Characteristics of semi-displacement craft at increasing speed are introduced. A description of drag components is followed by an overview of fifteen major model test series, providing data for parametric variation of geometries around a parent form. This is followed by an introduction to resistance estimation using regression expressions derived from model test data. The influence of variations in geometric parameters on performance is discussed. Transverse stability at speed is discussed, followed by seakeeping quality for round bilge craft, including motions, accelerations, slamming, and broaching in the following seas. Finally, assessment of maneuverability is introduced together with the use of appendages such as trim tabs and interceptors, foils, and fins to improve performance.