Manufacturer recommended a stiffener at the aft end of each outboard rib due stress cracks on the original aircraft. I added a full size rib stiffener from .020 6061 T6 to each rib and the extra stiffener per the manufacturer recommendation from .040 6061 T6. Note: the manufacturer recommended stainless steel for the latter. After discussing with several experienced builders, I agreed the stainless steel was overkill and used the aluminum stiffener instead. I dimpled the assembly and used countersunk rivets in case someone wanted to add Sea Fins at a later date.
