In addition to a basic Garman GPS depth sounder, a good radio is also necessary in this day and age for a variety of reasons to include receiving alerts from the coast guard, security warning notices, boat to boat communications, and etc. If you are going to be operating your boat in large waters, radar is very important if you can afford it. I frequent the busy waters of the NorthEast, and have frequently been in dense fog. I was n a CD 16 on LI Sound several year's ago in dense fog, and felt helpless as idiots with radar sped by our boat at high speed. Large boats and ferrys plied those waters, too, and there I was sitting there helpless traveling at only 3 mph, because I could barely see my hand in front of my face. For those of you thinking I had other options to avoid the fog, this happened to me in the middle of the day and with bright sunshine when the wind suddenly reversed its direction and blew a heavy fog bank over us in only a few minutes time. And as it happens, it was the worst place first to be blinded by heavy fog: right near the mouth of the heavily trafficed Thames River. We now have radar on our Marinaut, and we have never regretted its expense.
Rich