Try also different colorsettings. My favorites is grayscale, in my oppinion its the best. When you find an interesting target, scan it severall times from different angels and distance. You will find that you get a big variety in sharpness and shadows, and som pictures can be really good and some just crap. The quality of pics can also vary a lot from one day to an other dependig on the acoustic conditions in the waters around your target.
Good luck Kimi.. ,;)