I can give you some answers based on my experiences with my Lowrance Elite 5 DSI unit :

It should not "hurt" the unit or transducer to leave it running while the TM & tdx are out of the water. I've done this quite often with my unit, and it still works fine. I've used the unit w/tdx out of the water to measure boat speed by GPS, to navigate a lake via the map while on plane, and in the confines of my home to manually enter a couple hundred waypoints (via separate power/tdx cord and portable battery).

I keep my DI freq. at 800kHz almost all the time, just for crisper images in the depths of water I normally fish (<25ft). The 455kHz setting is supposed to give a better image at greater depths, while the 800kHz setting gives a better image in shallower water. The lower the frequency, the stronger the signal & thus the deeper it penetrates with clarity of the image. The angle of the fan shaped DI signals are 45deg for 800kHz & 75deg for 455kHz.

I don't have 2d capability on my unit. But, as I understand it, the greens/blues are the lighter strength return signals from the outer area of the cone and the yellow/red returns are the more intense signal returns from the inner area of the cone. They can also show the density of whatever object is being shown ... such as a big fish or tightly grouped bait ball showing in the yellow/red coloration, while a scattered bait ball might show more in the green/blue coloration. The on screen image of a 2d signal does not designate where within the cone that the signal is coming from ... and neither does a DI signal. Only SI gives you which side of the tdx (boat) the image is coming from.

I prefer the blue gradient color pattern for my DI unit, as it seems to give a better image without the eye strain of the other color combinations. The color palette is a personal choice deal.

On the clutter factor ... if your unit has a "sensitivity" option, turn it down and see if most of that clutter goes away. Contrast probably won't do much to the garbage signals of clutter, but you may want to check what setting you have the "Surface Clarity" set on. The higher the Surface Clarity setting, the less clutter you should see in the upper portion of your screen ... but, you may lose some signal sensitivity, making your screen images look less crisp. Also ... turbid water can give off a lot of "clutter" signals (from all the minute particles suspended in the water).

If you haven't already done so ... put this link into your "favorites" or print it out : http://www.lowrance.com/Root/Lowranc...0518-001_w.pdf .... it will give you a rundown on all the different menus & options within those menus.

And running your unit in "Advanced Mode" gives you the whole range of options to tweak from, rather than just running it in the factory default mode.

... cp