth. Mine would never do that. Deepest Ive personally ever noticed it reading is maybe 500 feet any deeper than that it just blinks. Is this just because his transducer is stronger? Mine does have high chirp and I run in on that setting primarily unless im in shallower water. I have noticed that in shallower water I get a cleaner picture on 200 khz. Does this sounds right or do I have my setting wrong? Wish i had some pictures of my screen to show.
I looked at the larger of my two transducers Its an Airmar but I couldnt find any parts numbers on it so I attached a picture of it incase that helps. I also looked on Airmars web site and see that the TM185 - TM275 basically look the same so might now be able to tell externally i guess
Im not targeting one specific species. I just like fishing. There are days when I'm in shallow water, there are days where I'm rock fishing in deeper water. My push to get the electronics kinda more dialed in is for the deeper water blue fin that are typically caught on the falling jigs or sinker rigs. I feel like right now with the way its set up unless i was sitting still I would probably drive right over them and never know they were even there.
Any info is appreciated. Thank you !

 

[JohnnyK87137]

You have high chirp for the transom mount short fat one an a side scan sonar is the long skinny one. High chirp will get you down to about 600 and when offshore you should set it read the top 300 feet. The side scan will work when you select it to work on the proper app in the mfd (evo3 ) you’re friends rig most defiantly has a low chirp transducer probably a additional box to strengthen the power and possibly even higher than 1k

 

[ShadowX]

Hi Everyone,
When I purchased my center console it had two transducers on it. They are both hooked to a 12" Simrad NSS evo3 screen. So channel 1 / channel 2 input.
I have been using the boat for about a year now and getting pretty comfortable with the electronics. I just want to make sure I'm getting the most out of my set up. I was in a friends boat one day going over some deep water ( couple thousand feet) and I had noticed his Simrad was reading the depth. Mine would never do that. Deepest Ive personally ever noticed it reading is maybe 500 feet any deeper than that it just blinks. Is this just because his transducer is stronger? Mine does have high chirp and I run in on that setting primarily unless im in shallower water. I have noticed that in shallower water I get a cleaner picture on 200 khz. Does this sounds right or do I have my setting wrong? Wish i had some pictures of my screen to show.
I looked at the larger of my two transducers Its an Airmar but I couldnt find any parts numbers on it so I attached a picture of it incase that helps. I also looked on Airmars web site and see that the TM185 - TM275 basically look the same so might now be able to tell externally i guess
Im not targeting one specific species. I just like fishing. There are days when I'm in shallow water, there are days where I'm rock fishing in deeper water. My push to get the electronics kinda more dialed in is for the deeper water blue fin that are typically caught on the falling jigs or sinker rigs. I feel like right now with the way its set up unless i was sitting still I would probably drive right over them and never know they were even there.
Any info is appreciated. Thank you !

View attachment 1377039

View attachment 1377040

First, your friend might have a different transducer operating at medium or low chirp. The depth penetration depends on the power output of the transducer, the frequency that the transducer use and the cone angle of the sonar energy.

You can go into your sonar settings, installation and it should show you exactly which transducer you have. Your transducer has an internal XID chip which identifies the model number so the transducer can automatically set the correct values. Another way is to look at the end of the cable and there is usually a tag that has the model number unless it was cut off.

Assuming you have the TM185HW model, the 500 foot depth is about right. The higher frequency has lower depth penetration due to attenuation. The medium chirp goes down to approximately 1500 feet and the low chirp is around 3000 feet. The calculator also tells you the beam angle which is critical in determining your max depth. Note, these are just estimates, some people get deeper penetration, while others get slightly less and it depends on the type of water and the water clarity.

2022 Bottom Coverage Calculator | AIRMAR

Airmar calculator to help determine bottom coverage under your boat. See bottom coverage and upper water column coverage and cone angles.

www.airmar.com

The 500 feet depth with the high and wide chirp beam is the best for fishing for tuna. Most people don't fish deeper than 500 feet unless they are targeting marlin or other deep water fish. When you are in open waters deeper than 500 feet, you have to set your fish finder to a fix depth (ie: 500 feet) and change it to manual gain. Turn up your gain until you see a horizontal band of noise. Its usually 40-200 feet and represents the "thermocline" which is where the warm surface water is separated from the deeper cold waters. This tells you that your gain is set high enough to pick up these small differences. You can back up the gain slightly if you want less noise. At this time, you should be able to meter fish if they swim by. You can also test this at around 500 feet of depth where you know fish are around to get familiar with the electronics.

If you don't make these two changes, what happens is the fish finder tries locate the deep bottom, but doesn't find it, so it keeps switching depth and gain sensitivity (if you have it on automatic). If the settings are wrong, it would not pick up anything. That is why you MUST set a fixed depth. The gain change is something I do in shallow or deeper waters because it lets me know its at the optimal gain. Even though you see more noise, it also picks up smaller baits and other information that is useful for fishing.

Another possibility is the transducer is mounted slightly canted where the beam is not directly perpendicular to the boat. It can cause the signal to not bounce back properly when you are in deeper depths. This is less of a problem with wider beam transducers, but the narrow high chirp beams are sensitive to slight misalignments. You can tell if you are misaligned vertically by driving your boat straight and making a slight left turn and then a right turn. If the signal improves or degrades as you turn to one side, it means there are a slight angle misalignment from side to side. As a result, you will have limited depth reading or the depth would create a broken bottom reading when you are on plane. It takes more effort to getting the angle just right but its worth it once its correct.

 

[DesolateGreg]

You have high chirp for the transom mount short fat one an a side scan sonar is the long skinny one. High chirp will get you down to about 600 and when offshore you should set it read the top 300 feet. The side scan will work when you select it to work on the proper app in the mfd (evo3 ) you’re friends rig most defiantly has a low chirp transducer probably a additional box to strengthen the power and possibly even higher than 1k

Thank you for the info. I am gonna try to go out this weekend and play with the side scan. When I go to the regular echo screen I can pick channel 1 or channel 2 but when I go to the side scan it doesn't give me such an option. Do you happen to know how that works and if there is a specific input that I need to be hooked for the side scan transducer?

 

[DesolateGreg]

First, your friend might have a different transducer operating at medium or low chirp. The depth penetration depends on the power output of the transducer, the frequency that the transducer use and the cone angle of the sonar energy.

You can go into your sonar settings, installation and it should show you exactly which transducer you have. Your transducer has an internal XID chip which identifies the model number so the transducer can automatically set the correct values. Another way is to look at the end of the cable and there is usually a tag that has the model number unless it was cut off.

Assuming you have the TM185HW model, the 500 foot depth is about right. The higher frequency has lower depth penetration due to attenuation. The medium chirp goes down to approximately 1500 feet and the low chirp is around 3000 feet. The calculator also tells you the beam angle which is critical in determining your max depth. Note, these are just estimates, some people get deeper penetration, while others get slightly less and it depends on the type of water and the water clarity.

View attachment 1377050

2022 Bottom Coverage Calculator | AIRMAR

Airmar calculator to help determine bottom coverage under your boat. See bottom coverage and upper water column coverage and cone angles.

www.airmar.com

The 500 feet depth with the high and wide chirp beam is the best for fishing for tuna. Most people don't fish deeper than 500 feet unless they are targeting marlin or other deep water fish. When you are in open waters deeper than 500 feet, you have to set your fish finder to a fix depth (ie: 500 feet) and change it to manual gain. Turn up your gain until you see a horizontal band of noise. Its usually 40-200 feet and represents the "thermocline" which is where the warm surface water is separated from the deeper cold waters. This tells you that your gain is set high enough to pick up these small differences. You can back up the gain slightly if you want less noise. At this time, you should be able to meter fish if they swim by. You can also test this at around 500 feet of depth where you know fish are around to get familiar with the electronics.

If you don't make these two changes, what happens is the fish finder tries locate the deep bottom, but doesn't find it, so it keeps switching depth and gain sensitivity (if you have it on automatic). If the settings are wrong, it would not pick up anything. That is why you MUST set a fixed depth. The gain change is something I do in shallow or deeper waters because it lets me know its at the optimal gain. Even though you see more noise, it also picks up smaller baits and other information that is useful for fishing.

Another possibility is the transducer is mounted slightly canted where the beam is not directly perpendicular to the boat. It can cause the signal to not bounce back properly when you are in deeper depths. This is less of a problem with wider beam transducers, but the narrow high chirp beams are sensitive to slight misalignments. You can tell if you are misaligned vertically by driving your boat straight and making a slight left turn and then a right turn. If the signal improves or degrades as you turn to one side, it means there are a slight angle misalignment from side to side. As a result, you will have limited depth reading or the depth would create a broken bottom reading when you are on plane. It takes more effort to getting the angle just right but its worth it once its correct.

Wow thank you so much for all this info. Im going to absorb all this , make some notes and take the boat out to just mess with settings and see how it helps.
I did notice there is a wedge block between the transom and the transducer but that angle would all depend on how the boat sits in the water
One question for you once I get my settings for depth and gain dialed in how fast should i expect to be able to go and still actually read whats going on down under the boat. Meaning if i have all my settings dialed in and im driving at 20 knts should i expect to be able to see any readings or will I have to be going much slower
Thanks again

 

[lougio]

Your display should tell you what transducer and frequency you have it set to. At least my Garmin 7610 does. I would assume that Simrad does as well.

 

[ShadowX]

Wow thank you so much for all this info. Im going to absorb all this , make some notes and take the boat out to just mess with settings and see how it helps.
I did notice there is a wedge block between the transom and the transducer but that angle would all depend on how the boat sits in the water
One question for you once I get my settings for depth and gain dialed in how fast should i expect to be able to go and still actually read whats going on down under the boat. Meaning if i have all my settings dialed in and im driving at 20 knts should i expect to be able to see any readings or will I have to be going much slower
Thanks again

We can read the bottom with the boat travelling at 25 knots with our transom mounted transducer (TM265LH). It sometimes break up depending on the ocean conditions. The beam is very narrow on our transducer so the beam is more likely to not bounce back to the boat when the waves toss the boat around. On the high wide chirp, you are more likely to get better signal because the beam is wider. It seems like if the boat is on high chirp, we are able to get cleaner readings. On the low chirp settings, the noise tends to wash out the display when we are on plane.

It really depends a lot on the water condition, depth, the amount of turbulence, any obstructions upstream of the transducer and the alignment of the transducers. If the sea is calm, you are more likely to read the bottom. On rough days with a lot of waves, the boat may have more issues holding bottom with a transom mounted transducer. There is a lot of reasons, but the main one is the mounting location and alignment of the transducer. If you mount it in a location without clean clear turbulent water flowing through, you are more likely to not get good readings. Every boat is different, so you have to follow the suggested mounting guidelines.

Pushing the transducer deeper into the water seems like it would get better readings, but sometimes it works against you. You are more likely to throw a big roostertail make it worse. What you do is make incremental changes at a time. Move the transducer up and down to see if it improves or gets worse. Don't change the angle at the same time. If you change angle and push it up and down, you don't know if the angle change or the depth is what cause it to improve or get worse. It usually takes a couple of tries before you get results you like.

 

[ShadowX]

Thank you for the info. I am gonna try to go out this weekend and play with the side scan. When I go to the regular echo screen I can pick channel 1 or channel 2 but when I go to the side scan it doesn't give me such an option. Do you happen to know how that works and if there is a specific input that I need to be hooked for the side scan transducer?

The side scan has to be plugged into a specific port on your NSS EVO3 shown below for it to work. Your normal transducer has to be on the port 5.

If you have a dual frequency transducer like the TM265 or TM275, you can't have a structure scan transducer on the same system. The XID on the transducer is on the high chirp connection. The low chirp side has no XID, so the Simrad assumes the port 6 will be the low chirp connection. This prevents you from using a structure scan transducer. Even if you plug in the structurescan transducer, it does not show up on the structurescan list. The only way is to either connect it to another Simrad unit that is networked with your current Simrad unit or using a separate sonar box.

 

[DemersalAngler]

High frequency returns information more quickly, and low frequency returns slower. Thus when on plane with low frequency you may have mooved past the return before it was received.

A couple tips for marking on plane are turn you're ping speed to max, and turn up the scroll speed. Ping speed is the rate at wich the the MFD generates power, and scroll speed is the rate of information flow from right to left on the MFD screen.

 

[ShadowX]

High frequency returns information more quickly, and low frequency returns slower. Thus when on plane with low frequency you may have mooved past the return before it was received.

A couple tips for marking on plane are turn you're ping speed to max, and turn up the scroll speed. Ping speed is the rate at wich the the MFD generates power, and scroll speed is the rate of information flow from right to left on the MFD screen.

That is not correct.

Sound travels about 5000 feet per second under water. The speed of the boat is trivial compared to the speed of the sonar signal. Even at 25 mph, the boat moves 36 foot per second. The signal that bounces back is not a narrow beam, but a cone of sound that is reflected from the object or bottom. At 36 feet away, you can still pick up the return signal. There are many people who can still track the ocean bottom at 25+ mph at high chirp. If you are in much deeper water (2000+ feet), that is a different story.

The difference in the speed of sound between 50 KHz to 200 KHz is neglibible. What makes a difference is that higher frequency sounds has higher attenuation compared to lower frequency, so the signal degrades faster with depth than at low frequencies.

The cone angle of the sonar also has a huge impact on the signal level and bounces back. The sound energy drops as a square root function due to the area it has to spread. I did a calculation a while back with excel and it shows with different cone angles (25 vs 30 degrees) the diameter of the sonar energy at a fixed depth (500 feet). The power density drops by almost half with just a 5 degree difference. You would need to almost double the power just to make up for the signal loss at the maximum depth with a 5 degree cone angle difference.

Power (W)	Depth (feet)	Cone angle (degrees)	Diameter (ft)	Area (ft^2)	Power density (W/ft^2)
1000	500	25	222	38,601.16	0.0259
1000	500	30	268	56,389.05	0.0177