said concavity at said trailing end of said concavity having a depth sufficient to accommodate said impeller such that {HEAD ~ a central hub} of said impeller is positioned at an elevation substantially equal to {TAIL ~ an elevation} of said output shaft of said engine 
said concavity at said trailing end of said concavity having a depth sufficient to accommodate said impeller such that { HEAD ~ a central hub } of said impeller is positioned at an elevation substantially equal to { TAIL ~ an elevation } of said output shaft of said engine
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH