This is a propeller on a boat, that is half in, half out, of the water. They provide more speed on light, fast boats. If you require more information, google "surface drive" or "wave piercing propeller". Companies like Arneson and Seafury manufacture these. Wikipeda has only 3-4 lines on it, and it says nothing. http://en.wikipedia.org/wiki/Surface_piercing_propeller Why are these 'better' than conventional propellers? Is there an equation for it that I could enter numbers into to see? They say that there is less drag from the propeller shaft, and less cavitation due to the churning of the water, but how does it produce more thrust with only half of the contact area? They are larger than regular propellers but I still don't see.