Refers to a lady with ample breasts, or ample everything, whose physique built to perform a motorboat
would be an easy task. The motorboating may be done anywhere on the corpus where one can press the face in between any skinfolds, 'as long as the cheeks are warmed'.
Before Oprah Winfrey lost all that weight she was extremely motorboatable. Now she still retains some motorboatability, but only of the more conventional variety.