Maybe I am wrong if so help me out !

Your graph is taking 3 dimensional information and translating into a 2 dimensional image. If it shows me a hump I know how wide and tall it is but how do you know how deep ? How do you know what is on the two sides you aren't looking at ?

Are there any graphs out there that you give a 3d map ?

The Matrix finder and several others have the 3D options. I believe you have to be in pretty deep water for them to be accurate, though.

Mr. Wiggles,

All you have to do is train your brain to take the 2 dimentional screen info and translate it back into 3 dimentional image - thats all you do! LOL

Actually you are looking at a signal interpretation by the software and not a two dimensional image. A flat line representation of the bottom terrain that varies with wave action, transducer angle and distance to bottom or target. Fish on the outside of the transducer cones area appear as hashes or small dots could be 30# fish. As you plot the bottom or coverage area your transducer is covering, you are normally looking at a circular area plane, that on most lakes at 20-30' depth (average open water fish depth) could be a circle no larger than 20'. If the hump or profile is only 20' wide you could "see" both sides. Go to Lowrances tutorial page and you can get a lot more detailed information.

IN 30 ft of water you are looking at approximatly
10 foot diameter circle. That means there could
be a whale 6 ft from the centerline of your boat
and it would not show up.
In your question , with one pass, you can't
tell a hump from a ridge. With several passes
you can tell at what depth the hump tops out, how deep and steep the drops are on each side and how
big an area the top of the hump is.
Also with one pass, unless you are lucky, you will not know if the hump is holding fish, again
because you are looking at only a thin slice
of the hump as you move over it.
There is a small hump close to home that in
years past, I would make one pass over and move
on if I saw no fish. This year I have explored
it more closely and caught many fish that I would
have missed in the past.
Good luck
MO

Just remember: only the column of pixels on the right hand side of the screen are under you right now; everything to the left of that is history.

The transducer can detect objects that are within a cone-shaped area, with the point of the cone being at the transducer, and the base being on the bottom of the lake. The diameter of the cone is about one-third the depth, so an object 10 feet down will be somewhere inside a 3-foot circle around your transducer. At 21 feet, it's inside a 7-foot circle. You don't know exactly where it is, front-to-back or side-to-side.

What the screen shows as the bottom is the shallowest bottom within the cone. To find out where the sides of the hump are, you have to move the boat. I use marker bouys sometimes.

I have wondered about this-- is there some
lag time ? or is the far right of the screen
real time? I have heard that there is some
lag time and that is why some people still use
flashers. When I mark something interesting,
I always throw a bouy well behind the boat. I figure by the time I see it , I have passed it.
good luck
MO

There is some lag time and if you are going very fast by the time the sonar "draws" an arch the fish is history as mentioned above. However, it's all relative because how many of you are looking for one fish? If you "mark" several schools of fish in a general area then the fact that they may be 15ft behind you becomes somewhat irrelevant, the exception is when fishing extremely tight structure.

The more important thing that has so far been overlooked, Mr Wiggles is on to the basic premise, is that if a million fish were to line up in a perfect horizontal line and you passed over them in a perpindicular fashion it would show on your sonar as one arch.........what if they lined up in two lines one on top of the other....or three or four.....foolish you say because it doesn't happen, well maybe.

I think the best way to learn your graph is to pay close attention to what the screen looks like when you're actually in a school of sandies and you're catching them. From that point on, you should know what you're looking for. I know it really helped me and gives me a lot more confidence regarding what I'm seeing on the graph.

Real time return is dependent on the bottom type and true RMS your unit is outputting. The harder the bottom the more clean return you get. The BEST way to determine your particular sounders return time is to troll with the trolling motor over a known submerged object and see how far you have gone past before the sonar "redraws" the screen. Refresh rate is very important when you purchase a sonar. The top of the line sonars now give pretty much real time returns. When you are 20 feet or shallower, the ping rate is almost instantaneous, as you go deeper the ping return takes longer, that is why for water over 300' deep you would want a 50hZ transducer. For most freshwater applications the ping rate in the 150 to 200hZ band works best and gives the most complete detail. On the newer units you can manually adjust your ping rate to compensate for receiver interference from other nearby boats. Think of an old submarine movie when the destroyer is Pinging for the submerged sub, same principle employed in small graphs, the more pings the more returns to draw the picture, up to a limiting point when all you would get would be snow. Basically when you manually tune your graph (sensitivity) you are increasing or decreasing the sonar ping rate.

The Eagle 320 & 480 show a real-time flasher-style return on the right hand edge of the screen, to the right of the graph. Also, the literature for these units claims that changes in sensitivity actually increase or decrease the cone angle by changing the output power (volume maybe?). Ping speed and chart speed are variables that can be set by the user; I haven't experimented with them yet myself, though.

Interestingly, if your boat is stationary any fish holding under it will show up as a solid line across the screen. A school of bait all spread out at a particular depth will also draw a horizontal line.

This is something I have intended to do for a long time, I want to know what the distance is
with my console unit and my big motor at idle. I know the perfect place to test it ( sunken bridge)
but never seem to get around to it.
good luck
MO