fin 14 u2032 disposed thereon the first centralizer 20 a and a second centralizer 20 b comprise rigid ribs 22 a and 22 b respectively extending radially from the casing string 8 to form the annulus 4 between the casing string 8 and the wall 4 a of the borehole 12 the centralizers 20 a 20 b may comprise set screws 24 a 24 b to facilitate coupling the centralizers 20 a 20 b adjacent to the outer sleeve 10 on the casing string 8 the centralizers 20 a 20 b prevent or limit engagement of the exterior surface 14 or the fin 14 u2032 with the wall 4 a of the borehole 12 in other embodiments the ribs of the centralizers may be pitched at an angle and formed to increase the level of turbulence of the annular flow rotation of the outer sleeve 10 on the casing string 8 moves spiral fin 14 u2032 through the cement slurry 7 within the annulus 4 and the exterior surface 14 of the outer sleeve 10 against the cement slurry in the annulus 4 alternately the outer sleeve 10 may comprise a plurality of generally parallel spiraling fins on the exterior surface 14 it should be understood that these and other embodiments may be useful especially in a horizontal portion 70 of a borehole see fig1 to propel or assist in moving a cement slurry through the annulus 4 and reduce the equivalent circulating density ecd of the cement slurry fig2 is also an enlarged elevation view of the float device 6 sealably engaged with a stinger 36 a on the end of.