When looking for hard bottom offshore, there are a few things that you can do in order to find it. The first thing you can do is use a depth sounder or fish finder in order to locate areas of the seafloor where the bottom is hard. You can also look for areas where there is little to no vegetation growing on the seafloor, as this is often an indicator of a hard bottom. Another method that can be used is to drag a weighted line or chain along the seafloor until it hits something solid, which will be the hard bottom.