Thread: Test

Why fish arch....(Lowrance.com sonar tutorial)

The reason fish show as an arch is because of the relationship between the fish and the cone angle of the transducer as the boat passes over the fish. As the leading edge of the cone strikes the fish, a display pixel is turned on. As the boat passes over the fish, the distance to the fish decreases. This turns each pixel on at a shallower depth on the display. When the center of the cone is directly over the fish, the first half of the arch is formed. This is also the shortest distance to the fish. Since the fish is closer to the boat, the signal is stronger and the arch is thicker. As the boat moves away from the fish, the distance increases and the pixels appear at progressively deeper depths until the cone passes the fish.

If the fish doesn't pass directly through the center of the cone, the arch won't be as well defined. Since the fish isn't in the cone very long, there aren't as many echoes to display, and the ones that do show are weaker. This is one of the reasons it's difficult to show fish arches in shallow water. The cone angle is too narrow for the signal to arch.

Remember, there must be movement between the boat and the fish to develop an arch.

Here's an "un-talked-about" image size phenomenon in SI discussions...
Structure image ratio size ...SI vs 2d

In my 1197:
A brushpile that shows as the size of a golfball on the 2d screen...shows as the size of a quarter in the SI screen...

In a 798:
That very same brushpile would show as the size of a quarter on the 2d screen...but show as the size of a peanut in the SI screen...

Structure images are roughly 1/4 size in SI as to what you are used to seeing in 2d...And if you "split" the screen... Structure images are smaller even still...

Buy the biggest screen you can afford...Unless you want to look at "peanut sized" brushpiles...

Rickie

GPS Latitude and Longitude Converter

The 798 comes with this xducer...
XNT 9 SI 180 T :: Humminbird

You can trade in the unopened compact xducer for the HDSI xducer here...
XHS 9 HDSI 180 T :: Humminbird

The HDSI xducer has different size 455kHz crystals than the stock in-the-box Compact xducer which can give better quality 455kHz SI images...

The HDSI xducer also has crystals for the 800kHz SI beam but they would not be utilized in the 798 (because the 798 does not have the circuitry needed to use the 800kHz beam ...)

Some say the upgrade to the HDSI xducer improves the image quality of the 455kHz SI image that the 798 uses...

Conversely, some say they see no difference in image quality...

Maybe someone that has upgraded their xducer to the HDSI xducer for their 798 will chime in...

Rickie

Below is a depiction of the 455kHz SI beam and the 83/200kHz 2d beams that are included with your 798..

The SI sonar beam is in the shape of a thin slice..
The 2d sonar beams are conventional cone shaped...

For the SI ....Each time the unit pings, the unit takes the echo information in that thin slice and plots that echo information on the SI image across the very top of the SI image in a thin line...

The very next ping echo information is plotted at the top of that same SI image... Pushing the previous echo Information down on the image...

It is this pinging, plotting, stacking (of the thin lines of echo information on the image) .... That builds the SI image on the screen...( it is not a camera snapshot of the bottom)...

The DI in the 798 is a computer generated image created from the data received from the Si crystals in the xducer (it will not be as good of a quality image as can be obtained from a unit that has "dedicated DI crystals" in the xducer...

Keep the chart speed matching the boat speed... 1mph=1 chart speed, 2mph=2chart speed...etc...

Set the SI range to a "left and right range" of about 60-70 ft... Less will make structure look bigger - more will make structure look smaller....
You can set the SI to left OR right only to make structure look bigger...

Choose a pallete that is pleasing to your eyes... Your eyes are different than anyone elses...

Take snapshots and recordings and view them at home to study the images for uninterupted learning of image interpretation...

Use the Si sensitivity setting as a brightness control for the SI image ... Different water conditions/bottom compositions will lighten and darken the SI image...

Ask lots of questions... Pm me if need be...

It is possible to take advantage of HB's xducer trade in policy and trade in the SI compact xducer (that comes with the 798) for the HDSI xducer (and pay the difference)...some users see a image quality improvement with the 455kHz crystals in the bigger xducer.... (you willl not be able to take advantage of the 800kHz crystals in the HDSI xducer even with the exchange because the 798 does not have the internal circuitry to read the data from the 800 kHz cryatals)...

Rickie

455kHz SI beam
img]http://i477.photobucket.com/albums/rr134/rnvinc/SI_diagram_3Drendering_480ft2.jpg[/img]


83/200kHz 2d beams
img]http://i477.photobucket.com/albums/rr134/rnvinc/dualbeamPLUS_screenshots1.jpg[/img]

AC to DC converter...

Amazon.com: Sunforce AC/DC Power Converter: Automotive

SI interpretation is sometimes difficult for new users...this is basically because the visual perspective of the SI image is different from any sonar display we've ever seen before...

The difficulty in SI display interpretation lies in fact that the SI display image is a 2 dimensional aspect image of a 3 dimensional underwater world...

Sonar displays are incapable of rendering a true 3 dimensional image.... (well I guess just about any display in incapable of rendering a "true" 3 dimensional image)...

So,.... the SI techno-developers decided to "bend the rules of 2 dimensional displays" and take 1 of the 3 dimensions of the physical underwater world and display it in the same "visual" plane in the SI image as the other 2 dimensions in the sonar display....

There are "3" dimension planes in the actual physical underwater world:
- 1. "Horizontal width"- (rendered into the SI image by the SI Range width that shows as "left and right" on the SI image)...
- 2. "Horizontal length"- (rendered into the SI image by the sonar history that shows as "top to bottom" of the SI image)...
- 3. "Verticle depth"- (rendered into the SI image by taking the actual verticle plane of the "water column" and laying it flat down in the same 2 dimensional plane on sonar display as the 2 horizontal planes mentioned above...

What I have tried to do with this 3d rendering program is show how the SI unit processor renders the actual verticle "water column" in the underwater world .... and morphs that verticle plane data into a 2 dimensional sonar display...

It is my goal to shorten the "learning curve" of SI interpretation for new users that are having difficulty understanding the "3 dimensional underwater world" as seen on the "2 dimensional sonar display's SI image"...

As you watch this video... Keep your eyes trained on the sunken barge in the right SI beam as the "water column" morphs from the 2 dimensional sonar display image to the actual verticle plane of "water depth" in a 3 dimensional visual aspect ....and then the morphs back into the 2 dimensional SI image...



Rickie