Topic: 898 shallow water readings since 5.7 update

[muskietim]

Installed 5.7 update per instructions (reset defaults etc) and ever since when in water under 10 feet the unit sometimes will not read the depth correctly. If the boat is in 7 feet of water it could read 7 ft but the then seconds later it will show 16 or 18 feet. It seems that once the water is deeper than 10 feet this i intermittent problem stops.

The boat has both the SI/DI transducer and a high speed transducer on the transom with the proper cable to join them, sorry don't remember the numbers of those parts. Prior to the update to 5.7 everything worked correctly.  I have tried adjusting the sensitivity, switching from 83Hz, 200 Hz and both but that has not changed anything.

Any one else seen this problem and have any ideas on how to fix it?

Tim

[offroad]

Tim
      l too have the 898 but my unit performs better with this update. The unit is on my trolling motor and l think since this last update it now has reduced interfearance and beter shallow water performance. In fact l cant wait for this update to be released for my 1197 l am just using the Transducer that came with the unit.

[Humminbird_Greg]

Tim,
Is this with a second (or third, fourth…) sonar unit running or when the trolling motor is being used?
Do you remember if you may have had the Noise Filter menu turned up with the older software?  This would have been reset when you set the menus to the factory defaults.

[muskietim]

Greg,

No other units are running and the trolling motor was not on. I do not remember if the noise filter had been adjusted or not. I do not have access to the unit until this weekend so will look at the noise filter then.

Tim

[Humminbird_Greg]

Try adjusting the Surface Clutter menu as well when at those shallower water depths as well.
If that does not help than try setting the Water Type menu to the “Salt (deep)” menu setting and try adjusting the Surface Clutter menu again.

[Rüdiger]

No problems, my unit works better in shallower water after the 5.7 update.

mvh
Rüdiger

[MonteSS]

My unit has had that exact problem since new and still has it after 5.7.

Only sonar on and one transducer on stern. Same with trollong motor on or off.

I will try what you advised OP to do tomorrow.

Thanks...Bill

[MonteSS]

I bumped the surface clutter fron 1 to 2 and it seems to work fine now in shallow water.

Thanks....Bill

[Moose1am]

It also helps to switch the sensitivity to a lower setting instead of using auto sensitivity.  Also check which frequency you are using. 83 KiloHertz or 200 KiloHertz.  That will make a difference in the cone angle.  Narrower cone works better in shallow water IMHO.  I turn the surface clutter setting down to 1 which is max filtering of the surface clutter.   
 
Check the transducer and make sure it's sitting parallel with the water's surface and that the boat is not listing to one side. 
Check the power level of the 83 KHz  power setting.  The default is zero on a scale of -10 to +10.    I think that this setting is seperate from the 200 KHz sensitivity setting but am not for sure.   Perhaps Humminbird Greg or someone else from Humminbird could comment on this feature.

Remember that if you are over a hard bottom the sonar sounds can bounce off the rock bottom and then bounce off the bottom of a metal boat and back down to the rock bottom several times if you have a high sensitivity setting.  Multiple bounces can make the control head think it's in deeper water.  Solution is the turn the sensitiviy down.  I learned this many years ago when I used the very first commerical fisherman sonar unit. (Lowrence's "little green box")  I gave a speech on this unit in my High School Speech Class.    If you learn to use a unit like the round flashers you learn a lot about how sonar works.  Thinks like water density and salinity can also influence how sound travels in the water. 
 
Salt water being less dense (not pure water H2O Wise) may retard the speed of sound vs Fresh Water.  The Solids dissolved in the salt water may slow down the speed of sound or speed it up.  Can't remember which way this happens.  But there is a big difference in the way that sound waves propogage (move) though saltwater vs fresh water.  I would think that the salt water setting reduces the sound's power setting.  But I'm not sure and could be wrong.  Consult with Humminbird to find out which way this works.
I wonder if you can set the max and min values for depth if that would help too?  I leave these at the Humminbird Default Settings and have not really played with these settings except by accident.  Sometimes my four way cursor button sticks and wierd things happen to my settings. :O(
BTW  I also have the 5.7 update installed on my 898C SI unit and have been using it a lot this week.  I've been testing the various settings more than actually fishing this week. 

Remember that the sensitivity settings can be adjusted SEPERATELY for the 800 and 455 kHz Si and Di as compared to the 83 and 200 kHz settings for the regular sonar.   Even though all sounds are produced and received by the same transducer. 
Try setting the unit to use Clear Mode and White Bottom Mode in the Sonar Menu.  Those will both filter out the returns a little better than Max Mode or Structure ID mode.

Remember that 83 kHz sound waves will go deeper into the water with more power than the 200 kHz sound waves. The cone angle of the 83 kHz sound waves will be narrower than the 200 kHz sound waves.
So in shallower water with a hard bottom the 83 kH sound waves will bounce off the hard bottom much better than the 200 kHz sound waves.  Turn the sensitivity setting down on the 83 kHz frequency setting.  The sensitivity setting for the 83 kHz frequency is set to zero where the range of settings goes from -10 to zero up to +10.  Set the sensitivity down to about -5 and see if that helps in shallow waters.  Remember this only affects the 83 kHz sound waves and not the 200 kHz sound waves.  You can also turn down the sensitivity of the all the different sound waves using the sonar menu (see page 89 of the manual).

PS: Now I'm confused. The manual is telling us that the 83 kHz frequency is the wider beam and the 200 kHz is the narrower beam.  I'm not sure but just read on the Lowrance Web site where it talks about how sonar works and there it said just the opposite.  I guess that the thing to remember is that these two frequencies can have different cone angles.   So I'll have to so some more research. 
According to the from of the Humminbird 898CSI manual where it talks about how sonar works it said that the 83 kHz sound goes deeper.  See page 2.
But on page 2 is also shows that the 200 kHz beam is narrower than the 83 kHz beam.    I guess I thought that a narrower beam would go deeper and be more focused for some reason.  It works that way with a flash light in the fog.
 
One more thing to try out.  Noise filter settings can be used in shallow water to filter out noise and reduce the signal or echos.  Try adjusting this setting to High 1 or High 2 or High 3 and see what that does to your shallow water hard bottom displays.

[Humminbird_Greg]

Moose,
The Sensitivity setting in most modern units that use a processor will not affect how the unit reads the lake bottom.  It just influences how it shows the sonar information that it receives.

The 83kHz Sensitivity menu makes adjustments in addition to what the main Sensitivity menu is adjusted to.  In this way you can ‘balance’ the 83kHz sonar readings shown with those shown for the 200kHz sonar.

Most of the time when you are in shallower water, the sonar has enough energy to reflect off the water’s surface and bounce back off of the lake bottom again – sometimes multiple times.  This is more dependant on the type and shape of lake bottom that you are over.  Harder and flatter lake bottoms (I state “lake” here but the same applies to rivers, ponds, creeks, oceans,…) make this more likely to happen.

The speed of sound through salt water is faster than in freshwater, though due to all the extra ‘stuff’ (salt, mineral content, plankton, zooplankton,…) in salt water it has a higher absorption loss (reduces the sonar signal power level faster) than in freshwater.

Wide angle transducer beams will not work as deep or as far versus a narrow transducer beam – but this is only true if you are comparing the same frequency here.  Lower frequencies carry farther in water, air and land than higher frequencies due (when comparing sonar beams of the same width).  Even though our 83kHz beam has a wider angle than the 200kHz beam; the lower frequency enables it to work to a farther distance than the narrower and more focused 200kHz beam.

[Moose1am]

Thanks Greg. It's no wonder I was confused.  I assumed that the frequency of the sound waves determined the cone angle. I guess that's not true?
Now that you posted I think I have figured it out.  High Frequency like the 800 kHz SI wave will dissapate faster than the 455 kHz freq sound waves.  Therefore the 455 kHz waves will travel father away and have more energy to bounce back to the receiver (transducer).
Now this explains why I was seeing more fish arches when I was using 83 kHz frequency setting for my regular sonar screen.   The 83 kHz frequency will see more fish in the shallow water since the beam is 60 deg cone angle and spreads out and sees more of the water than the 200 kHz.  It makes good sense now. 
So what you are saying is that the received sounds are filters and the sending unit sends out the same power at all times?  What about the RT flasher screen on the Right Side of the Screen in 2 D screens? 
Sensitivity settings when increased just filter less out with the microprocessor.   There was a very good article in the Fishing Facts magazine back in the 1980's that explained a lot about how fishing sonar units work and what their weaknesses are.  It was complete with diagrams that showed how blind spots exist for graphic sonar imaged when fish hide below the overhang of a underwater cliff.  The processor can't show all the signals that bounced back up to the tranducer.  I have tried to scan this article and show the pictures a few times but I was never able to get the pictures the right size on the forums.  I am getting better at figuring out graphic and pixel sizes now days so maybe I'll try to scan this magazine article again as it's a great reference source for those wanting to learn more about the limitations of sonar and how it works. 
 

[Humminbird_Greg]

Moose,
The size and shape of the transducer element mainly control the shape of the sonar beam but frequency does play a part in that as well. The standard 200/83kHz 2D sonar that we use comes from a single element.  So the lower frequencies produce a wider beam pattern than does a higher frequency if you are using the same size and shape element.

It’s not just the lower frequency of the 83kHz that allows you to see more fish arches Moose.  The wider beam does help in that you would be seeing more fish because the beam is covering a wider area.  The wider beam also helps in showing fish as an arch versus just some pixels on the screen.  This all has to do with how the arch is formed and a wider beam makes this more possible.

The transmit power level that we use is controlled mostly by the water depth that you are in.  Changing the Sensitivity or any other menu that you have access to does not change the amount of power we put into the water.  What looks like turning the power up and down when you use the Sensitivity menu is somewhat like you are saying in that more or less filtering is talking place.  It is more of a visual filtering versus an actual signal filtering.  All of the returned sonar signals are assigned a specific color level.  What the Sensitivity menu does is change those assigned color levels.  If a sonar return were assigned a very low color (possibly the background color as it is so weak) and you turn the Sensitivity level up; that very weak sonar return may now be assigned a color that now gets displayed – so you may see sonar returns at higher levels that you did not see before.  Sonar returns that were already shown would get assigned a stronger color showing that they have a higher relative returned sonar signal strength.  The opposite is also true: sonar returns that were shown with strong colors may be shown as weaker colors when you turn the Sensitivity menu down and you may be able to turn it low enough that some sonar returns are no longer shown.

The signals in the RTS Window are more raw in form.  I don’t think that any of the Sensitivity or filter menu changes you have access to affect this data.  It also gets updated faster than the Chart history display due to this (up to 40X per second in water less than about 40 feet deep).

That article was correct in that there are “sonar shadows” created by some underwater structures, which is worse with wider sonar beams than with narrower sonar beams.  This is true for all types of sonar (2D, Si and DI).  Sonar units are limited in being able to only show one sonar signal strength per pixel (or whatever means that they are using to show the sonar returns).  Keep in mind though that there have been many advancements in recreational sonar units since the 1980’s.  I would be interested in reading the article if you can scan and e-mail me a copy of it.


Sorry for the hijacking of this thread... 

[nmanley]

It also helps to switch the sensitivity to a lower setting instead of using auto sensitivity.  I turn the surface clutter setting down to 1 which is max filtering of the surface clutter.   
 

This was the biggest factor in my unit to start reading the shallow depths correctly.   

[Moose1am]

Hey Greg: I posted this on the Bass Boat Central Web site on the Humminbird Sonar Threads under the thread" Make the brush pile show up better or something to that effect.  I can go find it and give you a direct link.  I scanned most all the article that's applical to how sonar actually works. Remember it was printed in 1976 though.  Or was it 1986. It was a very long time ago.  But you should be able to read it there.  I was trying to make it a little bit larger but I made it too big and then I reduced the size again on my photobucket account which the images are linked to.

http://www.bbcboards.net/zerothread?id=743251
 
Note: Credit is given to Fishing Facts Magazine as they are the author of the article I am talking about here.  It was written and researched by the Editor and Publisher of Fishing Facts Magazine back in 1976.  Mr George Pazik

Moose,
The size and shape of the transducer element mainly control the shape of the sonar beam but frequency does play a part in that as well. The standard 200/83kHz 2D sonar that we use comes from a single element.  So the lower frequencies produce a wider beam pattern than does a higher frequency if you are using the same size and shape element.

It’s not just the lower frequency of the 83kHz that allows you to see more fish arches Moose.  The wider beam does help in that you would be seeing more fish because the beam is covering a wider area.  The wider beam also helps in showing fish as an arch versus just some pixels on the screen.  This all has to do with how the arch is formed and a wider beam makes this more possible.

The transmit power level that we use is controlled mostly by the water depth that you are in.  Changing the Sensitivity or any other menu that you have access to does not change the amount of power we put into the water.  What looks like turning the power up and down when you use the Sensitivity menu is somewhat like you are saying in that more or less filtering is talking place.  It is more of a visual filtering versus an actual signal filtering.  All of the returned sonar signals are assigned a specific color level.  What the Sensitivity menu does is change those assigned color levels.  If a sonar return were assigned a very low color (possibly the background color as it is so weak) and you turn the Sensitivity level up; that very weak sonar return may now be assigned a color that now gets displayed – so you may see sonar returns at higher levels that you did not see before.  Sonar returns that were already shown would get assigned a stronger color showing that they have a higher relative returned sonar signal strength.  The opposite is also true: sonar returns that were shown with strong colors may be shown as weaker colors when you turn the Sensitivity menu down and you may be able to turn it low enough that some sonar returns are no longer shown.

The signals in the RTS Window are more raw in form.  I don’t think that any of the Sensitivity or filter menu changes you have access to affect this data.  It also gets updated faster than the Chart history display due to this (up to 40X per second in water less than about 40 feet deep).

That article was correct in that there are “sonar shadows” created by some underwater structures, which is worse with wider sonar beams than with narrower sonar beams.  This is true for all types of sonar (2D, Si and DI).  Sonar units are limited in being able to only show one sonar signal strength per pixel (or whatever means that they are using to show the sonar returns).  Keep in mind though that there have been many advancements in recreational sonar units since the 1980’s.  I would be interested in reading the article if you can scan and e-mail me a copy of it.


Sorry for the hijacking of this thread... 

[Humminbird_Greg]

Thanks Moose, I will try and read it when I get a few spare minutes.