Skerry Rails

I am finally needing some help with my Skerry. I am having troubles understanding the directions for intalling the rails on to the hull of the Skerry. The part that has me stumped is tapering the rails, I think I am making it way more complicated than it needs to be but I just can't figure it out. Just to help me picture it, am I just removing a quarter inch of material from the bottom of the rail as if it were on the boat? if anyone has a picture of a completed rail or something that explains what I am trying to  accomplish it would be greatly appreciated. Thanks! 

What I did was remove about 1/4 inch tapering back to nothing from the front and back(fore and aft) of the rails.  My rails are slightly less than 3/4 inch tapering to slightly more than 3/4 inch from the fore/aft to midship

I also forgot to ask but why are the inner rails tapered but the outer ones are not? Won't that cause and over hang?

Once you get the outer rails on, turn the boat over and taper the outer rails to match the inner rails.