Lack of experience,I'm having trouble locating reefs and wrecks. Although I'm using an $150.00 fishfinder I believe it is working because, fishing the northshore in 100' I'll see the contours and depths.I'll punch in th cordinances in my GPS for the ocean,pan the area and only see the depths and thick dense bottom on my finder'seldom any structure sticking up to believe I'm over a wreck and going to have a successful fishing experience. Please help 