BN2. Is my memory correct? When the Islander was first designed/prototype built, I think I recall reading that the CAA were horrified by the wing, hundreds of proud rivet heads etc and so very un-aerodynamic from a drag point of view. B & N were tasked by the CAA to re-skin the wing with balsa wood to achieve a more laminar flow so the CAA could show them the difference a smooth wing would make. Just 1 - 2 kts as I recall.
The extra production costs could never offset an extra 1-2 kts. The warty wing remained as designed by B & N.