Callaway Big Bertha Hawkeye VFT Fairway Wood. The Callaway Big Bertha Hawkeye VFT fairway woods feature Callaway's Variable Face Thickness (VFT) Technology which allows manufacture of a very thin - yet strong - clubface. One of the earliest fairway woods to benefit from the 'trampoline effect' whereby the face 'gives' slightly on contact with the ball and then, in a fraction of a second, restores itself, catapulting the ball off for increased distance.