a safety shroud for attachment to the rear surface of the transom of an unmodified boat hull equipped with an inboard engine and a propeller tube and shaft rigidly fixed to the engine and extending with clearance through an enlarged opening in the transom , and a propeller on the shaft ; the shroud being longitudinally and transversely downward concave to overlie the top and partly enclose the sides of the propeller , the shroud in longitudinal section being upwardly and rearwardly curved from the forward bottom edge of the shroud to just ahead of the propeller zone and then extending straight rearwardly . the lateral edges of the shroud extend generally upwardly and rearwardly from the forward bottom edge of the shroud to merge with the top rear edge thereof . preferably the shroud is composed of inner and outer interconnected plastic shells , the outer shell having a downward concave reinforcing strut , closed at its bottom by the inner shell , and having a metal rudder support shaft therein . the shroud and boat together constitute a new and improved combination .