Looks like a Voith Schneider propeller to me. Highly maneuvrable propulsion device, useful in the "HOLY SH*T STOP RIGHT NOW" world of minesweeping.
http://en.wikipedia.org/wiki/Voith-Schneider
Edit - Hang on a minute, does that picture show them to be above or below the waterline? And they're a bit canted...
I wonder.