i think this is correct
Props come in many different configurations from 2 to 5 blades, with the primary aim of providing propulsion in both forward and reverse (astern) directions. The propeller is design for primarily forward motion, as such is not as efficient in the reverse direction.
Propellers can be right hand and left hand, for example a right hand prop turns clockwise looking from the back of the boat.
The propeller in simple terms screws its way through the water, like a screw being screwed into a piece of wood, in a perfect world the forward movement of the propeller, know as PITCH, would be for example on a 19inch pitched prop in one rotation of the propeller be forward 19 inches. However there is an element of SLIP which means the propeller does not move forward by the pitch, this is the ADVANCE.
PITCH- how far you would travel in the perfect world in one rotation of the propeller
ADVANCE- is the amount of forward movement taking into account the water SLIP
Propellers are designed to reduce the cativation, this in simple terms is bubbles that form on the blades, this also reduces the efficacy of a propeller
Paddlewheel effect – this is noticeable at low speeds, it is always there but at high speeds it is minimal compared with the forward motion of high speed. Basically a propeller will act as a paddle, for example a RH (Right Hand) prop in reverse will tend to pull the boat to port. Yachts take advantage of this when mooring, e.g. one way this will help mooring, the other it will force the boat from the jetty.
Boatless - better get down the pub and drown my sorrows