i really dont no how to advise you but i can tell you my setup and how i use mine. i have my transducer mounted just behind my step on triton bass boat using it only with the outboard running i run my unit with the noise filter off.....i use only 200khz 2d.....(thats the narrow beam)i think 25 degree angle........the di......i use the wide setting and just adjust the sensitivity to the bottom hardness and try to keep contrast very low .chart speed will affect whats on the screen,but i just run mine on telpedhe default setting of 5.... i use mainly 455khz ..... it seems to work the best, but the 800khz is useful also. i have both a 597hd/di with the dedicated down looking crystal and the 998 hd/si/di that has the di comming from the two si crystals that ive been comparing and so far im liking the 998 di better. i hope that ive helped you some. good luck