The Opal had a laminar flow airfoil that was a point design, ie great for records but poor low speed. There are much better airfoils that could have been chosen and certainly better ones for overall performance and much better low speed. So essentially down to the airfoil he choose but not a inherent airframe issue. Secondly performance of the foil was drastically reduced by the stickers placed on the wing for promotion of the sponsors. Witnesses stated this had a huge effect on the wings performance as it disturbed the flow over the wing. Had they been painted- it would not have been a issue. So- no stickers and pick a much better airfoil for the intended use.