[Fr. Frank]

Forward & reverse performance in a single inboard is a compromise in propeller design. A propeller designed to be very efficient while turning in one direction get that efficiency at the expense of efficiency in the opposite direction. To gain efficiency in reverse will necessarily mean a sacrifice of efficiency going forward. The sacrifice is not always proportional, however. A 10% sacrifice in forward rotational efficiency can mean a gain of 30-40% efficiency in reverse.

That being said, one thing most seamen tend to forget is that a single screw inboard hull, while backing, can only turn in one direction. An inboard propeller is often called a wheel, which helps to understand how it works. A right-hand rotation screw is turning counter-clockwise while shifted into reverse. If the wheel (prop) was touching the ground, which direction would the wheel want to roll? When backing, the hull will want to go in that directions, also. This is called "prop walk". Also bear in mind that in reverse, thee thrust of the propeller is directed AWAY from the rudder. For these reasons, a right-hand rotation single screw inboard will not back to starboard, and usually won't back up straight, either. AT best, they will have only a very slight tendency to back to port, being nearly straight.

A bigger rudder won't stop that, although the offset of a rudder and the shape and can help a little. For this you need to find the proper Reynolds number of the foil, and how changes to the foil affect you particular hull shape. (A rudder is nothing but a vertical hydro-foil)

After all that, know that squared blades on an inboard wheel are generally very inefficient in reverse, as are any wheels with cupped blades, although both are very good forward. If you spend a lot of time offshore at trolling speeds, a four-blade is good, and generally gives you better acceleration as well. Three-blade heavy-cup props are better for running on plane in rough water, have a much lower slip ratio, a lower cavitation factor, and are less likely to ventilate in a chop.

Beyond this, for propellers you get into rake, angle of attack, progression of pitch, and pretty detailed stuff.

Bottom line: learn to use what you have well first, then consider changes, and test each change carefully.