He also introduced the major advance of hull shapes that can plane, and which can therefore reach beyond the usual speed limits for small sailing boats. In effect, a boat which is planing is skimming along the surface, with the bow of the boat not in the water. This results in less friction because of reduced waterline length, reduced displacement (the amount of water needing to be pushed aside by the boat), and reduced 'wetted area'. The driving force provided by the sails has to overcome less resistance, and therefore speed increases dramatically.