hollow interior of the support tube 214 are thus in an area where only air is present when the aerator is operating thus the fouling of the plates 238 242 at their crossed intersection is prevented if the area where the plates 238 242 crossed were located at the air water interface solid materials would tend to gather at the intersection of the plates 238 242 in order to prevent fouling of the propeller mechanism 210 at the point where the plates 238 242 intersect with the outer surface of the support tube 214 the plates 238 242 have tapered ends 255 that extend from the support tube 214 with a gradually increasing transverse dimension as is best seen in fig1 the propeller blades 216 have a maximum transverse dimension indicated by a line 246 the first plate 238 as seen in fig1 has a maximum transverse dimension approximately the same as the maximum transverse dimension of the propeller blades 216 as seen in fig1 the maximum transverse dimension of the plate 238 extends over a large portion of the longitudinal or axial dimension of the plate 238 similarly the maximum transverse dimension of the combined second and third plates 240 242 is also approximate to the maximum transverse dimension of the propeller blades 216 the main function of the plates 238 242 is.