So if I am looking at say 100 feet on both sides and it is 20 feet deep.  The images showing on the 25 foot line is 5 feet to the side of the boat?  Is this correct or is it 25 feet from the side of the boat?

Do yourself a favor and look up both Doug Vaherenberg, and The Technological Angler on Youtube. You will learn more than you will ever need to know about side imaging.

 

The quick easy answer to your question is it is 5 feet to the side of the transducer.  
 

I’ve written software that reads my sonar recordings so I can view them at home and side imaging math is very complicated and in some special cases things can get weird.

1 hour ago, shaff1101 said:

So if I am looking at say 100 feet on both sides and it is 20 feet deep.  The images showing on the 25 foot line is 5 feet to the side of the boat?  Is this correct or is it 25 feet from the side of the boat?

Neither - they should be about 15 feet to the side of the boat in that example.

14 minutes ago, Team9nine said:

Neither - they should be about 15 feet to the side of the boat in that example.

Huh?

7 minutes ago, Tennessee Boy said:

Huh?

The distance an object is shown on the screen is the distance from the transducer, the hypotenuse of a triangle. The depth is the vertical leg of the right triangle. Solve for the missing length, the actual distance to the side of the boat. The greater the depth, the greater the discrepancy in what is real and what is shown (always actually shorter/closer).

 

Technological Angler

Just watch this video. Get a cold beer and a note pad and PAY ATTENTION. 

 

 

37 minutes ago, Hower08 said:

Just watch this video. Get a cold beer and a note pad and PAY ATTENTION. 

 

 

so i watched this and i know a little about side imaging but i never realized that your distance of sidescan was a total of depth and outward distance.  most of my lakes i fish are shallow so it isn't as big of a deal but still...great info.

12 hours ago, Team9nine said:

The distance an object is shown on the screen is the distance from the transducer, the hypotenuse of a triangle. The depth is the vertical leg of the right triangle. Solve for the missing length, the actual distance to the side of the boat. The greater the depth, the greater the discrepancy in what is real and what is shown (always actually shorter/closer).

 

Technological Angler

I have a lot of respect for the Technological Angler guy and this started me on a search for the truth.  The issue is "slant range distortion"  and does Humminbird correct it or not.  The link you posted suggest they do not.  My understanding was they do correct it and they show actual computed horizontal range.  After some research,  it depends on if the unit has contour mode turned on.  When it is off,  the water column is displayed and everything is displayed as the slant range from the transducer like you described.   When contour mode is turned on,  the bottom is graphed at linear horizontal distance.  I'm glad I understand that now.  

 

I should mention that everything that I've just stated applies to the Humminbird Solix.  I don't know if it applies to other models.

Geometry was not my strong suit.  Questions:  If I cast my lure based on the waypoint (distance from the transducer) and let it free fall, as with a spinning reel, would the lure fall beyond the actual target structure (assuming no line/water friction, which is of course impossible)?  If with baitcasting reel casting to the same waypoint but not allowing the lure to free fall (again discounting line/water friction) would the lure land closer to the target structure?  Seems to me that in both cases you would have to cast somewhat beyond the waypoint (distance from the transducer) because there "is" line buoyancy/friction, whatever, causing parabolic decent of the lure.  

12 hours ago, flyfisher said:

so i watched this and i know a little about side imaging but i never realized that your distance of sidescan was a total of depth and outward distance.  most of my lakes i fish are shallow so it isn't as big of a deal but still...great info.

 

That would be because it isn’t, at least not in the way he explained it ?

 

40 minutes ago, Tennessee Boy said:

I have a lot of respect for the Technological Angler guy and this started me on a search for the truth.  The issue is "slant range distortion"  and does Humminbird correct it or not.  The link you posted suggest they do not.  My understanding was they do correct it and they show actual computed horizontal range.  After some research,  it depends on if the unit has contour mode turned on.  When it is off,  the water column is displayed and everything is displayed as the slant range from the transducer like you described.   When contour mode is turned on,  the bottom is graphed at linear horizontal distance.  I'm glad I understand that now.  

 

I should mention that everything that I've just stated applies to the Humminbird Solix.  I don't know if it applies to other models.

Agreed - Also not sure how other companies (Lowrance, etc.) account (or don’t) for this. I run a pair of ‘Birds and keep contour mode off 90% of the time...but I was also always good at math ?

I use side imaging mainly to make waypoints then using the casting circles on my helix to position my kayak accordingly so i can hit the intended target.  I have had limited success in finding structure i see as i paddle past but in a kayak it is somewhat difficult to turn and shoot so to speak quickly from a paddling standpoint.