I have a HDS 7 Combo on my rib and have been playing with Insight Genesis for some time now. It allows you to record you sonar data as a SL2 file and then upload it to your account to produce massively detailed contour maps.
Awesome thing is you don't even need to the top spec as it will work on the Elite HDi series.You just need a unit that is a fish finder and GPS combo.
Its now free to create the maps and download them back to your plotter. There is also a Social mapping layer allowing you to download maps shared by other users. Here are some screen shots of some small areas I have surveyed in the Solent.