No system will pinpoint them since no two units are identically calibrated. To find a piece, you need to buoy the #'s then execute a search pattern until you find the structure. Then buoy the structure and record the actual #'s for your unit. My Loran C is usually off by .1-.2 from any published #'s. That's equivalent to like 75 - 100'. It can take hours to get on a piece especially in deep water. But the second time you go your repeatability will be improved. During the summer, I take a day or two just to search for new bottom and get my #'s down.