My normal approach is to use a hatchet to remove all the side wood, leaving me with a very thick stave which is at bow dimensions when viewed from the back. Then if there's enough wood to get two bows I'll do the splitting trick where you drill holes all the way along the line you want and split carefully between each hole. Or I'll saw the line, or half split half saw etc. Usually though, I just make one bow per log, and use the axe to remove everything I don't want.
