Grooved balls can move faster in water

Two wooden buoyant croquet balls of identical weight (in air) were released simultaneously at the bottom of a swimming pool. One ball’s surface had grooves that were arranged in concentric rings. Water resistant wood putty filled the grooves of the second ball which was then sanded to make a smooth spherical surface. Small holes were drilled through the balls along the axes of the concentric rings to guide their vertical movement up taut lines held fixed at the bottom of the pool and at the top above the water surface. Twenty runs were made: the grooved ball reached the surface first in every run by a significant time difference. It is concluded that grooves on the surface of a ball can substantially reduce the frictional interaction between the water and the ball, compared with that on a ball with a smooth surface.