The main difference between the GHT and most traditional turbines is its utilization of lift-based propulsion instead of drag-based propulsion. The indicator of the type of propulsion is the tip-speed ratio of the blades. Tip-speed ratio refers to how many times faster the tip of a blade is moving relative to the speed of the current. The GHT has an average tip-speed ratio of 2, meaning in a 5 m/s current the blades are moving at 10 m/s into the current.
Traditional fan-shaped turbines operating under a drag-based principle can have tip-speed ratios higher than 7! The speed of the blades relative to the currents in which they are moving can vary along its length and can have adverse effects on the operation of the turbine.