From Wayne P’s link, #9, the discussion about marking a waypoint, I thought DS had a narrower cone than 2D.
If someone reading this has access to a laser range finder and a purely verticle target like a bridge pylon or retaining wall, I’d be interested in their results.
Say what???Originally Posted by bhjr.
It might help you to think about it the simplest of terms. Sonar is nothing but a measuring device. It determines how far objects are away. Then the software performs the graphic functionality to display on the screen. For example, when you set the screen to display 100' left and right, it has no effect on the sonar scanning. The transducer sends out the sound the same distance all the time, which is determined by the capabilities of the unit/transducer and frequency setting. It is only the user that is setting the viewing range on the screen. That being said, an example would be; boat is in 80' of water, screen is set to view 100' left and right. The screen will display black space on both sides of the boat center line. This black space is the water column directly below the boat down to the bottom, NOT the water column 80' to the left and right of the boat. So if the screen displays a stump on the bottom at the right side 80' line that stump is NOT 80' to the right of the boat. It is directly 80' down below the boat. If that stump is shown at the 90' line to the right of the boat, it is NOT 90' to the right of the boat, it is only a few feet to the right of the boat. This is where the math would come in to determine distace right and left based on depth/distance, etc. The other consideration would be the angle of the bottom. Main thing to remember is the sonar transducer is measuring distance within its beam width on a straight line all the time and adjusting the screen is only changing the viewing parameters, not the scanning parameters.
Side Imaging (a Humminbird thing) covers from the water's surface to past vertical under the transducer on both sides==more than 180 degrees left to right. That is how SI can display the same subject on both sides when the transducer is directly above it.
The first several generations of Humminbird Side Imaging units did not have Down Imaging at all from a Down Imaging piezo. They had composite DI views created by blending the two SI pulses. Some current Humminbird Helix SI models still have the composite DI views, not true Down Imaging.
This is from one of those:
When the Helix MEGA SI units came out, they have a dedicated Down Imaging piezo but the SI coverage is no different.
This is from one of those:
Wayne Purdum
Charlottesville, Va.
Helix 12 MEGA SI+ G4N, Helix 15 MEGA SI+ GPS G4N
SOLIX 12 SI/G3, Helix 8 MEGA SI+ G4N, Ultrex 80/Advanced, MEGA360,
MEGA LIVE, LIVE TL, MEGA LIVE 2, Xplore 10
Post #23 has it. The distance numbers on the screen are all about software interpreting what you want to view. A rock that is shown on the screen to the left of the boat and above the 80' line is 80' from the transducer. So the distance is actually slant range. However, I've done the math for a bunch of depths and the slant range is not all that different until the depth gets really deep. What I will typically do, is set my range at whatever is appropriate. Then I mentally change the number scale so the first value is 0 and distribute the rest of the values out to the distance I have the unit set for. If in 10' of water and there is a rock sitting on top of the first return, I know it is 0' laterally from the gunnel of the boat. However, it IS 10' away from the transducer. I just extrapolate from there. Really is it that important? Just set a waypoint using the crosshairs and as long as your GPS receiver is located close to the transducer that is imaging the structure, you can get back to it but navigating to the coordinates.
NoCAL
2004TR-21X/2015 250 ProXS
2B112175
If you are in 20' of water and your SI shows a post at 50' out then the post is 30' away? Say the post goes all the way to the top of the water, still 50' out. Since the top of the post is in 0' of water how far away is the top of the post?
Man…you’re gonna stress some of these guys out with comments like that. Lol.
Find something looks cool to fish, drop a waypoint on it. Go back over it with downscan or 2d, if it looks good, fish it…does not need to be overthought.
98 feet
2020 Ranger Z519 | 2020 Mercury Pro XS 225 4S | Helix 10SI | Helix 10 MDI G3N | Helix 10 MDI G3N | Noco GENIUS 10X4
Fury 3 22P True Pitched | Power Pole Pro 2's | Ghost TM | Mega 360 | MEGA LIVE | Atlas 8in Jack Plate | Trick Step | 3X Amped 80ah Lithiums
Oh yeah, thanks. I almost forgot we were supposed to be fishing!
I use side image to find a rock ,brush ,tree etc and than drop livescope on it and get the real picture
Replied to wrong person.
If the post is straight up and down, side imaging will show it as having an angle. If it shows it as a dot, then the post has an angle exactly perpendicular to your sonar's direction.
Therefore if the top of the post is in 0' and shows it is 50' out, then the top is 50' out. If it shows it as straight up and down with no angle (a perfect dot), then it is actually leaning away from your boat exactly perpendicular to the sonar's direction.
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Check out "Fish the Moment" website. Johnny has some very good videos on this.
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