reaction fin
reaction fin
[rē′ak·shən ‚fin] (naval architecture)
A multiple fin or stationary propeller installed ahead of a ship's propeller, with fins warped so that water flowing into the propeller rotates in the direction opposite, resulting in elimination of race rotation aft of the propeller, and thereby in increased efficiency.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.