A bearing stave for use in a water-lubricated bearing having a discontinuous surface with a plurality of discrete, separated contact locations for contacting the shaft, the discontinuous surface being made of slippery polymer alloy. Each supporting shaft includes retaining pieces around a recess at an inner side, and the retaining pieces are inserted into the bearings and leading-end flanges thereof are resiliently engageable with opening edges of the bearings. The dual frequency antenna module includes a first antenna, a second antenna, a first connecting portion, and a second connecting portion. The power source for the motors is contained within the hub shaft, with a battery recharge port located on the hub shaft.