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]