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sonar screen help

Old 06-11-2009, 09:54 AM
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Default sonar screen help

Can someone please clarify for me what I think I'm seeing on my sonar/ff screen? I've read the manual and swear I can't find the answer - probably cause it's so stinking obvious and Lowrance didn't think there was anyone as dumb as me out here .

Say the sonar screen is showing the water's bottom running pretty flat left to right and then it drops down on the far right of the screen. I am assuming this means that I am approaching a drop-off running across the path of my boat. I will be moving from shallow water into deeper water passing over a shelf. Am I correct?

Then this line drop-off scrolls right to left to the middle of the sonar screen, meaning I'm directly over the drop-off and the water aft is deeper than aft. Right?

Then this line drop-off scrolls right to left to the left of the sonar screen, meaning I've passed over the shelp and the shallow water is moving away aft of my boat. Right again?
Old 06-11-2009, 11:30 AM
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Default Interpreting Sonargrams

The usual convention for display of rasterized SONAR echoes is for the newest information to appear at the extreme right of screen, and the oldest information appears at the extreme left of screen. The screen shows echo response plotted against time. The older echoes scroll off to the left, replaced by newer echoes coming in from the right.

The plot does not show any sort of direction relative to the boat, except downward to the sea floor. All echoes originated from below the boat. If the boat maintains a steady course, speed, and heading, one could interpret older echoes as being dead astern.

Unless you have a forward-looking SONAR, all echoes are from bottom terrain which you have already passed over or are currently over. The sonargram does not show future bottom depths, other than the extent to which the spread of the sound beam of the echosounder might travel slightly ahead of the boat.

The vertical axis of the display also shows the time interval between the initial ping and the return echo. The top of the display is closer in time to the initial echo ping; the bottom of the display is longer in time since the echo ping. In this way, the depth of water below the boat can be deduced.

The amplitude of the echo signal is represented in various manners. In grayscale displays, the stronger the echo the darker the screen representation. In color displays, various colors are associated with different echo signal strengths. I do not believe there is a standard for this colorization. If you have a color echosounder you will soon learn to associate certain colors with stronger echoes.

The LOWRANCE website has a good tutorial on the basics of echosounder operation. You might benefit from it.

http://www.lowrance.com/en/Support/T...onar-Tutorial/

Old 06-11-2009, 12:11 PM
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Thanks. I've read all that and I believe I'm over-thinking this.

So it sounds like the opposite of what I thought. What I'm seeing on the screen is relative (sort of) to my boats position/movement? The transducer is
"looking" down and showing what I would see if I was looking across the bottom in the direction the boat is moving.
Old 06-11-2009, 05:36 PM
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I'm not quite sure what you're asking but what the transducer is showing is exactly whats under the stern of the boat right now. That appears at the far right of the screen as mentioned. So whatever you see on the far right of the screen, you know that that is under the boat at that exact moment.
Old 06-12-2009, 05:45 AM
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sorry, i told y'all it was a dumb question.

boat is moving forward at xx speed and I see this coming onto the right of the screen...


-------------
\
---



that's telling me i'm on a drop-off. but, is that ridge running across/side to side/port to starboard or is it running with/front to back/fore to aft? If I wanted to work something up/down the ridge I assume i'd be casting off the side of the boat. am I right?

Last edited by kone; 06-12-2009 at 06:14 AM.
Old 06-12-2009, 06:00 AM
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fore and aft-the front of your boat is right to left on your screen--right- front left-rear
Old 06-12-2009, 06:16 AM
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Originally Posted by kone View Post
sorry, i told y'all it was a dumb question.

boat is moving forward at xx speed and I see this coming onto the right of the screen...


-------------
\
---



that's telling me i'm on a drop-off. but, is that ridge running across/side to side/port to starboard or is it running with/front to back/fore to aft? If I wanted to work something up/down the ridge I assume i'd be casting off the side of the boat. am I right?
Diagram didn't come out as I wanted:

___________
..................\
....................\_____
Old 06-12-2009, 12:33 PM
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Originally Posted by IKAT View Post
fore and aft-the front of your boat is right to left on your screen--right- front left-rear
While this is quite true, it doesn't really answer your question. The ONLY way to tell which way the 'shelf' as you call it, is running, would be to associate the screen pic with the actual bank terrain. Or, buy a UW camera. We would need to know the exact depth of water even to guess what you are seeing because the cone angle and depth will determine how much bottom you are over or approaching. Hard to say if it is a hole or a shelf. For example......my boat is 8 feet wide and I have a DR mounted on each side about 2 to 4 feet ahead of stern. I can't see my DR weights unless I am at least 25 feet deep. Then I can see them both.

Edd
Old 06-12-2009, 04:15 PM
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The display on your screen is built one vertical line at a time. The current line being built is on the far right of your display. The rest of the display scrolling off to the left on your screen is just a visual history of that far right vertical line. If you motor over a dropoff that decends at a 45 degree angle the picture on your screen will vary according to your speed. The faster you go the steeper the drop will appear and conversly, if you're trolling dead slow, the drop could look much more gradual than it really is. If you are in 100 feet of water and stop over a rock that comes up to 50 ft, the picture on your screen will look like a flat bottom at 50 ft. Think of you display as a history of what the tranducer saw rather than a picture of the bottom.
Old 06-12-2009, 06:40 PM
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Originally Posted by epanzella View Post
The display on your screen is built one vertical line at a time. The current line being built is on the far right of your display. The rest of the display scrolling off to the left on your screen is just a visual history of that far right vertical line. If you motor over a dropoff that decends at a 45 degree angle the picture on your screen will vary according to your speed. The faster you go the steeper the drop will appear and conversly, if you're trolling dead slow, the drop could look much more gradual than it really is. If you are in 100 feet of water and stop over a rock that comes up to 50 ft, the picture on your screen will look like a flat bottom at 50 ft. Think of you display as a history of what the tranducer saw rather than a picture of the bottom.
Ed's last sentence says it all. Unless you are at anchor and not moving, everything you see on the screen, except for the extreme right hand information, represents where you have been, or what your transducer has been over most recently. Imagine your face with a scuba mask looking straight down from the transducer. The mask prevents you from looking forward, and allows you to "see" only directly down, or perhaps a little behind where you have been.
Old 06-12-2009, 10:11 PM
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To get a better idea of the terrain under the boat run across the same area at a number of different angles. With the info already given about what your screen is telling you when you see an area you want to get a better idea about mark the position on the GPS and cross over the spot at the different angles. With practice you get better at using those different 2 dimentional pictures on the FF screen and getting an idea of the actual 3D layout of the bottom in your head. Add the current and drift info with that and you'll get an idea on how you want to set up on the spot to start fishing.
Old 06-13-2009, 05:18 AM
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very helpful responses. thanks everyone!

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