How many Navagear readers are both boat nuts AND science geeks? Probably quite a lot, actually. I found this story at gCaptain fascinating:
by Bart Stockdill, M.A.Sc., P.Eng., Mechanical Engineer, Robert Allan Naval Architects and Marine Engineers
Water will boil at room temperature if the pressure is low enough. In fact, the pressure has to be very low, about 2% of standard atmospheric pressure at sea level.
Just like a wing generating lift, marine propellers use pressure differences across their blades to generate thrust. The pressure distribution on a propeller blade depends on its shape and how that shape influences the speed of the water flowing
around the blade. As the flow speeds up, the pressure drops and conversely when the flow slows down, the pressure rises.
Thus the blade is shaped to promote higher speed on the forward or suction side and lower speed on the aft or pressure side. If the blade shape is too aggressive, very low pressure can result. Indeed, this pressure can be low enough to reach the boiling point of water which then leads to cavitation.