Personal preference should play a role in determining oar length also. I had the opportunity to run many different size boats and different length oars over the years, which I know is not always possible for many boaters.As a river guide, sometimes starting a river trip, you showed up and had to take the equipment that was left.( first come first served was the rule) That meant a 14. ft. boat with 8 ft. oars or 12 ft. oars or maybe rowing with one 10 ft. oar and one 12 ft. oar at the same time.(you all know where this is going). Using the a basic formula 10 ft. boat 8 ft.oars to 8.5 ft. oars, 14 ft. boat 8.5 ft. to 10 ft. oars, 16 ft. boat 10 ft. to 12 ft.( 33 ft. rubber bridge span pontoon boat, nothing under 15 ft. hand made tead wood oars., might haved aged myself here). Observing boats on the rivers I think most rivers rafters stay within these limits. I personaly like the shortest length oar for the length of the boat with the widest blade possible. Oar tower heigth should depend on where your knees are when you have your oars blades out of the water and oar handles at lowest point and moving foward, handles should clear your knees in rowing position, that depends on if you use a kick bar (foot bar) or have your feet on rowing frame level with bottom of your seat. Adjustments can also be made to distance from oar towers to front of rowing seat.