Just got a Humminbird 718 and trying to get it set up. I can not get it to mark fish unless I turn on fish Id (12 hours of fishing and not one arch). I am also having a hard time telling the hardness of structure... everything seems to be the same. wanted to know if any has the unit and could help. 

^{You must be moving to see an arch.}

Not sure on the fish marking problem, but, the darker the color, the more dense the structure. For example, rock would be dark, and grass beds would be lighter in color...hope it helps

Not sure on the fish marking problem, but, the darker the color, the more dense the structure. For example, rock would be dark, and grass beds would be lighter in color...hope it helps

everything seems to show the same... Dark 

Have you tried adjusting the sensitivity?

Have you tried adjusting the sensitivity?

yes it helped some but still did not mark any fish. going to try and got out today and play with the sensitivity more. 

Are you 100% sure there are fish where you are looking? Are you sitting on top of or going over fish which you are catching and not seeing them on the screen? As far as bottom composition, a hard bottom is shown as a hard line. A soft bottom is fuzzy, dense weeds are fuzzy, light weeds are noticeable as fuzzy clumps shooting up from the bottom. You may want to check your chart speed. It should be close to the boat speed meaning 3mph= chart speed 3. If you are sitting on top of a school and vertical jigging then you'll want the chart speed on 10 to get fast returns.   

thanks for the help everyone... went back out today and was able identify weeds, hard bottom, and i think I sawn a school of bait fish. still not arches.  

thanks for the help everyone... went back out today and was able identify weeds, hard bottom, and i think I sawn a school of bait fish. still not arches.  

Arches are all about time and distance of a sonar echo.

 

Do you understand why/how a LCR sonar unit "draws" an arch when it diplays stuff suspended in the water column?

 

If not refer to the Lowrance web site and their sonar tutorial.