HELP understand Sonar Screen Orientation

[buhuskies]

I just ordered a new sonar fishfinder and have a question.

As an example, say the transducer is mounted on the stern of the boat like found most often. Then you have the LCD screen. heres the question:

When looking at the screen, what part of the screen represents the stern and what part represents the bow etc?

Use this photo of the FF I just purchased as an example:

Is the Left of the screen what is behind my boat?
or
Is the top of the LCD screen what is directly behind my boat?

Please help me understand the correlation between the transducer and the screen. Thanks!

 

[jtexas]

Re: HELP understand Sonar Screen Orientation

only the very right-hand column of pixels is under you right now...everything else is history. in the pic, you just floated over a submerged brushpile that has debris around it, which might or might not be fish.

general rule, a lit pixel represents an object inside a circle with its center directly under your transducer and a diameter approximately 1/3 the depth. So an object at 30' is somewhere within 5 feet, give or take, of your transom (or trolling motor depending on 'ducer mount)....aft, port, starboard, or forward, or directly underneath, you have no way of knowing.

that's with a 20? cone angle, they claim that high sensitivity settings give you more coverage....probably true......but I try to remember that rule of thumb.........

the "fish ID" feature draws a fish on the screen any time it detects an underwater object......you'll do better to turn it off & learn to interpret the sonar returns yourself. here's an actual school of white bass attacking a school of shad

 

[JB]

Re: HELP understand Sonar Screen Orientation

Excellent explanation by jtex.

Only thing I can add relates to your question about what is under the bow. It is not on the screen, but will be when your stern is over that spot.

 

[buhuskies]

Re: HELP understand Sonar Screen Orientation

Thanks JTexas and JB, thats kind of what I thought.

That the screen is read right to left more or less, with the right side being closest to the stern and the left side being what was already passed over. I'll have to reread the part about the lit pixel and depth etc but in time I will learn how to read this thing. The one I bought (Humminbird 565) has got pretty good resolution, being 640 X 320 and should give pretty good detail. I've got an inexpensive unit too that came new on a boat (probably around $79 worth of quality) and that boat is used on pretty deep reservoirs but I haven't used that for much more then water temps and depth (which is really nice to know) but I do see ARCs on it and realize not all are fish. This new one will be worth learning more about and used more for finding fish too. Thanks again for all your help!!

Also, what is a "soft" bottom versus a hard bottom?
Also, when you say "lit" pixel, do you mean hollow as opposed to dark?
I know the hollow ones are in that narrow beam correct?

 

[jtexas]

Re: HELP understand Sonar Screen Orientation

I was using "lit pixel" to mean "dark", or "activated"....a pixel is a single dot on the screen, it takes more than one pixel to draw a hollow shape.

dual beam, I don't know about those - I guess it has two concentric cones, one narrow, one wide?

anyway, the radius of the circle that your sonar "sees" is the tangent of half the cone angle times the depth of the object...at least, that's the "general rule".

hard bottoms like rock, or roadbeds show up as a wider line than soft bottoms like mud or silt. the illustration you posted is probably showing a softer bottom than my pic.

also, when you're over an uneven bottom, it's going to draw the shallowest point as the depth....so fish holding close to the bottom might not show up unless the bottom is fairly flat and level. Saturday I was fishing with two other boats, catching sandbass left & right on the bottom in 35 to 38 feet of water, but none of us were marking any fish on the graph.

 

[Boatist]

Re: HELP understand Sonar Screen Orientation

Great job Jtex, as good as I have seen anywhere.
On bottom hardness can not compare between depth finders. Yes wider is harder, but even on the same unit changing sensitivity will also change the with of the bottom echo. Only way you can really compare is to set the sensitivity and white line then travel around and see how the bottom signal changes. I find in the fall the water get clearer and it a good time to troll around in shallow water and compare what you see in the water and how it displays. This is one place where color unit make it a little easier to find hard bottoms or rocks.